CA1230709A - Procedure for producing refined groundwood pulp - Google Patents
Procedure for producing refined groundwood pulpInfo
- Publication number
- CA1230709A CA1230709A CA000469917A CA469917A CA1230709A CA 1230709 A CA1230709 A CA 1230709A CA 000469917 A CA000469917 A CA 000469917A CA 469917 A CA469917 A CA 469917A CA 1230709 A CA1230709 A CA 1230709A
- Authority
- CA
- Canada
- Prior art keywords
- chips
- hardwood
- pulp
- softwood
- mixture
- 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.)
- Expired
Links
- 238000000034 method Methods 0.000 title claims abstract description 24
- 239000011121 hardwood Substances 0.000 claims abstract description 53
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims abstract description 45
- 239000011122 softwood Substances 0.000 claims abstract description 24
- 239000000203 mixture Substances 0.000 claims abstract description 15
- 238000007670 refining Methods 0.000 claims abstract description 14
- 239000000243 solution Substances 0.000 claims abstract description 14
- 229910001854 alkali hydroxide Inorganic materials 0.000 claims abstract description 5
- 150000008044 alkali metal hydroxides Chemical class 0.000 claims abstract description 5
- GEHJYWRUCIMESM-UHFFFAOYSA-L sodium sulfite Chemical compound [Na+].[Na+].[O-]S([O-])=O GEHJYWRUCIMESM-UHFFFAOYSA-L 0.000 claims abstract description 4
- 239000012670 alkaline solution Substances 0.000 claims abstract description 3
- 235000010265 sodium sulphite Nutrition 0.000 claims abstract description 3
- 238000005470 impregnation Methods 0.000 claims description 5
- 239000000463 material Substances 0.000 claims description 2
- 230000027455 binding Effects 0.000 abstract description 5
- 238000009739 binding Methods 0.000 abstract description 5
- 238000002156 mixing Methods 0.000 abstract description 5
- 238000007639 printing Methods 0.000 abstract description 3
- 239000003513 alkali Substances 0.000 description 6
- 238000000227 grinding Methods 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 6
- 238000010025 steaming Methods 0.000 description 6
- 241000218657 Picea Species 0.000 description 5
- 238000011282 treatment Methods 0.000 description 5
- 239000002023 wood Substances 0.000 description 5
- 241000183024 Populus tremula Species 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- 238000000149 argon plasma sintering Methods 0.000 description 3
- 230000003287 optical effect Effects 0.000 description 3
- LSNNMFCWUKXFEE-UHFFFAOYSA-L sulfite Chemical compound [O-]S([O-])=O LSNNMFCWUKXFEE-UHFFFAOYSA-L 0.000 description 3
- 229920001131 Pulp (paper) Polymers 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 2
- 238000002203 pretreatment Methods 0.000 description 2
- 239000007858 starting material Substances 0.000 description 2
- 238000005406 washing Methods 0.000 description 2
- 206010000060 Abdominal distension Diseases 0.000 description 1
- 102100031260 Acyl-coenzyme A thioesterase THEM4 Human genes 0.000 description 1
- 101000638510 Homo sapiens Acyl-coenzyme A thioesterase THEM4 Proteins 0.000 description 1
- -1 Na2SO3 Chemical compound 0.000 description 1
- 229920002522 Wood fibre Polymers 0.000 description 1
- 208000024330 bloating Diseases 0.000 description 1
- 230000009172 bursting Effects 0.000 description 1
- 150000001720 carbohydrates Chemical class 0.000 description 1
- 235000014633 carbohydrates Nutrition 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 238000007645 offset printing Methods 0.000 description 1
- 239000005416 organic matter Substances 0.000 description 1
- 230000008092 positive effect Effects 0.000 description 1
- 230000036647 reaction Effects 0.000 description 1
- 230000000930 thermomechanical effect Effects 0.000 description 1
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
- D21C5/00—Other processes for obtaining cellulose, e.g. cooking cotton linters ; Processes characterised by the choice of cellulose-containing starting materials
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21B—FIBROUS RAW MATERIALS OR THEIR MECHANICAL TREATMENT
- D21B1/00—Fibrous raw materials or their mechanical treatment
- D21B1/02—Pretreatment of the raw materials by chemical or physical means
- D21B1/021—Pretreatment of the raw materials by chemical or physical means by chemical means
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Paper (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The present invention concerns a procedure for produc-ing refined groundwood pulp from chips, in the procedure being used softwood and hardwood chips in such manner that the pulp that is obtained contains in mixture both matter from softwood and matter from hardwood. In the procedure, the hardwood chips are prior to the refining step pretreated by impregnating them with an alkaline solution, and the essential feature of the invention is that in the pretreatment is used an alkali hydroxide solution with concentration in the range 0.1-0.5 M, and that the pretreated hardwood chips are mixed with the softwood chips, whereafter the mixture thus obtained is refined to groundwood pulp. The pretreatment solution is preferably a sodium hydroxide solution, and it may also contain sodium sulphite. The mixing of the pretreated hardwood chips and the softwood chips is most advantageously done so that the proportion of hardwood chips in the mixture is 30-60%. The binding strength and opacity of the groundwood pulp thus obtained are such that the pulp is appropri-ate e.g. for making printing paper.
