US20230416988A1

US20230416988A1 - A method for preparing modified pulp

Info

Publication number: US20230416988A1
Application number: US18/031,207
Authority: US
Inventors: Gustaf Westberg; Timo Lehmuskallio; Merja Valtanen
Original assignee: UPM Kymmene Oy
Current assignee: UPM Kymmene Oy
Priority date: 2020-10-15
Filing date: 2021-10-14
Publication date: 2023-12-28
Also published as: WO2022079357A1; FI20206014A1; EP4229237A1

Abstract

A method is disclosed. The method may comprise adding a hydrophobization agent to wet pulp; drying the wet pulp, thereby obtaining dried pulp; wherein the dried pulp is intended for defibrillating into fibers, thereby obtaining the modified pulp; or the method further comprises defibrillating the dried pulp into fibers, thereby obtaining the modified pulp.

Description

TECHNICAL FIELD

The present disclosure relates to a method for preparing modified pulp, to modified pulp, and to articles prepared therefrom.

BACKGROUND

A significant portion of plastic products end up in landfills and to the environment, such as in oceans and waterways. Plastics are not biodegradable or are biodegraded only very slowly, producing microplastics. Single use items are often used e.g. in packaging, consumer products, cosmetics and healthcare. Therefore, there is a need to provide single use items that are produced from materials other than plastic and that may be biodegradable.
Natural fibers, such as wood fibers, are re-newable raw materials well suited for producing single use items. However, single use items may require a level of barrier properties against e.g. water and/or grease. A plastic film may be added to such items, but then such an item is no longer plastic-free. Alternatively, e.g. a biodegradable barrier layer may be sprayed on such items, but this may increase costs and complicate the process of producing such items.

SUMMARY

A method for preparing modified pulp is disclosed. The method may comprise adding a hydrophobization agent to wet pulp; and drying the wet pulp, thereby obtaining dried pulp. The dried pulp may be intended for defibrillating into fibers, thereby obtaining the modified pulp; or the method may further comprise defibrillating the dried pulp into fibers, thereby obtaining the modified pulp.
A method for preparing modified pulp is also disclosed, wherein the method may comprise defibrillating dried pulp, thereby obtaining the modified pulp. The dried pulp may be obtainable by adding a hydrophobization agent to wet pulp and by drying the wet pulp.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the embodiments and constitute a part of this specification, illustrate various embodiments. In the drawings:

FIG. 1 is a flow chart illustration of an embodiment of the method; and

FIG. 2 illustrates the absorption time measurements of modified (left) and unmodified fluff pulp (right).

