NZ620422B2 - Method for increasing the advantages of strength aids in the production of paper and paperboard - Google Patents

Abstract

Disclosed is a method for manufacturing paper, paperboard or cardboard comprising the steps of (a) pulping an aqueous cellulosic material containing a starch; (b) preventing at least a portion of the starch from being microbialiy degraded by treating the aqueous cellulosic material containing the starch with one or more biocides; and (h) adding a dry and/or wet strength polymer to the cellulosic material. arch with one or more biocides; and (h) adding a dry and/or wet strength polymer to the cellulosic material.

Description

Method for increasing the advantages of strength aids in the production of paper and paperboard FIELD OF THE INVENTION The invention relates to a method for manufacturing paper, oard or cardboard comprising the steps of (a) pulping an aqueous cellulosic material containing a starch; (b) preventing at least a portion of the starch from being microbially degraded by treating the aqueous cellulosic material containing the starch with one or more biocides. which are at least partially added to the osic material in the thick stock area, where the cellulosic material has a stock tency of at least 2.0%; and (h) adding a dry and/or wet strength r to the oellulosic material.

Further, the invention relates to a method to increase the strength of paper, paperboard or cardboard, preferabiy the dry strength and/or the wet strength, comprising steps (a), (b) and (h) as bed above.

BACKGROUND PRIOR ART Strengths polymers (also referred to as strength resins. strength aids, strength additives and the like) are extensively ed in paper manufacture. It is often distinguished between dry th polymers and wet strength polymers, though dry strength polymers often impart a certain degree of wet strength to the paper, and vice versa. Today, the most common types of synthetic dry and/or wet strength polymers are based on polyvinylamine or polyacrylamide. Other resins such as polyvinyi alcohol or lattices are used, but generally these are seen in surface applications to the paper, rather than as d additives.

Similarly, styrene acrylic resins have shown or performance when applied through surface application rather than as stock additives.

A number of polymers are commercially available as dry or wet strength polymers. They can be classified in the following three categories: CONFIRMATION COPY (i) Polymers capable of only tomiing hydrogen bonds to starch and/or cellulose fibers, such as certain polyacrylamides, usually do not provide significant degrees of wet strength but can improve the dry strength of paper. (ii) rs capable of additionally forming ionic bonds to starch and/or cellulose fibers. such as highly cationic polyvinylamines, can provide dry strength and some permanent wet strength to the paper. (iii) Polymers capable of covalently bonding to the cellulose fibers. such as glyoxylated polyacrylamide and epichlorohydrin polyamido~polyamines, achieve dry strength and temporary or permanent wet th of paper.

The cross-linking agents provide wet strength as well as dry strength properties. This material forms a covalent bond with the hydroxyl group on ose, and is widely used in applications where wet strength is tolerated and desired.

The wet strength achieved with epichlorohydrin functionalized polymers is of permanent nature, while the wet strength achieved with glyoxylated polyacrylamide is of a temporary nature, losing effectiveness during prolonged exposure to water. This enables re-pulping of broke or waste paper to be readily achieved without special treatment. The dry strength obtained is often greater than that achieved with other tional strength resins. nyl alcohol, starches or gums.

The glyoxylated polymers typically are less effective in s where there are high levels of anionics (e.g. anionic trash), such as secondary fiber furnishes. Here the resin complexes with both soluble and insoluble materials, thus reducing the adsorption of the resin onto the fibers. This can be overcome by the addition of ic promoters (e.g. alumn or uminium chloride), or by careful charge control using other chemical additives in the furnish, such as polyamide wet strength resins or cationic sizes (l. Thorn et al., Applications of Wet-End Paper try, 2nd edition, Springer, 2009).

Dry and/or wet strength resins are not satisfactory in every respect. particularly because they do not always show l performance, particularly in papermaking plants having partially or fully closed water ts.

Native or ally modified starch is also extensively utilized in paper manufacture. it has been ed that for production of woodfree uncoated and coated fine papers up to 40 kg starch per ton of paper are applied. ing paper made from 100% recovered paper can only be produced economically and in the required y by adding cost effective biosynthetic starch products. Therefore. these papers are produced with an average starch ption of 40 kg t". mainly by surface application. A further 25 kg t'1 is applied as an ve in the ting piant. This means that a high amount of starch is typically returned to the production process via recovered papers, where conventionally it is nearly not ed in the paper sheet. Therefore, this uncontrolled starch quantity leads to a considerable load in the white water circuit (usual COD levels from 5,000 to 30,000 mg Oz I“) and finally also in the waste water (cf. H Holik, Handbook of paper and board, Wiley—VCH Verlag GmbH & Co. KGaA, tst ed, 2006, Chapter 3.4.3).

Starch that is released in the wet end of a papermaking machine by the pulping of waste paper or broke is not fixed to fiber except through natural retention and it does not usually contribute to strength parameters.

WO 40 A2 discloses methods of making paper or paperboard. In one method, at least one cellulytic enzyme composition and at least one cationic polymer ition are introduced to a paper making pulp at about the same time to form a treated pulp.

EP 0,361,763 A2 discloses a composition for flocculating paper— or boardmaking filler comprising particles of starch in aqueous suspension, and a flocculating agent, eg a polyacrylamide- A1 discloses a papermaking process, wherein a first strength agent is added to a stock suspension containing pulp and optionally other ves prior to its being formed into a web at the wet end of a papermaking machine.

DE 24 33 325 A1 discloses a process for the manufacture of paper and cardboard from waste paper in closed circuits.

A2 discloses an aqueous printing ink and coating composition containing colorant, one or more high molecular weight starches and one or more water soluble acrylic polymers or co-polymers.

US 20061289139 A1 ses a method of improving retention and ge in a papermaking process. The method provides for the addition of an associative polymer, starch or a starch tive and optionally a siliceous material to the papermaking slurry.

US 2005/155731 A1 discloses a paperrnaking process, wherein a first th agent is added to a stock suspension containing pulp and optionally other additives prior to its being formed into a web at the wet end of a papen'naking machine.

A1 discloses fiber products. comprising in their body at least 20 % by weight of cellulose fibers. and adequate amounts of an acid and a cationic retention aid for the acid, that can be marked by means of a laser beam.

A1 relates to the manufacture of insulation paper facing having improved ion or inhibition in the growth of mold and/or fungus.

US 2004/171719 A1 ses a starch composition that is made by g a starch and combining the cooked starch with a polymer, the polymer containing anionic groups or potential anionic groups.

There is a demand for a method for manufacturing paper, paperboard or cardboard which has advantages compared to the s of the prior art.

SUMMARY OF THE INVENTION The invention relates to a method for manufacturing paper, paperboard or cardboard comprising the steps of (a) pulping an aqueous cellulosic al containing a starch; (b) preventing at least a portion of the starch from being microbially degraded by ng the aqueous cellulosic material containing the starch with one or more biocides, which are at least partially added to the cellulosic material in the thick stock area, where the cellulosic al has a stock tency of at least 2.0%; and (h) adding a dry and/or wet strength polymer to the cellulosic material.

Further, the invention relates to a method to increase the strength of paper, paperboard or cardboard, preferably the dry strength, comprising steps (a), (b) and (h) as described above.

It has been found that treating of waste paper or broke with a sufficient amount of a suitable biocide, eg. an oxidizing and/or non-oxidizing biocide program, during or after pulping, can WO 26578 prevent microbiological degradation of starch contained in waste paper or broke thereby decreasing the electrical conductivity of the aqueous phase of the cellulosic material.

Surprisingly, at 3 thus vely decreased electrical conductivity, the strength performance of dry and/or wet strength polymers such as cellulose reactive polymers bearing aldehyde functional groups can be substantially ed. Thus, it has been surprisingly found that when ng the electrical conductivity by adding ent amounts of le biocides. the consumption of dry and/or wet strength polymers that are needed in order to achieve a desired dry strength of the paper, paperboard or cardboard, can be substantially decreased.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows the dependency of redox potential (Figure 1A), pH value (Figure 18), and electrical conductivity (Figure 10) on the dosage of biocide in an experiment that was conducted on a paper mill.

Figure 2 shows an experiment conducted on a paper mill where increasing the e dosage immediately resulted in a substantial decrease of electrical conductivity from about 2000 pS/om to about 1500 uS/crn within only 1 day.

Figure 3 shows the dependency of performance of dry and/or wet strength polymers depending upon the electrical tivity of the s phase of the cellulosic material.

The performance of the dry and/or wet strength polymer is expressed in terms of an efficiency ratio that takes into account the increase of CMT, burst strength. tensile strength and dosage of dry and/or wet strength polymer.

DETAILED DESCRIPTlON OF THE INVENTION The control of microbiological activity in papermaking machines with both ing and non- oxidizing biocides is well documented. There is also wide spread literature on the use of starch as a dry and/or wet strength polymer and the use of synthetic dry and/or wet strength polymers which can be used either in addition to starch applied at both the wet and and on the surface of the paper sheet or as full or partial replacement of the starch.

The ion is concerned with the use of an effective biocide, e.g. an oxidizing and non- oxidizing microbiological control program, not only to prevent slime formation like in conventional paper manufacture, but to t the degradation of starch (nonionic/native/ cationiclanionic) present from the g of waste paper or broke; in combination with the use of a dry and/or wet strength polymer, preferably of a cellulose reactive polymer bearing aldehyde functional groups, in order to e paper strength, particularly dry th and/or wet strength. it has been found that microbial degradation of starch. which is released 9.9. by pulping recycled waste furnish, causes a substantial increase of electrical conductivity, particularly in partially or fuliy closed water circuits. r, it has been found that such starch ation can be effectively prevented by means of suitable biocides in le amounts (amylase control). Surprisingly, the thus achieved reduction of electrical conductivity provides much better dry and/or wet strength mance of conventional dry and/or wet strength polymers such as glyoxylated polyacrylamides and other cellulose ve rs bearing aldehyde functional groups.

The invention relates to the use of a biocide, e.g. an oxidizing and/or non-oxidizing biocide, as the first step in preventing starch degradation by microbiological activity se control), and the use of a dry and/or wet strength polymer in order to improve the dry and/or wet strength properties of the paper, paperboard or cardboard.

Thus, the method according to the invention features a two step approach: 1.) avoidance of microbiological starch degradation in board or papermaking machine approach flows with 2.) addition of dry and/or wet strength polymers providing a better performance because of the relatively low electrical conductivity achieved by step 1.).

A first aspect of the invention relates to a method - for treating a osic material used to cture paper; and/or — for making a paper product; and/or — for manufacturing paper, paperboard or ard; and/or - to increase the strength of paper. paperboard or cardboard; preferably the dry strength and/or wet strength; and/or - to decrease the consumption of dry and/or wet strength polymer; the method in each case comprising the steps of (a) pulping an aqueous cellulosic material containing a starch; (b) preventing at least a portion of the starch from being microbially degraded by treating the s cellulosic material containing the starch with one or more biocides, which are at PCT/EPZO] 2/003582 least partially added to the cellulosic material in the thick stock area, where the cellulosic material has a stock consistency of at least 2.0%; and (c) optionally, de-inking the cellulosic material; (d) ally, ng the oellulosic material; (e) optionally, bleaching the cellulosic material; (f) optionally, refining the cellulosic material; (9) ally, screening and/or cleaning the cellulosic material in the thick stock area; (h) adding a dry and/or wet strength r, preferably having a weight average molecular weight of at most 1,500,000 g/mol, more preferably at most 1,000,000 g/mol, still more preferably at most 500,000 g/mol, to the cellulosic material. (i) optionally, ing and/or cleaning the cellulosic material in the thin stock area, i.e. after diluting the thick stock into a thin stock; (j) optionally, forming a wet sheet from the osic material; (k) optionally, ng the wet sheet; and (I) optionally, drying the drained sheet.

In a preferred embodiment, the water circuit of the papermaking plant on which the method ing to the invention is performed is a e system, Le. a closed system. in another preferred embodiment, the water circuit of the papermaking plant on which the method according to the invention is performed is an open system.

Preferably, step (b) is performed at least partially aneously with step (a) or after step (a). Preferably, step (h) is performed at least partially after step (a). Preferably, step (h) is performed at least partially after step (b).

For the purpose of the specification, the term "nonedegraded starch" and the expression "preventing at least a portion of the starch from being microbially degraded" refers to any type of starch that preferably originates from waste paper or broke and in the course of the pulping preferably has ially maintained its molecular structure. This does include slight degrees of degradation, but compared to conventional processes, the structure of the non- degraded starch does preferably substantially not change (in terms of microbiological degradation) during the pulping and papermaking processes. 2012/003582 In a preferred embodiment, the method according to the invention comprises the additional step of adding starch to the cellulosic material. Thus, in this ment, the starch that is processed in accordance with the invention preferably originates from two sources: the first source is the starting material, eg. waste paper, already ning starch, and the second source is starch that is additionally added to the cellulosic material. The additionally added starch may be any type . i.e. native, anionic, cationic, non-ionic and the like. It may be added to the ceilulosic material in the thick stock area or in the thin stock area. When it is added in the thick stock area. it is preferably added at the machine chest, more preferably to the outlet of the machine chest. Alternatively or additionally, the starch can be added at the size press. In a preferred embodiment, the starch is sprayed, egg. in form of an aqueous solution, between the plies of a multi—piy paper, paperboard or cardboard.

The basic steps of paper manufacture are known to the skilled artisan. In this regard it can be referred to, e.g., C.J. nn, Handbook of Putping and Papermaking, Academic Press; 2 edition (1996); JP. Casey, Pulp and Paper, WiIey—Interscience; 3 edition (1983); and E.

Sibstrom et at, Analytical Methods in Wood Chemistry, Pulping and Papermaking ger Series in Wood Science), Springer; 1 edition (1999).

The raw al for paper is fiber. For the purpose of the specification, "pulping" is to be regarded as the process of separating the fibers, suitable for papermaking, from osic material such as recovered (waste) paper.

Modern papermaking typically involves seven basic operations: 1) fiber pretreatment; 2) fiber bIending; 3) furnish cleaning and screening; 4) slurry distribution and metering; 5) web ion and water removat by mechanical means; 6) web compaction and water l by means of heat; and 7) sheet finishing, by means of calendering, sizing, g, glazing. or converting of paper.

In practice, there are us variants of methods for manufacturing paper, paperboard or ard. All these variants have in common. however, that the overall method can be divided into the following sections which will be referred to the following to define preferred embodiments of the method according to the invention: (I) measures taking place before pulping; (II) measures associated with pulping; (III) measures taking pIace after pulping but still outside the papermaking machine; (IV) measures taking place inside the papermaking e; and (V) measures taking place after the papemnaking machine.

WO 26578 Typically, sections (I) to (II) are concerned with the processing of a thick stock of cellulosic al, s during section (III) the cellulosic material is converted from a thick stock to a thin stock by dilution with water, and section (IV) is thus concerned with the processing of a thin stock of osic material. All areas in which measures take place before dilution, preferably during step (lll) are preferably referred to as the “thick stock area”, whereas the remainder is preferably referred to as the "thin stock area“. ln a red embodiment of the invention, the water used for pulping the cellulosic material containing the starch is brought in contact with at least a part of the biocide, optionally provided as aqueous composition, in section (l) of the method for the manufacture of paper, i.e. before pulping.

In another preferred embodiment of the invention, the cellulosic material containing the starch is brought in contact with at least a part of the biocide. ally provided as aqueous composition, in section (ll) of the method for the manufacture of paper, i.e. in the course of pulping. n (ll) encompasses step (a) of the method according to the invention, s the supply of the cellulosic material containing the starch into the pulping device (pulper) and its removal therefrom are usually not considered as belonging to the pulping step per se, but are at least partially assed by section (II) as well. ln still another preferred embodiment of the invention, the cellulosic material ning the starch is brought in contact with at least a part of the biocide, optionally provided as aqueous composition, in section (III) of the method for the manufacture of paper, i.e. after g but still outside the papermaking machine. Preferably, the biocide is added to the cellulosic material containing the starch in the thick stock area.

Preferably, pulping is the first step in paper cturing where the cellulosic material is brought into contact with substantial amounts of water thereby generating aqueous slurry, i.e. an aqueous sion of cellulosic fibers, also referred to as pulp. Said pulp forms an intermediate, fibrous material for the manufacture of paper or paperboard.

The site of pulping is referred to as the pulper. i.e. a reaction vessel used for the manufacturing of an aqueous dispersion or suspension of the osic material. Sometimes, a pulper is also referred to as a hydrapulper or hydropulper. in case that recovered (waste) paper is used as the starting material for the paper manufacturing process, suitable recovered (waste) paper is typically directly introduced to the pulper. Waste paper may be also mixed with a quantity of virgin material to improve the quality of the cellulosic material.

For the e of the specification. the term "celiulosic material" refers to any material sing cellulose including recovered (waste) paper. Further, the term losic material" refers to all intermediate and final products during the paper making s. which originate from recovered (waste) paper, such as dispersions or suspensions of celiulosic material, pulped celiulosic material, de—inked celiulosic material, blended celiulosic material, bleached celiulosic material, refined celiulosic material, screened osic material and the final paper, oard or cardboard. Therefore, the term "ceiluiosic material" encompasses pulp, slurry, , stock, and the like.

The starch contained in the celiulosic material does not necessarily originate from the cellulose starting material (recycled material and the like). it is also possible that the entire amount of cellulose starting material is virgin material not containing any starch and that the starch contained in the celiulosic material originates from another source, preferably from a ulation unit ing the pulper with recycle water from the wet end of the papermaking machine. in a preferred embodiment, the celiulosic material containing the starch originates from waste paper or broke, but may be blended with e.g. virgin material (=> recycle pulp and blended pulp, respectively).

In a preferred embodiment, the starch content of the celiulosic material containing the starch, la. the waste paper or broke that is ed as starting al, is at least 0.1 wt.—%, more preferably at least 0.25 wt.-%. or at least 0.5 wt.-%, or at least 0.75 wt.—%, or at least 1.0 wt.— %. or at least 1.5 wt.-%, or at least 2.0 wt.-%, or at least 3.0 wt.-%, or at least 5.0 wt.-%, or at least 7.5 wt.-%, or at least 10 wt.-%, or at least 15 Wt.'%, based on the weight of dry celiulosic material. in another red embodiment, the starch is added to the celiulosic material, e.g. to virgin material. in the course of paper manufacture, preferably in the thick stock area. Preferably, a portion of the y added starch is fixated to the celiulosic fibers before the web is formed and the water is drained off. Due to recirculation of at least a portion of the water drained from the pulp, another n of the starch is returned to the beginning of the overall process. Thus, the starch does not arily originate from waste paper, but may alternatively or additionally also originate from the method itself.

