FI121545B - Method for improving the properties of pulp - Google Patents

Description

Method for improving the properties of pulp

Background of the Invention

The invention relates to improving the properties of pulp, in particular nonwood pulp, by selectively removing some of its fines.

5 Pulp fine is generally understood to mean a fraction that passes through a 200 mesh wire on a McNett machine, or fibers shorter than 0.2 mm. It is known that pulp fines are not homogeneous but can be divided into chips and fibril-like particles, both of which affect the pulp properties in different ways (Brecht & Klemm 1953). The fines of pulp are known to have many effects on the properties of pulp and paper.

The fines of chemical wood pulp are formed mainly by milling and are called secondary fines. In particular, the fines have a positive effect on the strength properties of the pulp, e.g. the tensile strength.

In contrast, chemical nonwood pulps are utilized mainly in the form of non-pulverized because of their good bonding properties and because of the high content of fines limiting their dewatering properties, which are further degraded during milling. Particularly, straw fibers have a very high content of fines by nature, and straw fibers also have poor dewatering properties. Nonwood pulp fines are mainly primary fines and have been found to have a positive effect on both tensile strength and opacity (Rousu & Niinimäki 2007).

Because nonwood pulp fines reduce pulp dewatering, an attempt is made to limit the amount of fines in the pulp by removing it, for example by reducing the amount of foliage in the raw material pre-treatment. It is known that pretreatment of a raw material, such as wheat straw, can remove fines, and that pretreatment can reduce the content of inorganic components of the pulp, such as silicon, achieve higher pulp holocellulose content and increase fiber length (Ma et al. 1992, Pa-30 patheofanous et al. 1995, Petersen 1988, Paavilainen & Tulppala 1996). In addition to these, fines removal has been found to improve the dewatering properties, bulk and air permeability as well as strength (Ma et al. 1992, Paavilainen & Tulppala 1996, Paavilainen et al. 1999). Straw pulp has a particularly slow dewatering. Thus, it has been suggested that the optimum removal rate of fines 35 for wheat straw pulp would be 10% by weight (Ma et al. 1992).

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According to the prior art described above, it is proposed to remove pulp fines generally during the pretreatment of the raw material and in relatively large quantities, which causes loss of pulp and may adversely affect other properties of the pulp. The pulp feedstock pre-treatment 5 is typically carried out in a multi-stage pre-treatment, often involving first dry treatment followed by wet treatment. In addition, the disadvantage of multi-stage pretreatment is that in the dry treatment, in addition to the fines, a lot of desirable material and fiber is also removed, and in the wet treatment, a lot of wastewater is generated. In addition, wet treatment is not suitable for all pulping processes due to the excess water entering the process. In addition, these process steps require their own investment.

US 7005 034 B1 discloses a process for the production of mechanical pulp, wherein the unbleached wood or nonwood material is first subjected to a first refining to form a primary fines and then a second refining to produce a secondary fines. The pulp is subjected to fractionation after the first milling before the second milling to separate the primary fines, after which the primary fines are removed from the pulp. This method relates to the production of mechanical pulp, not chemical pulp.

Conversely, methods for selectively removing pulp fines in minimized quantities have been described or proposed in the art so that important properties of the pulp can be improved without substantially compromising other properties while maintaining the simplest process arrangements.

BRIEF DESCRIPTION OF THE INVENTION

It has surprisingly been found that even with very little fines removal, the drainage properties of the pulp and the brightness of the pulp can be significantly improved without substantially diminishing other pulp properties such as pulp tensile strength and opacity. It has also been found that the quality and composition of the pulp 30 has a very large influence on the various properties of the pulp. The fines to be removed consist mainly of epidermis cells, small parenchyma cells, silicate and cork cells, and various fragments of tubular cells and related non-fibrous cell types. Typical for these particles is their small size and their small width-to-length ratio 35, as well as their lamellar appearance. It has been found that a similar healing effect, for example on dewatering, is obtained by removing only a very small part of the particulate components from the total mass than is achieved by removing the fine fraction as such. Thus, by removing only a portion of the fines, a high pulp yield ratio is achieved with the corresponding properties of pulp and paper.

