CA1071805A - Drainage and wet stretch improvement in mechanical pulps - Google Patents
Drainage and wet stretch improvement in mechanical pulpsInfo
- Publication number
- CA1071805A CA1071805A CA289,427A CA289427A CA1071805A CA 1071805 A CA1071805 A CA 1071805A CA 289427 A CA289427 A CA 289427A CA 1071805 A CA1071805 A CA 1071805A
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- CA
- Canada
- Prior art keywords
- pulp
- mechanical
- drainage
- sodium sulphite
- pulps
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C3/00—Pulping cellulose-containing materials
- D21C3/02—Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes
- D21C3/022—Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes in presence of S-containing compounds
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/001—Modification of pulp properties
- D21C9/002—Modification of pulp properties by chemical means; preparation of dewatered pulp, e.g. in sheet or bulk form, containing special additives
- D21C9/004—Modification of pulp properties by chemical means; preparation of dewatered pulp, e.g. in sheet or bulk form, containing special additives inorganic compounds
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- Chemical & Material Sciences (AREA)
- Inorganic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Paper (AREA)
Abstract
DRAINAGE AND WET STRETCH IMPROVEMENT
IN MECHANICAL PULPS
ABSTRACT OF THE DISCLOSURE
The drainage and wet stretch properties of mechanical pulp are improved by cooking the mechanical pulp under controlled conditions so as to permit greater use of mechanical pulp in newsprint. The pulp is cooked in sodium sulphite solution at elevated temperature for a time sufficient to cause reaction with the pulp but insufficient to cause substantial dissolution of lignin from the pulp.
IN MECHANICAL PULPS
ABSTRACT OF THE DISCLOSURE
The drainage and wet stretch properties of mechanical pulp are improved by cooking the mechanical pulp under controlled conditions so as to permit greater use of mechanical pulp in newsprint. The pulp is cooked in sodium sulphite solution at elevated temperature for a time sufficient to cause reaction with the pulp but insufficient to cause substantial dissolution of lignin from the pulp.
Description
The present invention relates to the production of mechanical pulp of improved properties.
Traditionally newsprint is manufactured from a -furnish consisting of about three parts groundwood and one part chemical pulp. Groundwood, manufactured by pressing logs against a revolving abrasive stone, is obtained in yields approaching 100% and is the cheapest component of the furnish. Aside from economy, groundwood contributes several desirable properties to the sheet. Particularly the high light scattering coefficient of groundwood con- -tributes to paper opacity and allows the use of a thinner sheet. The high oil absorption of groundwood improves ink - acceptance during printing. Pollution problems associated ' with the manufacture of groundwood are minimal.
The chemical pulp component is usually manufactured by either the kraft or sulphite process in yields ranging from 45% to 65%. Chemical pulps are expensive, make heavy demands on the mill's wood resources, and entail formidable pollution problems. The present trend in newsprint manu-facture, therefore, is towards reduction in the use of chemical pulps . - , Chemical pulps are used because they impart proper-ties to the furnish which improve its runability. Runability refers to that combination of properties which allows the wet web to be transported at high speed through the forming, pressing and drying section of the paper machine and allows the dry sheet to be reeled and printed with not more than an acceptable number of breaks. Runability is the key`to :~o7~805 paper machine and pressroom efficiency, which in turn is the key to profita~ility. Despite the above-noted dis-advantages of chemical pulps, they remain a virtually indispensable component of newsprint furnish for reasons of runability.
Surprisingly, the mechanism by which chemical pulps improve runability is not well understood. There is a growing body of evidence that the properties crucial to efficient operation on high speed paper machines are high - -wet web stretch and drainage rate. Stretch, both wet and dry, prevents breaks by preventing concentration of stresses around paper defects, where breaks usually originate. High drainage rate lowers the water content to yield a less -fragile web. These effects have been discussed in recent articles by D. M. Harvey, A. J. Barnet and L. M. Lyne in Pulp and Paper Canada (7) T154-6 (July 1977) and by D.F.
