CA1193808A - Chemical pulp having improved strength, drainability and beatability, and a process of making said pulp - Google Patents
Chemical pulp having improved strength, drainability and beatability, and a process of making said pulpInfo
- Publication number
- CA1193808A CA1193808A CA000415980A CA415980A CA1193808A CA 1193808 A CA1193808 A CA 1193808A CA 000415980 A CA000415980 A CA 000415980A CA 415980 A CA415980 A CA 415980A CA 1193808 A CA1193808 A CA 1193808A
- Authority
- CA
- Canada
- Prior art keywords
- pulp
- salts
- beatability
- drainability
- weight
- 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 28
- 230000008569 process Effects 0.000 title claims abstract description 14
- 229920001131 Pulp (paper) Polymers 0.000 title claims abstract description 9
- 150000003839 salts Chemical class 0.000 claims abstract description 37
- 239000007864 aqueous solution Substances 0.000 claims abstract description 4
- 238000010411 cooking Methods 0.000 claims abstract description 3
- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 claims description 20
- 229910052938 sodium sulfate Inorganic materials 0.000 claims description 11
- 235000011152 sodium sulphate Nutrition 0.000 claims description 11
- 239000004133 Sodium thiosulphate Substances 0.000 claims description 5
- AKHNMLFCWUSKQB-UHFFFAOYSA-L sodium thiosulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=S AKHNMLFCWUSKQB-UHFFFAOYSA-L 0.000 claims description 5
- 235000019345 sodium thiosulphate Nutrition 0.000 claims description 5
- 230000001627 detrimental effect Effects 0.000 claims description 3
- 150000002500 ions Chemical class 0.000 claims description 3
- 150000003384 small molecules Chemical class 0.000 claims 2
- 239000000126 substance Substances 0.000 abstract description 8
- 238000010009 beating Methods 0.000 description 28
- 239000000835 fiber Substances 0.000 description 12
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 12
- 238000001035 drying Methods 0.000 description 8
- 230000000694 effects Effects 0.000 description 7
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 6
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 6
- 239000000499 gel Substances 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 6
- 229910021653 sulphate ion Inorganic materials 0.000 description 6
- 230000008961 swelling Effects 0.000 description 5
- 229920002678 cellulose Polymers 0.000 description 4
- 239000001913 cellulose Substances 0.000 description 4
- 239000001257 hydrogen Substances 0.000 description 4
- 229910052739 hydrogen Inorganic materials 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- GSEJCLTVZPLZKY-UHFFFAOYSA-N Triethanolamine Chemical compound OCCN(CCO)CCO GSEJCLTVZPLZKY-UHFFFAOYSA-N 0.000 description 3
- 230000008859 change Effects 0.000 description 3
- ZBCBWPMODOFKDW-UHFFFAOYSA-N diethanolamine Chemical compound OCCNCCO ZBCBWPMODOFKDW-UHFFFAOYSA-N 0.000 description 3
- 229940043237 diethanolamine Drugs 0.000 description 3
- 230000002427 irreversible effect Effects 0.000 description 3
- 229960004418 trolamine Drugs 0.000 description 3
- 239000007832 Na2SO4 Substances 0.000 description 2
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 description 2
- 239000000654 additive Substances 0.000 description 2
- 235000012501 ammonium carbonate Nutrition 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 239000004202 carbamide Substances 0.000 description 2
- 239000000460 chlorine Substances 0.000 description 2
- 229910052801 chlorine Inorganic materials 0.000 description 2
- -1 chlorine ions Chemical class 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 238000011020 pilot scale process Methods 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 239000011122 softwood Substances 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- HZAXFHJVJLSVMW-UHFFFAOYSA-N 2-Aminoethan-1-ol Chemical compound NCCO HZAXFHJVJLSVMW-UHFFFAOYSA-N 0.000 description 1
- ATRRKUHOCOJYRX-UHFFFAOYSA-N Ammonium bicarbonate Chemical compound [NH4+].OC([O-])=O ATRRKUHOCOJYRX-UHFFFAOYSA-N 0.000 description 1
- 229920003043 Cellulose fiber Polymers 0.000 description 1
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 238000007605 air drying Methods 0.000 description 1
- 239000001099 ammonium carbonate Substances 0.000 description 1
- BFNBIHQBYMNNAN-UHFFFAOYSA-N ammonium sulfate Chemical compound N.N.OS(O)(=O)=O BFNBIHQBYMNNAN-UHFFFAOYSA-N 0.000 description 1
- 229910052921 ammonium sulfate Inorganic materials 0.000 description 1
- 235000011130 ammonium sulphate Nutrition 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000009172 bursting Effects 0.000 description 1
- 206010061592 cardiac fibrillation Diseases 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000032798 delamination Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 230000002600 fibrillogenic effect Effects 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000000877 morphologic effect Effects 0.000 description 1
- 238000010979 pH adjustment Methods 0.000 description 1
- 230000035515 penetration Effects 0.000 description 1
- 230000035699 permeability Effects 0.000 description 1
- 238000013031 physical testing Methods 0.000 description 1
- 238000006116 polymerization reaction Methods 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000004904 shortening Methods 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 239000007921 spray Substances 0.000 description 1
- 239000007858 starting material Substances 0.000 description 1
- 235000011149 sulphuric acid Nutrition 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 238000010977 unit operation Methods 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
- 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
Landscapes
- 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)
- Paints Or Removers (AREA)
Abstract
A CHEMICAL, PULP HAVING IMPROVED STRENGTH, DRAINABILITY
AND BEATABILITY, AND A PROCESS OF MAKING SAID PULP
Abstract of the Disclosure:
A chemical pulp which may be bleached or unbleached and has improved strength, drainability and beatability is described. In order to obtain the desired characteris-tics, one or more low-molecular water-soluble salts have been added to the pulp. Also a process of making the chemical pulp is described, in which process the pulp which is undried after cooking, is treated with an aqueous solution of one or more low-molecular salts.