DETAILED DESCRIPTION

In a first aspect, a method for preparing modified pulp is disclosed. The method may comprise adding a hydrophobization agent to wet pulp; and
drying the wet pulp, thereby obtaining dried pulp;
wherein the dried pulp is intended for defibrillating into fibers, thereby obtaining the modified pulp; or the method further comprises defibrillating the dried pulp into fibers, thereby obtaining the modified pulp.
In a second aspect, a method for preparing modified pulp is disclosed. The method may comprise defibrillating dried pulp, thereby obtaining the modified pulp; wherein the dried pulp is obtainable by adding a hydrophobization agent to wet pulp and by drying the wet pulp.
Any embodiments described below in this specification may be understood as relating to the first aspect and/or to the second aspect.
The method may be a method for reducing the absorption time of the modified pulp.
With the method, it may be possible to modify the absorption properties of the modified pulp significantly. In particular, the absorbency of the modified pulp, and subsequently articles prepared therefrom, may be reduced, and the absorption time of modified pulp may be dramatically longer than that of an otherwise comparable pulp. Such modified pulp may be considered water-repellant, at least compared to a comparable pulp that has not been treated with a hydrophobization agent; water penetration to the pulp network may be dramatically reduced. Such modified pulp may be used for purposes in which the natural absorption properties of the pulp fibers are not desirable, for example in the preparation of single use items and articles used e.g. in packaging, consumer products, cosmetics and/or healthcare. Examples of such items and articles are described below. With the modified pulp, such single use items and articles may have barrier properties against water and/or grease due to the absorption properties of the modified pulp. This may reduce or even obviate the need to add a plastic film or other barrier layer to the item or article. Further, even if the modified pulp may still absorb water to an extent, it may not necessarily con-dense but may still maintain its bulk. The single use items or articles may thus have improved durability, in particular when a plastic film or other barrier layer is not added thereto.
With the method, fibers of the pulp may be impregnated with the hydrophobization agent effi-ciently, such that the modified absorbency properties are still present (at least to a significant extent) even after the defibrillating of the dried pulp into fibers, which process may typically destroy any modifi-cations done to fibers prior to the defibrillating. The method may be relatively efficient and does not require a complicated or energy consuming process. The modifi-cation by the hydrophobization agent may also assist in the defibrillating.
Thus it may be possible to produce single use items and other articles in a more environmentally friendly manner.
The modified pulp may be modified defibrillated pulp. The modified pulp may, in some embodiments, be modified fluff pulp.
In the context of this specification, the term “defibrillated pulp” may be understood as referring to pulp obtainable by defibrillating dried (i.e. dry) pulp. For example, the defibrillated pulp may be obtainable by defibrillating according to one or more embodiments described below.
In the context of this specification, the term “fluff pulp” may be understood as it is commonly understood in the field. Fluff pulp is often made from long fibre softwoods. It is typically intended for applications that require high absorbency, such as a raw material in the absorbent core of personal care products such as diapers, feminine hygiene products, air-laid absorbent towelling, as such, or with superabsorbents and/or synthetic fibres. However, in embodiments that relate to “modified fluff pulp”, the pulp may otherwise have properties similar to regular fluff pulp (to which no hydrophozation agent has not been added), but it may have different absorption properties (due to the effect of the hydrophobization agent), as set cut in this specification. The method for preparing the modified pulp may be similar to methods for preparing fluff pulp, and so the modified pulp may have many properties otherwise similar to fluff pulp.
The pulp in the wet pulp may comprise or be pulp obtainable from softwood, such as spruce, pine, fir, larch, Douglas f-r or hemlock. Additionally or alternatively, it may comprise or be pulp obtainable from hardwood, such as birch, aspen, poplar, alder, eucalyptus, oak, beech or acacia, or from a mixture of a softwood and a hardwood. The pulp may be e.g. Scandinavian pulp. The pulp may comprise or be pulp obtainable from long fibre softwood(s). The pulp may be chemical pulp. The pulp may contain, in addition to the cellulose fibers, e.g. hemicellulose and residual lignin, and optionally other components.
The dried pulp may have a dry matter content of about 85 to 99% (w/w) based on the total weight of the dried pulp, and/or the pulp may be dried so as to have a dry matter content of about 85 to 99% (w/w) based on the total weight of the dried pulp.
The dried pulp may be understood as referring to the pulp prior to the defibrillating. The dried pulp may be e.g. in the form of bales or rolls prior to the defibrillating. For example, the dried pulp may be obtainable in such a form, and it may subsequently be defibrillated e.g. in a converting line.
The dried pulp may be dried fluff pulp or dried pulp intended or suitable for producing fluff pulp.
The density of the dried pulp may be e.g. in the range of 0.4-0.7 cm³/g. The density of the dried pulp may be e.g. in the range of 0.45-0.65 cm³/g, or 0.5-0.6 cm³/g.
The density may be determined e.g. according to the standard ISO 3034.
The dried pulp may have a bursting strength according to the Mullen method, i.e. a Mullen value, in the range of 350-1500 kPa.
The term “defibrillating” may be understood as referring to mechanically defibrillating the pulp. The defibrillating may separate fibers in the pulp from each other. The pulp may thus be defibrillated into single fibers, or at least partially into single fibers. This process may also be referred to as defibrizing, defibration and/or defibrillation.
The defibrillating may be done on the dried pulp in dry form, i.e. the dried pulp may be dry (in dry form) when defibrillated.
The defibrillation may be done such that the lengths of the fibers of the pulp are not essentially or significantly shortened by the defibrillation, i.e. the length of the fibers of the pulp is essentially the same before and after the defibrillation. The defibrillation may be done such that the fibers are not disintegrated into fibrils (at least to a significant extent).
The defibrillating should therefore not be understood as referring to e.g. fibrillation that may result in nanofibrillar cellulose. The modified cellulose may thus also be understood as not referring to or including nanofibrillar and/or microfibrillar cellulose.
After the defibrillation, the defibrillated modified pulp may be used further, for example by forming articles thereof as described below or by forming other products thereof.