Rutland, A. Y. Jones, P. M. Shallhorn, J. Tichy and A.
Karnis in Pulp and Paper Canada 78 (4) T99-105 (April 1977).
In conventional mechanical pulps, wet stretch is obtained at the expense of drainage, i.e. highly refined pulps have a high wet stretch but a low drainage rate, while for lightly refined pulps, the opposite is true. Mechanical pulps can also be manufactured in refiners, both open dis-charge type and in pressurized units at higher temperatures.
The resulting pulps, called refiner mechanical pulp (RMP) and thermomechanical pulp (TMP) are of higher quality than groundwood pulp, are obtained in yields over 95% with minimal pollution problems. They are however not a sub-stitute for chemical pulps and are generally not acceptable as the sole furnish for a newsprint machine.
Attempts have been made to further upgrade mechanical - pulps by chemical pretrea,tment of the wood chips prior to refining. A variety of such processes are currently under ' development and are referred to as chemimechanical (cMæ) and thermochemimechanical (TCMP). These treatments in general increase energy requirements of manufacture. While ' useful properties are developed at some cost, substantial improvements are in general not observed in the properties of primary importance to runability, namely drainage and wet stretch. We have now made the surprising and unexpected discovery that both drainage and wet stretch of mechanical pulps can be increased by a chemical treatment carried out after the refining or grinding operation.
It has now been surprisingly found that both the drainage and wet stretch properties of mechanical pulps can be improved by a controlled chemical treatment of such pulps after formation thereof.
In accordance with the present invention, there is B provided a method of pre~rcltmcnt of mechanical wood pulp which comprises cooking the pulp with aqueous sodium sulphite solution containing sufficient alkali to maintain a pH
greater than about 3 during ,,the cooking. The cooking is effected at an elevated temperature for a time sufficient to cause reaction with the pulp and increase the drainage and wet stretch thereof but for a time insufficient to cause substantial dissolution of lignin from the pulp and insufficient to result in a pulp yield below about 90%.
The improvement in both drainage and wet stretch properties achieved by the present invention permits use of the treated pulps in newsprint to achieve high runability without or with a decreased proportion of chemical pulp.
.
~ ~ _ 4 ~
The procedure of the present invention may be carried out on any of the types of mechanical wood pulp mentioned above, namely, groundwood pulp, RMP, TMæ, cMæ and TCMP, and the improvement in drainage and wet stretch proper-ties is achieved on each of these mechanical pulp types.
By "mechanical pulp" as used herein is meant wood which has been reduced to fibrous form by mechanical action.
Mechanical pulps are frequently produced by refin-ing in two stages. In the manufacture of thermomechanical pulp, for example, the pressurized refining stage is con-ventionally followed by atmospheric refining. The chemical -treatment of this invention may be applied to the pulp between the stages of refining to achieve the beneficial effect. - -The invention may also be applied to separate fractions separated from mechanical pulps. For example, mechanical pulps are generally separated into "accept" and "reject" fractions by means of screens or hydrocyclonic separators prior to use. The invention may be applied separately to either or both fractions from such separations.
Specifically, the invention consists of treating mechanical pulp with sodium sulphite with or without sodium bisulphite or additional alkali such as sodium hydroxide or sodium carbonate, at an elevated temperature for a time sufficient to cause reaction with the pulp but not long enough to cause substantial dissolution of lignin from the pulp.
It has been found that, as the reaction proceeds, the pH of the medium drops, probably as a result of hydrolysis of acetyl groups on the pulp. If the pH drops below 3, there is risk of damaging the fibre through hydrolytic action with consequent loss of strength. Wood fibre which has been subjected to mechanical action, such as refining, is particu-larly susceptible to acidic degradation. It is therefore essential to the present invention that sufficient alkali be present in the chemical charge to prevent a pH drop below 3 during treatment. The exact amount of alkali required varies according to the acetyl content of the wood supply and cannot be specified exactly, but is readily established by experimentation.