A suitable salt content is 0.1-10% by weight, based upon the weight of the dried pulp.
AND BEATABILITY, AND A PROCESS OF MAKING SAID PULP
Abstract of the Disclosure:
A chemical pulp which may be bleached or unbleached and has improved strength, drainability and beatability is described. In order to obtain the desired characteris-tics, one or more low-molecular water-soluble salts have been added to the pulp. Also a process of making the chemical pulp is described, in which process the pulp which is undried after cooking, is treated with an aqueous solution of one or more low-molecular salts.
A suitable salt content is 0.1-10% by weight, based upon the weight of the dried pulp.
Description
~ ~3i3~
The present invention comprises chemical pulps having improved strength, drainability and beatability, and a process of making said pulp.
In the production of lignocellulose-based sheet structures from a suspension of fibres and water, the fibre is first treated mechanically in the wet state.
This operation, the beating operation, is one of the most important unit operations of paper technology.
By different beating methods, it is possible to obtain different quality characteristics in the sheet, and it is possible to change the usefulness of diferent fibre raw materials.
However, the mechanical treatment principles for achieving different product characteristics are extreme-ly uncertain, and primarily the basic mechanisms of the beating process are unknown, for which reason beat-ing may be said to be effected more or less by ancient tradition.
The fibre material has a complex morphological structure~ and the changes which occur in the beating zone are heterogeneous, which makes it difficult to give a more detailed description thereof. Traditionally, the beating effect is divided into - fibre length shortening - fines production - delamination - external fibrillation - swelling 3~
- dislocations - reduced degree of polymerization~
As a result of these beating effects~ the tensile strength of the fibre in the wet state is increased, whereas the modulus of elasticity is decreased. Beaten and dried fibres have higher values of ~oth tensile strength and modulus of elasticity than unbeaten fibres.
The greatest change in the characteris~ics of the paper occurs in the initial beating phase. Usually, an increase in density, elongation at break and in all strength characteristics, with the exception of the tearing strength, is obtained; whereas opacity, permea-bility to air and dimensional hygrostability are re-duced.
An analysis of the effect of the beating operation, and the cause therefor, on the finished paper~ is render-ed difficult by the insufficient knowledge of the origin of the paper qualities. Generallyg it may be said that the fine material formed and the softening (which implies increased swelling) of the fibre are highly importantO
The swelling of the cellulose fibre may be regardPd on the basis of the physical chemistry for gels, and it will be seen how different parameters~ such as pH, temperature, salt content etc. affect the swelling con-dition of the fibre as well as the swelling level of the fine fibre fraction.
27 Traditionally, the beating efficiency is increased by modifying the construction of the beating element ~ ~ ~il3~
and the concentration of the cellulose material in the beating apparatus. Moreover, also changes in tempera-ture and pH and the addition of different chemicals have been tried to achieve a desired increase in beat-ing efficiency in connection with the papermaking pro-cess, i.e. in the further treatment of the pulp as first dried.
A mechanical modification of the beating element has given no incontestable results. However, a develop-ment towards hiqher strength characteristics in beated lignocellulose materials after treatment in present day beating equipment can be seen. Regarding the change in the chemical conditions during beating~ no major effects have been observed as compared with what is obtained by conventional papermaking technology.
The present invention has for its objec~ to provide a chemical pulp having improved strength, drainability and beatability A further object of the invention is to provide a process of making a chemical pulp having improved strengthJ drainability and beatability.