According to the invention, the cellulosic material contains a starch. For the e of the specification, the term "starch" refers to any modified or non-modified starch typically employed in paper manufacture. Starch is a polysaccharide carbohydrate consisting of a large number of glucose units joined together by idic bonds. Starch is ed by all green plants as an energy store. Starch is composed of two types of molecules: the linear and helical amylose and the branched amylopectin. Depending on the origin, native starch usually contains 20 to 25% amylose and 75 to 80% amylopectin. By physical, enzymatic or al treating native starch, a variety of modified starches can be prepared, including nic, anionic and cationic starches.

Preferably, the starch contained in the cellulosic material has an amylose content within the range of from 0.1 wt.—% to 95 wt.-%.

In a preferred embodiment of the invention, the starch contained in the cellulosic material is substantially pure amylase, i.e. has an amylose content of about 100 wt.-%. In another preferred embodiment of the invention, the starch ned in the cellulosic material is substantially pure amylopectin, i.e. has an amylopectin content of about 100 wt.-%. ln still another red embodiment, the amylose content is within the range of 22.5:20 wt.-%, whereas the amylopectin content is preferably within the range of 77.5120 wt.-%.

In a preferred embodiment, the starch is nic, preferably native starch. In another preferred embodiment, the starch is anionic. In still r red embodiment, the starch is cationic. In yet another preferred embodiment, the starch contains both charges, anionic as well as ic. whereas the relative content may be balanced, dominated by anionic charges or dominated by cationic charges.

In a red embodiment, the starch that is contained in the cellulosic material, preferably before pulping, has a weight average lar weight of at least 25,000 g/mol. in a preferred embodiment, the relative weight ratio of the starch and the cellulosic materiai (solid contents) is within the range of 11201175) or 1150140) or 1:000:90) or 12(200i90) or 12(400t200) or 12(6001-200) or 118001200).

A person skilled in the art knows that the cellulosic material may contain further components besides cellulose, such as als used for the chemical and semi-chemical g step, dyes, bleaching agents, , etc.

If not expressly stated otherwise, percentages based on the cellulosic material are to be regarded as being based on the overall composition containing the cellulosic al and the starch (solids content).

If not explicitly stated vise, for the purpose of the specification, the term "paper—making process" or "method for the manufacture of paper" refers to the manufacturing of paper as well as to the manufacturing of paperboard and cardboard.

For the purpose of the specification, the cellulosic starting material for the manufacturing of paper, paperboard and/or cardboard, which originates from red ) paper, is referred to as le material", whereas fresh starting material is referred to as n material“. It is also possible that a blend of virgin material and recycle material is used as the starting material for the paper making process, which is herein referred to as ”blend material". Furthermore, it is also possible that the cellulosic starting material is "broke" or "coated broke" (recess material) which, for the purpose of the specification, shall be encompassed by the term “recycle material".

For the purpose of the specification, the pulp which originates from virgin material, recycle al or blend material is ed to as n pulp", "recycle pulp" and ”blend pulp", respectively.

Typically, water is added during the mechanical pulping step to the cellulosic material, is. to the virgin, recycle or blend material, to produce the respective cellulosic pulp, is virgin, recycle or blend pulp. The respective pulp is usually a fibrous aqueous dispersion or fibrous aqueous suspension of the cellulosic al.

The mechanical pulping process is typically performed by exposing the cellulosic material to mechanical force, more specifically shearing force.

According to the invention, biocide is present during the pulping step andlor is added thereafter, preferably shortly fter. Microorganisms coming from waste paper also play a role in the degradation of starch contained in the waste paper, particularly when the waste paper is stored for days or months and subjected to microorganism activity during this storage time. Treating waste paper with biocide during pulping cannot reverse the effects caused by microorganism activity upon the starch during waste paper e. r, growth conditions of microorganism improve significantly during pulping — when the paper gets in contact with process water - and the inventors have found that it is advantageous to add the biocide at this stage of the process. Since the degradation caused by the microorganisms usually takes more time than a few minutes, the inventors have found that it may also be sufficient to add the biocide shortly after pulping.

For that purpose, the cellulosic material that contains the starch, i.e. the virgin. recycle or blend material, is brought into contact with biocide. If the biocide is added shortly after the g step, it is preferably added to the cellulosic al 1 to 60 minutes after the pulping step has been finished. ln order to treat the cellulosic al containing the starch with biocide ing to the invention, it is apparent to a person skilled in the art that at least a part of the total amount (total inflow) of biocide is added to the cellulosic material ning the starch at any time during the pulping step (a), is. after the pulping has been commenced, or y after the pulping has been completed. The e can be added continuously or discontinuously.

For the purpose of the specification, the term "continuously" means that the amount (inflow) of the biocide for the specific dose is added to the osic material containing the starch without interruption.

For the purpose of the specification, the term "discontinuously" means herein that the addition of the biocide to the cellulosic material containing the starch is performed by means of pulses of a predetermined length which are interrupted by periods during which no biocide is added at this feeding point.

A skilled person is aware that paper making processes as such are typically uous processes. Thus, any "amount" or "dosage" of biocide, dry and/or wet strength polymer and further additive, respectively, that is to be added to the cellulosic material refers to a reapective "inflow" of said biocide, dry and/or wet th polymer and further additive, respectively, in order to achieve a desired predetermined local concentration thereof in the stream of the cellulosic material. Said inflow may be uous or discontinuous.

Accordingly. when the "amount" or "dosage" of biocide, dry and/or wet strength polymer and further additive, respectively. is divided into portions that are added to the cellulosic material at different locations and/or during different process steps, each n refers to a partial WO 26578 inflow of said biocide, dry and/or wet strength polymer and further additive, respectively, in order to achieve a desired predetermined local concentration f, i.e. downstream with respect to its feeding point.

Typically, water is added to the cellulosic material, i.e. to the virgin, recycle or blend material, prior to and/or during the pulping step. At least a part of the total amount (total inflow) of the biocide may be ved, dispersed or suspended in said water used to repulp the osic material containing the starch, i.e. to the , recycle or blend material. ln this embodiment, the biocide and the water used for the pulping may already be brought into contact with one another before pulping is initiated.

In a preferred embodiment ing to the invention, the biocide is in contact with the water used for the pulping at least 10 min before pulping commences, or at least 30 min, or at least 60 min, or at least 120 min, or at least 150 min, or at least 180 min, or at least 210 min, or at least 240 min, or at least 300 min, or at least 360 min, or at least 420 min, or at least 480 min.

Typically, the pulping step (a) may take several minutes to several hours. In another preferred embodiment, at least one part of the total amount (total inflow) of the biocide is added to the osic material during the pulping period.

For the purpose of the specification, the term "pulping period" is defined as the total time the pulping step is performed.

For example, in case that the pulping step takes a total time of 1 hour (pulping period), the biocide may be added discontinuously or continuously to the pulper at any point of time or during any time interval, e.g., up to 120 s after the pulping step has been commenced. in step (b) of the method according to the invention the cellulosic al containing the starch is d with one or more biocides, which are at least partially added to the cellulosic material in the thick stock area, where the cellulosic material has a stock consistency of at least 2.0%, preferably thereby preventing microbial degradation of at least a portion of the starch. In a preferred embodiment, step (b) is at least lly simultaneously performed with step (a) of the method according to the invention, i.e. the biocide treatment is performed during pulping. in another preferred embodiment, step (b) is performed after step (a) has been completed. A skilled person recognizes that any full or partial time overlap of steps (a) and (b) is possible and in accordance with the invention.

In a preferred embodiment, the total amount (total inflow) of biocide is added to the cellulosic material during the pulping step (a) discontinuously or uously; is. 100 wt.-% of the total amount (total inflow) of the biocide is added to the cellulosic al, i.e. to the virgin. recycle or blend material, during the pulping step (a).

In another preferred method, further parts of biocide may be added at any time preferably up to 480 min after the pulping step (a) has been commenced at any suitable place in order to avoid degradation of the starch. This embodiment es the addition of further parts of the biocide either during the pulping step (a) or preferably up to 60 minutes after pulping has been completed. ln a red embodiment, at least a part of the total amount (total inflow) of the biocide is added to the cellulosic material containing the starch at any preferably time up to 60 s after the pulping step (a) has been completed.

In a preferred embodiment, one or more biocides are added to the cellulosic material at at least 2 different feeding points, more preferably at least 3 different feeding points, and still more preferably at least 4 different feeding points on the papermaking plant, where cal or different biocides or biocide combinations can be added at the various feeding points.

According to the method of the invention, step (b) ably serves the purpose of avoiding degradation of the starch, which is contained in the cellulosic material, by eradicating the microorganisms that are ise capable of degrading the starch (amylase control). in a preferred embodiment, the one or more biocides are discontinuously added to the cellulosic material on a continuously ing papermaking plant. The one or more biocides are preferably added by means of pulsed feed rates, Le. peaks in the local concentration of the e in the cellulosic material reaching the critical local concentration that is necessary in order to eradicate the rganisms thereby effectively preventing starch from being degraded. In other words, the cellulosic material passing the feeding point(s) of biocide is transiently locally enriched by biocide in predetermined intervals (biocide intervals) that are interrupted by intervals during which no biocide is locally added ve intervals).

Preferably, a biocide interval lasts typically at least about 2 minutes. but may also last e.g. up to about 120 minutes. ably, the biocide is added to the cellulosic al on a continuously ing papermaking plant during 24 h by means of at least 4, 8, 12, 16, 20, , 40, 50, 60, 70 or more biocide intervals that are separated from one r by a respective number of passive intervals, wherein during each biocide interval the desired and predetermined local concentration of the biocide in the osic material is reached.

In another preferred embodiment, the one or more biocides are continuously added to the cellulosic material on a continuously operating papermaking plant.

Preferably, biocide is added to the cellulosic material at at least two feeding points. which are located downstream of one another. For e, biocide is added at a first feeding point and at a second feeding point being located downstream with respect to the first feeding point. Depending upon the half-life and distribution of the biocide in the cellulosic material, the cellulosic material passing the second g point may already locally contain biocide that has been added thereto upstream at the first feeding point. Thus, the amount of biocide locally added at the second feeding point can be lower than the amount locally added at the first g point in order to reach the same desired and ermined local concentration of the biocide in the osic material that is necessary in order to eradicate the microorganisms thereby effectively preventing starch from being degraded.

Preferably, biocide, more preferably an ing two-component biocide, is added in n (I) and/or (II); and optionally also in section (III) and/or (IV) of the papermaking plant; more preferably in section (I) and/or (II); as well as in section (IV) of a papermaking plant comprising a papermaking machine, wherein section (I) includes measures taking place before pulping; section (II) includes measures associated with pulping; section (III) includes measures taking place after pulping but still outside the papermaking e; and section (IV) includes measures taking place inside the papermaking machine.

At least one part of the biocide is preferably added during the pulping step (a) or shortly fter. Provided that the biocide which was initially added during g step (a) is not completely removed or consumed in the subsequent steps, the biocide is also present in the process steps (0), (d). (e), (f) and (g), if any, which follow the pulping step (a).

In a preferred embodiment, at least one part of the remainder of the total amount (total inflow) of the biocide is added to the cellulosic material during any of steps (c), (d), (e), (f) and/or (9). For example, 50 wt.-% of the total amount (total inflow) of the biocide may be added continuously or discontinuously, prior to and/or during the pulping step (a) and the remaining 50 wt.-% of the total amount (total inflow) of the biocide may be added WO 26578 continuously or discontinuously, prior to, during and/or after the process steps (c), (d), (e), (f) and/or (9).

Provided that the biocide which was added during step (b) and ally in the process steps (c), (d), (e). (f), and (9), if any, which follow the pulping step (a), is not completely removed in the subsequent steps, said biocide is also present in the papermaking machine.

A great variety of microorganisms can be found in the pulping process. Each type of pulp has its own microbial characteristics. in general, the microorganisms observed in paper manufacture are species of bacteria, yeast and fungi; algae and protozoa exist but rarely cause problems. Problems caused by microorganisms can be very different. Very well known problems are slime formation and corrosion.

Species of the following bacteria genera belong to the usual contaminates of pulp: Achromobacter, mycetes, Aerobacter, Alcaligenes, Bacillus, Beggiatoa, Crenothrix, Desulphovibrio, Flavobacterium, nella, Leptothrix, Pseudomonas, Sphearotilus, and Thiobacillus. Species of Alcaligenes, Bacillus and Flavobacterium as well as species of the yeast, Monifia, cause pink slime. Red or brown slime is caused by the bacteria that form ferric hydroxide, namely species of Crenothrix, Gallionella and Leptothrix. Species of Thiobacr'llus and Beggiatoa are corrosion bacteria in that they oxidize sulphides to sulphuric acid. Species of Desulphovibrio are also corrosion bacteria for the opposite reason. Species of the latter genus reduce sulphate to en sulphide which interacts with metal to cause ion. Metallic sulphides are also black, which is another unwanted effect of sulphate- reducing ia.

Among the fungi, s of the following genera are found most frequently in pulp systems: Aspergillus, Basidicmyces, Cephalosporium, Cladosporium, Endomyces, Endomyopsis, Mucor, Penicillium, and Trichoderma. Blue stain on wood is caused by Cephalosporium and Cladosporium. y, species of the following genera of yeast may be isolated from pulp: Monilia, Pullularia, Rhodotoru/a and Saccharomyces. For further details it is referred to H.W. ore, Handbook of Biocide and Preservative Use, r Paper and Pulp, Chapman & Hall, 1995.

Most predominant species expriming amylase and thus causing starch degradation include mycetes, Aerobacter, Bacillus, toa, Desulphovibrio, Flavobacterium, Gallionella, Leptothrix, Pseudomonas, Thiobacillus; Aspergillus, Basidiomycetes, Cephalospon’um, ces, Endomycopsis, Mucor, Penicillium; aria, and Saccharomyces.

Thus. the purpose of adding biocide according to the invention ially serves the purpose of eradication one or more of the aforementioned microorganisms and the dosages of biocide are preferably adapted accordingly.

The biocide may be s, solid or liquid; organic or inorganic; oxidizing or non-oxidizing.

The biocide may be employed in substance or in dilution with a suitable solvent, preferably water, in solution or dispersion, suspension or emulsion.

The biocide may be a one-component biocide, a two-component e or a multi- component biocide.

The biocide preferably has a comparatively short half-life, i.e. is decomposed comparatively quickly thereby losing its biocidial action. When a combination of two or more biocides is employed, the half—life of at least one biocide within said combination is ably comparatively short. Preferably, under the conditions of the method according to the invention (temperature, pH and the like), the half-life of the biocide is not more than 24 h, or not more than 18 h, or not more than 12 h, more ably not more than 10 h, still more preferably not more than 8 h, yet more preferably not more than 6 h, most preferably not more than 4 h and in ular not more than 2 h. The halfslife of a given biocide can be easily determined by routine experimentation, preferably under the general ions of the method according to the invention. it has been surprisingly found that biocides having a atively short half-life are effective in ting starch degradation by ating the microorganisms, which would otherwise decompose the starch, but do not cause problems in the waste water system, which typically also relies on microorganisms that should not be eradicated by the biocide. Further, it has been surprisingly found that biocides having a comparatively short half-life can be employed at comparatively high concentrations without causing substantial problems ing the waste water treatment.

In the US. biocides to be employed in the production of paper and paper board for use in contact with food must be on the approved list of the US Food and Drug Administration (FDA).

In a preferred embodiment, the biocide is selected from oxidizing and idizing es.

Examples of oxidizing biocides include one component systems such as ClOz, H202 or NaOCl; and two component systems sing e.g. a nitrogenous compound. preferably an inorganic ammonium salts in combination with an oxidant, preferably a halogen source. more preferably a chlorine source, most preferably hypochlorous acid or a salt thereof, such as NH4Br/NaOCl or SO4/NaOCl; and two component systems comprising e.g. c biocides in combination with an oxidant, preferably a halogen source, more ably a chlorine , most preferably hypochlorous acid or a salt thereof, such as bromochloro- ,5-dimethylimidazolidine~2,4-dione (BCDMH)/NaOCl, or dimethylhydantoin (DMH)/NaOCl,. in a particularly preferred embodiment, the e is an oxidizing two—component biocide where the first component is a nitrogenous compound, preferably selected from ammonia, amines, inorganic or organic salts of ammonia, and inorganic or organic salts of amines; and the second component is a halogen source, preferably a chlorine . The combinations NH4BrINaOCl or (NH4)ZSO4/NaOCl are particularly preferred exidizing biocides.

Preferred nitrogenous compounds include ammonium salts, methylamine, dimethylamine, ethanolamine, ethylenediamine, diethanolamine, triethanolamine, dodecylethanolamine, hexdecylethanolamine, oleic acid ethanolamine, triethylenetetramine, dibutylamine, tributylamine, glutamine, dilaurylamine, disteaiylamine, tallow-methylamine, coco-methyl- amine, n-acetylglucosamine, diphenylamine, ethanolmethylamine, diisopropanolamine, n- methylaniline, n~hexyl-n-methylamine, n—heptyl—n-methylamine, n—octyl-n—methylamine, n— nonyl-n-methylamine, n-decyl-n-methylamine, mdodecyl-nmethylamine, n-tridecyl-n-methyl- amine, a-decyI-n-methylamine, n-benzyl-n-methylamine, n—phenylethyl-n-methylamine, n—phenylpropyl-n-methylamine, n—alkyl-n-ethylamines, n-alkyl—n-hydroxyethylamines, n-alkyln-propylamines , n-propylheptyl—n-methylamine, n-ethylhexyl-n-methylamine, n-ethylhexyl-n- butylamine, n—phenylethyl-n-methylamine, n-alkyl-n-hydroxypropylamines, n-alkyl-n— isopropylamines, n-alkyl-n-butylamines and n~alkyl-n-isobutylamines, n-alkyl-n-hydroxyalkyl- amines, hydrazine, urea, guanidines, biguanidines, polyamines, y amines, secondary amines, cyclic amines, bicyclic amines, oligocyclic amines, aliphatic amines, aromatic amines. primary and ary en containing polymers. es of um salts include ammonium bromide, ammonium carbonate, ammonium chloride, ammonium fluoride, um hydroxide, ammonium iodide, ammonium nitrate. ammonium phosphate, and ammonium sulfamate. Preferred nitrogenous nds are ammonium bromide and ammonium chloride.

Preferred oxidants include chlorine, alkali and alkaline earth lorite salts, hypochlorous acid, chlorinated isocyanurates, bromine, alkali and alkaline earth hypobromite salts, hypobromous acid, bromine chloride. halogenated hydantoins. ozone and peroxy compounds such as alkali and alkaline earth ate salts, alkali and alkaline earth percarbonate salts, alkali and alkaline earth persulfate salts, hydrogen peroxide, boxylic acid, and peracetic acid. Particularly preferred halogen sources include reaction products of a base and a n, such as hypochlorous acid and the salts thereof.