The present invention concerns a procedure for produc-ing refined groundwood pulp from chips, in the procedure being used softwood and hardwood chips in such manner that the pulp that is obtained contains in mixture both matter from softwood and matter from hardwood. In the procedure, the hardwood chips are prior to the refining step pretreated by impregnating them with an alkaline solution, and the essential feature of the invention is that in the pretreatment is used an alkali hydroxide solution with concentration in the range 0.1-0.5 M, and that the pretreated hardwood chips are mixed with the softwood chips, whereafter the mixture thus obtained is refined to groundwood pulp. The pretreatment solution is preferably a sodium hydroxide solution, and it may also contain sodium sulphite. The mixing of the pretreated hardwood chips and the softwood chips is most advantageously done so that the proportion of hardwood chips in the mixture is 30-60%. The binding strength and opacity of the groundwood pulp thus obtained are such that the pulp is appropri-ate e.g. for making printing paper.
Description
~L23~9 The present invention concerns a procedure for produc-ing refined groundwood from chips, in said procedure being used softwood chips and hardwood chips so that the resulting refined groundwood contains, mixed together, matter both from softwood and from hardwood, and in said procedure the hardwood chips being pretreated before the refining step by impregnating them with an alkaline solution.
It is known in prior art that small quantities of hard-wood may be added to softwood when producing groundwood mechani-cally by the thermogroundwood method. The addition of hardwood has a positive effect on the optical properties of the refined mechanical pulp, but the use of hardwood has been restricted ~y the fact that the strength properties of the refined mechanical pulp deteriorate rapidly with increasing amount of hardwood.
If is furthermore known in prior art that when hardwood is used for manufacturing groundwood, the hardwood chips are impregnated with chemicals before refining. A prerequisite for achieving adequately uniform impregnation has been that the treatment has been vigorous enough. In the chemical treatment, the effective factor is an alkali, such as NaOH, which reacts with the carbohydrates of the wood, bloating and softening the structure of the wood. At the same time, however, the alkall causes the wood material to become darker and reduces the fines content and light scattering coefficient of the resulting refined groundwood. In order to prevent darkening of the wood also sul-phite, e.g. Na2SO3, has been used in the chemical treatment. The sulphite further reduces the fines amount and the light scatter-ing coefficlent of the groundwood, which determlnes the opacityof the paper manufactured from the groundwood.
When such pulp is used in producing printing paper which in addition to softwood contains hardwood treated as described above, the critical factors are the dust-making of the paper on one hand and the opacity of the paper on the other.
~k~
~23~)~09 These critical factors limit the hardwood proportion in the groundwood to 10-15%.
The present invention provides a process which enables the proportion of hardwood to be increased to be substantially greater than before in refined groundwood intended for manufac-turing printing paper. The invention is characterized in that in the pretreatment of the hardwood an alkali hydroxide solution is used of which the concentration is in the range 0.1-0.5 M, that the pretreated hardwood chips are admixed to the softwood chips, and that thereafter the chip mixture thus obtained is refined to groundwood.