The dried pulp may be defibrillated by shredding. Any suitable shredding device may be used. For example, the pulp may be defibrillated by a hammer mill. Other shredding devices may be contemplated, for example shredding devices suitable for defibrillating pulp into fluff pulp. The shredding device may be at least one of a hammer mill, a pin mill, a saw-toothblade, or a briseur.
The hydrophobization agent may, in principle, be any agent capable of hydrophobizing the pulp.
The hydrophobization agent may comprise or be a resin, wax, a wet glue resin, or any mixture or combination thereof.
The resin may be e.g. a hydrophobization resin. An example of such a resin could be e.g. tall oil resin.
The hydrophobization agent may be capable of binding to the pulp by forming hydrogen bonds with the pulp. For example, it may be capable of binding to the pulp by forming hydrogen bonds only (as opposed e.g. to forming a covalent bond with the pulp).
However, hydrophobization agents capable of binding to the pulp by forming a covalent bond (or covalent bonds) with the pulp may also be contemplated. An example of such hydrophobization agent could be e.g. alkenyl succinic anhydride (ASA) or alkyl ketene dimer (AKD). Such hydrophobization agents could form e.g. ester bonds with the hydroxyl groups of the cellulose of the pulp.
In an embodiment, the hydrophobization agent consists of a resin (such as a thermoplastic resin), wax, a wet glue resin, and any mixture or combination thereof.
The hydrophobization agent may comprise or be a thermoplastic resin. In an embodiment, the hydrophobization agent consists of a thermoplastic resin.
The resin, such as a thermoplastic resin, may be e.g. an ovenable resin, i.e. a resin suitable for and/or approved for use in an oven.
The hydrophobization agent may be e.g. a composition comprising one or more components, for example any suitable hydrophobization component described in this specification (such as a resin, wax, a wet glue resin, or any mixture or combination thereof) and optionally water and/or an aqueous solution. Alternatively or additionally, two or more hydrophobization agents or components may be added separately to the wet pulp.
The hydrophobization agent may be a liquid or in the form of a liquid. In other words, the hydrophobization agent may be water-based. In embodiments in which the hydrophobization agent or composition comprises one or more components that are not fully water-soluble, such components may be e.g. in the form of an emulsion in the hydrophobization agent or composition.
The hydrophobization agent may, in some embodiments, be added to a wet pulp with a pH in the range of 2-6. In other words, the pH of the wet pulp may be in the range of 2-6 when the hydrophobization agent is added thereto. Alternatively or additionally, the pH may be in the range of 2.5-5; or of 2.5-5.5; or of 2.5-4.5.
The term “wet pulp” may be understood as referring to pulp suspended in water and/or an aqueous solution. In other words, the wet pulp may be e.g. pulp slush. For example, the wet pulp may be pulp at a wet end of a pulp production process (i.e. wet end pulp). For example, it may be pulp at a wet end of a fluff production process. Thus the hydrophobization agent may be added to the pulp at a wet end.
In other words, the hydrophobization agent may be added to the pulp suspended in water and/or an aqueous solution, such that the water and/or aqueous solution has a pH in the range of 2-6, or any other pH described in this specification.
The pulp (wet or dried) may be obtainable by a treatment with a debonder, or it may be treated with a debonder. The debonder may render the pulp more easily defibrillated. The debonder may be e.g. a surfactant capable of disrupting interfiber hydrogen bonds.
The method may be a method for producing an article. In such a method, the method may further comprise forming an article of the modified pulp. The article may be formed at least partially of the modified pulp; other components may be included, if desired and/or necessary. The article may be formed e.g. by form pressing or wet pressing. Heat, steam and/or underpressure may be applied to the article when form pressing. However, other suitable methods for forming the article from the modified pulp may be contemplated. The modified pulp described in this specification may be well suited e.g. for form pressing, as the defibrillation allows for pressing and/or otherwise forming the modified pulp into various forms.
A modified pulp obtainable by the method according to the first or second aspect, and according to one or more embodiments described in this specification, is also disclosed.
A modified pulp is also disclosed. The modified pulp may be defibrillated and exhibit an absorption time of at least 20 seconds. In some embodiments, the modified pulp may exhibit an absorption time of at least 50 seconds, or at least 100 seconds.
The absorption time may be measured using a 3 g sample of the modified pulp, e.g. according to the standard SCAN-C 33:80.
The modified pulp may be obtainable by the method according to the first or second aspect, and according to one or more embodiments described in this specification.
The absorption capacity of the modified pulp may be in the range of 7-12 g/g (i.e. 7-12 H₂O g/g).
The modified pulp may have a bulk of 16-24 cm³/g. In certain embodiments, the modified pulp may have a bulk of 17-23 cm³/g, or 19-22 cm³/g.
The modified pulp may be modified defibrillated pulp and/or modified fluff pulp.
The modified pulp may be dry modified pulp (as opposed to being e.g. in the form of a gel). The dry modified pulp may have a moisture content of e.g. about 6-10% (w/w).
An article obtainable from or formed of the modified pulp according to one or more embodiments described in this specification is also disclosed.
The article may be formed at least partially of the modified pulp; other components may be included, if desired and/or necessary. The article may be formed e.g. by form pressing or wet pressing. Heat, steam and/or underpressure may be applied to the article when form pressing. However, other suitable methods for forming the article from the modified pulp may be contemplated.
The article may be an article that is intended not to absorb water and/or grease, at least to a significant extent. Various articles and items may therefore be contemplated.
The article may be a single use article or a single use item. Examples of such articles may include e.g. a container (such as a food container), a catering item, a casing, a tray, a cup, a utensil, cutlery (such as a fork, a knife, or a spoon), a plate, or a packaging article. The article may be a filter or an insulator.
The modified pulp and/or articles formed therefrom may, at least in some embodiments, be biodegradable.
A method for producing an article is also disclosed, the method comprising forming the article of the modified pulp according to one or more embodiments described in this specification. The article may be an article according to one or more embodiments described in this specification.