Preferred salts of hypochlorous acid e LiOCl, NaOCl, KOCl, Ca(OCl)2 and Mg(OCl)2, which are preferably provided in aqueous solution. Preferred inorganic salts of ammonia include but are not d to NH4F, Nchl, NH4Br, NH4l, NHiHcoa, (NH4)2C03, NH4N03, NH4H2POZ, NH4HZPO4, (NH4)2HPO4, NH4803Ni-l2, NH4l03, NH4SH, (NH4)ZS, NH4H803, (NH4)2803, NH4HSO4, (NH4)ZSO4, and (NH4)28203. red organic salts of ammonia include but are not limited to NH4OCONH2, CchOZNH4 and HCOZNH4. The amine can be a primary or ary amine or the amine portion of an amide; for example urea, or alkyl derivatives thereof such as N-N’—dimethyl urea, or N’-N’-dimethylurea. The combination of NH4Br and NaOCl is particularly preferred and known e.g. from US 7,008,545, EP-A 517 102, EP 785 908, EP 1 293 482 and EP 1 734 009. ably, the relative molar ratio of said first component and said second component is within the range of from 100:1 to 1:100, more preferably 50:1 to 1:50, still more preferably 1:20 to 20:1, yet more ably 1:10 to 10:1, most preferably 1:5 to 5:1 and in particular 1:2 to 2:1.

Compared to strong oxidizers, biocides of this type, i.e. ations of ammonium salts with hypochlorous acid or salts thereof, have particular advantages.

For a number of years, strong oxidizers have been used to control microbial populations in the paperrnaking industry. Maintaining an ive level of oxidizer is not always easy or economically viable because paper process streams t a high and variable "demand" on the oxidizer. This demand is caused by the presence of organic materials such as fiber, starch, and other colloidal or particulate organic als in the process. These organic materials react with and consume the er, making it much less effective at controlling microbial populations. In order to achieve an effective oxidizer residual in high-demand s, such as papermaking machines, the oxidizer must be overfed to surpass the demand in the system. Overfeeding strong oxidizers not only leads to higher treatment costs but can also cause many adverse side effects in the paperrnaking system. These side effects include sed consumption of dyes and other costly wet and additives (for example, optical brighteners and sizing agents), increased corrosion rates, and reduced felt life. Some oxidizers also greatly contribute to the amount of nated organic compounds (AOX) produced in the papemiaking process. Furthermore. excessive residuals of certain oxidizers may be adequate for controlling microbial tions in the bulk fluid but are ineffective at controlling biofilm due to limited penetration into the biofilm matrix.

In contrast to strong oxidizers, biocides produced by blending ammonium salts, such as an ammonium bromide solution. with eg. sodium hypochlorite and mill freshwater under specific reaction ions can be described as a weak oxidizer. The biocide is produced onsite and immediately dosed to the paper system. The dosage required depends on several factors, including freshwater usage, water recycle, and presence of reducing . Biocides of this type thus have a comparatively short half—life and therefore do not accumulate which could cause problems concerning the waste water treatment. Further, they are not too aggressive, i.e. do not oxidize the other constituents of the cellulosic material but are comparatively selective for rganisms.

Oxidizing one or two component biocides of this type can be employed alone, or preferably, particularly when the starting material comprises recycle pulp, in combination with non- oxidizing biocides. es of non-oxidizing biocides include but are not limited to quaternary ammonium compounds, benzyl—C12-,e-alkyldimethyl chlorides (ADBAC), pothexamethylenebiguanide (biguanide), 1,2-benzisothiazol—3(2H)—one (BIT), bronopol (BNPD), bis(trichloromethyl)— sulfone. diiodomethyl-p-tolylsulfone, sulfone, bronopol/quaternary ammonium compounds, benzyl-Cizw-alkyldimethyl chlorides (BNPD/ADBAC), bronopoI/didecyldimethylammonium chloride (BNPD/DDAC), bronopol/S-chloro—Z-methyI-ZH-isothiazol-3—one/2-methyl—2H-iso— lone (BNPD/Iso), NABAM/ sodium dimethyldithiocarbamate, — dimethyldithiocarbamate—N,N-dithiocarbamate (NABAM), methyldithiocarbamate. sodium dimethyldithiocarbamate, 5-chloro—Z-methyl—4—isothiazolin-3~one (CMlT), 22* dibromo-Z-cyanoacetamide (DBNPA), DBNPA/bronopolliso (DBNPA/BNPD/lso), 4,5- dichloro-Z-n-octyl-S-isothiazolinone (DCOIT), ldimethylammonium chloride (DDAC), ldimethylammoniumchloride, alkyldimethylbenzylammoniumchloride (DDAC/ADBAC), dodecylguanidine drochloride/quaternary ammonium compounds, benzyl-Cme- alkyldimethyl chlorides (DGH/ ADBAC), dodecylguanidine monohydrochloride/methylene dithiocyanate (DGH/MBT), gluteraldehyde (Glut), gluteraldehyde/quatemary ammonium compounds/benzylcoco alkyldimethyl chlorides (Glut/coco), gluteraldehyde/ ldimethylammonium chloride (Glut! DDAC), gluteraldehyde/S-chloromethyl-2H-isothiazol-3— one] 2-methyl-2H-isothiazoIone (Glut/ISO), aldehyde/methylene dithiocyanate (Glut/MBT), S-chloromethyl-2H-isothiazoi—3-one/2—methyl-2H-isothiazol~3-one (lso), methyiene dithiocyanate (MBT), 2-methyiisothiazolinone (MIT), methamine oxirane (methamine oxirane), sodium bromide (NaBr), nitromethylidynetrimethanol, 2-n-octyl isothiazolin-3~one (OlT), bis(trichloromethyl) sulphone/ quaternary ammonium compounds, benzyl-Ci2,15-alkyidimethyl chlorides (sulphoneIADBAC). symclosene, terbuthylazine, dazomet (thione), tetrakis(hydroxymethyi)phosphonium sulphate(2:1) (THPS) and p- [(diiodomethyl)suiphonylltoluene (tolyl sulphone), and mixtures thereof.

A skilled person knows that a single biocide or a single multi-component biocide can be employed or a combination of different biocides.

In a particularly preferred embodiment of the invention, preferably when the starting material comprises recycle pulp, the biocide is a e system, preferably comprising a first biocide composed of an nic ammonium salt in combination with a halogen source, preferably a chlorine source, more preferably hypochlorous acid or a salt thereof, and a further biocide, preferably ed from the non-oxidizing and/or organic es, preferably non-oxidizing organic biocides. For the purpose of the specification, unless expressly stated ise, the one or more biocides referred to in step (b) may encompass said further biocide, if present.

In a preferred embodiment, the non-oxidizing biocide ses bronopol (BNPD) and at least one isothiazolone compound (iso) ed from the group consisting of 1,2- othiazol-3(2H)-one (BIT), romethyl~4-isothiazolin-3—one , 4,5-dichloro- 2-n-octylisothiazolinone (DCOIT), methylisothiazolinone (MIT), 2-n-octyl isothiazoiin—S-one (OiT); and/or a sulfone selected from bis(trichloromethyi)sulfone and diiodomethyl-p—tolylsulfone. The combination bronopol/5-chloroQ-methyl-ZH-isothiazol—S— oneIZ-methyI-ZH—isothiazol-Bcne (BNPD/lso) is particularly preferred. in another preferred embodiment, the non-oxidizing biocide comprises compounds bearing quaternary um ions in combination with bronopol (BNPD) or in combination with a sulfone selected from bis(trichloromethyl)sulfone and methyl-p-tolylsuIfone. The biocide system, preferably comprising an oxidizing biocide and a non-oxidizing biocide, is particularly preferred when the nce time of the biocide in the thick stock is comparatively long, i.e. the time from the point in time when the biocide is added to the cellulosic al until the point in time when the osic material enters the papermaking machine. In a preferred embodiment. the above biocide system comprising a first and a further biocide is employed when said residence time is at least 1 h, or at least 2 h, or at least 4 h, or at least 6 h, or at least 8 h, or at least 10 h.

Said biocide system is particularly preferred when the starting materiai comprises recycle pulp. When the starting material essentially ts of virgin pulp, however, the on of a further biocide is preferably omitted.

When such combination of es is employed. at least a portion of the first e is preferably added to pulper dilution water, while the further biocide is preferably added to the outlet of the pulper and/or to the inlet of the fiber clarification.

A further one or two component biocide (further biocide) that differs in nature from the biocide of step (b) (first biocide) may be also added to the cellulosic material containing the (nonvdegraded) starch prior to, during or after the process steps (0) to (g) and/ or after the cellulosic material has been supplied to the papermaking machine. in a preferred embodiment, at least one part of the remainder of the total amount (total inflow) of the biocide (first biocide) and/or another biocide (further biocide) is added to the cellulosic al subsequent to any of steps (0), (d), (e), (1') and/or (9), i.e. at the papermaking machine. For example, 50 wt.—% of the total amount (total inflow) of the first biocide may be added discontinuously or continuously prior to and/or during the pulping step (a) and/or after the process steps (c), (d), (e), (f) and/or (9), and the remaining 50 wt.-% of the total amount (total inflow) of the first e may be added discontinuously or continuously, at the papermaking machine. ln a preferred embodiment, further biocide (i.e. another portion of the first biocide and/or a further biocide differing in nature from the first biocide) is added to the cellulosic material ning the (non-degraded) starch at the wet and of the papermaking machine, ably at the wire section. In a preferred embodiment, said further biocide is added at the machine chest or mixing chest, or at the regulating box, or at the constant part of the papermaking machine. In a preferred embodiment, at least a portion of said further biocide is added to one or more water streams of the papermaking plant selected from the group consisting of pulper on water, white water (such as white water 1 and/or white water 2), clarified shower water. clear filtrate, and inlet of ciarification. Adding at least a portion of said further biocide to the pulper dilution water is particularly red.

The dosage of the one or more biocides depends upon their antimicrobial efficacy. According to the ion, biocide is dosed in an amount sufficient to prevent ntial ation of the starch contained in the cellulosic material. Suitable dosages for a given biocide can be determined by e experimentation or by comparing the number of microorganisms WO 26578 before and after on of the biocide (taking into account that biocides typically need some time in order to eradicate microorganisms).

The addition of biocides during the papermaking process has been known for many years.

The presence of microorganisms in the pulp and papermaking s is unavoidable and thus, steps are taken to control their growth and numbers. It would be unrealistic to attempt to kill all the microorganisms. Instead the objective is typically to control. or suppress, the multiplication of microorganisms and thus to curtaii their metabolic activities.

In conventional methods for manufacturing paper, paperboard or cardboard the build up of slime is one of the most important indicators that microbial growth and microbial activities must be curtailed. in conventional methods for manufacturing paper, paperboard or cardboard, the biocide is typically added for the conventional purpose of avoiding slime formation, corrosion and/or wet and , lling wet and deposition or for odor control, but not for the purpose of avoiding microbial ation of the starch. which is contained in the cellulosic material, by ating the microorganisms that are otherwise capable of degrading the starch with the intention to (re-)iixate this starch later on with polymers as described hereinafter.

The above conventional purposes require comparatively low amounts of biocides keeping only relatively small sections of the overall papermaking plant antimicrobially lled. In contrast, the avoidance of starch degradation according to the invention, i.e. the partial or full eradication of the microorganisms that are capable of ing the starch (amylase control), typically requires substantialty higher amounts/concentrations of e. As further shown in the experimental section, the amount of biocide that is preferably employed in accordance with the ion in order to avoid starch degradation is at least 2 times. ably at least 3 times higher than the amount of biocide conventionally employed in papermaking processes for conventional purposes. Furthermore. the distribution of the biocide that is preferably ed by g the biocide at various feeding points d in various sections of the papermaking plant in the method according to the invention in order to avoid starch degradation at any places is not conventional. For example. according to the product specification of aqueous ammonium bromide compositions currentiy marketed as microbiological control agent precursor for paper manufacture, the recommended dosage varies merely from 150 — 600 g/t of dry fiber at an active content of 35%, which corresponds to a maximum dosage of only 210 g ammonium bromide per ton of dry fiber. However, by such a conventional biocide treatment, i.e. by 210 g/t of dry fiber and without addition of r biocide at further ons, the starch that is contained in the remainder of the papermaking plant is still substantially degraded.

In a preferred embodiment of the method according to the invention, step (b) involves the reduction of the t of microorganisms that are contained in the cellulosic material and that a capable of degrading starch by treating the cellulosic material containing the starch with a sufficient amount of a suitable biocide.

In another preferred embodiment of the method according to the invention, step (b) involves the partial or full avoidance, prevention, suppression or reduction of starch degradation by microorganisms that are contained in the cellulosic material and that a capable of degrading starch by treating the osic material containing the starch with a sufficient amount of a suitable biocide.

In r preferred embodiment of the method according to the invention, step (b) es the l or full preservation of starch against degradation by microorganisms that are contained in the cellulosic material and that a capable of degrading starch by treating the cellulosic material containing the starch with a sufficient amount of a suitable biocide.

Degradation of the starch contained in the cellulosic material can be monitored by measuring various parameters, eg. pH value, electrical conductivity, ATP (adenosine triphosphate) content. redox potential, and extinction. Microbiological activity need to be reduced significantly in the entire system, compared to conventional biocide treatments. Thus, the efficacy of a given biocide in a given amount with respect to its effect on the prevention of starch degradation can be investigated by routine experimentation, i.e. by monitoring pH value, electrical conductivity, ATP content, redox-potential, and/or extinction (iodine test) and comparing the ion t biocide treatment to the situation with biocide treatment after a ent bration period (typically at least 3 days, preferably 1 week or 1 month).

A d person is fully aware that papermaking plants comprise a water circuit to which more or less fresh water is added (open system and closed system, respectively). The cellulosic material is brought into contact with the process water at or before pulping step (a), is further diluted by addition of process water when the thick stock is converted into thin stock, and is separated from the process water on the papermaking e where sheet formation takes place. The process water is returned (recycled) through the water circuit in order to reduce the ption of fresh water. The parameters of the process water in the water t are typically equilibrated, the equilibrium being influenced by system size, added quantity of fresh water, properties of the starting material, nature and amount of additives, and the like.

In a preferred embodiment of the invention, the process water of a continuously operating papermaking plant, on which the method according to the ion is performed, is at least partially recycled. Preferably, at least 5 vol.-% or at least 10 vol.-% or at least 25 vol.-% or at least 50 vol.-% or at least 75 vol.-% or at least 90 vol.-% of the process water are recycled, i.e. the added fresh water preferably amounts to at most 95 vol.—% or at most 90 vol.—% or at most 75 vol.—% or at most 50 vol.-% or at most 25 vol.-% or at most 10 vol.-%.

When changing the process conditions in accordance with the invention, e.g. by addition of higher ties of biocide at various locations, some ters spontaneously change locally and reach an equilibrium in the entire system within hours or days, e.g. redox potential, ATP level and oxygen reduction potential (ORP), whereas other ters typically need more time to equilibrate, e.g. pH value and electrical conductivity.

Typically. the undesired starch degradation leads to a decrease of the pH value of the aqueous osic al. Thus, efficient prevention of starch degradation by eradication of rganisms due to biocide treatment can be red by measuring the pH value of the aqueous phase of the cellulosic material. Preferably, in step (b) of the method according to the invention the one or more biocides are continuously or discontinuously added to the cellulosic material in quantities so that after 1 month of treatment, preferably after two months of treatment on a continuously operating papermaking plant, the pH value of the aqueous phase of the cellulosic material has been increased by at least 0.2 pH units, or by at least 0.4 pH units, or by at least 0.6 pH units. or by at least 0.8 pH units, or by at least 1.0 pH units, or by at least 1.2 pH units, or by at least 1.4 pH units. or by at least 1.6 pH units, or by at least 1.8 pH units, or by at least 2.0 pH units, or by at least 2.2 pH units. or by at least 2.4 pH units. ed to the pH value that was measured, preferably at the same location, preferably at the wet end entry of the papermaking e immediately before biocide was added for the first time or before the addition of higher amounts of biocide than conventionally employed was started, i.e. compared to a situation where microorganisms had been degrading the starch thereby g a decrease of the pH value. Preferably, in step (b) of the method according to the invention the one or more biocides are continuously or discontinuously added to the cellulosic material in quantities so that after 1 month of treatment, preferably after two months of treatment on a continuously operating papermaking plant, the pH value of the aqueous phase of the cellulosic al measured at the wet end entry of the papermaking machine has been decreased by not more than 2.4 pH units, or by not more than 2.2 pH units, or by not more than 2.0 pH units, or by not more than 1.8 pH units, or by not more than 1.6 pH units, or by not more than 1.4 pH units, or by not more than 1.2 pH units, or by not more than 1.0 pH units, or by not more than 0.8 pH units, or by not more than 0.6 pH units, or by not more than 0.4 pH units. or by not more than 0.2 pH units, ed to the pH value of a ition containing the starting material (virgin pulp and recycle pulp. respectively) as well as all additives that have been added to the cellulosic material in the corresponding concentrations until it reaches the wet end entry of the papermaking machine.

Typically, the undesired starch degradation also leads to an increase of electrical conductivity of the aqueous cellulosic material. Thus, efficient prevention of starch degradation by eradication of microorganisms due to biocide treatment can be monitored by measuring the electrical conductivity of the aqueous phase of the cellulosic material.

Preferably, in step (b) of the method according to the invention the one or more biocides are continuously or discontinuously added to the cellulosic material in ties so that after 1 month of treatment, preferably after two months of treatment on a continuously operating aking plant, the electrical conductivity of the aqueous phase of the cellulosic material has been decreased by at least 5%, or by at least 10%, or by at least 15%, or by at least %, or by at least 25%, or by at least 30%, or by at least 35%, or by at least 40%, or by at least 45%, or by at least 50%, or by at least 55%, or by at least 60%, or by at least 65%, or by at least 70%, or by at least 75%, or by at least 80%, compared to the electrical conductivity that was measured, preferably at the same location, preferably at the wet and entry of the papermaking machine immediately before biocide was added for the first time or before the on of higher amounts of biocide than conventionally employed was started, i.e. compared to a situation where microorganisms had been degrading the starch thereby causing an se of ical tivity. Preferably, in step (b) of the method ing to the invention the one or more biocides are continuously or discontinuously added to the cellulosic material in quantities so that after 1 month of treatment, preferably after two months of ent on a continuously operating papermaking plant, the electrical conductivity of the aqueous phase of the cellulosic material measured at the wet end entry of the papennaking machine has been increased by at most 80%, or by at most 75%, or by at most 70%, or by at most 65%, or by at most 60%, or by at most 55%, or by at most 50%, or by at most 45%, or by at most 40%, or by at most 35%, or by at most 30%, or by at most %, or by at most 20%, or by at most 15%, or by at most 10%, or by at most 5%, compared to the electrical conductivity of a composition containing the ng al (virgin pulp and recycle pulp, respectively) as well as all additives that have been added to the cellulosic WO 26578 material in the corresponding concentrations until it reaches the wet end entry of the papermaking machine.