Detailed Description of the Invention

The present invention relates to a process for improving the properties of a nonwood pulp, in particular its filtration and / or lightness of the pulp, wherein the nonwood pulp is produced by sulphate, sulphite or soda processes, solvent-based processes or ionic processes. The process is characterized in that fines particles having an average length (average maximum dimension) of up to 0.18 mm and a width (average average dimension) of up to 0.05 mm are removed from the pulp.

By nonwood pulp in the present invention is meant mas-15 saw, which is made from grassy plant fibers, so-called fibers, deciduous fibers or fruit seed fibers. Examples of useful fibers based on herbaceous plants include straw, e.g., cereal straw (wheat, rye, oats, barley, rice), reeds, e.g., reed, lake reed, papyrus, cane, and bamboo, and hay, e.g., esparto, sabai and lemon grass. Examples of such fibers are flax, such as fiber flax stems and oil flax stems, hemp, oriental hemp, kenaf, jute, ramie, paper silk, gampi fiber, and mitsumata fiber. Examples of deciduous fibers are e.g. Manilla hemp and sisal. Examples of fruit seed fibers include cotton seed hairs and cotton lint fibers, kapok and coconut fiber.

Among the herbaceous plants useful in the present invention that are useful in the present invention include lake reed, reed canary grass, timothy, dog grass, yellow catfish, Eastern catfish, red foxtail, white foxtail, red clover, goat pea and bat.

Particularly preferred according to the invention is a pulp made from herbaceous plants, such as straw pulp. In one embodiment, pulp made from annual herbaceous plants is used. In another embodiment, pulp made from perennial non-woody plants is used. According to the invention it is also possible to use agricultural waste material which includes e.g. the aforesaid cereal straw.

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For nonwood pulps, for example, the fines content of wheat pulp is typically in the range of 20 to 25% by weight, based on dry weight.

The pulp may be a nonwood pulp obtained by any of the conventional pulping processes, such as pulp by the sulphate, sulphite or soda process. The pulp may also be pulp prepared by solvent-based processes such as formic and / or acetic acid, alcohol-based or ionic processes. The pulp may be bleached or unbleached pulp.

According to the present invention, fine particles having an average length of up to 0.18 mm and a width of up to 0.05 mm are removed from the nonwood pulp. Preferably, the particles have an average length of up to 0.10 mm and a width of up to 0.04 mm.

Definition of particle size '' of an average length of up to 0.18 mm or 0.10 mm 'in the present invention means that the particle size distribution of particles to be removed has an average length (average maximum dimension) of at most 0.18 mm or up to 0.10 mm, respectively. . Further, respectively, their width (average small dimension) is at most 0.05 mm and 0.04 mm.

The particles to be removed preferably have a plate-like shape. In a particularly preferred embodiment, the particle width to length ratio is equal to or greater than 1:10, more preferably equal to or greater than 1: 5, and in particular equal to or greater than 1: 2, up to a value of 1: 1.

The fines particles to be removed are mainly composed of epidermal cells, parenchymal cells, silicate cells, tubular cell fragments, cork cells and / or corresponding non-fibrous cells and / or combinations of these cells and / or portions of cells of said nonwood plants. Parenchymal cells, as used herein, are small parenchymal cells having a length (maximum dimension) of not more than 0.18 mm as defined above. The fines particles to be removed comprise at least 50%, preferably at least 75% of the cell types in question.

The amount of fines particles to be removed is typically less than 8%, preferably less than 5%, based on the total dry weight.

For example, filtering, screening, grading or differential pressure equipment may be used to remove fines. Suitable industrial devices for these include: filters, strainers, sorters (including pressure sorter) and hydrocyclones (vortex cleaners).

In a preferred embodiment, screening is used with a screen aperture size in the range of 180 to 40 µm, preferably 100 to 40 µm, especially 5 60 to 40 µm.

Removal of the fines can be performed before the pulp is produced for the pulp raw material, during pulping or after the pulping.