The alkali requirement may be met entirely with sodium sulphite. However, since only half of the sodium of sodium sulphite is available for neutralization, it is usually more economical to meet part of the alkali require-ments by additions of sodium hydroxide or sodium carbonate.
The pH of the mixture, however, is preferably kept below about 12, because hemicelluloses are dissolved from wood fibre by higher pH's, with consequent loss in yield.
In a preferred embodiment of the invention, the amount of sodium sulphite used is in the range of 4% and 10%
by weight based on the mechanical pulp, although lower con-centrations down to about 1% by weight may be used with reduced beneficial effect. Below 1% sodium sulphite improve-ments are too small to justify the expense of treatment.
Similarly improvements are observed with chemical charges up to about 25% by weight of the pulp, but the additional cost is not justified by the small additional improvement.
Generally, therefore, a chemical charge of between about 1% and about 25% by weight, preferably between about 4% and about 10% by weight, of the mechanical pulp, is us~d. The ~071805 chemical charge preferably has a pH between about 9 and abou~ 12, and contains sodium sulphite and sufficient alkali to maintain a pH greater than 3 throughout the reaction.
It is preferred to carry out the reaction at consistencies between 5~ and 50%, preferably around 25%.
Lower consistencies increase equipment size and energy costs, and decrease reaction rate because of dilution of the reactants, necessitating longer reaction times. Con- -sistencies higher than 50~ are not readily prepared by mechanical pressing.
The time and temperature of reaction may be varied over a wide range. The-essential requirements are that the reaction must be allowed to effect an increase in drainage and wet stretch and must not be allowed to proceed far enough to yield substantial dissolution of lignin, as the ; latter would decrease pulp yield and create a pollution problem. Practically, the application of our invention is restricted to pulp yields in excess of 90% by weight based on starting mechanical pulp. The minimum reaction time to yield beneficial results usually is about 30 min. at 100C, with shorter times being used at higher temperatures. The --effects of time and temperature are combined in a calculated quantity called the "H-Factor". Anyone familiar with chemical pulping is aware of the way in which H-Factor may -be used to vary time and temperature simultaneously to yield a given degree of cooking. In the practice of the invention, the pulp is exposed to a minimum degree of cooking corres-ponding to 30 minutes at 100C, and a maximum degree of cooking corresponding to a pulp yield of 90% by weight.
The invention is illustrated by the following Examples:
Example 1 This Example illustrates the application of the invention to various mechanical pulps.
Mechanical pulps were treated with a solution of sodium sulphite at pH 9.0 and pressed to 25% consistency.
The amount of chemical remaining with the pulp was 4% by weight based on the dry fibre content. Pulps were then heated at 140C for 30 minutes in an autoclave, handsheets prepared and paper properties measured. The results obtained are reproduced in the following Table I:
TABLE I - -Groundwocd TMP RMP TCMæ
Before After Before After Before After Beore After Property Drainage (sec.) 3.32 2.77 1.32 0.95 1.40 1.14 0.71 0.63 Wet Stretch % 5.0 6.5 4.7 7.9 4.5 7.6 3.5 6.0 Burst 10.5 12.8 22.0 18.0 12.9 13.4 16.3 15.8 Bre~ng Length 2660 2820 3600 3050 2710 2650 3150 3000 qear 39 39 105 108 64 71 107 99 Dry Stretch 1.32 1.41 1.94 2.50 1.72 1.75 1.62 2.00 It will be seen from the results of Table I that that chemical treatment of each pulp improved the drainage and increased the stretch in every case, without adverse effect on other properties.
Example 2 :
This Example illustrates the effect of reaction temperature on pulp properties.