Preferably, the one or more biocides are continuously or discontinuously added to the cellulosic al in ties so that, preferably after 1 month of treatment, more preferably after two months of treatment on a uously operating papennaking plant. the electrical conductivity of the aqueous phase of the cellulosic material is at most 7000 uS/cm, or at most 6500 pS/cm, or at most 6000 pS/cm, or at most 5500 uS/cm, or at most 5000 uS/cm, or at most 4500 pS/cm, or at most 4000 uS/cm, or at most 3500 pS/cm, or at most 3000 uS/cm, or at most 2500 uS/cm, or at most 2000 pS/cm, or at most 1500 pSIcm, or at most 1000 uS/cm.

Preferably, the method according to the invention includes the continuous or discontinuous measuring of at least one parameter selected from the group consisting of redox potential, ATP level, oxygen reduction potential (ORP), pH value and electrical conductivity of the cellulosic material, preferably electrical conductivity, and the regulating of the biocide dosage in view of the value measured for said at least one parameter in order to e strength performance and to maintain improved strength performance, respectively.

Preferably, in step (b) of the method according to the invention the one or more biocides are continuously or discontinuously added to the cellulosic material in quantities so that after 1 month of treatment, preferably after two months of treatment on a continuously operating papermaking plant, the dosage of dry and/or wet strength polymer, which is added to the cellulosic material in step (h) in order to achieve a predetermined dry strength and/or wet strength of the paper, can be decreased by at least 5%, or by at least 10%, or by at least %, or by at least 20%, or by at least 25%, or by at least 30%. or by at least 35%, or by at least 40%, or by at least 45%, or by at least 50%, or by at least 55%, or by at least 60%, or by at least 65%, or by at least 70%, or by at least 75%, or by at least 80%, ed to the dosage of the same dry and/or wet strength polymer that was added under the otherwise identical conditions ately before biocide was added for the first time or before the addition of higher amounts of biocide than conventionally employed was started, in order to achieve the same predetermined dry strength and/or wet th of the paper, i.e. ed to a ion where microorganisms had been degrading the starch thereby causing an increase of electrical conductivity and thus requiring higher dosages of dry and/or wet strength polymer in order to achieve the desired predetermined dry strength and/or wet strength of the paper. 2012/003582 Typically, the undesired starch degradation also leads to a decrease of extinction when subjecting the aqueous cellulosic material to an iodine test. Thus, efficient prevention of starch degradation by eradication of microorganisms due to biocide treatment can be monitored by measuring the extinction of the starch that is contained in the s phase of the cellulosic material by means of the iodine test. Preferably. in step (b) of the method according to the invention the one or more biocides are continuously or discontinuously added to the osic material in quantities so that after 8 hours, preferably after 2 days, more preferably after 3 days of treatment, more preferably after 1 week of treatment on a continuously ing paperrnaking plant, the extinction of the starch contained in the aqueous phase of the cellulosic material has been increased by at least 5%, or by at least %, or by at least 15%, or by at least 20%, or by at least 25%, or by at least 30%, or by at least 35%, or by at least 40%, or by at least 45%, or by at least 50%, or by at least 55%, or by at least 60%, or by at least 65%, or by at least 70%, or by at least 75%, or by at least 80%, compared to the extinction that was measured, preferably at the same location, preferably at the wet end entry of the aking machine immediately before biocide was added for the first time or before the addition of higher s of biocide than conventionally employed was started, i.e. compared to a situation where microorganisms had been degrading the starch thereby causing a decrease of tion. In a preferred embodiment, the extinction of native starch is monitored. This can be done at a particular wave length (for details it is referred to the experimental section). According to the invention, the increase of starch content can be higher. For example, depending on the ition of the starting material, the starch content in the very beginning, is when biocide treatment commences, can be about zero. in a preferred embodiment, the starch that is contained in the cellulosic material, preferably after the pulping step has been completed, has a weight average lar weight of at least ,000 glmol.

In a preferred embodiment, the one or more biocides are dosed in an amount so that after 60 s the content of microorganisms (MO) in [cfu/ml] in the cellulosic material ning the starch is at most 1.0x107, or at most 5.0x105, or at most 1.0x106; or at most 7.5x105, or at most 5: or at most 2.5x105, or at most 1.0x‘l 05, or at most 7.5x104; or at most 5.0x10", or at most 2.5x10“, or at most 1.0x10“; or at most 7.5x103, or at most 5.0x103, or at most 4.0x103; or at most 3.0x103, or at most 2.0x103, or at most 1.0)(103. In another preferred ment, the biocide is dosed in an amount so that after 60 s the content of microorganisms (MO) in [cfu/ml] in the cellulosic material containing the starch is at most 9.0x102, or at most 8.0x102. or at most 7.0x102; or at most 6.0x102, or at most 5.0x102, or at most 4.0x102; or at most 3.0x102, or at most 2.0x102, or at most 1.0x102; or at most 9.0x10‘, or at most 8.0x10‘, or at most 7.0x10‘; or at most ‘, or at most 5.0x10‘, or at most 4.0x10‘; or at most 3.0x10‘, or at most 2.0x10‘, or at most ‘.

Preferably, the redox potential of the cellulosic material ses by addition of the biocide to a value within the range of from -500 mV to +500 mV, or from -150 mV to +500 mV, or from -450 mV to +450 mV, or from ~100 mV to +450 mV, or from -50 mV to +400 mV, or from «25 mV to +350 mV, or from 0 mV to +300 mV. For example, before the biocide is added, the redox potential of the cellulosic material may be 400 mV and after the addition of the biocide it is increased to a value of, e.g., -100 mV to +200 mV.

A positive value of the redox potential indicates an ive system, whereas a negative redox potential tes a ive system. Suitable methods for measuring the redox potential are known to the skilled . in this regard it can be ed to eg. H. Holik, Handbook of Paper and Board, Wiley-VCH, 2006.

Preferably, the ATP (adenosine triphosphate) level of the cellulosic material, expressed in RLU (relative light units), decreases by addition of biocide to a value within the range of from 500 to 400,000 RLU, or from 600 to 350,000 RLU, or from 750 to 300,000 RLU, or trom 1,000 to 200,000 RLU, or from 5,000 to 100,000 RLU. For example, before biocide is added, the ATP level may exceed 400.000 RLU and after the addition of biocide it is decreased to a value of, 9.9., 5,000 to 100,000 RLU. in a preferred embodiment, the ATP (adenosine triphosphate) level of the cellulosic material, expressed in RLU ive light units), decreases by addition of biocide to a value within the range of from 5000 to 500,000 RLU, more preferably 5000 to 25,000 RLU.

ATP detection using bioluminescence provides another method to ine the level of ial contamination. Suitable methods for ATP detection using bioluminescence are known to the skilled person. in a preferred embodiment, the one or more biocides are dosed to the cellulosic material at a feed rate related to the finally produced paper of at least 5 9/ metric ton (=5 ppm), preferably within the range of from 10 9/ metric ton to 5000 9/ metric ton, more preferably from 20 9/ metric ton to 4000 9/ metric ton, still more preferably from 50 9/ metric ton to 3000 9/ metric ton, yet more preferably from 100 9/ metric ton to 2500 9/ metric ton, most preferably from 200 9/ metric ton to 2250 9/ metric ton, and in particular from 250 9/ metric ton to 2000 9/ metric ton, based on the finally produced paper.

In a preferred embodiment, particularly when the biocide is organic and non-oxidizing, e.g. bronopol/5-chloromethyl-2H-isothiazolone/2-methyl-2H-isothiazol-B-one (BNPD/lso), the biocide is closed to the cellulosic material at a feed rate related to the finally produced paper of from 25 to 2,500 g/ton paper. more ably 50 to 2,000 g/ton paper, still more preferably 75 to 1,500 glton paper, yet more ably 100 to 1,250 g/ton paper, even more preferably 125 to 1,000 gltcn paper, most preferably 150 to 900 g/ton paper. and in particular 175 to 850 g/ton paper, based on the finally produced paper.

In a preferred embodiment, the one or more biocides comprise a two ent system comprising an inorganic ammonium salt and a halogen source, preferably a chlorine source, more preferably hypochlorous acid or a salt thereof, wherein the molar ratio of the inorganic um salt to the hypochlorous acid or salt thereof is within the range of from 2:1 to 1:2.

Under these circumstances, preferably when the starting material of the process according to the invention comprises recycle pulp, said two component system is preferably dosed to the cellulosic material at a feed rate related to the finally produced paper of at least 175 9/ metric ton, or at least 200 9/ metric ton, or at least 250 gf metric ton, or at least 300 9/ metric ton; or at least 350 9/ metric ion, or at least 400 9/ metric ton, or at least 450 91/ metric ton, at least 500 9/ metric ton, or at least 550 9/ metric ton; more preferably at least 600 9/ metric ton, or at least 650 91 metric ton, or at least 700 9/ metric ton, or at least 750 9/ metric ton, or at least 800 9/ metric ton, or at least 850 g/ metric ton, or at least 900 9/ metric ten, or at least 950 9/ metric ton, or at least 1000 9/ metric ton; or at least 1100 9/ metric ton, or at least 1200 9/ metric ton, or at least 1300 9/ metric ton, or at least 1400 9/ metric ton, or at least 1500 9/ metric ton; or at least 1750 g/ metric ton, or at least 2000 9/ metric ton; in each case based on the weight of the inorganic ammonium salt and relative to the finally produced paper. Under these circumstances, preferably when the ng material of the process according to the ion does not comprise e pulp, i.e. essentially consists of virgin pulp, said two component system is preferably closed to the celiulosic material at a feed rate rotated to the finally produced paper of or at least 50 9/ metric ton, or at least 100 9/ metric ton, or at least 150 9/ metric ton, or at least 200 9/ metric ton, or at least 250 g/ metric ton, or at least 300 9/ metric ton, or at least 350 9/ metric ton, or at least 400 9/ metric ton, or at least 450 g/ metric ton, or at least 500 9/ metric ton, or at least 550 9/ metric ton, or at least 600 g/ metric ton, or at least 650 9/ metric ton; or at least 700 9/ metric ton, or at least 750 9/ metric ton, or at least 800 9/ metric ton, or at least 850 9/ metric ton, or at least 900 9/ metric ton; or at least 950 9/ metric ion, or at least 1000 9/ metric ton; in each case based on the weight of the inorganic ammonium salt and relative to the finally produced paper. 2012/003582 In a red embodiment, particularly when the biocide is oxidizing, e.g. a two component system comprising an ammonium salt and a halogen , preferably a chlorine source, more ably hypochlorous acid or a salt thereof, biocide is closed to the cellulosic al to a concentration of active substance that is equivalent to elemental chlorine at a tration within the range of from 0.005 to 0.500 % active substance as Clz per ton produced paper. more preferably from 0.010 to 0.500 % active substance as Clz per ton produced paper, still more preferably from 0.020 to 0.500 % active substance as Clz per ton produced paper, yet more preferably from 0.030 to 0.500 % active substance as Cl; per ton produced paper, most preferably from 0.040 to 0.500 %, and in particular from 0.050 to 0.500 % active substance as Clz per ton produced paper. ln another preferred embodiment, particularly when the biocide is oxidizing, e.g. a two component system comprising an ammonium salt and a halogen source, ably a chlorine source. more preferably hypochlorous acid or a salt thereof, biocide is dosed to the cellulosic material to a concentration of active substance that is equivalent to elemental chlorine at a concentration within the range of from 0.005 to 0.100 % active substance as Cl; per ton produced paper, more preferably from 0.010 to 0.100 % active substance as Clz per ton produced paper, still more preferably from 0.020 to 0.100 % active substance as Clz per ton produced paper, yet more preferably from 0.030 to 0.100 % active substance as Clz per ton produced paper, most ably from 0,040 to 0.100 % active substance as Cl; per ton produced paper, and in particular from 0.050 to 0.100 % active substance as Clz per ton produced paper.

In still another preferred embodiment, particularly when the biocide is oxidizing, e.g. a two component system sing an ammonium salt and a halogen source, preferably a chlorine source, more preferably hypochlorous acid or a salt f. biocide is dosed to the cellulosic al to a concentration of active substance that is equivalent to elemental chlorine at a concentration within the range of from 0.010 to 0.080 % active substance as C12 per ton produced paper, more preferably from 0.015 to 0.080 % active substance as Clz per ton produced paper, still more preferabiy from 0.020 to 0.080 % active substance as Clz per ton produced paper, yet more preferably from 0.030 to 0.080 %, most ably from 0.040 to 0.080 % active substance as Cl; per ton produced paper, and in particular from 0.050 to 0.080 % active substance as Clz per ton produced paper.

The above concentrations of the biocide are expressed as equivalent concentrations of elemental chlorine. The determination of the concentration of a biocide (based on active substance) that is equivalent to a particular concentration of elemental chlorine is known to the person of ordinary skill.

Particularly preferred embodiments A‘ to A6 concerning the biocide added in step (b) of the method according to the invention (first biocide) and the onal organic biocide (further biocide) are summarized in Table 1 here below: Table 1: First bidCIde oxadizmg, two ing, two component component com onent comment com uonent com nent - feeding point in n in section in section in section in section in section (I) and/or (II); (I) and/or (II); (I) and/or (II); (I) and/or (ll); (I))and/or (II); (t) and/or (II); and and as well as in as well as in as well as in as well as in optionally ally section n n section (IV); also in also in (Ill) and/or (ill) and/or (Ill) andfor but section section preferably (Ill) and/or (Ill) and/or not in section r biocide - feeding point in section in section in section in section in section (II); in section (II); (I) and/or (II); (I) and/or (II); (I) and/or (II); (I) and/or (II); but but and as well as in as well as in but preferably preferably optionally section (III); section (IV); preferably neither in neither in also in but but neither in section (I) section (I) section (III) preferably preferably n (III) nor (ill) nor nor (Ill) nor andior (IV) not in section not in section (IV) (IV) wherein sections (I) to (IV) refer to the sections of a papermaking plant comprising a papermaking machine, n section (I) includes measures taking place before pulping; section (II) includes measures associated with pulping; section (III) includes measures taking place after pulping but still outside the papermaking machine; and section (IV) includes measures taking place inside the papermaking machine.

Most preferred feeding points of the first biocide, which is ably oxidizing, are located in section (II), (Ill) and/or (IV) of a papermaking plant. When the feeding point of the first biocide is located in n (I), it is preferably located at the pulper dilution water of a papermaking plant. When the feeding point of the first biocide is located in section (ll), it is preferably located at the pulper, preferably at the outlet of the pulper, or at the dilution water after the pulper of a paperrnaking plant. When the feeding point of the first biocide is located in section (ill), it is preferably located at the white water, e.g. at the white water 2, prior to clarification or at the inlet of cation of a papermaking plant. in preferred embodiments, it is d at the clear fittrate, the shower water, and/or the return water tank of a papermaking plant.

When the feeding point of the first biocide is located in section (IV), it is preferably located at the white water, e.g. at the white water 1, preferably prior to the fan pump, the thin stock g, and/or the broke pulper of a papermaking plant.

Most preferred feeding points of the further biocide, which is preferably organic non- oxidizing, are located in n (ll), (lll) and/or (IV) of a papermaking plant. When the feeding point of the further biocide is located in n (I), it is preferably located at the pulper dilution water of a papermaking plant. When the feeding point of the further biocide is located in n (It), it is preferably located at the pulper, preferably at the outlet of the pulper of a papermaking plant. When the feeding point of the r biocide is located in section (til), it is preferably located prior to the thick stock storage, prior to the mixing chest, prior to the machine chest, prior to the thick stock sorting, at the broke thickeners, at the broke pulpers, at the dilution water after the pulper, prior to the clarification or at the inlet of clarification of a papermaking plant. When the feeding point of the further e is located in section (IV), it is preferably d at the shower water for the press section or at the shower water for the wire section of a aking plant.

In a preferred embodiment, the stock consistency of the cellulosic material in pulping step (a) is within the range of from 3.0 to 6.0%, or from 3.3 to 5.5%, or of from 3.6 to 5.1%, or from 3.9 to 4.8%, or from 4.2 to 4.6%. In another preferred embodiment, the stock consistency of the cellulosic material in pulping step (a) is within the range of from 10 to 25%, or from 12 to 23%, or from 13 to 22%, or from 14 to 21%, or from 15 to 20%. le methods for measuring the stock consistency of cellulosic materials are known to the skilled person. in this regard it can be referred to e.g. MH. Waller, Measurement and Control of Paper Stock Consistency, Instrumentation Systems &, 1983; H. Holik, Handbook of Paper and Board, Wiley-VCH, 2006.

Pulping step (a) may be med at ambient conditions.

In a preferred embodiment, pulping step (a) is performed at elevated temperature.

Preferably, pulping step (a) is performed at a temperature within the range of from 20°C to 90°C, more preferably of from 20°C to 50°C.

In a preferred ment, pulping step (a) is performed at a pH value of from 5 to 13, or from 5 to 12, or from 6 to 11, or from 6 to 10, or from 7 to 9. The desired pH vaiue may be adjusted by the addition of acids and bases, respectively. in a preferred embodiment ing to the invention, pulping step (a) is performed in the presence of one or more biocides and further auxiliaries. Said further auxiliaries may comprise, but are not d to inorganic materials, such as talcum, or other ves.

Typically, the pulped cellulosic material containing the (non—degraded) starch, i.e. virgin, recycle or blend pulp, may be subjected to further process steps all being encompassed by section (III) of the method for the manufacture of paper, paperboard or cardboard, which follow the pulping step (a) of section (II). These steps may se, but are not limited to (c) de-inking the cellulosic material; and/or (d) ng the cellulosic material; and/or (e) bleaching the cellulosic material; and/or (f) refining the cellulosic material; andlor (g) screening and/or cleaning the cellulosic material in the thick stock area; and/or (h) adding a dry and/or wet strength r to the cellulosic material; (i) screening and/or cleaning the cellulosic material in the thin stock area, i.e. after diluting the thick stock into a thin stock. in this respect, it should be emphasized that the aforementioned steps (c) to (g) and (i) are optional only, meaning that any one, any two, any three or any four of steps (c) to (g) and (i) may be omitted. it is also possible that the six steps (c) to (g) and (i) are omitted during the paper making process. According to the invention step (b). the treatment of the cellulosic material containing the starch with one or more biocides, is mandatory and may be pen‘ormed either during the pulping step (a) and/or after the pulping step (a), Provided that step (b), the treatment of the cellulosic material containing the starch with one or more es, is at least lly performed after the pulping step (a), it can either be performed before step (c) or at any time during the aforementioned steps (0) to (g). Preferably, however, step (b) is performed before the ceiiulosic al containing the starch is diluted from a thick stock (being processed at the thick stock area) to a thin stock (being further processed at the thin stock area), i.e. before step (i).