EXAMPLES

Reference will now be made in detail to various embodiments, an example of which is illustrated in the accompanying drawing.
The description below discloses some embodiments in such a detail that a person skilled in the art is able to utilize the embodiments based on the disclosure. Not all steps or features of the embodiments are discussed in detail, as many of the steps or features will be obvious for the person skilled in the art based on this specification.
FIG. 1 describes an embodiment of a method for preparing modified pulp.
Pulp in wet format, i.e. wet pulp, is provided at 1, for example as a pulp slush. A hydrophobization agent 2 is added to the wet pulp, such that the hydrophobization agent binds to the fibers of the wet pulp at least partially. The wet pulp that has been treated with the hydrophobization agent is then dried at 3 to provide the pulp in a dry format, i.e. as dried pulp, at 4, for example as bales or rolls. In an embodiment, the method may continue futher to a shredding process 5 e.g. at the same site or process. In other embodiments, the pulp in dry format 4 may be e.g. sold to an end user that may then star their own process by obtaining the pulp in dry format 4 and by defibrillating it at the shredding process 5. A skilled person may thus understand that not all steps of the method depicted in FIG. 1 need take place in the same process or site, but that different steps of the method may be performed by different operators e.g. at different locations.
In the shredding process 5 the pulp in dry format is at least partially defibrillated into single fibers, resulting in modified defibrillated pulp 6. The shredding process may be performed mechanically e.g. using a suitable shredding device, such as a hammer mill or a pin mill.

Example 1

The properties of regular softwood fluff pulp samples were investigated. In order to reduce dust formation of the fluff pulp, hydrophobization agent containing a thermoplastic resin and a paraffin wax (BIM Kemi) was added to pulp slush either at an amount of 5 kg/t (sample 5) or at 7 kg/t (sample 7), and the resulting pulp slush was dried. The dried pulp was then defibrillated using a hammer mill to produce modified fluff pulp. Control sample A was prepared by drying pulp slush to which no hydrophobization agent was added and by defibrillating the dried pulp to produce regular fluff pulp. Sheets were prepared from all samples. Properties of the sheets are shown in Table 1.

TABLE 1

Characteristics of sheets prepared from modified (Resin
5 and 7) and unmodified (A) fluff pulp samples.

		Resin 5	Resin 7
SHEET CHARACTERISTICS	A	5 kg/t	7 kg/t

BASIS WEIGHT	wet	g/m²	726	726	726
BASIS WEIGHT	dry	g/m²	685	685	703
APPARENT		kg/cm³	0.53	0.57	0.57
DENSITY
FIBER LENGTH		mm	2.1	2.02	2.08
FINES	<0.40 mm	%	6.76	6.53	6.19
LONG FIBERS	>1.85 mm	%	54.20	55.88	57.56
KLEMM		mm	121	72	33

According to a Mullen test performed to all samples, it appeared that the bursting strength of sheets prepared from modified fluff pulp was lower than that of sheets prepared from unmodified fluff pulp. Fiber lengths and fines appeared comparable across all samples.
Unexpectedly it was found that the modified fluff pulps exhibited significant water repellency and modified absorption properties.
The Klemm test was performed by cutting a 25 cm strip of each sheet and by measuring the length along which the strip absorbed water within 10 min. According to the Klemm test, the modified fluff pulps absorbed less water.
Results of other absorption measurements are shown in Table 2.

TABLE 2

Characteristics of modified (Resin 5 and 7) and unmodified
(A) fluff pulp samples after defibrillation.