Mechanical pulps impregnated with 4% by weight of sodium sulphite at pH 9 were heated for 30 min. at various temperatures. The resulting pulps had the properties repro-duced in the following Table II:
TABLE II
Property TMP TCMP
Befor,e 100C 140CBefore 100C 140C
Drainage, sec. 1.32 1.19 - 0.95 0.71 - 0.89 0.63 ~et Stretch, ~ 4.7 5.0 7.9 3.5 3.8 6.0 Burst 22.0 22.4 18.0 - 16.3 17.1 15.8 Breaking Length 3600 3740 3050 3150 3100 3000 Tear 105 103 108107 108 99 Dry Stretch, % 1.94 2.24 2.50 1.62 1.98 2.00 pH after reaction - 6.02 4.19 - 6.77 6.10 The results of the above Table II show significant improvement in the drainage and wet stretch characteristics of TMP even at 100C and both pulps show further improvement by heating at 140C.
This Example illustrates the effect of the amount of chemical on pulp properties.
TMP impregnated with 4% by weight and 10% by weight sodium sulphite at pH 9 was heated 30 min. at 140C, handsheets made and properties measured. The results are reproduced in the following Table III: -TABLE III
Property Before 4% 10%
- Drainage, sec. 1.32 0.95 1.16 ~et Stretch, % 4.7 7.9 7.9 Burst 22 18 23.7 Breaking Length 3600 305C 3820 Tear 105 108 96 Dry Stretch, ~ 1.94 2.50 2.92 pH after reaction - 4.19 6.83 g , - ' ,:
iO71805 The results of Table III show beneficial effects at both chemical levels. The main effect of the higher chemical level is to maintain a higher pH throughout the reaction, leading to improvement in burst and breaking length.
This Example illsutrates the effect of pH during the reaction on pulp properties.
Mechanical pulps heated with 4% by weight sodium sulphite at a range of pH's yielded products having the properties set forth in the following Table IV:
TABLE IV
TMP TCMP
- Before After Before After Original pH 7.0 7 9 Temp.of reaction C 140 140 140 Drainage, sec. 0.81 0.64 0.71 0.61 0.63 Wet Stretch, ~ 4.4 10.6 3.5 7.6 6.0 Burst 17.2 8.7 16.3 9.9 15.8 Breaking Length 2970 1810 3150 2020 3000 Tear 117 106 107 112 108 Dry Stretch 1.61 2.05 1.62 1.89 2.00 pH after reaction - 2.51 - 2.72 6.10 - It is apparent from the results of Table IV that when the pH dropped below 3, heating was accompanied by serious decreases in burst and breaking length. It was also observed this degradation was more severe at higher temperatures and longer reaction times.
.
The present invention, therefore, provides a method of treatment o mechanical pulp which improves both its drainage and wet stretch properties. Modifications are possible within the scope of the invention.
.
'-: -' . : .- '
Traditionally newsprint is manufactured from a -furnish consisting of about three parts groundwood and one part chemical pulp. Groundwood, manufactured by pressing logs against a revolving abrasive stone, is obtained in yields approaching 100% and is the cheapest component of the furnish. Aside from economy, groundwood contributes several desirable properties to the sheet. Particularly the high light scattering coefficient of groundwood con- -tributes to paper opacity and allows the use of a thinner sheet. The high oil absorption of groundwood improves ink - acceptance during printing. Pollution problems associated ' with the manufacture of groundwood are minimal.
The chemical pulp component is usually manufactured by either the kraft or sulphite process in yields ranging from 45% to 65%. Chemical pulps are expensive, make heavy demands on the mill's wood resources, and entail formidable pollution problems. The present trend in newsprint manu-facture, therefore, is towards reduction in the use of chemical pulps . - , Chemical pulps are used because they impart proper-ties to the furnish which improve its runability. Runability refers to that combination of properties which allows the wet web to be transported at high speed through the forming, pressing and drying section of the paper machine and allows the dry sheet to be reeled and printed with not more than an acceptable number of breaks. Runability is the key`to :~o7~805 paper machine and pressroom efficiency, which in turn is the key to profita~ility. Despite the above-noted dis-advantages of chemical pulps, they remain a virtually indispensable component of newsprint furnish for reasons of runability.