Devices that are suitable for the subsequent steps after pulping step (a) are known to the skilled person. For example, the osic material containing the egraded) starch may be pumped from the pulper into a stock vat, a mixing vat and/or a machine vat before it is ed to the papermaking machine (i.e. to the so-called "constant part" of the papermaking machine).

The temporal sequence of steps (0) to (Q) can be freely chosen, meaning that the al sequence of steps (c) to (9) does not necessarily follow the alphabetical order as indicated.

Preferably, however, the order is alphabetical.

Further process steps such as storing the cellulosic al in storage tanks or additional washing and/or screening steps may be incorporated after any of the process steps (a) to (9)- In a preferred embodiment, the temporal sequence of the process steps is selected from the group consisting of (a)-+(9); (a)~»(C)->(g); (a>~—*(d)—+(g); (a)—+(e)—r(g); (a)—r(f)—r(g); (a)-’(C)—r(d)—*(g); (a)—>(0)—+(e)—>(g); (a)~—>(C)—>(f)—’(9); d)—'(e)~+(9); (a)—>(d)~+(f)-+(9): (at-)(e)->(f)—r(9); (a)a(C)—->(d)~*(e)~+(9); (al—r(C)->(d)-*(f)-+(g); (a)—>(C)—’(e)—*(f)-*(Q); (a)-+(d)-+(e)~>(f)—>(9); and (a)—>(C)—>(d)~>(6)—>(f)—)(9); wherein, for the purpose of the specification, the symbol "—»" means "followed by"; and further process steps such as storing the cellulosic material in storage tanks or additional washing and/or screening steps may be incorporated after any one of the process steps (a) to (9). Step (b), the treatment of the cellulosic al containing the starch with the biocide, can also be incorporated after any one of the s steps (a) to (g).

A person skilled in the art is aware that after each of the process steps (a) to (g), the mixture comprising the cellulosic material and the biocide may be supplied to storage tanks, before it is re-introduced to r process steps of the paper making process.

It is also apparent to a person d in the art that at least one part of the remainder of the total amount (total inflow) of the biocide may be added to the osic material, when it is stored in storage tanks after any of process steps (a), (c), (d), (e), (f) and (g).

In general, the pulping step (a) is performed before the cellulosic material containing the (non-degraded) starch enters the aking e. In a preferred embodiment, at least one part of the biocide is added to the water used for pulping prior to or during the pulping step to the cellulosic material, i.e. to the virgin, recycle or blend material. Said addition takes WO 26578 place preferably at least 5 minutes, or at least 10 minutes, or at least 20 minutes, or at least minutes, or at least 40 minutes before the celiulosic material is supplied to the wet end of the papermaking machine, e.g. through the flow box.

In a preferred embodiment, said on takes place preferably at most 360 minutes, or at most 300 minutes. or at most 240 minutes, or at most 180 minutes, or at most 120 minutes, or at most 60 minutes before the celiulosic material is supplied to the wet end of the papermaking machine. e.g. through the flow box. ably, the time period during which the cellulosic material is in contact with biocide is within the range of from 10 minutes to 3 days. in a preferred embodiment of the method according to the invention, the time period during which the oellulosic material is in t with biocide is at least 10 minutes, or at least 30 minutes, or at least 60 minutes, or at least 80 minutes, or at least 120 minutes.

In a red embodiment of the method according to the invention, the time period during which the cellulosic material is in contact with biocide is ably within the range of 12:10 hours, or 24:10 hours, or 481-12 hours, or 72:12.

The duration of g step (a) is not critical to the invention. After the pulping step. the pulp ing to the invention may be subjected to a de-inking step (0), wherein the virgin pulp, recycle pulp or blend pulp is de-inked, preferably in the presence of the biocide.

After the pulping step, the pulp according to the invention may be subjected to a ng step (d). The blending (d), also referred to as stock preparation, is typically performed in a so-called blend chest, i.e. a reaction vessel wherein additives such as dyes, fillers (e.g., talc or Clay) and sizing agents (e.g., rosin, wax, further starch, glue) are added to the puiped cellulosic material, preferably to virgin pulp, e pulp or blend pulp, preferably in the presence of the biocide. s are preferably added to improve printing properties, smoothness, brightness, and opacity. Sizing agents typically improve the water resistance and printability of the final paper, paperboard and/or cardboard. The sizing may also be performed on the papennaking machine, by surface application on the sheet.

After the pulping step, the pulp according to the invention may be subjected to a bleaching step (e). Typically, the bleaching (e) is performed to whiten the pulped cellulosic material, preferably in the presence of the e. In said bleaching process, chemical bleaches such wo 26578 as hydrogen peroxide, sodium bisulfite or sodium hydrosulfite are typically added to the pulped cellulosic al to remove the color.

After the pulping step, the pulp according to the invention may be subjected to a refining step (f). The refining (f) is preferably med in a so-oalled pulp beater or refiner by fibrillating the fibers of the cellulosic material, preferably in the presence of the biocide. The purpose is preferably to brush and raise fibrils from fiber surfaces for better bonding to each other during sheet formation resulting in stronger paper. Pulp heaters (e.g., der beater, Jones— Bertram beater, etc.) process batches of pulp while refiners (e.g., Chaflin refiner, Jordan refiner, single or double disk refiners, etc.) process pulp continuously.

After the pulping step, the pulp according to the invention may be subjected to a screening step (9). The screening (g) is preferably applied to remove rable fibrous and non- fibrous material from the cellulosic material, ably in the ce of the biocide, preferably by the use of rotating screens and fugal cleaners.

Before the cellulosic material enters the papemiaking machine the cellulosic material which is present as a “thick stock" is diluted with water to “thin the . After dilution, the pulp according to the invention may be subjected to a further screening and/or cleaning step (i). fter, typically close to the end of the paper—making process, the cellulosic material is supplied to a papermaking machine, where it typically enters the wet end of the papermaking machine.

This is where section (IV) of the overall method for the manufacture of paper. paperboard or cardboard begins.

For the purpose of the specification the term "papermaking machine" preferably refers to any device or component thereof that basically serves the formation of sheets from an aqueous suspension of the cellulosic material. For example, the pulper is not to be regarded as a component of the papermaking machine.

Typically, a papermaking machine has a wet end which comprises a wire section and a press section, and a dry end which comprises a first drying n, a size press. a second drying n, a calender, and "jumbo" reels.

WO 26578 The first section of the wet end of the papem'iaking machine is lly the wire section. where the cellulosic material is supplied through a flow box to the wire section and distributed evenly over the whole width of the papermaking e and a significant amount of water of the aqueous dispersion or aqueous suspension of the cellulosic material is drained away.

The wire section, also called forming section, can comprise one layer or multi layers, wherein multi preferably means 2, 3, 4, 5, 6, 7. 8 or 9 layers (plies). Subsequently, the cellulosic material enters preferably the press section of the papermaking machine where remaining water is squeezed out of the cellulosic material, which tonne a web of cellulosic material, which then in turn is preferably supplied to the dry and of the papermaking e.

The so~called dry and of the papermaking machine comprises preferably a first drying section, optionally a size press, a second drying section, a calender, and "jumbo" reels. The first and the second drying section se preferably a number of steam-heated drying cylinders, where synthetic dryer fabrics may carry the web of cellulosic material round the cylinders until the web of cellulosic material has a water content of approximately 4 to 12%.

An s solution of starch may be added to the surface of the web of the cellulosic material in order to improve the surface for printing purposes or for strength properties.

Preferably, the web of cellulosic material is then supplied to the calender, where it is smoothed and ed. Subsequently, the cellulosic material is typically reeted up in the so— called "jumbo" reel n. in a preferred embodiment, the method according to the invention is performed on a papermaking plant that can be regarded as having an open water supply and thus an open water circuit. Papermaking plants of this type are typically characterized by a effluent plant, i.e. by an effluent stream by means of which an aqueous composition is continuously drawn from the system.

In another preferred embodiment, the method according to the ion is performed on a papermaking plant that can be regarded as having a closed water recycle circuit. aking plants of this type are typically characterized by not having any effluent plant, i.e. there is no t stream by means of which an aqueous composition is continuously drawn from the system, while the paper, of course, contains some residual moisture. All papermaking plants (closed and open systems) typically allow for evaporation of (gaseous) water. s closed systems do not allow for liquid effluent streams. It has been surprisingly found that the method according to the ion is of particular advantage in such closed water recycle circuit. Without the method according to the invention, the starch in the liquid phase would concentrate from e step to recycle step and finally and up in a highly viscous pasty composition not useful for any paper manufacture. By means of the method according to the invention, however, starch is fixated, preferably re-fixated to the fibers thereby avoiding any concentration effect from recycle step to recycle step.

In a preferred ment. at least 50 wt.—%, of the biocide, which is present during step (b), is still t when the cellulosic material containing the (non-degraded) starch enters the wet end of the papennaking machine. In case that the loss of biocide during the paper making process is too high, further parts of the biocide may be added during any of the process steps (c), (d), (e), (f) and/or (g). ln another preferred embodiment, at most 50 wt.—% of the biocide, which is present during step (b), is still present when the cellulosic material ning the (non-degraded) starch enters the papermaking machine.

According to the invention, step (h) ses adding a dry and/or wet strength polymer to the cellulosic material. Dry and/or wet strength polymers are known to the skilled person. In this regard, it can be referred to e.g., C.J. Biermann, Handbook of g and Papermaking, ic Press; 2 edition ; JP. Casey, Pulp and Paper, Wiley—lnterscience; 3 edition (1983); H Holik, Handbook of paper and board, Wiley-VCH Verlag GmbH & Co. KGaA, ist ed, 2006; and l. Thorn et al., Applications of Wet-End Paper Chemistry, 2nd edition, Springer, 2009.

For the purpose of the specification, dry and/or wet strength polymers are to be regarded as polymers typically employed in order to improve the dry strength and/or wet th of the paper, paperboard or cardboard.

The dry and/or wet strength polymer may be added to the cellulosic material containing the starch at any stage of paper manufacture in the thick stock area, or at any stage of paper manufacture in the thin stock area. It is apparent to a person skilled in the art that at least a part of the total amount (total inflow) of the dry and/or wet strength polymer may be added to the osic material, i.e. to the virgin, recycle or blend material, during or after the pulping step (a).

For the purpose of specification, the term “thick stock area” refers to any stage of paper manufacture where the cellulosic material is present as "thick stock". Analogously, the term "thin stock area" refers to any stage of paper manufacture where the osic material is present as thin stock. Typically, thick stock is sed at any steps of conventional processes for the manufacture of paper or paperboard taking place before step (i). The terms "thick stock“ and "thin stock" are known to the person skilled in the art. Typically, on the papermaking machine thick stock is diluted before step (i) thereby yielding thin stock. For the e of the specification, "thick stock" preferably has a solids content (= stock consistency) of at least 2.0 wi.—°/o, preferably at least 2.1 wt.-%. more preferably at least 2.2 wt.-%. still more preferably at least 2.3 wt.-%, yet more preferably at least 2.4 wt.-% and most preferably at least 2.5 wt.-%. Thus, for the purpose of the specification, cellulosic material having the above solids content is preferably to be ed as thick stock, s cellulosic al having a lower solids content is to be regarded as thin stock. in a preferred embodiment, the dry and/or wet strength polymer is added to the cellulosic material containing the (non-degraded) starch during any of steps, (a), (c), (d), (e), (f) or (g), i.e. before the osic al containing the (non-degraded) starch is diluted to a “thin stock" and before the osic material containing the (non-degraded) starch enters the papermaking machine. in a preferred embodiment, the dry and/or wet strength polymer is added to the cellulosic material containing the starch after the biocide has been added. it is also possible, that the biocide and the dry and/or wet strength polymer are added simultaneously to the osic material containing the starch. Further, it is possible that a first part of the dry and/or wet th r is added to the cellulosic material containing the starch before a first part of biocide is added and subsequently a second part of dry and/or wet strength polymer is added, or vice versa. in a preferred embodiment, the dry and/or wet strength polymer is added to the cellulosic material containing the starch after the g step has been completed.

It is apparent to a person skilled in the art that the amount (inflow) of dry and/or wet strength polymer may be added continuously (uninterruptedly) or discontinuousiy (interruptedly) with respect to one feeding point. Furthermore, the total amount (total inflow) of dry and/or wet strength polymer can be divided in at least two parts, from which at least one part is continuously or discontinuousiy added to the cellulosic material containing the starch during or after the pulping step (a) and the other part is continuously or discontinuousiy added elsewhere, i.e. at one or more other feeding points. in a preferred embodiment, the total amount (total inflow) of dry and/or wet strength polymer is added to the cellulosic material after the pulping step (a) continuously or discontinuousiy, 2012/003582 Le. 100 wt.-% of the total amount (total inflow) of the dry and/or wet th polymer is preferably added to the cellulosic material, Le. to the virgin, recycle or blend material after the pulping step (a).

In a preferred embodiment, at least one part of the total amount (total inflow) of the dry and/or wet strength polymer is added to the sic al subsequent to any of steps (c), (d), (e), (f) and/or (9). For example, 50 wt.-°/o of the total amount (total inflow) of the dry and/or wet strength polymer may be added continuously or discontinuously, during any of steps (a), (c), (d), (e), (f) and/or (9) and the remaining 50 wt.-% of the total amount (total inflow) of the dry and/or wet strength polymer may be added continuously or dlscontinuously, at any other processing step, e.g. within the thick stock area or the thin stock area.

The optimum point to add a dry and/or wet strength polymer can differ from one papermaking plant to another.

In a preferred embodiment, the dry and/or wet strength polymer is added to the thick stock, before the last refining has been carried out. In another preferred embodiment, the dry and/or wet strength polymer is added to the thick stock, after the last refining has been d out.

Good mixing can be essential in order to obtain the best performance. Therefore, addition to a well-stirred chest or the down leg of the thick stock ieveI box is preferred.

In a preferred embodiment, a diiute dry and/or wet th polymer is added to a pipeline, where optimum mixing is achieved by means of a multipoint injection system.

Particularly preferred embodiments B1 to 84 concerning preferred feeding points of the dry and/or wet strength polymer according to the invention are summarized in Table 2 here below: Dry and/or wet strenth ol mer (II) and/or (ll) and/or (II), but (Ill), but (IV), but preferably preferably neither (Ill) wherein ns (II) to (IV) refer to the sections of a aking plant comprising a papermaking machine, wherein section (II) includes measures ated with pulping; section (III) es measures taking place after g but still outside the papermaking machine; and section (IV) includes es taking place inside the aking machine.

Particularly preferred embodiments of the method according to the ion relate to combinations of any of embodiments A‘ to A6 as summarized in Table ‘l with any of embodiments B1 to B7 as summarized in Table 2; particularly A‘+B‘, A‘+BZ, A1+Ba, AWE“, A1+BS, A‘+B°, A1+B7; A2+B‘. A2+l32, A2+B3, A2+B4, A2+85, A2+BG, A2+B7; A3+B‘, A3+BZ, A3+B3, A3+B4, A3+35, A3+BG, A3+B7; A4+B‘, A4+Bz, A4+B3, A4+B4, A“+B", A“+B“, A4+B’; A5+B‘, A5+BZ, A5+B3, A5+B4, Ashes. A5+BG, A5437; A6+B‘, AG-l-Bz, A6+53, A5+B4, A6+85, A5486, A6+B7.

The dry and/or wet strength polymer is preferably added to the thick stock, i.e. at the thick stock area of the papermaking plant. in a preferred embodiment, the feeding point of the dry and/or wet strength polymer is located at or after the chest which is located after the , and/or at or before the fan pump of the papermaking plant. Preferably, the feeding point of the dry and/or wet th r is located at or after the mixing chest before the machine chest, and/or before the fan pump of the papermaking plant. Preferably, the feeding point of the dry and/or wet strength polymer is located at the machine chest andior before the fan pump of the papermaking plant. Preferably, the feeding point of the dry and/or wet strength polymer is located at the outlet of the machine chest and/or before the fan pump of the papermaking plant. Preferably, the feeding point of the dry and/or wet strength polymer is located at the regulating box and/or before the fan pump of the papermaking plant.

The optimum dosage of a dry and/or wet strength polymer varies from application to application, papermaking plant to papermaking plant and grade to grade. Preferred dosages fall in the range of 0.2 to 0.5 wt.-%, based on active content, although dosages as low as 0.05 wt.-% have been successful. This is particularly the case when a ic promoter is employed. Preferred cationic promoters are so-called "anionic trash collectors". preferably selected from the group consisting of polyamines, polyDADMAC, polyaluminium chloride, ium chlorohydrate and alumn.

The exact dosage typically depends on the charge—balance in the wet-end. Measuring the charge helps to achieve the optimum dosage. in a preferred embodiment, the dry and/or wet strength polymer is dosed to the cellulosic material containing the starch to a concentration of at least 50 g/metric ton, or at least 100 g/metric ton, or at least 250 g/metric ion, or at least 500 g/metric ton, or at least 750 g/metric ton, or at least 1,000 g/metric ton. or at least 1,250 ic ton, or at least 1,500 g/metric ton. or at least 2,000 g/metric ton, or at least 3,000 g/metric ton, or at least 4,000 g/metric WO 26578 ton, wherein the metric tons are preferably based on the overall composition ning the cellulosic material, and the grams are preferably based on the dry and/or wet strength polymer as such (active content). More preferably, the dry and/or wet strength polymer is dosed to the cellulosic material to a concentration of from 100 to 5,000 9! metric ton, or from 200 to 4.500 glmetric ton, or from 250 to 4.000 9/ metric ton, or from 300 to 3,500 9/ metric ton wherein the metric tons are preferably based on the overall composition containing the cellulosic material, and the grams are preferably based on the dry and/or wet strength polymer, respectively, as such e content). ln a ularly preferred embodiment, the dry and/or wet strength r is dosed to the cellulosic material to a concentration of from 500 to 10,000 9/ metric ion, or 500 to 9,000 9/ metric ton, or 500 to 8,000 9/ metric ton, or 500 to 7,000 9/ metric ton, or 500 to 6,000 9/ metric ton, or 500 to 5,000 9/ metric ton, or from 500 to 4,500 g/metric ton, or from 500 to 4,000 9/ metric ton, or from 500 to 3,750 9/ metric ton, or from 500 to 3,500 9/ metric ton, or from 500 to 3,250 9/ metric ton, or from 500 to 3,000 9/ metric ton, or from 500 to 2,500 9/ metric ton, or from 500 to 2,000 9/ metric ton, wherein the metric tons are preferably based on the overall ition containing the cellulosic material, and the grams are preferably based on the dry and/or wet strength polymer, respectively, as such (active content, dry basis).

Preferably, the dry and/or wet strength polymer belongs to any one of the following three categories: (i) poiymers e of only forming hydrogen bonds to starch and/or cellulose fibers, such as certain polyacrylamides, (ii) polymers capabie of additionally forming ionic bonds to starch and/or cellulose fibers, such as highly cationic nyiamines, (iii) polymers capable of covalently bonding to the cellulose fibers, such as glyoxylated polyacrylamide and epichlorohydn‘n polyamido-polyamines.