The essential feature of the lnvention is that the pre-treatment of the hardwood chips with a 0.1-0.5 M alkali hydroxide solution is very mild compared with the way in which the hardwood has been treated heretofore. This kind of mild pretreatment is rendered feasible by the circumstance that according to the pre-sent invention the pretreated hardwood chips are reflned to groundwood in mixture with the softwood chips. The mildly treated hardwood fibres have viscoelastic characteristics approx-imating those of softwood fibres, whereby prerequisites for mix-ing and simultaneously refining hardwood and softwood exist, and the proportion of hardwood in the mixture can be increased up to 70%. Most appropriately, the proportion of hardwood in the mix-ture that is being refined is on the order of 30-60~.
In procedures of prior art using hardwood chips, the vigorously pretreated hardwood has been separately refined to groundwood, and only then has it been admixed to pulp obtained from softwood. Associated with the mild pretreatment of the invention, separate refining of the hardwood would cause dlffi-culties, owing to non-uniform absorption of the alkali hydroxide.
No difficulties will, however, arise when the mildly pretreated hardwood is refined, as taught by the invention, together with softwood: in this case, the softwood fibres, which have larger dimensions and are more elastic, keep the blade gap of the refiner stable and equalize the stress peaks acting on the hard-wood fibres. The entire mixture thus undergoes uniform refining treatment.
A particular advantage of the mildly alkaline pretreat-ment of the invention is that the good optical characteristics of the hardwood fi~res are preserved, and the binding strength of the fibres improves. It is, therefore, possible by the procedure of the invention to produce pulp with high hardwood content which meets the requirements set by offset paper, as regards binding strength and opacity.
In the procedure of the invention, the quantity of dis-solving organic matter is so low that the pulp need not bewashed. This reduces considerably the investment costs of the installation. Moreover, the quantities of chemicals and steam required in the pretreatment are less than before, thus reducing the running costs of the process. On the whole, the invention introduces a simple and flexible process in which the proportions of hardwood and softwood can be varied within a wide range and in which the investment costs are lower than in any equivalent meth-ods of prior art.
The alkaline hydroxide solution used in pretreating the hardwood chips may be, for instance, a sodium hydroxide solution with 5-20 g NaOH per litre. Since the sodium hydroxide concen-tration is low, sulphite addition is not absolutely needed. How-ever, also a solution with e.g. 5-50 g Na2S03 per litre may be contemplated in the pretreatment.
For boosting the absorption of alkali, the chips are treated with steam before being impregnated. The alkali solution to be used for impregnation is cold. In order to boost the reac-tions between the absorbed alkali and the wood, the impregnatedchips are also treated with hot steam. Such steaming follows 0~,, immediately on the impregnation step, and according to the inven-tion it may take place at normal pressure within the temperature range 60-100C. It is, however, possible that the steaming tem-perature is even higher, e.g. 100-130C, and that slight over-pressure is used in the steaming step.
The invention is desc~ibed in the following more indetail referring o the accompanying drawings, wherein:-Fig. 1 presents in diagram form a refined groundwood production process according to the invention; and Fig.s 2-5 present certain physical characteristics of refined groundwood pulps at different CSF values in some exem-plary cases.
The starting materials of the refined groundwood pro-duction process of Fig. 1 are hardwood and softwood chips (aspen and spruce), stored in silos 1 and 2. Hardwood chips are con-ducted form the silo 1 to a washing step 3, whence the chips arefurther transferred to be pretreated. In the pretreatment, the chips are pre-steamed (step ~)~ and the chips are impregnated at room temperature with dilute sodium hydroxide solution, prefer-ably such containing 10 g NaOH per litre (step 5). The impregna-tion may be accomplished e.g. by conducting the chips with theaid of a conveyor through a tank containing sodium hydroxide solution, in such manner that the time which the chips stay in the tank is about 5 minutes. After the sodium hydroxide treat-ment, the chips go to a separate steaming space (step 6), where most appropriately prevalls a temperature about 90C and normal atmospheric pressure. The steam needed in the steaming step ls obtained from the grinding process. Subsequent to the steaming, the pretreated hardwood chlps are conducted together with the softwood chips, whlch have gone through the washing phase 7, to a mixing tank 8, where the two kinds of chips are mixed e.g. in proportlon 1:1.