Surprisingly, the mechanism by which chemical pulps improve runability is not well understood. There is a growing body of evidence that the properties crucial to efficient operation on high speed paper machines are high - -wet web stretch and drainage rate. Stretch, both wet and dry, prevents breaks by preventing concentration of stresses around paper defects, where breaks usually originate. High drainage rate lowers the water content to yield a less -fragile web. These effects have been discussed in recent articles by D. M. Harvey, A. J. Barnet and L. M. Lyne in Pulp and Paper Canada (7) T154-6 (July 1977) and by D.F.
Rutland, A. Y. Jones, P. M. Shallhorn, J. Tichy and A.
Karnis in Pulp and Paper Canada 78 (4) T99-105 (April 1977).
In conventional mechanical pulps, wet stretch is obtained at the expense of drainage, i.e. highly refined pulps have a high wet stretch but a low drainage rate, while for lightly refined pulps, the opposite is true. Mechanical pulps can also be manufactured in refiners, both open dis-charge type and in pressurized units at higher temperatures.
The resulting pulps, called refiner mechanical pulp (RMP) and thermomechanical pulp (TMP) are of higher quality than groundwood pulp, are obtained in yields over 95% with minimal pollution problems. They are however not a sub-stitute for chemical pulps and are generally not acceptable as the sole furnish for a newsprint machine.
Attempts have been made to further upgrade mechanical - pulps by chemical pretrea,tment of the wood chips prior to refining. A variety of such processes are currently under ' development and are referred to as chemimechanical (cMæ) and thermochemimechanical (TCMP). These treatments in general increase energy requirements of manufacture. While ' useful properties are developed at some cost, substantial improvements are in general not observed in the properties of primary importance to runability, namely drainage and wet stretch. We have now made the surprising and unexpected discovery that both drainage and wet stretch of mechanical pulps can be increased by a chemical treatment carried out after the refining or grinding operation.
It has now been surprisingly found that both the drainage and wet stretch properties of mechanical pulps can be improved by a controlled chemical treatment of such pulps after formation thereof.
In accordance with the present invention, there is B provided a method of pre~rcltmcnt of mechanical wood pulp which comprises cooking the pulp with aqueous sodium sulphite solution containing sufficient alkali to maintain a pH
greater than about 3 during ,,the cooking. The cooking is effected at an elevated temperature for a time sufficient to cause reaction with the pulp and increase the drainage and wet stretch thereof but for a time insufficient to cause substantial dissolution of lignin from the pulp and insufficient to result in a pulp yield below about 90%.
The improvement in both drainage and wet stretch properties achieved by the present invention permits use of the treated pulps in newsprint to achieve high runability without or with a decreased proportion of chemical pulp.
.
~ ~ _ 4 ~
The procedure of the present invention may be carried out on any of the types of mechanical wood pulp mentioned above, namely, groundwood pulp, RMP, TMæ, cMæ and TCMP, and the improvement in drainage and wet stretch proper-ties is achieved on each of these mechanical pulp types.
By "mechanical pulp" as used herein is meant wood which has been reduced to fibrous form by mechanical action.
Mechanical pulps are frequently produced by refin-ing in two stages. In the manufacture of thermomechanical pulp, for example, the pressurized refining stage is con-ventionally followed by atmospheric refining. The chemical -treatment of this invention may be applied to the pulp between the stages of refining to achieve the beneficial effect. - -The invention may also be applied to separate fractions separated from mechanical pulps. For example, mechanical pulps are generally separated into "accept" and "reject" fractions by means of screens or hydrocyclonic separators prior to use. The invention may be applied separately to either or both fractions from such separations.
Specifically, the invention consists of treating mechanical pulp with sodium sulphite with or without sodium bisulphite or additional alkali such as sodium hydroxide or sodium carbonate, at an elevated temperature for a time sufficient to cause reaction with the pulp but not long enough to cause substantial dissolution of lignin from the pulp.