The dry and/or wet strength polymer may be non-ionic, cationic, anionic or amphoteric.

For the purpose of the specification, the term "cationic polymer" preferably refers to water- soluble and/or water-swellable polymers, preferably soluble polymers, which have a positive net charge. The cationic polymers may be branched or unbranched, cross~linked or not cross-linked, grafted or not grafted.

For the purpose of the specification. the term “anionic polymer" preferably refers to water— soluble and/or water-swellable polymers, preferably water-soluble polymers, which have a negative net charge. The anionic polymers may be branched or unbranched, cross-linked or not linked, grafted or not grafted.

A person skilled in the art knows the meaning of the terms "branched polymer", "unbranched polymer”, "cross-linked polymer" and "graft polymer". Definitions for these terms may be found preferably in A. D. Jenkins et al. Glossary of Basic Terms in Polymer Science. Pure & Applied Chemistry 1996, 68, 2287-2311.

For the purpose of the specification the term -swellable" preferably refers to the increase in volume of polymer particles associated with the uptake of water (of. D. H. Everett.

Manual of s and ology for Physicochemical Quantities and Units. Appendix ll, Part l: Definitions, Teminology and Symbols in d and Surface Chemistry. Pure & d Chemistry 1972, 31, 579-638). The swelling behavior of polymers may be measured at different temperatures and pH values in water. The swollen s of the polymers are determined at als, after removal of the surface water, until equilibrium swelling is ed. The percent swelling is preferably calculated by the following equation: %swelling = 100 x [(Wt - W0) [W3], where we is the initial weight and W, the final weight of the gel at time t (cf. l. M. rbiny et al. Preparation, characterization, swelling and in vitro drug release behaviour of polyiN—acryloylglycine-chitosan] interpolymeric pH and lly-responsive hydrogels. European Polymer Journal 2005, 41, 2584-2591).

The dry and/or wet strength rs according to the invention may preferably display a %swelling of at least 2.5%, or at least 5.0%. or at least 7.5%, or at least 10%, or at least %, or at least 20% measured in demineralized water at 20 °C and pH 7.4 in phosphate buffer after equilibrium swelling is attained.

For the purpose of the specification, the term "polymer" preferably refers to a material composed of macromolecules containing >10 monomer units (of. G. P. Moss et al. Glossary of Class Names of Organic Compounds and Reactive intermediates Based on Structure.

Pure & Applied Chemistry 1995, 67, 1307-1375).

The dry and/or wet strength polymer may each consist of a single type of dry and/or wet th polymer or may be contained in a composition comprising different dry and/or wet strength polymers.

The dry and/or wet strength polymers may be lymers, which preferably comprise ionic, preferably cationic monomer units as the only monomer component. Further, the dry and/or wet strength rs may also be copolymers, i.e. bipolymers, terpolymers. quaterpolymers, etc., which comprise, e.g., different ionic, preferably cationic monomer units; or ionic, preferably cationic as well as non-ionic monomer units.

For the purpose of the specification, the term "homopolymer" preferably refers to a polymer derived from one species of monomer and the term "copolymer" preferably refers to a polymer derived from more than one species of monomer. Copolymers that are obtained by copolymerization of two r species are termed bipolymers, those obtained from three monomers terpolymers, those obtained from four monomers quaterpolymers, etc. (cf. A. D.

Jenkins et al. Glossary of Basic Terms in Polymer Science. Pure & Applied Chemistry 1996, 68, 2287-231 1). in case that the dry and/or wet strength r is a copolymer. it is preferably a random mer. a statistical copolymer. a block copolymer, a periodic copolymer or an alternating copolymer. more preferably a random copolymer. in a particularly preferred embodiment, the dry and/or wet strength polymer is a copolymer with one of the co—monomers being acrylamide or viylamine and vinylamide, respectively. Thus, preferably the dry and/or wet strength polymer ing to the invention is preferably based on polyacrylamide or polyvinylamine which in turn may be obtained by fully or partially hydrolyzing polyvinylamide.

A person skilled in the art knows the meaning of the terms "random copolymer", "statistical copolymer", "periodic copolymer“, "block copolymer" and "alternating mer“. Definitions for these terms may be found preferably in A. D. Jenkins et at. Glossary of Basic Terms in Polymer Science. Pure & Applied Chemistry 1996, 68, 311.

For the purpose of the specification, the term "ionicity" shall refer to the net charge of a polymer as well as to its quantitative, preferably molar content of ionic monomer units based on the total t of monomer units, preferably expressed in %.

Preferably, the dry and/or wet strength polymer comprises r units that are derived from radically polymerizable, ethylenically rated rs. Therefore, in a red embodiment the polymer backbone of the dry and/or wet strength polymer is a carbon chain that is not interrupted by heteroatoms, such as nitrogen or oxygen.

PCT/EPZM 2/003582 Preferably, the dry and/or wet strength polymer independently of one another is derived from ethylenically unsaturated monomers that are preferably radically polymerizable- Preferably, the dry and/or wet strength polymer is an ionic r, more preferably a cationic, anionic or amphoten'c polymer. ably. the ionicity of the ionic dry and/or wet strength polymer is at most 95 mole.-%, or at most 90 mole.-%, or at most 85 mole.-%, or at most 80 mole.—%, or at most 75 mole.-%, or at most 70 mole.-%, or at most 65 mole.—%, or at most 60 %. or at most 55 mole.-%, or at most 50 mole.-%. or at most 45 mole.-%, or at most 40 mole.-%, or at most 35 mole.—%, or at most 30 mole.-%, or at most 25 mole.—%, or at most 20 mole.—%, or at most 15 mole.—%. or at most 10 mole.-%, or at most 5 mole.-%, ve to the total amount of monomer units. if the dry and/or wet strength polymer according to the invention is amphoteric, Le. comprises anionic as well as cationic monomer units, the preferred ionicities preferably refer to the total content of ionic monomer units including anionic and cationic monomer units.

Preferred ionicities, preferably cationicities or anionicities, of the dry and/or wet strength polymer according to the invention are summarized as embodiments C1 to C8 in Table 3 here below: Table 3: 1018 20118 30128 40138 50148 60158 80178 more preferably 5.0140 1017 20116 30125 40134 50143 60152 80170 still more ably 5.0135 1016 20114 30122 40130 50138 60146 80162 at more preferably 5.0130 1015 20112 30119 40126 50133 60140 80154 even more preferably 5.0125 1014 20110 30116 40122 50128 60134 80146 most preferably 5.0120 1013 2018 30113 40118 50123 60128 80138 in particuiar 5.0115 1012 2016 30110 40114 50118 60122 80130 Preferably, the dry and/or wet strength polymer has a weight average lar weight of at most 1,500,000 g/mol, or at most 1,400,000 g/mol, or at most 1,300,000 g/mol, or at most 000 g/mol, or at most 000 g/mol, or at most 1,000,000 g/mol, or at most 900,000 glmol, or at most 800,000 glmol, or at most 700,000 g/mot, or at most 0 g/mol, or at most 500,000 g/mol, or at most 400,000 glmol, or at most 300,000 g/mol.

Preferred weight e lar weights of the dry and/or wet strength polymer according to the invention are summarized as embodiments D1 to D‘5 in Table 4 here below: WO 26578 Table 4: fi-I-Ii-fi-fi-fi-fi- even more preferably 75:50 150:90 10001-500 most preferably 75:45 1000:1100 Particularly preferred embodiments of the method according to the invention relate to combinations of any of embodiments C1 to C8 as summarized in Table 3 with any of embodiments II)1 to D6 as ized in Table 4; particularly C‘+D‘, C2+D', 03+D‘,C4+D‘, 05+o‘, c6+o‘, c’+o‘, 03+o‘; ch02, (324432, cit-02. c4+oz, 05+02, 06m? c7+02, c3+oz; ; C2+D3; C3+D3; C4+D3, 05+03, 061.03, C7+D3. Ce+D3; C1+D4. C2+D4. C3+D4. CA+D4' 05+o‘, cam“, c7+o‘, cam"; c’+os, ch05, (33405. C‘+D5, 05+05, C6+D5. c7+o5, C8+D5; c‘+o'=, 02m“, can)“, c4405, ch06. came, c7+os, and cams.

Dry and/or wet strength polymers have been available in the paper industry for many years.

Preferred examples of dry and/or wet strength polymers according to the invention include but are not limited to natural polymers or semi-synthetic polymers such as starch. either in its native or ally modified form, and synthetic polymers.

Preferred synthetic polymers for improving the dry th and/or wet strength of paper include copolymers of acrylamide. Anionic and cationic versions of this chemistry are much in use today. normally combined with a cationic promoter, to aid adsorption on the paper fibers. rylamide technology may be enhanced by adding aldehyde reactivity. thoxylated poiyacrylamides may improve strength through the use of latent reactive aldehyde groups, which o inter-polymer linking during the drying of the paper sheet at 80-100° C.

Preferred synthetic polymers for improving the dry strength andior wet strength of paper also include polyamido poiyamine rs, further reacted with epichlorohydrin, which have been used successfully in the paper industry for many years also as wet strength resins.

These additives are very reactive, especially at pH values greater than about 5, particulany greater than about 6, and temperatures of 30 to 60 °C. Cross-linking between polymer chains takes place within the treated paper sheet, decreasing the solubility of the resin and preventing water from disrupting the inter-fiber hydrogen bonding. For the purpose of the specification, these polymers encompass and are also referred to as polyamide polyamine epichlorohydrin polymers, polyamido amine epichlorohydrin polymers and polyamino amine epichlorohydrin polymers, The invention can be used in a combination with other polymer ents in order to further improve the strength properties of the paper product. The polymer components can be cationic, or anionic, or amphoteric, or nonionic synthetic, or a l polymers, or combinations thereof. Examples include but are not limited to cationic starches or amphoterio starches; c polymers, such as a polyacrylic acid, mers of acrylamide and acrylic acid, and carboxymethyl cellulose; ic polymers, such as a cross-linked polyamide- amines, polydialIyldimethylammonium chlorides, linear or branched polyamines, poly- ethyleneimines, fully or partially yzed polyvinylamines, copolymers of diallyl- dimethylammonium chloride and acrylamide. mers of 2-acryloylethyltrimethyl- ammonium chloride and acrylamide. cationic guar and other natural gum; polymeric aldehyde-functional compounds, such as lated polyacrylamides, aldehyde celluloses and aldehyde functional ccharides; amphoteric polymers such as terpolymers of mide, acrylic acid, and diallyldimethylammonium chloride, or acrylamide, acrylic acid, and 2-acryloylethyltrimethylammonium chloride; substantially nonionic water—soluble polymers such as nonionic polyethyleneoxide or polyacrylamide; and water-insoluble latexes such as polyvinylacetate or styrene-butadiene ccpolymers.

For the purpose of the cation, "substantially nonionic polymer" are polymers having an ionicity of at most 2 mole.-%, more preferably at most 1 mole.—%, i.e. at most 1 mole.-% and at most 2 mole.-%, tively, of all monomer units bear ionic groups.

In a preferred embodiment of the method according to the invention. the dry and/or wet strength polymer is selected from the group consisting of (i) ncn~ionic. anionic, cationic or amphoteric cellulose ve polymers capable of forming covalent inter-polymer cross-linkages with cellulose. preferably through aldehyde functional groups and/or 3-hydroxy-azetidinium onal groups of the dry and/or wet strength polymer; and (ii) l or synthetic non-ionic, anionic, ic or amphoteric polymers.

PCT/EPZO] 2/003582 A skilled person recognizes that combinations of polymers of the above categories (i) and (ii) can also be ageously used in the method according to the invention.

Preferably. the (i) non-ionic. anionic. cationic or amphoteric cellulose reactive polymers are reaction products - of ionic or nonionic, linear or branched, cross-linked or non-cross-linked homo- or copolymers comprising monomer units derived from vinylamides. which are optionally fully or partially hydrolyzed; and/or from other monomers that form ines and/or polyamides such as polyalkylenepolyamine and dibasic acids; and/or from (meth)acrylamides; or of polysaccharides - with epihalohydrin, preferably epichlorohydrin. or with cellulose reactive agents comprising at least one aldehyde functional group. preferably glyoxal.

When the dry and/or wet th polymer is the on t of epihalohydrin with a polymer, the latter is preferably a polyamine or a polyaminoamide.

When the dry and/or wet strength polymer is the reaction product of a ose reactive agent comprising at least one aldehyde functional group with a polymer, the latter is preferably a polyacrylamide or a copolymer of acrylamide with one or more ionic, preferably cationic monomers, ably selected from polydiallyldimethylammonium chloride and 2- acryloylethyltrimethylammonium chloride.

Preferably, the cellulose reactive agents that are employed in the synthesis of cellulose ve dry and/or wet strength polymers according to the invention comprise at least one functional group capable of reacting with the polymer and at least one aldehyde functional group that remains unreacted once the cellulose reactive agent has been ntly linked to the r through the functional group capable of reacting with the r. Said unreacted aldehyde functional groups render the thus obtained polymer cellulose reactive.

For the purpose of the specification, these polymers are also referred to as aldehyde functional polymers. in a preferred ment, the functional group capable of reacting with the polymer is also an de functional group. Thus, preferably, the cellulose reactive agents se at least two aldehyde functional groups and are preferably selected from the group consisting of glyoxal, glutaraldehyde, succinaldehyde, furan dialdehyde, 2-hyroxyadipaldehyde, - hyde starch, and combinations thereof.

Polymeric aldehyde-functional rs preferably comprise glyoxylated rylamides. glyoxylated polyvinylamides. de—rich cellulose, aldehyde-functional polysaccharides. and aldehyde functional cationic. anionic or non-ionic starches. Exemplary materials e those disclosed in US 4.035.229; US 4.129.722; US 4,217,425: US 5,085,736; US .320.711: US 5.674.362; US 5,723,022; US 6,224,714: US 6.245.874; US 6,274,667; US 6.749.721; US 7,488,403; US 7,589,153; US 7,828,934; US 7,897,013; U32011/0083821, WO 00/43428; WO 00/50462 A1; WO 01/34903 A1 all of which are herein incorporated by reference.

The polymeric aldehyde-functional polymers can have a molecular weight of about 10.000 g/mol or greater, more specifically about 100.000 g/mol or greater, and more specifically about 500,000 g/mol or greater. atively, the polymeric aldehyde-functional compounds can have a molecular weight below about 200,000 glmol, such as below about 60,000 g/mol.

Further examples of aldehyde-functional polymers of use in the present invention include dialdehyde guar, aldehyde—functional wet strength additives further comprising carboxylic groups as disclosed in WO 01/83887; dialdehyde inulin; and the dialdehyde~modified anionic and amphoteric polyacrylamides disclosed in WO 00111046; herein incorporated by reference. de-containing surfactants as disclosed in US 6,306,249 can also be used.

When used in the present invention, the aldehyde—functional polymers ably have at least 5 milliequivalents (meq) of aldehyde per 100 grams of polymer. more specifically at least 10 meq. more specifically still about 20 meq or r. and most specifically about 25 meq per 1 00 grams of polymer or greater.

Aldehyde-rich cellulose can include cellulose oxidized with periodate solutions. as disclosed in US 5,703,225, cellulose treated with enzymes, such as the cellulase-treated cellulose disclosed in WO 97/27363 and the de-modified cellulose products sed in EP 1,077,286—A1, all of which are incorporated herein by reference.

In a preferred embodiment. the polymeric aldehyde-functional polymer is a glyoxylated polyacrylamide. such as a cationic glyoxylated polyacrylamide. Such compounds e xylated polyacrylamides described in US 932 and US 933. which are incorporated herein by reference. Another example of a glyoxylated polyacrylamide is a glyoxylated poly(acrylamide-co-diallyl dimethyl ammonium chloride). At times it may be advantageous to utilize a mixture of high and low molecular weight glyoxylated polyacrylamides to obtain a desired effect. in a particularly red embodiment. the cellulose reactive dry and/or wet strength polymer is selected from glyoxylated polyacrylamide (GPAM). glyoxylated polyvinylamines ), polyamine-epihalohydrin polymers. and polyamino-polyamide epichlorohydrin polymers (PAE).

Glyoxylated polyacrylamides (GPAM) are typically prepared by treating polyacrylamides, preferably ionic, more ably cationic copolymers of acrylamide with ionic comonomers such as polydiallyldimethylammonium chloride or 2-acryloylethyltrimethylammonium chloride, with glyoxal. The glyoxal reacts with one of its aldehyde functionalities at the amide onality of the acrylamide thereby functionatizing the polymer by free de groups.

Functionatized, preferably glyoxylated polyvinylamines (GPVAm) can be prepared by reacting a starting polyvinylamine with at least a dialdehyde, wherein the starting polyvinytamine is a polymer formed from N-vinylformamide or N-vinylacetamide which polymer is at least partially yzed to impart a degree of primary amino functionality, prior to the reaction with the hyde. Exemplary dry and/or wet th polymers of this type include those disclosed in US 2009/0126890, which is herein incorporated by reference.

Preferred lated polyacrylamides (GPAM) according to the invention are glyoxylated cationic copolymers, preferably copolymers of acrylamide and cationic comonomers selected from polydiallyldimethylammonium chloride and loylethyltrimethylammonium chloride, and preferably have a) a weight average molecular weight within the range of 200,000i150,000 g/mol, preferably 2000001100000 g/mol; and an ionicity of at most 10 mole.—%. preferably within the range of 3.0129 mole.~%; or b) a weight average molecular weight within the range of 0i150,000 g/mol, preferably 200,000t100,000 g/mol; and an ionicity within the range of 25120 mole.-%, preferably within the range of 25:10 mole.—%.

In a preferred embodiment, a polymer bearing amino groups is reacted with epihalohydrin, ably epichlorohydrin thereby yielding another type of polymer that is capable of forming covalent bonds to cellulose. In this regard, it can be distinguished between polyamine epihalohydrin polymers, polyamlcle ohydrin polymers, and polyamine-polyamide epihalohydrin polymers, all of which are preferred dry and/or wet strength polymers according to the ion. Preferred polyamine-epihalohydrin polymers and polyamino- polyamide-epihalohydrin polymers according to the ion e inoamideepihalohydrin polymers, polyamidepolyamine—epihalohydn‘n polymers. polyaminepolyamide- epihalohydrin polymers. aminopolyamide-epihalohydrin polymers. and polyamide-epihalo~ hydrln polymers; potyalkylene polyamine-epihalohydrin polymers; polyaminourylene- epihalohydrin polymers; copolyamide-polyurylenevepichlorohydrin rs; and polyimide~ ylene-epichlorohydrin rs. Exemplary dry and/or wet strength polymers of this type e those disclosed in US 2,926,154; US 3,125,552; US 3,311,594; US 3,332,901; US 3,700,623; US 3,772,076; US 531; US 3,855,158; US 3,887,510; US 3,992,251; US 4,035,229; US 4,129,528; US 4,147,586; US 4,450,045; US 4,501,862; US 4,515,657; US 4,537,657; US 4,722,964; US 5,082,527; US 5,316,623; US 5,318,669; US 5,502,091; US 5,525,664; US 5,614,597; US 5,633,300; US 5,656,699; US 5,674,358; US 5,904,808; US 5,972,691; US 6,179,962; US 6,355,137; US 6,376,578; US 6,429,253; US 740; and US 7,291,695, all of which are herein incorporated by reference.