These and other objects are achieved in that the wooden raw material after cooking is mixed with an aqueous solution of one or more low~molecular salts Preferably, 0.1-10% by weight of salt, based upon the dry pulp, are incorporated.
27 The basic idea of the present invention is that a low-molecular salt shall be present during drying, at least in the initial phase thereofu It is known that the swelled fibre "collapses"
when pulp is dried, i.e. the gel structure disappears.
A subsequent addition of water in the manufacture of paper does not cause the fibre to revert to its original state, i.e. this process is at least partly irreversible.
One explanation why the swelled fibre "collapses" upon drying is that, when the water is removed, ~he cellulose chains will come so close to one another that hydrogen bonds are established between these chains. In this manner, the cavities in the gel structure of the pulp will disappear. The subsequent addition of water during the continued treatment of the pulp is unable to break the hydrogen bonds, and an irreversible '~collapse" has ~hus occurred.
Surprisingly~ it has now been found that it is possible to interfere with the formation of hydrogen bonds by adding water-soluble low-molecular salts to the pulp already after the production9 but prior to the drying thereof~ These salts penetrate into the ca-vities of the gel structure and form therein steric hindrances preventing the cellulose chains from getting close to one another, whereby the formation of hydrogen bonds is substantially eliminated By substantially preventing~ in the manner described abovet the irreversible "collapse" of the fibre gel 27 structure, the fibres can again swell when water is added and~ on the whole, revert to the state befor~
the drying.
In this manner, improved strength, dralnability and beatability of the treated pulp as compared with untreated pulp are obtained.
For carrying t~le process according to the present invention into effect, the undried, bleached or unbleach-ed chemical pulp is mixed with an aqueous solution of suitable low-molecular salts. After this addition, the pulp is dried in conventional manner, for instance by using a flash drier, by the supply of heat through ra-diation or convection (for instance by means of a fan drier for pulp) or by means of heated surfaces to which, if desired, a pressure has been applied ~for instance a cylinder drier for pulp).
Suitable salts for adding to the pulp are low-mole-cular water soluble salts. It is important that the molecular si~e of these salts be sufficiently small to enable the salts to penetrate into the gel structure and to be deposited therein while forming a steric hin-drance.
Furthermore~ it is important that the added salt does not form ions detrimental to the subsequent use of the pulp. Thus~ it will be appreciated thatl when the pulp is again suspended in water after drying~ a large part of these deposited salts will be redissolved, and consequently a salt forming chlorine ions is not always suitable because chlorine ions are frequently 27 undesired in the subsequent treatment. Since the final use of the pulp often is not known to the pulp producer, 3~
it is preferred to use a salt which is used in other contexts in the production of pulp and paper. Examples of suitable salts are sodium sulphate and sodium thio-sulphate which are chemicals commonly used by the pulp industry. Also organic salts may be us~d, provided that their molecules are sufficiently small for penetration into the cavities of the ~el structure Very small amounts of the active component are required to obtain the desired effects~ Generally, some tenths of a per cent~ based upon the dry weight of the pulp will suffice, but up to about 10~ by weight may be used~
An alternative method of imparting the desired characteristics to the pulp is to admix to untreated pulp, in suitable proportions, a pulp treated in the above mentioned manner so that the entire pulp mixture will have the desired characteristics.
The following Examples of embodiments of the present invention must not be taken to restrict the scope of the invention as defined by the appended claims.
EXAMPLES
The tests accounted for in the Examples were made in accordance with the SCAN Test methods puklished and recommended by the Central Laboratories of the Cellulose Industries in Denmark, Finland, Norway and 5weden:
The following SCAN methods have been used:
27 SCAN:C lg Drainage resistance of pulp according to the Schopper-Riegler method.
~ ~.33~8 SCAN:C 24 seating of pulp in a PFI ~Paper Research Institute) mill.
SCAN:C 25 Laboratory beating in Valley beater SCAN:C 26 Manufacture of laboratory sheets for physical testing.
SCAN:C 27R Light scatter coefficient.
SCAN:C 28 Determination of the physical characteris~
tics of laboratory sheets.
SCAN:C 24 Bursting strength.
SCAN-C 11 Tearing strength of paper and board.
SCAN:P 16 Tensile strength and elongation.