It has been found that, as the reaction proceeds, the pH of the medium drops, probably as a result of hydrolysis of acetyl groups on the pulp. If the pH drops below 3, there is risk of damaging the fibre through hydrolytic action with consequent loss of strength. Wood fibre which has been subjected to mechanical action, such as refining, is particu-larly susceptible to acidic degradation. It is therefore essential to the present invention that sufficient alkali be present in the chemical charge to prevent a pH drop below 3 during treatment. The exact amount of alkali required varies according to the acetyl content of the wood supply and cannot be specified exactly, but is readily established by experimentation.
The alkali requirement may be met entirely with sodium sulphite. However, since only half of the sodium of sodium sulphite is available for neutralization, it is usually more economical to meet part of the alkali require-ments by additions of sodium hydroxide or sodium carbonate.
The pH of the mixture, however, is preferably kept below about 12, because hemicelluloses are dissolved from wood fibre by higher pH's, with consequent loss in yield.
In a preferred embodiment of the invention, the amount of sodium sulphite used is in the range of 4% and 10%
by weight based on the mechanical pulp, although lower con-centrations down to about 1% by weight may be used with reduced beneficial effect. Below 1% sodium sulphite improve-ments are too small to justify the expense of treatment.
Similarly improvements are observed with chemical charges up to about 25% by weight of the pulp, but the additional cost is not justified by the small additional improvement.
Generally, therefore, a chemical charge of between about 1% and about 25% by weight, preferably between about 4% and about 10% by weight, of the mechanical pulp, is us~d. The ~071805 chemical charge preferably has a pH between about 9 and abou~ 12, and contains sodium sulphite and sufficient alkali to maintain a pH greater than 3 throughout the reaction.
It is preferred to carry out the reaction at consistencies between 5~ and 50%, preferably around 25%.
Lower consistencies increase equipment size and energy costs, and decrease reaction rate because of dilution of the reactants, necessitating longer reaction times. Con- -sistencies higher than 50~ are not readily prepared by mechanical pressing.
The time and temperature of reaction may be varied over a wide range. The-essential requirements are that the reaction must be allowed to effect an increase in drainage and wet stretch and must not be allowed to proceed far enough to yield substantial dissolution of lignin, as the ; latter would decrease pulp yield and create a pollution problem. Practically, the application of our invention is restricted to pulp yields in excess of 90% by weight based on starting mechanical pulp. The minimum reaction time to yield beneficial results usually is about 30 min. at 100C, with shorter times being used at higher temperatures. The --effects of time and temperature are combined in a calculated quantity called the "H-Factor". Anyone familiar with chemical pulping is aware of the way in which H-Factor may -be used to vary time and temperature simultaneously to yield a given degree of cooking. In the practice of the invention, the pulp is exposed to a minimum degree of cooking corres-ponding to 30 minutes at 100C, and a maximum degree of cooking corresponding to a pulp yield of 90% by weight.
The invention is illustrated by the following Examples:
Example 1 This Example illustrates the application of the invention to various mechanical pulps.
Mechanical pulps were treated with a solution of sodium sulphite at pH 9.0 and pressed to 25% consistency.
The amount of chemical remaining with the pulp was 4% by weight based on the dry fibre content. Pulps were then heated at 140C for 30 minutes in an autoclave, handsheets prepared and paper properties measured. The results obtained are reproduced in the following Table I:
TABLE I - -Groundwocd TMP RMP TCMæ
Before After Before After Before After Beore After Property Drainage (sec.) 3.32 2.77 1.32 0.95 1.40 1.14 0.71 0.63 Wet Stretch % 5.0 6.5 4.7 7.9 4.5 7.6 3.5 6.0 Burst 10.5 12.8 22.0 18.0 12.9 13.4 16.3 15.8 Bre~ng Length 2660 2820 3600 3050 2710 2650 3150 3000 qear 39 39 105 108 64 71 107 99 Dry Stretch 1.32 1.41 1.94 2.50 1.72 1.75 1.62 2.00 It will be seen from the results of Table I that that chemical treatment of each pulp improved the drainage and increased the stretch in every case, without adverse effect on other properties.
Example 2 :
This Example illustrates the effect of reaction temperature on pulp properties.