~ '70 9 The mixing phase is followed by refining the chip mix-ture by the thermomechanical method to pulp, this step represent-ing a technique known in itself in prior art. The chip mixture goes from the mixing tank 8 to two consecutive refining steps 9, in which it is refined with the aid of disc refiners to pulp 10.
The completed pulp is usable e.g. as starting material in manu-facturing offset printing paper.
In Fig.s 2-5, certain physical characteristics of refined groundwood pulps at different CSF (Canadian Standard Freeness) values are presented. Fig.s 2 and 3 refer to the ten-sile and tearing indices illustrating the strength properties of the pulp; Fig.4 concerns the light scatter~ng coefficient of the pulp, illustrating the optical properties of the pulp; and Fig. 5 the proportion of long fibres in the pulp, illustrating the bind-ing strength of t.he pulp. The four curves plotted in each Figure represent four different kinds of pulp, conforming to the Table following below.
NaOH Spruce AspenBirch ~g/l) (%) (%) (%) t~ 10 60 20 20 The first vertical column in the Table represents the pretreatment of the hardwood used in preparing the pulp, stating the NaOH concentration of the solutlon used in impregnating the chlps. The topmost horizontal row in the table, whereln the NaOH
concentratlon 0 has been entered, refers to groundwood pulp ln producing which no pretreatment with alkali was carried out and which therefore is not a groundwood pulp according to the inven-tion. The other three pulps, in contrast, are pulps produced astaught by the invention. Scrutiny of the Figures reveals that in ~;~3~)709 the pulps produced as taught by the invention all characteristics are at least on a satisfactory level. The pulp in the production of which no alkali pretreatment was carried out has a higher light scattering coefficient than the pulps which were produced as taught by the invention, but in binding strength chaLacteris-tics it is inferior to said pulps.
In the following is furthermore presented a Table in which are compared the characteristics of pulps made b~ separate refining of softwood chips and hardwood chips pretreated as taught by the invention and those of pulps obtained by mixture refining as taught by the invention.
Pulp mixes CSF Density Tensile Tearing Bursting 3 index inde~ index (ml) (kg/m (Nm/g) (mNm g) (kpam2/g) Aspen/Spruce Mixed grinding 73 467 45.1 8.7 2.53 Separate grind-ing 123+75 450 36.4 6.8 2.12 D:o 123+128 434 36.2 7.8 2.05 Aspen/Spruce Mixed grinding 88 414 34.9 7.0 1.89 Separate grind-ing 123+75 453 34.8 6.8 1.96 Mixed grinding 125 399 31.9 7.1 1.78 Separate grlnd-ing 123-~128 414 33.1 G.4 1.77 Startlng ~
Aspen CTMP 123 452 35.0 4.3 1.64 SprUce TMP 128 395 38.910.1 2.43 445 43.210.2 2.65 1~:3~7~
It is seen in the Table that with the 70% hardwood pro-portion essentially the same result is achieved in mixed and sep-arate refining as regards the quality of the pulp. In contrast, when the proportion of hardwood is 50%, substantially better pro-cessability and strength properties of the pulp are achieved inmixed refining than in separate refining~
/.
~ - 7
It is known in prior art that small quantities of hard-wood may be added to softwood when producing groundwood mechani-cally by the thermogroundwood method. The addition of hardwood has a positive effect on the optical properties of the refined mechanical pulp, but the use of hardwood has been restricted ~y the fact that the strength properties of the refined mechanical pulp deteriorate rapidly with increasing amount of hardwood.