Sodium sulphate (Na2so4) was dissolved in water to a suitable concentration~ in which solution an un~
dri~d and bleached softwood sulphate pulp having an initial water content of about 80~ was dispersed to a final pulp concentration of 5~. After some minutes, the pulp was dewatered by draining and pressing to a dry solids content of about 35%. After air drying at about 60C, the pulp was beaten in a Valley beater where the pH was adjusted to 5 after slashing with NaOH or H2SO~. The concentration of sodium sulphate in the dried pulp was calculated on the basis of the dry solids con~
tents of the initial pulpl the concentration of the dispersion~ and the pressed pulp. The reference used was a sample which had been dispersed in water without 27 the addition of salt and which otherwise had been subject ed to the same treatment as aboveO
The following comparison values between the reference and samples having different contents of sodium sulphate were obtained:
Tensile index, kNm/kq Beating time, min. 10 20 Ref. 61 83 92~5 Sample 3~ Na2SO~ 72.5 92 100.~
Sample 6~ " 74~5 94.5102.5 Sample 10~ " 75.0 93.0104.5 The procedure according to Example 1 was repeated, but at a drying temperature of 90-95C and with 5% of sodium sulphate in the dried sample. The following re-sults were obtained:
Tensile index~ kNm/kg Beating time, min~ 10 20 30 Ref. 58 79~5 89 Sample 67 89.5 99.5 The procedure according to Example 1 was repeated, but beating was effected in a PFI millO The sodium sul-phate concentrations in the dried pulp were those stated 27 in the Table.
The following results were obtained upon comparison with the same drainage, 30SR:
Na2S04, %
Number of beating revs 4600 4200 3800 3500 Tensile index, kNmjkg 94100 105 107 The following results were obtained upon comparison with the same tensile index, 85 kNm/kg l\la2S04 ~ g6 Number of beating revs 3200 2400 20001700 EXP~PLE 4 The procedure according to Example 1 was repeated, but the pulp was an undried and unbleached softwood sulphate pulp. The concentration of sodium sulphate in the dried pulp is stated in the Table~ The following results were obtained:
Te~sile index~ kNm/kg Beating time, min.10 20 30 Ref.
Sample 0.5~ Na2S04 44.5 64~5 77~0 Sample 2.5% " 47 66~5 79.5 lhe procedure according to Example 1 was repeated, but the salt was sodium chloride. The following results were obtained:
Tensile index, kNm/kg Beating time, min. 10 20 30 Ref. ~1 83.5 9205 Sample 5~ NaCl-~2 89.5 102.0 The procedure according to Example 1 was repeated, but the salt was sodium thiosulphate. The following results were obtained:
Tensile index, kNm/kg Bea~ing time, min. 10 20 30 Ref. 59.0 82.S 92~5 Sample 3~ Na2S20367.089.5 9700 Sample 6~ " 74.0 95.5 106.5 3~
EXAMPLE~: 7 The procedure according to Example 1 was repeated, but the pulp was undried and unbleached sulphate pulp to which sodium thiosulphate had been added. The fol-lowing results were obtainedO
Tensile index, kNm~kg Beating timeO min. 10 20 Ref. 36.5 5~.u 69.0 Sample 1~ Na2S203 42.5 62.~ 77~0 Sample 2.5% " 47.0 66.0 81.5 The procedure according to Example 1 was repeated, but the additives were monoethanol amine ~MEA), diethanol amine (DEA) and triethanol amine (TEA), respectively.
The following results were obtained:
Tensile index~ kNm/kg Beating tim~ min.10 20 30 Ref. 57.5 80.U 92.0 Sample 3% MEA 69.0 90.0 100.5 Sample 3~ DEA 70.0 89.5 9805 Sample 1.5% TEA ~ 84.~ 98.5 ~3~
E~AMPLE g The procedure according to Example 1 was r2peated, but the pulp was unbleached sulphate pulp and the additive consisted of urea. The following results were obtained:
Tensile index, kNm/kg Beating time9 min. 10 20 30 Ref. 36.5 56.0 69.~
Sample 2.5% urea 42.5 62 5 78.5 The procedure according to Example 1 was repeated, but with the difference tha~ the starting material was a dried and bleached sulphate pulp. No significant diffe rences between the reference and a 3%, 6% and 10%, respec-tively, addition of Na2SO4 were observed.
An undried and unbeaten bleached sulphate pulp was dried in conventional manner on a papermaking machine on a pilot scale. The wet web was sprayed wi~h a solution of chemicals ~see the Table) ahead of the pre~s sectionc The final amount of chemicals added to the clried pulp was estimated by extraction with hot water~ In the case of ammonium carbonate which is gasified upon drying of the pulp, the amount added was calculated on the basis of the concentration and flow of the other chemi-cals through the spray pipe. The pulp thus dried was ~ispersed in a pulper and beaten, whereupon paper was .
produced on a pilot scale, all in accordance with known technique. During the paper production, only chemicals were added to control the pH to 6 (NaOH and H2SO4, respective-ly). The pH adjustment was carried out already in the pul-per. The results are shown in the Table below. To minimize the effect of the variation in the interrelation of the longitudinal/transverse strengths~ the Table indicates ngthlongitudinalX tenSile strength~t All strengths have been evaluated at one and the same beating operation~ The reference used was a pulp which upon drying had been sprayed with water~ but which other-wise had been subjected to the same treatment.