Mechanical pulps impregnated with 4% by weight of sodium sulphite at pH 9 were heated for 30 min. at various temperatures. The resulting pulps had the properties repro-duced in the following Table II:
TABLE II
Property TMP TCMP
Befor,e 100C 140CBefore 100C 140C
Drainage, sec. 1.32 1.19 - 0.95 0.71 - 0.89 0.63 ~et Stretch, ~ 4.7 5.0 7.9 3.5 3.8 6.0 Burst 22.0 22.4 18.0 - 16.3 17.1 15.8 Breaking Length 3600 3740 3050 3150 3100 3000 Tear 105 103 108107 108 99 Dry Stretch, % 1.94 2.24 2.50 1.62 1.98 2.00 pH after reaction - 6.02 4.19 - 6.77 6.10 The results of the above Table II show significant improvement in the drainage and wet stretch characteristics of TMP even at 100C and both pulps show further improvement by heating at 140C.
This Example illustrates the effect of the amount of chemical on pulp properties.
TMP impregnated with 4% by weight and 10% by weight sodium sulphite at pH 9 was heated 30 min. at 140C, handsheets made and properties measured. The results are reproduced in the following Table III: -TABLE III
Property Before 4% 10%
- Drainage, sec. 1.32 0.95 1.16 ~et Stretch, % 4.7 7.9 7.9 Burst 22 18 23.7 Breaking Length 3600 305C 3820 Tear 105 108 96 Dry Stretch, ~ 1.94 2.50 2.92 pH after reaction - 4.19 6.83 g , - ' ,:
iO71805 The results of Table III show beneficial effects at both chemical levels. The main effect of the higher chemical level is to maintain a higher pH throughout the reaction, leading to improvement in burst and breaking length.
This Example illsutrates the effect of pH during the reaction on pulp properties.
Mechanical pulps heated with 4% by weight sodium sulphite at a range of pH's yielded products having the properties set forth in the following Table IV:
TABLE IV
TMP TCMP
- Before After Before After Original pH 7.0 7 9 Temp.of reaction C 140 140 140 Drainage, sec. 0.81 0.64 0.71 0.61 0.63 Wet Stretch, ~ 4.4 10.6 3.5 7.6 6.0 Burst 17.2 8.7 16.3 9.9 15.8 Breaking Length 2970 1810 3150 2020 3000 Tear 117 106 107 112 108 Dry Stretch 1.61 2.05 1.62 1.89 2.00 pH after reaction - 2.51 - 2.72 6.10 - It is apparent from the results of Table IV that when the pH dropped below 3, heating was accompanied by serious decreases in burst and breaking length. It was also observed this degradation was more severe at higher temperatures and longer reaction times.
.
The present invention, therefore, provides a method of treatment o mechanical pulp which improves both its drainage and wet stretch properties. Modifications are possible within the scope of the invention.
.
'-: -' . : .- '
Claims (7)
1. A method of treatment of mechanical wood pulp, which comprises cooking said pulp with aqueous sodium sulphite solution containing sufficient alkali to maintain a pH
greater than about 3 during the cooking at an elevated temperature for a time sufficient to cause reaction with the pulp and increase the drainage and wet stretch thereof but for a time insufficient to cause substantial dissolu-tion of lignin from the pulp and insufficient to result in a pulp yield below about 90% by weight.
greater than about 3 during the cooking at an elevated temperature for a time sufficient to cause reaction with the pulp and increase the drainage and wet stretch thereof but for a time insufficient to cause substantial dissolu-tion of lignin from the pulp and insufficient to result in a pulp yield below about 90% by weight.
2. The method of claim 1 wherein the alkali content of the sodium sulphite solution is provided in part by sodium hydroxide and/or sodium carbonate.
3. The method of claim 1 wherein the initial pH of the sodium sulphite solution is between about 9 and about 12.
4. The method of claim 1 wherein the quantity of sodium sulphite used is about 1% to about 25% by weight of the mechanical pulp.