If is furthermore known in prior art that when hardwood is used for manufacturing groundwood, the hardwood chips are impregnated with chemicals before refining. A prerequisite for achieving adequately uniform impregnation has been that the treatment has been vigorous enough. In the chemical treatment, the effective factor is an alkali, such as NaOH, which reacts with the carbohydrates of the wood, bloating and softening the structure of the wood. At the same time, however, the alkall causes the wood material to become darker and reduces the fines content and light scattering coefficient of the resulting refined groundwood. In order to prevent darkening of the wood also sul-phite, e.g. Na2SO3, has been used in the chemical treatment. The sulphite further reduces the fines amount and the light scatter-ing coefficlent of the groundwood, which determlnes the opacityof the paper manufactured from the groundwood.
When such pulp is used in producing printing paper which in addition to softwood contains hardwood treated as described above, the critical factors are the dust-making of the paper on one hand and the opacity of the paper on the other.
~k~
~23~)~09 These critical factors limit the hardwood proportion in the groundwood to 10-15%.
The present invention provides a process which enables the proportion of hardwood to be increased to be substantially greater than before in refined groundwood intended for manufac-turing printing paper. The invention is characterized in that in the pretreatment of the hardwood an alkali hydroxide solution is used of which the concentration is in the range 0.1-0.5 M, that the pretreated hardwood chips are admixed to the softwood chips, and that thereafter the chip mixture thus obtained is refined to groundwood.
The essential feature of the lnvention is that the pre-treatment of the hardwood chips with a 0.1-0.5 M alkali hydroxide solution is very mild compared with the way in which the hardwood has been treated heretofore. This kind of mild pretreatment is rendered feasible by the circumstance that according to the pre-sent invention the pretreated hardwood chips are reflned to groundwood in mixture with the softwood chips. The mildly treated hardwood fibres have viscoelastic characteristics approx-imating those of softwood fibres, whereby prerequisites for mix-ing and simultaneously refining hardwood and softwood exist, and the proportion of hardwood in the mixture can be increased up to 70%. Most appropriately, the proportion of hardwood in the mix-ture that is being refined is on the order of 30-60~.
In procedures of prior art using hardwood chips, the vigorously pretreated hardwood has been separately refined to groundwood, and only then has it been admixed to pulp obtained from softwood. Associated with the mild pretreatment of the invention, separate refining of the hardwood would cause dlffi-culties, owing to non-uniform absorption of the alkali hydroxide.
No difficulties will, however, arise when the mildly pretreated hardwood is refined, as taught by the invention, together with softwood: in this case, the softwood fibres, which have larger dimensions and are more elastic, keep the blade gap of the refiner stable and equalize the stress peaks acting on the hard-wood fibres. The entire mixture thus undergoes uniform refining treatment.
A particular advantage of the mildly alkaline pretreat-ment of the invention is that the good optical characteristics of the hardwood fi~res are preserved, and the binding strength of the fibres improves. It is, therefore, possible by the procedure of the invention to produce pulp with high hardwood content which meets the requirements set by offset paper, as regards binding strength and opacity.
In the procedure of the invention, the quantity of dis-solving organic matter is so low that the pulp need not bewashed. This reduces considerably the investment costs of the installation. Moreover, the quantities of chemicals and steam required in the pretreatment are less than before, thus reducing the running costs of the process. On the whole, the invention introduces a simple and flexible process in which the proportions of hardwood and softwood can be varied within a wide range and in which the investment costs are lower than in any equivalent meth-ods of prior art.
The alkaline hydroxide solution used in pretreating the hardwood chips may be, for instance, a sodium hydroxide solution with 5-20 g NaOH per litre. Since the sodium hydroxide concen-tration is low, sulphite addition is not absolutely needed. How-ever, also a solution with e.g. 5-50 g Na2S03 per litre may be contemplated in the pretreatment.
For boosting the absorption of alkali, the chips are treated with steam before being impregnated. The alkali solution to be used for impregnation is cold. In order to boost the reac-tions between the absorbed alkali and the wood, the impregnatedchips are also treated with hot steam. Such steaming follows 0~,, immediately on the impregnation step, and according to the inven-tion it may take place at normal pressure within the temperature range 60-100C. It is, however, possible that the steaming tem-perature is even higher, e.g. 100-130C, and that slight over-pressure is used in the steaming step.