Sample Tensile index, kNm/kq RefO
0.7 % (NH4)2SO4 68.5 l.U ~ (NH4)2CO3 68.0 1.0 % Na2SO4 68.5
The present invention comprises chemical pulps having improved strength, drainability and beatability, and a process of making said pulp.
In the production of lignocellulose-based sheet structures from a suspension of fibres and water, the fibre is first treated mechanically in the wet state.
This operation, the beating operation, is one of the most important unit operations of paper technology.
By different beating methods, it is possible to obtain different quality characteristics in the sheet, and it is possible to change the usefulness of diferent fibre raw materials.
However, the mechanical treatment principles for achieving different product characteristics are extreme-ly uncertain, and primarily the basic mechanisms of the beating process are unknown, for which reason beat-ing may be said to be effected more or less by ancient tradition.
The fibre material has a complex morphological structure~ and the changes which occur in the beating zone are heterogeneous, which makes it difficult to give a more detailed description thereof. Traditionally, the beating effect is divided into - fibre length shortening - fines production - delamination - external fibrillation - swelling 3~
- dislocations - reduced degree of polymerization~
As a result of these beating effects~ the tensile strength of the fibre in the wet state is increased, whereas the modulus of elasticity is decreased. Beaten and dried fibres have higher values of ~oth tensile strength and modulus of elasticity than unbeaten fibres.
The greatest change in the characteris~ics of the paper occurs in the initial beating phase. Usually, an increase in density, elongation at break and in all strength characteristics, with the exception of the tearing strength, is obtained; whereas opacity, permea-bility to air and dimensional hygrostability are re-duced.
An analysis of the effect of the beating operation, and the cause therefor, on the finished paper~ is render-ed difficult by the insufficient knowledge of the origin of the paper qualities. Generallyg it may be said that the fine material formed and the softening (which implies increased swelling) of the fibre are highly importantO
The swelling of the cellulose fibre may be regardPd on the basis of the physical chemistry for gels, and it will be seen how different parameters~ such as pH, temperature, salt content etc. affect the swelling con-dition of the fibre as well as the swelling level of the fine fibre fraction.
27 Traditionally, the beating efficiency is increased by modifying the construction of the beating element ~ ~ ~il3~
and the concentration of the cellulose material in the beating apparatus. Moreover, also changes in tempera-ture and pH and the addition of different chemicals have been tried to achieve a desired increase in beat-ing efficiency in connection with the papermaking pro-cess, i.e. in the further treatment of the pulp as first dried.
A mechanical modification of the beating element has given no incontestable results. However, a develop-ment towards hiqher strength characteristics in beated lignocellulose materials after treatment in present day beating equipment can be seen. Regarding the change in the chemical conditions during beating~ no major effects have been observed as compared with what is obtained by conventional papermaking technology.
The present invention has for its objec~ to provide a chemical pulp having improved strength, drainability and beatability A further object of the invention is to provide a process of making a chemical pulp having improved strengthJ drainability and beatability.
These and other objects are achieved in that the wooden raw material after cooking is mixed with an aqueous solution of one or more low~molecular salts Preferably, 0.1-10% by weight of salt, based upon the dry pulp, are incorporated.
27 The basic idea of the present invention is that a low-molecular salt shall be present during drying, at least in the initial phase thereofu It is known that the swelled fibre "collapses"
when pulp is dried, i.e. the gel structure disappears.
A subsequent addition of water in the manufacture of paper does not cause the fibre to revert to its original state, i.e. this process is at least partly irreversible.
One explanation why the swelled fibre "collapses" upon drying is that, when the water is removed, ~he cellulose chains will come so close to one another that hydrogen bonds are established between these chains. In this manner, the cavities in the gel structure of the pulp will disappear. The subsequent addition of water during the continued treatment of the pulp is unable to break the hydrogen bonds, and an irreversible '~collapse" has ~hus occurred.
Surprisingly~ it has now been found that it is possible to interfere with the formation of hydrogen bonds by adding water-soluble low-molecular salts to the pulp already after the production9 but prior to the drying thereof~ These salts penetrate into the ca-vities of the gel structure and form therein steric hindrances preventing the cellulose chains from getting close to one another, whereby the formation of hydrogen bonds is substantially eliminated By substantially preventing~ in the manner described abovet the irreversible "collapse" of the fibre gel 27 structure, the fibres can again swell when water is added and~ on the whole, revert to the state befor~
the drying.