Polyamino-polyamide epichlorohydrin polymers (PAE) are typically prepared by a ep process that involves 1.) the condensation reaction between a polyalkylenepolyamine (usually diethylenetriamine) and a dibasic acid (usually adipic acid) to form a lower molecular weight polyamide that contains a number of secondary amine functionalities within the polymer backbone; and 2.) the treatment of this lower molecular weight polyamide with epichlorohydrin, principally by reaction at the secondary amine functional , to form a cationic, reactive 3-hydroxyazetidinium chloride and to develop further the molecular weight.

The formation of undesired oducts such as dichloropropanol and chloropropandiol is typically suppressed and preferably, the content of dichloropropanol is below 1000 ppm, more preferably below 100 ppm and most preferably below 10 ppm.

The dry and/or wet strength polymer, preferably cellulose reactive polymer according to the invention preferably comprises one cellulose reactive polymer, ably as the only polymer component; or is contained in a composition comprising two ent cellulose reactive polymers, preferably as the only polymer components; or three cellulose reactive polymers, preferably as the only polymer components; or four ose reactive polymers, preferably as the only polymer components; or even more than four cellulose reactive polymers, ably as the only polymer components.

Depending on the procedure used for the preparation of the dry and/or wet strength polymer, preferably cellulose reactive polymer, it may se further substances such as 2012/003582 polyfunctional alcohols, water-soluble salts, ing agents, free-radical initiators and/or their respective degradation products. reducing agents andlor their respective degradation products. oxidants and/or their respective degradation products, etc. in a preferred ment. the (ii) natural or synthetic non—ionic. c. cationic or amphoteric polymers are selected from the group consisting of a) native or chemically modified polysaccharides; preferably ed from native starch, cationic starch, c starch. non-ionic starch and carboxymethylcellulose; b) anionic homo— or mers comprising anionic monomer units derived from acrylic acid; optionally in combination with non~ionic monomer units derived from (meth)acrylamide; c) ic homo- or copolymers comprising cationic monomer units preferably derived from vinylamine, polydiaIlyldimethylammonium chloride, 2-acryloylethyltrimethylammonium chloride, and/or ethyleneimine; optionally in combination with non-ionic monomer units derived from mide and/or (meth)acrylamide; d) amphoteric polymers; preferably terpolymers comprising monomer units derived from (meth)acrylamide, (meth)acrylic acid, and diallyldimethylammonium chloride or 2-acryl- oylethyltrimethylammonium chloride; a) substantially nonionic water-soluble polymers; preferably selected from nonionic polyethyleneoxides and polyacrylamide; and f) water-insoluble latexes; preferably selected from polyvinylacetate and styrene-butadiene copolymers.

Preferred anionic homo- or copolymers of group b) according to the invention are anionic polyacrylamides. preferably copolymers of (meth)acrylic acid and (meth)acrylamide, and preferably have (i) a weight average molecular weight within the range of 300,000i200,000 g/mol, preferably 300,000:150,000 g/mol; and an ionicity within the range of 103:7.5 mole.-%, preferably within the range of 10:50 mole.-%; or (ii) a weight average molecular weight within the range of 300,000:200,000 g/mol, preferably 300.000i150.000 g/mol; and an ionicity within the range of 30125 mole.-%, preferably within the range of 30120 mole.-%; or (iii) a weight average molecular weight within the range of 13000001250000 g/mol, preferably 1,300.0001100.000 glmol; and an ionicity within the range of 10:75 mole.-%, preferabiy within the range of 10:25.0 mole.-%: or (iv) a weight average molecular weight within the range of 1,300,000i250,000 glmol, preferably 1.300,000:i:100,000 glmol; and an ionicity within the range of 30t25 mole.-%, preferably within the range of 30:20 %.

Preferred cationic homo- or copolymers of group 0) according to the invention are cationic polyacrylamides, preferably copolymers of (meth)acrylamide and cationic monomers selected from polydiallyldimethylammonium chloride and 2-acryloylethyltrimethylammonium chloride, and preferably have (i) a weight e molecular weight within the range of 400,000i150,000 g/mol, preferably 0:100,000 glmol; and an ionicity within the range of 25123 %, preferably within the range of 20:18 mole.—%; or (ii) a weight average molecular weight within the range of 1,200.000:350,000 g/mol, preferably 000t150,000 glmol; and an ty within the range of 25:23 mole.-%, preferably within the range of 20:18 mole.-%. in a red embodiment, the dry and/or wet strength polymer is a polyvinylamine , preferably a polyvinylamine having a weight average molecular weight of at most 1,500,000 glmol, more preferably at most 1,000,000 g/mol, still more preferably at most 500,000 g/mol.

Polyvinylamines are preferably made by the hydrolysis of polyvinylformamide yielding partially or fully hydrolyzed polyvinylformamide. PVAm polymers are very reactive, work over a broad pH range and are quite insensitive to the affects of sulphites, pH, and alkalinity. The mechanisms by which PVAm polymers impart strength to paper are not clear. PVAm polymers are amine—containing polymers that are typically not self-crosslinking rs and. apparently, lack functionality to ntly bond with hydroxyl or carboxylate groups on pulp fiber. Proposed mechanisms include multiple hydrogen bonding, multiple ionic bonding, low ature amide formation and aminal formation with cellulose chain ends. According to recent findings, dry strength and/or wet strength seems to result from fibril entanglement of two fibres, which are thus bonded to each other.

Exemplary dry and/or wet strength polymers based on polyvinylamines (PVAm) include those disclosed in US 4,818,341. US 4,940,514, US 4,957,977, US 807, US 7,902,312, US 7,922,867, US 2009/0145566, US 2010/0108279 all of which are herein incorporated by reference dry and/or wet th polymers.

Dry strength andlor wet strength is optimally enhanced by adding a combination of PVAm and an anionic copolymer on a polyvinylforrnamide basis. The strength-enhancing s of this combination coincide with the strengths attained in a ded conventional size press.

Combined application of the two als offers the onal benefits of improved dewatering in the wire and press sections, reduced steam consumption levels and higher speeds.

Preferably, these dry and/or wet strength polymers have a low molecular weight (medium structure) and can be preferably branched. The dosage is preferably within the range of from 250 g/ton dry paper to 5,000 glton dry paper, more preferably 500 g/lon dry paper to 5,000 g/ton dry paper. in a particularly preferred embodiment of the method according to the invention, the dry and/or wet strength polymer is selected from the group consisting of (i) non-ionic, anionic, cationic or amphoteric cellulose reactive polymers e of forming covalent inter—polymer cross-linkages with cellulose, preferably through functional groups of the dry and/or wet strength polymer selected from - aldehyde functional groups, preferably glyoxylated polyacrylamides; andlor - 3-hydroxy-azetidinium functional groups, preferably ine-epihalohydrin polymers and polyaminopolyamide-epihalohydrin polymers; and (ii) synthetic non-ionic, anionic, cationic or amphoteric polymers comprising mine units and/or (meth)acrylamide units and having a weight average molecular weight of at most 1,500,000 g/moi, more ably at most 1,000,000 g/mol, still more preferably at most 500,000 g/mol, preferably non-ionic, c, cationic or amphoteric polyvinylamine polymers or non—ionic, anionic, ic or amphoteric eth)acrylamide polymers.

In a preferred embodiment, two dry and/or wet strength polymers having identical or opposite charges are added to the cellulosic material. Preferably, the dry and/or wet strength polymers have opposite s and are based on starches, carboxymethyl celluloses, polyacrylamides, polvinylamines or combinations of these components.

Preferabiy, both polymer components are added after refining and apart from one another. red feeding points are before and after the machine chest feed pump. The further apart the two components, typically the better the results.

Preferably, further compounds are added to the cellulosic material in order to improve the performance of the dry and/or wet strength polymers. Typical examples of such further compounds include promoters.

The dry strength performance and/or wet strength performance of the dry and/or wet strength rs can depend upon the age and quality of the dry and/or wet strength polymer at the. time of its use, the wet-end papermaking conditions and the drying conditions which may influence the reaction of the dry and/or wet strength polymer to the cellulose fibers if the dry and/or wet strength polymer is cellulose reactive.

When the cellulosic material has a high content of anionic impurities (anionic trash) that cannot be easily removed by washing, fixing agents or so—called "anionic trash collectors" (ATC) can be added to the cellulosic material before the dry and/or wet strength polymers are added. Preferred "anionic trash collectors" are selected from the group ting of polyamines, polyDADMAC, polyaluminium chloride, aluminium chlorohydrate and alumn.

When the dry and/or wet strength polymer is a cellulose reactive polyamino-polyamide epichlorohydrin polymers (PAE), preferred anionic trash collectors are preferably polyamino— ide epichlorohydrin polymers that are added to the cellulosic material upstream. The cationic charge of these anionic trash collecting polyamino-polyamide epichlorohydrin polymers is preferably significantly higher than that of the polyamino-polyamide epichlorohydrin polymers (PAE) uently added as dry and/or wet strength polymers.

When c dry and/or wet strength polymers are used, it is common to have a strong cationic promoter to ensure that the dry and/or wet strength polymer is fixed onto the anionic fibers. In the case of acidic papermaking conditions, this promoter is preferably alum or polyaluminium chloride. Under neutral and alkaline aking conditions, a synthetic cationic additive is preferably used, e.g. a separate polyamine, which is ably added to the cellulosic material upstream, i.e. before the dry and/or wet th polymer is added to the cellulosic material. Feeding points after refining are preferred.

When cationic dry and/or wet strength polymers are employed, cationic promoters such as ines can also have a benefit and thus. are preferably added to the cellulosic al.

Aside from adding highly cationic additives that form complexes with anionic impurities that would ise impair the tion of the dry and/or wet strength polymers on the osic fibers, anionic rs are ably added to further increase the retention of dry andfor wet strength polymers. Carboxymethylcellulose and c polyacrylamides are among the preferred additives. The anionic polymers are preferably added to the thick stock after the addition of the dry and/or wet strength polymer. Addition to the thin stock is also possible, but less preferred, as this can lead to the formation of deposits. The ratio between the cationic dry and/or wet strength polymer and anionic polymer can be critical and needs to be ed in order to avoid formation of deposits.

The dry and/or wet strength polymer according to the invention may also be used in combination with an additional retention aid. The term “retention aid”, as used herein, refers to one or more ents which, when being applied to a stock of cellulosic material, improve the ion compared to a stock of cellulosic al in which no retention aids are present.

Suitable retention aids that may be employed in combination with the dry and/or wet strength polymer ing to the invention are preferably cationic polymers, including polyvinyiamine polymers, or anionic microparticulate materials. including anionic inorganic particles, anionic c particles, water-soluble anionic vinyl addition polymers, aluminium compounds and ations thereof. r, it is also possible that the dry and/or wet strength polymer fully or partially replaces retention aids as it may have properties of a retention aid itself, Anionic inorganic particles that can be used in combination with the dry and/or wet th polymer according to the invention include anionic silica-based particles and clays of the smectite type.

Anionic silica-based particles, i.e. particles based on Si02 or silicic acid, include colloidal silica, different types of polysilicic acid, colloidal aluminium-modified silica, aluminium silicates, and mixtures thereof. Anionic silica-based particles are usually supplied in the form of aqueous colloidal dispersions, led sols.

Clays of the smectite type that are suitable to be used in combination with the dry and/or wet strength polymer according to the invention include montmorillonite/ bentonite. hectorite, beidelite. nontronite and saponite, ably bentonite.

Anionic c particles that are preferably used in combination with the dry and/or wet strength polymer according to the invention include highly cross-linked c vinyl on polymers and co-polymers derivable from an anionic monomer such as acrylic acid, rylic acid and sulfonated vinyl addition monomers, which may be co-polymerized with non-ionic monomers, such (meth)acrylamide or alkyl (meth)acrylates; and anionic condensation polymers such as melamine-sulfonic acid sols. ium compounds that are preferably ed with the dry and/or wet strength polymer according to the invention include alum. aiuminates such as sodium ate, aluminium de, aluminium nitrate and poiyaluminium compounds. Suitable polyaluminium nds are for example polyaluminium chlorides, polyaluminium sulphates, polyaluminium compounds containing both chloride and sulphate ions, polyaiuminium silicate—sulphates, polyaluminium compounds and mixtures thereof. The polyaluminium compounds may also contain other anions, including anions derived from phosphoric acid, sulphuric acid, citric acid and oxalic acid.

Preferably, the dry and/or wet strength polymer and the additional retention aid are employed in such a ratio that the retention is improved compared to cellulosic material ning either the dry and/or wet th r alone or the onal retention aid alone.

In a preferred embodiment of the invention, the method comprises the additional step of (j) ing an auxiliary additive typically used in paper manufacture.

The invention can be used in a combination with other compositions in order to further improve the strength properties of the paper product. The compositions that may be used in combination with the invention can be a cationic, or an anionic, or an amphoteric, or a nonionic synthetic, or a natural polymer, or combinations thereof. For example, the invention can be used together with a cationic starch or an amphoteric starch. ln a preferred embodiment, the method according to the invention does not encompass the addition of cellulytic enzymes to the cellulosic material, preferably not the introducing of at least one cellulytic enzyme composition and at least one cationic polymer composition to a papermaking pulp at about the same time to form a treated pulp.

Dry and/or wet th polymers are preferably supplied either as a powder or as a water— based solution, sometimes as an emulsion. Thus, the dry and/or wet strength polymer ing to the invention may be solid, e.g. in form of a powder, in the form of a solution, dispersion, emulsion or suspension.

For the purpose of the specification, the term "dispersion" comprises preferably aqueous dispersions, in-oil sions and oil-in—water dispersions. A person skilled in the art knows the meaning of these terms; in this respect it may be also referred to EP 1 833 913, WO 02/46275 and W0 02/ 'l 6446.

Preferably, dry and/or wet strength polymer according to the ion is dissolved, dispersed. emulsified or suspended in a suitable solvent. The solvent may be water, an organic t, a mixture of water with at least one organic solvent or a mixture of organic solvents.

In another preferred embodiment, the dry and/or wet strength polymer according to the invention is in the form of a solution, n the polymer is dissolved in water as the only solvent or in a e comprising water and at least one organic solvent.

More preferably, the dry and/or wet strength polymer ing to the ion is in the form of a dispersion, an on or a sion, wherein the dry and/or wet strength polymer is dispersed, emulsified or suspended in a mixture comprising water and at least one organic solvent. Preferably, the dry and/or wet strength polymer is in the form of a dispersion, an emulsion or a suspension, wherein the dry and/or wet strength polymer is dispersed. emulsified or suspended in water as the only solvent, i.e. no organic solvent is present. In another preferred embodiment of the invention, the dry and/or wet strength polymer ing to the invention is in the form of a dispersion, wherein the dry and/or wet strength polymer is dispersed in water as the only solvent or in a mixture comprising water and at least one organic solvent. It is especially preferred that the dry and/or wet strength polymer dispersion according to the invention is substantially oil-free.

Suitable organic solvents are preferably low—molecular weight alcohols (e.g., methanol, ethanol, n~propanol. iso-propanol, n-butanol, iso-butanol, sec-butanol, tert-butanol, etc). low molecular weight ethers (e.g., dimethylether, diethylether, ropylether, di~iso-propyl' ether, etc), low molecular weight ketones (e.g. acetone, butan—2-one, pentane-Z-one, pentane-S-one, etc), low molecular weight hydrocarbons (e.g., n—pentane, n-hexane, petroleum ether, ligroin, benzene, etc.) or halogenated low molecular weight hydrocarbons (e.g., methylene chloride, form, etc.) or mixtures thereof.

The dry and/or wet strength r according to the ion may also be a solid, i.e. in particulate form, such as in the form of ates, pellets or powders.

The dry and/or wet th polymer in the form of a solution, dispersion, emulsion, suspension. granulate. pellets. or powder is preferably dispersed. emulsified, suspended, dissolved or diluted in a suitable solvent such as water, an organic solvent, a e of water with at least one organic solvent, or a mixture of at least two organic solvents, before being added to the cellulosic material.

In a particularly preferred embodiment of the method according to the invention, - the one or more biocides comprise an inorganic ammonium salt in combination with a halogen source. preferably a chlorine source, more preferably hypochlorous acid or a salt thereof; preferably NH4Br/NaOCl (first biocide); which is preferably added prior to or during g; and .. an organic, preferably non-oxidizing biocide (further biocide), which is preferably added independently from the first biocide; and - the dry and/or wet strength polymer is capable of forming covalent bonds to celiulose fibers, preferably selected from glyoxylated poly(meth)acrylamides and polyamino— poiyamide epichiorohydrin polymers.

In particularly preferred ments of the method according to the invention, (i) in step (b) the one or more biocides are continuously or tinuously added to the ceilulosic material in quantities so that - after 1 month of treatment on a uously operating aking plant, the pH value of the s phase of the osic al has been increased by at least 0.2 pH units. compared to the pH value that was measured, preferably at the same location, preferably at the wet and entry of the papermaking machine immediately before biocide was added for the first time or before the addition of higher amounts of biocide than conventionally employed was started, i.e. compared to a situation where microorganisms had been degrading the starch; and/or — after 1 month of treatment on a continuously operating papermaking plant, the electrical conductivity of the aqueous phase of the cellulosic materiai has been decreased by at least 5%, preferably at least 20%, more preferably at least 50%, compared to the electrical conductivity that was measured, preferably at the same location, preferably at the wet end entry of the papermaking machine immediately before biocide was added for the first time or before the addition of higher s of biocide than conventionally employed was started. i.e. ed to a ion where microorganisms had been degrading the starch; and/or ~ after 48 hours, preferably after 8 hours on a continuously operating papermaking plant, the extinction of the starch (corresponding to the concentration of free starch) contained in the aqueous phase of the cellulosic material has been increased by at least 5%, compared to the extinction that was ed, preferably at the same location, preferably at the wet end entry of the papermaking machine immediately before biocide was added for the first time or before the addition of higher amounts of biocide than conventionally employed was started, i.e. ed to a situation where microorganisms had been degrading the starch; and/or - after 48 hours, preferably after 8 hours on a uously operating papermaking plant, the tration of ATP in the aqueous phase of the cellulosic material has been decreased by at least 5%, compared to the concentration of ATP that was measured, preferably at the same on, ably at the wet and entry of the papermaking machine immediately before biocide was added for the first time or before the addition of higher s of biocide than conventionally employed was d. i.e. compared to a situation where microorganisms had been degrading the starch; and/or - after 48 hours, preferably after 8 hours on a continuously ing papermaking plant, the redox potential of the aqueous phase of the osic material has been increased to an absolute value of at least -75 mV; and/or the one or more biocides comprise an ammonium salt; preferably NH4Br in combination with a halogen source, preferably a chlorine source, more preferably hypochlorous acid or a salt thereof; and/or the one or more biocides comprise an ammonium salt, preferably NH4Br in combination with hypochlorous acid or a salt thereof, as first biocide and an organic, preferably non-oxidizing biocide as further biocide; (iii) the one or more biocides comprise an oxidizing e that is employed at a concentration equivalent to a concentration of at least 0.005 % active substance as Clg per ton produced paper, more preferably at least 0010 % active substance as Clg per ton produced paper; and/or (W) the one or more biocides are added to the thick stock, preferably at least a portion thereof is added to the dilution water for the pulper; and/or the starting material comprises virgin pulp or recycle pulp.