The invention is desc~ibed in the following more indetail referring o the accompanying drawings, wherein:-Fig. 1 presents in diagram form a refined groundwood production process according to the invention; and Fig.s 2-5 present certain physical characteristics of refined groundwood pulps at different CSF values in some exem-plary cases.
The starting materials of the refined groundwood pro-duction process of Fig. 1 are hardwood and softwood chips (aspen and spruce), stored in silos 1 and 2. Hardwood chips are con-ducted form the silo 1 to a washing step 3, whence the chips arefurther transferred to be pretreated. In the pretreatment, the chips are pre-steamed (step ~)~ and the chips are impregnated at room temperature with dilute sodium hydroxide solution, prefer-ably such containing 10 g NaOH per litre (step 5). The impregna-tion may be accomplished e.g. by conducting the chips with theaid of a conveyor through a tank containing sodium hydroxide solution, in such manner that the time which the chips stay in the tank is about 5 minutes. After the sodium hydroxide treat-ment, the chips go to a separate steaming space (step 6), where most appropriately prevalls a temperature about 90C and normal atmospheric pressure. The steam needed in the steaming step ls obtained from the grinding process. Subsequent to the steaming, the pretreated hardwood chlps are conducted together with the softwood chips, whlch have gone through the washing phase 7, to a mixing tank 8, where the two kinds of chips are mixed e.g. in proportlon 1:1.
~ '70 9 The mixing phase is followed by refining the chip mix-ture by the thermomechanical method to pulp, this step represent-ing a technique known in itself in prior art. The chip mixture goes from the mixing tank 8 to two consecutive refining steps 9, in which it is refined with the aid of disc refiners to pulp 10.
The completed pulp is usable e.g. as starting material in manu-facturing offset printing paper.
In Fig.s 2-5, certain physical characteristics of refined groundwood pulps at different CSF (Canadian Standard Freeness) values are presented. Fig.s 2 and 3 refer to the ten-sile and tearing indices illustrating the strength properties of the pulp; Fig.4 concerns the light scatter~ng coefficient of the pulp, illustrating the optical properties of the pulp; and Fig. 5 the proportion of long fibres in the pulp, illustrating the bind-ing strength of t.he pulp. The four curves plotted in each Figure represent four different kinds of pulp, conforming to the Table following below.
NaOH Spruce AspenBirch ~g/l) (%) (%) (%) t~ 10 60 20 20 The first vertical column in the Table represents the pretreatment of the hardwood used in preparing the pulp, stating the NaOH concentration of the solutlon used in impregnating the chlps. The topmost horizontal row in the table, whereln the NaOH
concentratlon 0 has been entered, refers to groundwood pulp ln producing which no pretreatment with alkali was carried out and which therefore is not a groundwood pulp according to the inven-tion. The other three pulps, in contrast, are pulps produced astaught by the invention. Scrutiny of the Figures reveals that in ~;~3~)709 the pulps produced as taught by the invention all characteristics are at least on a satisfactory level. The pulp in the production of which no alkali pretreatment was carried out has a higher light scattering coefficient than the pulps which were produced as taught by the invention, but in binding strength chaLacteris-tics it is inferior to said pulps.
In the following is furthermore presented a Table in which are compared the characteristics of pulps made b~ separate refining of softwood chips and hardwood chips pretreated as taught by the invention and those of pulps obtained by mixture refining as taught by the invention.