In this manner, improved strength, dralnability and beatability of the treated pulp as compared with untreated pulp are obtained.
For carrying t~le process according to the present invention into effect, the undried, bleached or unbleach-ed chemical pulp is mixed with an aqueous solution of suitable low-molecular salts. After this addition, the pulp is dried in conventional manner, for instance by using a flash drier, by the supply of heat through ra-diation or convection (for instance by means of a fan drier for pulp) or by means of heated surfaces to which, if desired, a pressure has been applied ~for instance a cylinder drier for pulp).
Suitable salts for adding to the pulp are low-mole-cular water soluble salts. It is important that the molecular si~e of these salts be sufficiently small to enable the salts to penetrate into the gel structure and to be deposited therein while forming a steric hin-drance.
Furthermore~ it is important that the added salt does not form ions detrimental to the subsequent use of the pulp. Thus~ it will be appreciated thatl when the pulp is again suspended in water after drying~ a large part of these deposited salts will be redissolved, and consequently a salt forming chlorine ions is not always suitable because chlorine ions are frequently 27 undesired in the subsequent treatment. Since the final use of the pulp often is not known to the pulp producer, 3~
it is preferred to use a salt which is used in other contexts in the production of pulp and paper. Examples of suitable salts are sodium sulphate and sodium thio-sulphate which are chemicals commonly used by the pulp industry. Also organic salts may be us~d, provided that their molecules are sufficiently small for penetration into the cavities of the ~el structure Very small amounts of the active component are required to obtain the desired effects~ Generally, some tenths of a per cent~ based upon the dry weight of the pulp will suffice, but up to about 10~ by weight may be used~
An alternative method of imparting the desired characteristics to the pulp is to admix to untreated pulp, in suitable proportions, a pulp treated in the above mentioned manner so that the entire pulp mixture will have the desired characteristics.
The following Examples of embodiments of the present invention must not be taken to restrict the scope of the invention as defined by the appended claims.
EXAMPLES
The tests accounted for in the Examples were made in accordance with the SCAN Test methods puklished and recommended by the Central Laboratories of the Cellulose Industries in Denmark, Finland, Norway and 5weden:
The following SCAN methods have been used:
27 SCAN:C lg Drainage resistance of pulp according to the Schopper-Riegler method.
~ ~.33~8 SCAN:C 24 seating of pulp in a PFI ~Paper Research Institute) mill.
SCAN:C 25 Laboratory beating in Valley beater SCAN:C 26 Manufacture of laboratory sheets for physical testing.
SCAN:C 27R Light scatter coefficient.
SCAN:C 28 Determination of the physical characteris~
tics of laboratory sheets.
SCAN:C 24 Bursting strength.
SCAN-C 11 Tearing strength of paper and board.
SCAN:P 16 Tensile strength and elongation.
Sodium sulphate (Na2so4) was dissolved in water to a suitable concentration~ in which solution an un~
dri~d and bleached softwood sulphate pulp having an initial water content of about 80~ was dispersed to a final pulp concentration of 5~. After some minutes, the pulp was dewatered by draining and pressing to a dry solids content of about 35%. After air drying at about 60C, the pulp was beaten in a Valley beater where the pH was adjusted to 5 after slashing with NaOH or H2SO~. The concentration of sodium sulphate in the dried pulp was calculated on the basis of the dry solids con~
tents of the initial pulpl the concentration of the dispersion~ and the pressed pulp. The reference used was a sample which had been dispersed in water without 27 the addition of salt and which otherwise had been subject ed to the same treatment as aboveO
The following comparison values between the reference and samples having different contents of sodium sulphate were obtained:
Tensile index, kNm/kq Beating time, min. 10 20 Ref. 61 83 92~5 Sample 3~ Na2SO~ 72.5 92 100.~
Sample 6~ " 74~5 94.5102.5 Sample 10~ " 75.0 93.0104.5 The procedure according to Example 1 was repeated, but at a drying temperature of 90-95C and with 5% of sodium sulphate in the dried sample. The following re-sults were obtained:
Tensile index~ kNm/kg Beating time, min~ 10 20 30 Ref. 58 79~5 89 Sample 67 89.5 99.5 The procedure according to Example 1 was repeated, but beating was effected in a PFI millO The sodium sul-phate concentrations in the dried pulp were those stated 27 in the Table.