On a continuously operating papennaking plant, at which the paper manufacture may optionaiiy be transiently shut down for maintenance purposes, a preferred embodiment of the ion includes the steps: (A) measuring a property of the aqueous phase of the cellulosic material selected from the group consisting of electrical conductivity, redox ial, pH value, tration of ATP and concentration of free starch; at a predetermined on of the papermaking plant. preferabiy at a location in the thick stock area or in the thin stock area; (B) manufacturing paper, paperboard or cardboard by the method according to the invention comprising steps (a), (b), (h,) and optionally (ha); (C) measuring the same property as measured in step (A), preferably at the same location, preferably at the wet end entry of the papermaking machine of the papermaking plant as in step (A), after time At, preferabiy after at least 1, 2, 3, 4, 5. 10, 14, 21 or 28 days, and comparing the value measured in step (C) with the value measured in step (A); (D) regulating, preferably optimizing the dosage of biocide added in step (b) and/or the dosage of dry and/or wet strength r added in step (h) in dependence of the result of the comparison made in step (C).

For the purpose of the specification. optimization preferably means that at minimized ption of biocide the substantiai alteration of the measured vaiue (m2 vs. m1) is prevented.

The method ing to the ion is suitable for the manufacture of paper, paperboard or cardboard. Preferably, the paper, paperboard or cardboard has an area weight of less than 150 g/m2, of from 150 g/m2 to 600 g/m2, or of more than 600 g/m2. In a preferred embodiment, the area weight is within the range of 15:10 g/mz, or 30:20 g/mz, or 50:30 g/mz, or 70i35 g/mz, or 150250 g/mz.

Another aspect of the invention s to the use of the dry and/or wet strength polymer as defined above in the method for manufacturing paper, paperboard or cardboard, to increase the strength of paper, paperboard or cardboard. Aii preferred embodiments that have been described above in connection with the methods according to the invention also apply to this aspect of the invention and thus. are not repeated hereinafter.

WO 26578 Still another aspect of the invention relates to the use of a biocide or combination of biocides as defined above for reducing the electrical conductivity of the aqueous phase of a cellulosic material in the manufacture of paper, paperboard or cardboard. All preferred embodiments that have been described above in tion with the s according to the invention also apply to this aspect of the invention and thus. are not repeated hereinafter.

Yet another aspect of the invention relates to the use of the biocide as defined above in the method for manufacturing paper, paperboard or cardboard, to increase the strength of paper1 paperboard or cardboard. All preferred ments that have been bed above in connection with the methods ing to the invention also apply to this aspect of the invention and thus, are not repeated hereinafter.

The ing examples further illustrate the invention are not to be construed as limiting its scope.

EXAMPLES Example 1: The following experiments were run on different commercially used paper mills throughout Europe. Examples 1 and 4 were run on a closed system, whereas the other Examples were run on open systems. The starting material was in each case 100% recycled papers. The following biocides were employed at the ing dosages and g points as summarized in Table 5: Table 5: ' sting B" " meters for settngs Senttig Settngt iD' 7 A:and D, .4. . 02 II1 02 :_.3 0C) 4 04 1.04 1 _:A.o1 1— ' 44:;- 0000eatsro —“ . - dosage [concentration : 0.020 : 0.019 0.019 { 0.017 of active substance i i » equivalent to elemental ; chlorine, expressed in ‘ % active substance as Clz per ton produced water. white water, white water, white water, white -. water 2, white water 1, clear water 1 , clear water 2, white water 1, filtrate, inlet water 1, , filtrate, inlet i clarified clarification clarification clarified '.hV"e°r water Shower wate. e lion weer 830 m0o - feeding points outlet pulper, outlet pulper, outlet pulper, outlet pulper , inietfiber inletfiber inletfiber ‘ , CEPI — Confederation of European Paper industries For ative purposes, it should be noted that ammonium bromide biocide is conventionally employed at dosages of 0.005 to 0.008 % active substance as Clz per ton produced paper, i.e. the dosage emptoyed in the ments in accordance with the invention is 2 to 10 times higher than the conventional dosage.

The pH vaiues and the ical tivity were measured and the results are ized in Table 6 here below: Table 6: ——_— _---pH changes 6.97 6.93 7.54 7-54 7-57 _--eiectrical conductivity changes — ive biocide 1 organic biocide in conventional amounts, absence of NH4Br biocide 2 NH4Br biocide in conventional amounts, absence of organic biocide 3 combination of NHABI' biocide with organic biocide in increased amounts as set forth in Table 3 As can be seen from the experimental results of Table 6, when adding biocide at a sufficient dose and at suitable feeding points distributed over the papermaking piant, a substantial decrease of electrical tivity and increase of pH can be achieved.

Figure 1 shows the dependency of redox potential (Figure 1A), pH value (Figure 18) and electrical tivity (Figure 1C) on the dosage of biocide in one experiment that was conducted on a paper mill (setting A). During month 1, conventional organic biocide was dosed in conventional s. During months 2 and 3, biocide was added in accordance with the invention. During months 4 and 5, conventional organic biocide was again dosed in PCT/EP2012/(l03582 conventional amounts. From month 6 onwards, biocide was again added in accordance with the invention. As can be seen from Figures 1A, 1B and 1C, when adding biocide at a sufficient dose and at suitable feeding points distributed over the papermaking plant, a substantial increase of redox potential and pH value as well as a substantial decrease of electrical conductivity can be achieved. e 2: Another experiment was ted at a paper miil that had been ing conventional, low amounts of biocide (NH4BrlNaOCl, < 400g/t). When increasing the feed rate of this biocide and adding organic, non—oxidizing biocide as a further biocide, it could be shown in one day only that the conductivity of the system can be substantially decreased.

Figure 2 shows that the increase of biocide dosage immediately ed in a substantial decrease of electrical conductivity from about 2000 uS/cm to about 1500 pS/cm within only 1 day. The dotted vertical line to the left indicates when the biocide dosage according to the invention was started, i.e. when the tional addition of NH4Br biocide was changed to biocide addition in accordance with the invention. and the dotted vertical line to the right indicates when the biocide dosage according to the invention was ated, i.e. when the conventional addition of NH4Br biocide was resumed. At the time interval inbetween the two dotted vertical lines, c biocide was added in addition to NH4Br biocide according to the invention.

Example 3: 36 experiments that were conducted at 19 paper mills were analysed with respect to the performance of dry and/or wet strength rs in dependence of the electrical conductivity.

The dry and/or wet strength rs that were employed in the experiments were two different glyoxylated poiyacrylamide products (GPAM), and the dosage of GPAM varied between 1.5 and 4 kg/t db vs. the cellulosic material with an average of 2.8 kg/t db.

The results are summarized in Figure 3. The trend line has a R2 value 0f 0.72 (standard ion).

Figure 3 shows the dependency of performance of dry and/or wet strength polymers depending upon the electrical conductivity of the aqueous phase of the csic material.

The performance of the dry and/or wet strength polymer is expressed in terms of an efficiency ratio that takes into account the increase of CMT (result of the concora medium test), burst strength, tensile strength and dosage of dry and/or wet th polymer. The efficiency was calculated in dependence of the th increase in "/0 and the dosage of the dry andfor wet strength polymer. A high dosage of dry and/or wet strength polymer with a low increase in paper strength gives a poor efficiency. whereas a low dosage of dry and/or wet strength polymer with a high increase of paper strength gives a good efficiency.

It is clear from Figure 3 that the efficiency ratio is much better when the electrical conductivity is low whatever the dosage. As can be seen from the mental data, particularly from the plot of the efficiency ratio vs. the electrical conductivity of the wet end: a low ical conductivity results in a high efficiency of the dry and/or wet strength polymer, whereas a high electrical conductivity results in a low ency of the dry and/or wet strength r.

Accordingly, when reducing the electrical conductivity by means of the biocide addition according to the invention, the performance of the dry and/or wet th polymer can be surprisingly increased.

Example 4: This experiment was conducted at a paper mill in order to further demonstrate the advantages of the invention under industrial conditions.

A comparative trial C was run without full loop biocide control so that the equilibrated electrical conductivity was 3500 uS/cm.

An ive trial l was run with full loop biocide control (biocide Spectrum® XD3899. Ashland lnc.; added at pulper dilution water, white water 1 and 2, and clarified shower water). so that the equilibrated electrical conductivity was 1950 pS/cm.

Every trial included an experiment in the absence of th aid ("Co" and "i0", respectively) as well as an experiment in the presence of strength aid (“CGPAMH and "loam". respectiveiy).

Ail other experimental parameters were kept constant. The experimental results are shown in the table here below: l l l l i V N aratweTrial 186:]"12 gr:ade c“ aoin _mf186-inn2 <>< III basis weight average 1337--_- :humiditV- m —- conductivity us/cm short loop: 3500 3500 , ORP short loop mV -453 .453 s—- pH short loop 624 624 :45—-j nmt--_- box box { —-—-box box ; nun-m- NH4Br biocide dosing points pulper dilution water; white water 2; white water 1; — clarified shower water “PAM PAM PAM PAM " IIretention aid bottom layer cat. cat. cat. catPAM I IIIZIIII: .7 dosage Spectrum X03399 [concentration of actwesubstanceequrvat to elemental chlorine, expressed in % active nce as Clz per ton produced paper] (*) measured once at trial it becomes clear from the above experimental resuits that due to the full loop biocide control in inventive example i - the electricai tivity decreased from 3500 uS/cm (Co and Comm) to 1950 uS/cm (lo and IGPAM); - the oxygen reduction potential (ORP) in the short loop increased from -453 mV (Co and CGPAM) to +45 ('0 and lGPAM); - the pH value in the short loop increased from 6.24 (Cu and CGPAM) to 6.93 (lo and lemon); - the ATP level in the short loop decreased from about 158,000 (Co and Cemm) to about ,000 ('0 and IGPAM)A Furthermore, it becomes clear that in the absence of the full |00p biocide l, the GPAM strength aid improves WO 26578 - the burst value by only 2.5% (Co = 482 kPa; Comm = 494 kPa); and - the short span compression (SCT) by only 4.3 % (Co = 3.30; Cepm = 3.44).

Under the conditions of the present invention. however, the performance of the strength aid is substantialiy better than under the comparative conditions. Under full toop biocide control, the SPAM strength aid improves - the burst value by 12.6% (lo = 488 kPa; lama = 550 kPa); and — the short span compression (SCT) by 9.9 % (IQ = 3.33; lgpm = 3.66).

Claims (16)

1. A method for manufacturing paper, paperboard or cardboard comprising the steps of (a) pulping an aqueous cellulosic material containing a starch; (b) preventing at least a portion of the starch from being microbially degraded by treating the aqueous cellulosic material ning the starch with one or more biocides, which are at least partially added to the cellulosic material in the thick stock area, where the cellulosic al has a stock tency of at least 2.0%; (h) adding a dry and/or wet strength polymer to the cellulosic material.

The method according to claim 1, wherein the one or more biocides are continuously or discontinuously added to the cellulosic al in quantities so that after 1 month of treatment on a continuously operating papermaking plant, the - electrical conductivity of the aqueous phase of the cellulosic material has been decreased by at least 5%, compared to the electrical conductivity that in each case was measured immediately before e was added for the first time; and/or - pH value of the aqueous phase of the cellulosic material has been increased by at least 0.2 pH units, ed to the pH value that in each case was measured immediately before biocide was added for the first time.

The method according to claim 1 or 2, wherein the one or more biocides are dosed in an amount of at least 5.0 g/ metric ton, based on the total amount of the composition containing the cellulosic material and the starch.

The method according to any one of the preceding , wherein the one or more biocides are oxidative and/or comprise two components.

The method according to any one of the preceding claims, wherein the one or more biocides comprise an inorganic ammonium salt in combination with a n source.

The method according to any one of the preceding claims, n additionally to the one or more biocides added in step (b), a further biocide is added to the cellulosic material which differs from the one or more biocides added in step (b).

The method according to claim 6, wherein the further e is added in section (i) and/or (II); and optionally, also in section (lll) and/or (IV) of a papermaking plant comprising a papermaking machine, wherein section (I) includes es taking place before g; section (ll) includes measures associated with pulping; section (III) includes measures taking place after pulping but still outside the papermaking machine; and section (lV) includes measures taking place inside the papermaking machine.

The method ing to claim 6 or 7, wherein the further biocide is non—oxidizing.

The method according to any one of claims 6 to 8, wherein the further biocide is an organic biocide selected from the group consisting of nary ammonium compounds, benzyl-C12-16~alkyldimethyl chlorides (ADBAC), polyhexamethylene- biguanide (biguanide), 1,2—benzisothiazol—3(2H)—one (BIT), bronopol (BNPD), bis- (trichloromethyl)sulfone, diiodomethyl-p-tolylsulfone, bronopol/quaternary ammonium compounds, benzyI-C12alkyldimethyl des (BNPD/ADBAC), bronopol/didecyl- dimethylammonium chloride (BNPD/DDAC), bronopol/5-chloromethyl-2H-isothiazol- 3-one/2-methyl-2H-isothiazol-B-one (BNPD/lso), NABAM/sodium dimethyldithio- carbamate, sodiumdimethyldithiocarbamate-N,N—dithiocarbamate (NABAM), sodium- methyldithiocarbamate, sodium dimethyldithiocarbamate, 5—chloro—2-methylisothi— azolinone (CMlT), 2,2—dibromo-Z—cyanoacetamide (DBNPA), bronopol/iso (DBNPA/BNPD/lso), 4,5—dichloro-2—n-octyl—3—isothiazo|inone (DCOIT), didecyl— dimethylammonium de (DDAC), didecyldimethylammoniumchloride, alkyl- dimethylbenzylammoniumchloride (DDAC/ADBAC), dodecylguanidine monohydro— chloride/quaternary ammonium compounds, benzyl-C12alkyldimethyl chlorides (DGH/ ADBAC), dodecylguanidine monohydrochloride/methylene dithiocyanate (DGH/MBT), gluteraldehyde (Glut), gluteraldehyde/quaternary ammonium compounds/ benzylcoco alkyldimethyl chlorides (Glut/coco), gluteraldehyde! didecyldimethyl- ammonium chloride (Glut/ DDAC), aldehyde/S-chloro-2—methyl-2H-isothiazol one/ 2-methyl-2H-isothiazolone (Glut/lso), gluteraldehyde/methylene dithiocyanate (Glut/MET), 5-chloro-2—methyl-2H-isothiazol-3—one/2-methyl—2H-isothiazolone (lso), methylene dithiocyanate (MBT), 2-methylisothiazolinone (MIT), methamine e mine oxirane), sodium bromide (NaBr), nitromethylidynetrimethanoI, 2- n-octyl-3—isothiazolinone (OIT), bis(trichloromethyl) ne/quaternary um compounds, benzyl—C12alkyldimethyl chlorides (sulphone/ADBAC), symclosene, terbuthylazine, dazomet (thione), tetrakis(hydroxymethyl)phosphonium sulphate(2:1) (THPS) and p-[(diiodomethyl)sulphonylltoluene (tolyl sulphone), and mixtures thereof.

10. The method according to any one of the ing claims, wherein the dry and/or wet strength polymer is selected from the group consisting of (i) nic, anionic, cationic or amphoteric cellulose reactive polymers capable of forming covalent inter-polymer cross-linkages with cellulose through aldehyde functional groups and/or 3-hydroxy-azetidinium functional groups of the dry and/or wet strength polymer; and (ii) natural or synthetic non-ionic, anionic, ic or amphoteric polymers.

11. The method according to claim 10, wherein the (i) non-ionic, anionic, cationic or amphoteric cellulose reactive polymers are reaction ts - of ionic or nonionic homo- or copolymers comprising monomer units derived from vinylamides, which are optionally fully or partially yzed, and/or from (meth)acry|amides; or of polysaccharides - with epichlorohydrin or with ose reactive agents comprising at least one aldehyde functional group.

12. The method according to claim 11, n the cellulose reactive agents comprise at least two aldehyde onal groups and are selected from the group ting of glyoxal, glutaraldehyde, succinaldehyde, furan dialdehyde, 2—hyroxyadipaldehyde, hyde starch, and combinations thereof.

13. The method ing to claim 10, n the (ii) natural or synthetic non-ionic, anionic, cationic or amphoteric polymers are selected from the group consisting of a) native or chemically modified polysaccharides; b) anionic homo- or copolymers comprising anionic monomer units derived from (meth)acrylic acid; optionally in combination with non—ionic monomer units derived from (meth)acrylamide; c) cationic homo- or copolymers comprising cationic monomer units derived from vinylamine, polydiallyldimethylammonium chloride, 2-acryloylethyltrimethylammo- nium de, and/or ethyleneimine; optionally in combination with non-ionic monomer units d from vinylamide and/or acrylamide; d) amphoteric polymers; e) substantially nonionic water-soluble polymers; and f) water—insolublelatexes.

14. The method according to any one of the preceding claims, which is performed on a continuously operating papermaking plant, and which es the steps: (A) measuring a property of the s phase of the cellulosic material selected from the group consisting of electrical conductivity, redox potential, pH value, concentration of ATP, and concentration of free starch; at a predetermined location of the papermaking plant; (B) manufacturing paper, paperboard or cardboard by the method according to any of the preceding claims comprising steps (a), (b), and (h); (C) measuring the same property as measured in step (A) after time At and comparing the value measured in step (C) with the value ed in step (A); (D) regulating the dosage of biocide added in step (b) and/or the dosage of dry and/or wet strength polymer added in step (h) in dependence of the result of the comparison made in step (C).

15. Use of a biocide or combination of es as defined in any one of claims 4 to 9 for reducing the ical conductivity of the aqueous phase of a cellulosic material in the manufacture of paper, paperboard or cardboard.

16. The method according to claim 1, substantially as herein described with reference to any one of the Examples and/or