FLUFF CHARACTERISTICS

SEC CONDITIONS		Resin	5	Resin 7
(rotor/feed/screen) 90/90/8	A	5 kg/t	7 kg/t

SEC	MJ/t	192	132	111
BULK	dry cm³/g	22.0	18.0	16.5
ABS.TIME	s	2.7	818	6900
ABS.CAPACITY	g/g	10.2	7.7	7.7
NETWORK	N	5.83	4.48	4.32

The absorption times (measured according to the standard SCAN-C33:80) of the modified fluff pulps were dramatically longer than that of the unmodified fluff pulp. The absorption capacities were also reduced to some extent.
FIG. 2 illustrates the absorption time measurements of modified (left) and unmodified fluff pulp (right). Cylindrical test pieces of the fluff pulps, having a mass of 3 g and a diameter of 50 mm, were prepared in a test piece former. Test pieces were placed in a vertical position and a load of 500 g was applied. The test pieces were placed on the surface of water in cups as shown in FIG. 2 so that they could absorb water from below. The test pieces of unmodified fluff pulp absorbed water within seconds and sank. The test pieces of modified fluff pulps however absorbed water very slowly.
SEC (shredding energy consumption, i.e. disintegration energy or defibration energy) was lower for the modified fluff pulps, indicating that the modified fluff pulps were softer than the unmodified. The exact SEC values are likely to have been affected by the measurement conditions; the SEC values were measured using relatively high rotation speeds (4500 rpm). The bulk measurement indicated that the modified fluff pulps were compressed slightly more when pressed. The network measurements indicated that the strengths of the modified fluff pulps were slightly lower, possibly due to reduced fiber bonds.
It is obvious to a person skilled in the art that with the advancement of technology, the basic idea may be implemented in various ways. The embodiments are thus not limited to the examples described above; instead they may vary within the scope of the claims.
The embodiments described hereinbefore may be used in any combination with each other. Several of the embodiments may be combined together to form a further embodiment. A method, a product, or a use, disclosed herein, may comprise at least one of the embodiments described hereinbefore. It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages. It will further be understood that reference to ‘an’ item refers to one or more of those items. The term “comprising” is used in this specification to mean including the feature(s) or act(s) followed thereafter, without excluding the presence of one or more additional features or acts.

Claims

1. A method for preparing modified pulp, wherein the method comprises adding a hydrophobization agent to wet pulp;

drying the wet pulp, thereby obtaining dried pulp;

wherein the dried pulp is intended for defibrillating into fibers, thereby obtaining the modified pulp; or the method further comprises defibrillating the dried pulp into fibers, thereby obtaining the modified pulp.

2. A method for preparing modified pulp, wherein the method comprises defibrillating dried pulp, thereby obtaining the modified pulp; wherein the dried pulp is obtainable by adding a hydrophobization agent to wet pulp and by drying the wet pulp.

3. The method according to claim 1, wherein the modified pulp is modified defibrillated pulp or modified fluff pulp, and/or the dried pulp is dried fluff pulp.

4. The method according to claim 1, wherein the pulp is defibrillated by shredding.

5. The method according to claim 1, wherein the hydrophobization agent comprises or is a resin, wax, a wet glue resin, or any mixture or combination thereof.

6. The method according to claim 1, wherein the hydrophobization agent is added to a wet pulp with a pH in the range of 2 to 6.

7. The method according to claim 1, wherein the method is a method for producing an article, and the method further comprises forming an article of the modified pulp.

8. Modified pulp, wherein the modified pulp is defibrillated and exhibits an absorption time of at least 20 seconds.

9. Modified pulp prepared by the method according to claim 1, wherein the modified pulp is defibrillated and exhibits an absorption time of at least 20 seconds.

10. The modified pulp according to claim 8, wherein the absorption capacity of the modified pulp is in the range of 7-12 g/g.

11. The modified pulp according to claim 8, wherein the modified pulp is modified defibrillated pulp and/or modified fluff pulp.

12. An article obtainable from or formed of the modified pulp according to claim 8.

13. The article according to claim 12, wherein the article is a single use article or a single use item.

14. A method for producing an article, the method comprising forming the article of the modified pulp according to claim 8.

15. The method according to claim 14, wherein the article is a single use article or a single use item.

16. The article of claim 12, wherein the article is form pressed.

17. The article of claim 13, wherein the article is a container, a catering item, a casing, a tray, a cup, cutlery, a utensil, a plate, or a packaging article; a filter; or an insulator

18. The method according to claim 7, wherein forming the article of the modified pulp comprises form pressing.