The following results were obtained upon comparison with the same drainage, 30SR:
Na2S04, %
Number of beating revs 4600 4200 3800 3500 Tensile index, kNmjkg 94100 105 107 The following results were obtained upon comparison with the same tensile index, 85 kNm/kg l\la2S04 ~ g6 Number of beating revs 3200 2400 20001700 EXP~PLE 4 The procedure according to Example 1 was repeated, but the pulp was an undried and unbleached softwood sulphate pulp. The concentration of sodium sulphate in the dried pulp is stated in the Table~ The following results were obtained:
Te~sile index~ kNm/kg Beating time, min.10 20 30 Ref.
Sample 0.5~ Na2S04 44.5 64~5 77~0 Sample 2.5% " 47 66~5 79.5 lhe procedure according to Example 1 was repeated, but the salt was sodium chloride. The following results were obtained:
Tensile index, kNm/kg Beating time, min. 10 20 30 Ref. ~1 83.5 9205 Sample 5~ NaCl-~2 89.5 102.0 The procedure according to Example 1 was repeated, but the salt was sodium thiosulphate. The following results were obtained:
Tensile index, kNm/kg Bea~ing time, min. 10 20 30 Ref. 59.0 82.S 92~5 Sample 3~ Na2S20367.089.5 9700 Sample 6~ " 74.0 95.5 106.5 3~
EXAMPLE~: 7 The procedure according to Example 1 was repeated, but the pulp was undried and unbleached sulphate pulp to which sodium thiosulphate had been added. The fol-lowing results were obtainedO
Tensile index, kNm~kg Beating timeO min. 10 20 Ref. 36.5 5~.u 69.0 Sample 1~ Na2S203 42.5 62.~ 77~0 Sample 2.5% " 47.0 66.0 81.5 The procedure according to Example 1 was repeated, but the additives were monoethanol amine ~MEA), diethanol amine (DEA) and triethanol amine (TEA), respectively.
The following results were obtained:
Tensile index~ kNm/kg Beating tim~ min.10 20 30 Ref. 57.5 80.U 92.0 Sample 3% MEA 69.0 90.0 100.5 Sample 3~ DEA 70.0 89.5 9805 Sample 1.5% TEA ~ 84.~ 98.5 ~3~
E~AMPLE g The procedure according to Example 1 was r2peated, but the pulp was unbleached sulphate pulp and the additive consisted of urea. The following results were obtained:
Tensile index, kNm/kg Beating time9 min. 10 20 30 Ref. 36.5 56.0 69.~
Sample 2.5% urea 42.5 62 5 78.5 The procedure according to Example 1 was repeated, but with the difference tha~ the starting material was a dried and bleached sulphate pulp. No significant diffe rences between the reference and a 3%, 6% and 10%, respec-tively, addition of Na2SO4 were observed.
An undried and unbeaten bleached sulphate pulp was dried in conventional manner on a papermaking machine on a pilot scale. The wet web was sprayed wi~h a solution of chemicals ~see the Table) ahead of the pre~s sectionc The final amount of chemicals added to the clried pulp was estimated by extraction with hot water~ In the case of ammonium carbonate which is gasified upon drying of the pulp, the amount added was calculated on the basis of the concentration and flow of the other chemi-cals through the spray pipe. The pulp thus dried was ~ispersed in a pulper and beaten, whereupon paper was .
produced on a pilot scale, all in accordance with known technique. During the paper production, only chemicals were added to control the pH to 6 (NaOH and H2SO4, respective-ly). The pH adjustment was carried out already in the pul-per. The results are shown in the Table below. To minimize the effect of the variation in the interrelation of the longitudinal/transverse strengths~ the Table indicates ngthlongitudinalX tenSile strength~t All strengths have been evaluated at one and the same beating operation~ The reference used was a pulp which upon drying had been sprayed with water~ but which other-wise had been subjected to the same treatment.
Sample Tensile index, kNm/kq RefO
0.7 % (NH4)2SO4 68.5 l.U ~ (NH4)2CO3 68.0 1.0 % Na2SO4 68.5
2-0 ~ Na254 73-~
~ .
~ .
Claims (8)
1. A chemical pulp having improved strength, drainability and beatability, characterised in that it contains one or more low-molecular water-soluble salts having a molecular size which is sufficiently small to enable the salts to penetrate into the gel structure and to be deposited therein.
2. A pulp as claimed in claim 1, where the added salts are such that they will not form ions detrimental to the subsequent use of the pulp.
3. A pulp as claimed in claim 1 or 2, where the salts are present in an amount of 0.1-10% by weight, based upon the dry weight of the pulp.
4. A pulp as claimed in claim 1 or 2, where the salts are present in an amount of 0.1-10% by weight, based upon the dry weight of the pulp; where the salts are chosen from the group comprising sodium sulphate, sodium thiosulphate, and organic salts having sufficiently small molecules that they may penetrate into the cavities of the gel structure.