5. The method of claim 4, wherein the quantity of sodium sulphite is from about 4% to about 10% by weight of the mechanical pulp.
6. The method of claim 1 effected at a consistency of about 5 to about 50%.
7. The method of claim 1 wherein the minimum cooking time is 30 minutes at a temperature of about 100°C.
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA289,427A CA1071805A (en) | 1977-10-25 | 1977-10-25 | Drainage and wet stretch improvement in mechanical pulps |
| FI783200A FI74051C (en) | 1977-10-25 | 1978-10-20 | Method of treating mechanical pulp to improve its drainage and wet elongation |
| JP13058378A JPS5473902A (en) | 1977-10-25 | 1978-10-25 | Treatment of machined pulp |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA289,427A CA1071805A (en) | 1977-10-25 | 1977-10-25 | Drainage and wet stretch improvement in mechanical pulps |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1071805A true CA1071805A (en) | 1980-02-19 |
Family
ID=4109848
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA289,427A Expired CA1071805A (en) | 1977-10-25 | 1977-10-25 | Drainage and wet stretch improvement in mechanical pulps |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JPS5473902A (en) |
| CA (1) | CA1071805A (en) |
| FI (1) | FI74051C (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0096548A1 (en) * | 1982-06-04 | 1983-12-21 | Macmillan Bloedel Limited | Two-stage chemical treatment of mechanical wood pulp |
| US4708771A (en) * | 1984-12-31 | 1987-11-24 | Bear Island Paper Company | Two stage process for sulfonating mechanical pulp fibers |
| US4731160A (en) * | 1986-03-19 | 1988-03-15 | Kamyr, Inc. | Drainage characteristics of mechanical pulp |
| US5169496A (en) * | 1991-04-23 | 1992-12-08 | International Paper Company | Method of producing multi-ply paper and board products exhibiting increased stiffness |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3773610A (en) * | 1970-12-11 | 1973-11-20 | Bauer Bros Co | Pressurized system for pulp refining including pressurized double disk treatment |
| JPS4838328A (en) * | 1971-09-17 | 1973-06-06 | ||
| JPS5214322A (en) * | 1975-07-25 | 1977-02-03 | Hitachi Ltd | Data processing unit |
| US4145246A (en) * | 1976-07-19 | 1979-03-20 | Crown Zellerbach Corporation | Process for making high-strength, high-yield sulfite-modified thermomechanical pulp and a linerboard composition produced therefrom |
-
1977
- 1977-10-25 CA CA289,427A patent/CA1071805A/en not_active Expired
-
1978
- 1978-10-20 FI FI783200A patent/FI74051C/en not_active IP Right Cessation
- 1978-10-25 JP JP13058378A patent/JPS5473902A/en active Granted
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4502918A (en) * | 1981-06-10 | 1985-03-05 | Macmillan Bloedel Limited | Two-stage chemical treatment of mechanical wood pulp with sodium sulfite |
| EP0096548A1 (en) * | 1982-06-04 | 1983-12-21 | Macmillan Bloedel Limited | Two-stage chemical treatment of mechanical wood pulp |
| US4708771A (en) * | 1984-12-31 | 1987-11-24 | Bear Island Paper Company | Two stage process for sulfonating mechanical pulp fibers |
| AU588006B2 (en) * | 1984-12-31 | 1989-09-07 | Bear Island Paper Company | System and process for sulfonating mechanical pulp fibers |
| US4731160A (en) * | 1986-03-19 | 1988-03-15 | Kamyr, Inc. | Drainage characteristics of mechanical pulp |
| US5169496A (en) * | 1991-04-23 | 1992-12-08 | International Paper Company | Method of producing multi-ply paper and board products exhibiting increased stiffness |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5473902A (en) | 1979-06-13 |
| FI74051C (en) | 1988-11-28 |
| JPS6247999B2 (en) | 1987-10-12 |
| FI783200A (en) | 1979-04-26 |
| FI74051B (en) | 1987-08-31 |
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