Pulp mixes CSF Density Tensile Tearing Bursting 3 index inde~ index (ml) (kg/m (Nm/g) (mNm g) (kpam2/g) Aspen/Spruce Mixed grinding 73 467 45.1 8.7 2.53 Separate grind-ing 123+75 450 36.4 6.8 2.12 D:o 123+128 434 36.2 7.8 2.05 Aspen/Spruce Mixed grinding 88 414 34.9 7.0 1.89 Separate grind-ing 123+75 453 34.8 6.8 1.96 Mixed grinding 125 399 31.9 7.1 1.78 Separate grlnd-ing 123-~128 414 33.1 G.4 1.77 Startlng ~
Aspen CTMP 123 452 35.0 4.3 1.64 SprUce TMP 128 395 38.910.1 2.43 445 43.210.2 2.65 1~:3~7~
It is seen in the Table that with the 70% hardwood pro-portion essentially the same result is achieved in mixed and sep-arate refining as regards the quality of the pulp. In contrast, when the proportion of hardwood is 50%, substantially better pro-cessability and strength properties of the pulp are achieved inmixed refining than in separate refining~
/.
~ - 7
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for producing refined groundwood pulp from chips, in which softwood chips and hardwood chips are treated so that the refined pulp that is obtained contains in mixture of material both from soft-wood and hardwood, and in which the hardwood chips are pretreated prior to the refining step by impregnation with an alkaline solution, the pretreatment of the hardwood being carried out with an alkali hydroxide solution having a concentration in the range of 0.1-0.5 M, the pretreated hardwood chips are mixed with the soft-wood chips and the chip mixture thus obtained is thereafter refined to groundwood pulp.
2. A process according to claim 1, wherein is used in the pretreatment a sodium hydroxide solution with 5-20 g NaOH per litre.
3. A process according to claim 2, wherein is used in the pretreatment a solution with 5-20 g NaOH
per litre and 5-50 g Na2SO3 per litre.
per litre and 5-50 g Na2SO3 per litre.
4. A process according to claim 1, 2 or 3 wherein the hardwood chips are steamed in conjunction with the pretreatment under a normal pressure at 60-100°C.
5. A process according to claim 1, 2 or 3 wherein hardwood and softwood chips are so mixed together that the proportion of hardwood chips in the mixture is at most 70%.
6. A process according to claim 1, 2 or 3 wherein hardwood and softwood chips are so mixed together that the proportion of hardwood chips in the mixture is at most 70% in the range 30-60%.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI834576 | 1983-12-13 | ||
| FI834576A FI68432C (en) | 1983-12-13 | 1983-12-13 | FOERFARANDE FOER FRAMSTAELLNING AV RAFFINERAD TRAEMASSA. |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1230709A true CA1230709A (en) | 1987-12-29 |
Family
ID=8518210
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000469917A Expired CA1230709A (en) | 1983-12-13 | 1984-12-12 | Procedure for producing refined groundwood pulp |
Country Status (4)
| Country | Link |
|---|---|
| CA (1) | CA1230709A (en) |
| FI (1) | FI68432C (en) |
| FR (1) | FR2556376B1 (en) |
| SU (1) | SU1524815A3 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2723598B1 (en) * | 1994-08-10 | 1996-10-18 | Sorgho Agro Ind Et Papetier Sa | PROCESS FOR DEMOELLING MARINE PLANTS, ESPECIALLY SORGHO, IN ORDER TO OBTAIN PAPER QUALITY FIBERS |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1022145A (en) * | 1950-07-18 | 1953-02-27 | Hellefors Bruks Aktiebolag | A method of manufacturing plates, cardboard, paper, moldings and the like from vegetable fibrous material |
| SE416481B (en) * | 1977-05-02 | 1981-01-05 | Mo Och Domsjoe Ab | METHOD AND DEVICE FOR TREATMENT OF WOOD TIP FOR REMOVAL OF HEAVY METALS AND RESIN |
-
1983
- 1983-12-13 FI FI834576A patent/FI68432C/en not_active IP Right Cessation
-
1984
- 1984-12-11 FR FR8418875A patent/FR2556376B1/en not_active Expired
- 1984-12-12 SU SU843829103A patent/SU1524815A3/en active
- 1984-12-12 CA CA000469917A patent/CA1230709A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| SU1524815A3 (en) | 1989-11-23 |
| FI68432B (en) | 1985-05-31 |
| FI68432C (en) | 1987-01-19 |
| FI834576A0 (en) | 1983-12-13 |
| FR2556376A1 (en) | 1985-06-14 |
| FR2556376B1 (en) | 1989-12-22 |
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