5. A process of making a chemical pulp having improved strength, drainability and beatability, characterized in that the pulp which is undried after cooking, is mixed with an aqueous solution of one or more low-molecular salts having a molecular size which is sufficiently small to enable the salts to penetrate into the gel structure and to be deposited therein.
6. A process as claimed in claim 5, where the added salts are such that they will not form ions detrimental to the subsequent use of the pulp.
7. A process as claimed in claim 5 or 6, where the salts are added in an amount of 0.1-10% by weight, based upon the dry weight of the pulp.
8. A process as claimed in claim 5 or 6, where the salts are added in an amount of 0.1-10% by weight, based upon the dry weight of the pulp; where the salts are chosen from the group comprising sodium sulphate, sodium thiosulphate, and organic salts having sufficiently small molecules that they may penetrate into the cavities of the gel structure.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE8106885-0 | 1981-11-19 | ||
| SE8106885A SE8106885L (en) | 1981-11-19 | 1981-11-19 | CHEMICAL MASS WITH IMPROVED STRENGTH, DRAINAGE FORM, AND PAINTABILITY AND SET TO MAKE IT |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1193808A true CA1193808A (en) | 1985-09-24 |
Family
ID=20345071
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000415980A Expired CA1193808A (en) | 1981-11-19 | 1982-11-19 | Chemical pulp having improved strength, drainability and beatability, and a process of making said pulp |
Country Status (5)
| Country | Link |
|---|---|
| BR (1) | BR8206713A (en) |
| CA (1) | CA1193808A (en) |
| FI (1) | FI70618C (en) |
| NO (1) | NO161332C (en) |
| SE (1) | SE8106885L (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5114534A (en) * | 1990-05-16 | 1992-05-19 | Georgia-Pacific Corporation | Drying cellulosic pulp |
| US5314582A (en) * | 1992-07-22 | 1994-05-24 | Chicopee | Cellulosic fiber of improved wettability |
| US6562743B1 (en) | 1998-12-24 | 2003-05-13 | Bki Holding Corporation | Absorbent structures of chemically treated cellulose fibers |
| US8946100B2 (en) | 2003-12-19 | 2015-02-03 | Buckeye Technologies Inc. | Fibers of variable wettability and materials containing the fibers |
| US11479915B2 (en) * | 2016-07-11 | 2022-10-25 | Stora Enso Oyj | Method for manufacturing intermediate product for conversion into microfibrillated cellulose |
-
1981
- 1981-11-19 SE SE8106885A patent/SE8106885L/en not_active Application Discontinuation
-
1982
- 1982-10-01 FI FI823350A patent/FI70618C/en not_active IP Right Cessation
- 1982-10-04 NO NO823323A patent/NO161332C/en unknown
- 1982-11-19 CA CA000415980A patent/CA1193808A/en not_active Expired
- 1982-11-19 BR BR8206713A patent/BR8206713A/en not_active IP Right Cessation
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5114534A (en) * | 1990-05-16 | 1992-05-19 | Georgia-Pacific Corporation | Drying cellulosic pulp |
| US5314582A (en) * | 1992-07-22 | 1994-05-24 | Chicopee | Cellulosic fiber of improved wettability |
| US5413676A (en) * | 1992-07-22 | 1995-05-09 | Chicopee | Cellulosic fiber of improved wettability |
| US6562743B1 (en) | 1998-12-24 | 2003-05-13 | Bki Holding Corporation | Absorbent structures of chemically treated cellulose fibers |
| US6770576B2 (en) | 1998-12-24 | 2004-08-03 | Bki Holding Corporation | Absorbent structures of chemically treated cellulose fibers |
| US8946100B2 (en) | 2003-12-19 | 2015-02-03 | Buckeye Technologies Inc. | Fibers of variable wettability and materials containing the fibers |
| US10300457B2 (en) | 2003-12-19 | 2019-05-28 | Georgia-Pacific Nonwovens LLC | Fibers of variable wettability and materials containing the fibers |
| US11479915B2 (en) * | 2016-07-11 | 2022-10-25 | Stora Enso Oyj | Method for manufacturing intermediate product for conversion into microfibrillated cellulose |
Also Published As
| Publication number | Publication date |
|---|---|
| NO823323L (en) | 1983-05-20 |
| FI823350A0 (en) | 1982-10-01 |
| NO161332C (en) | 1989-08-02 |
| SE8106885L (en) | 1983-05-20 |
| BR8206713A (en) | 1983-10-04 |
| FI70618C (en) | 1986-09-24 |
| FI823350L (en) | 1983-05-20 |
| FI70618B (en) | 1986-06-06 |
| NO161332B (en) | 1989-04-24 |
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| MKEC | Expiry (correction) | ||
| MKEX | Expiry |