In one preferred embodiment, the removal of the fines particles 10 is carried out directly after the pulp has been made to a finished pulp having a reduced consistency to 0.1-5%. Separation can be made, for example, from filtrates of pulp washers, paper machine and dryer, disk filter, pressure screen acceptor using a screen size of, for example, 0.05 to 0.2 mm screen size or hole screen or vortex cleaner with suitable pressure differences or different combinations.

The following examples are illustrative but not limiting of the invention.

The standards used in the examples were as follows: SR Chapter: SCAN-CM 19:65 20 Manufacture of Sheets of Paper: SCAN-P 26:76

Tensile strength: SCAN-P 38:80

Light absorption coefficient, opacity and brightness: ISO 2467

Track number: SCAN-C 1:00

Example 1.

The starting material used was a wheat pulp made with a mixture of formic and acetic acid bleached with the EPP sequence. The pulp was fractionated on a wire having a mesh size of 40 µm by removing a portion of the fines passing through the wire. The amount of fines removed corresponded to 2.34% of the total mass. The desiccation time of the pulp was measured on a Shopper Riegler 30 and the free dewatering time in a sheet mold at 13 ° C, and sheets of paper were prepared for testing the tensile strength of the pulp. Measurements were made of both the untreated starting mass and the fined pulp (40 µm wire passage removed).

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Mass fraction investigated SR number Free water Tensile strength, sheet removal Nm / g ______mould, s__

Removed 40 µm fraction__32,0__17.01-0150.76

Reference, not removed mi- 34.5 18.72 51.00 fractions_________

It was found that the SR number improved by 7.2% by removing the 40 µm wire pass (i.e. 2.34% by weight) and the sheet dewatering time by 9.1%. The tensile strength was not substantially changed in these experiments.

The separated fines were analyzed microscopically. It was found that the fines consisted mainly of epidermis cells, small parenchymal cells, silicate cells, fragments of tubular cells, cork cells and related non-fibrous particles and portions thereof. The particles were plate-like in shape and typically had a width to length ratio of greater than 1: 5.

Example 2.

The same wheat pulp as in Example 1 was fractionated on a wire having a mesh size of 50 µm by removing a portion of the fines passed through the wire. The amount of fines removed corresponded to 3.87% of the total mass. The pulp was measured with a 15 percolation time on a Shopper Riegler and a free dewatering time in sheet form at 13 ° C. Measurements were made both of the untreated starting mass (reference) and the fined pulp. In addition to the reference, pulp having various percentages of fines that had passed a 200 mesh standard wire (aperture 74 µm) was used for comparison.

20 ___________

Mass fraction examined SR number Free dewatering in _____ sheet form, p

Removed 50 pm fraction__30,5__15,28_

Removed 5% 200 mesh fraction__34,5__17,88_

Removed 10% 200 mesh fraction__32,5__16,83_

Removed 25% of 200 mesh fraction__31,5__16,30_

Removed 50% 200 mesh fraction__29,0__13,80_

For reference, no fractions 34.5__18.72_7 were removed

It was found that the SR number improved by 11.6% by removing the portion of pulp passed through the 50 µm wire (i.e., 3.87% by weight) and, accordingly, the dewatering time in sheet mold improved by 18.4%. Comparing, for example, the effect of 3.87% removal of the 50 µm wire-pass fraction to the effect of total fines 5 removal, it is found that the same dewatering efficiency would require about 35% fines reduction.

The average particle length of the separated fines as determined by optical analyzers was 0.18 mm. Microscopic analysis found the same particle types as in Example 1. The particle shape was also plate-like, but the width-length ratio was typically greater than 1:10.

Example 3.

The wheat pulp was fractionated by fractionating its fines (obtained by fractionating with a 200 mesh standard wire having a mesh size of 74 µm and weaving the permeable portion of the wire) into three portions as follows: (1) 50 µm permeate fines were removed from the fines; ), the fines that passed the 50 µm wire were stripped of the 40 µm wire passed fines and (3) the fines that passed the 40 µm wire were collected.

Mass fraction studied__ Number of pieces

Fiber fraction, ie the mass fraction remaining on a 200 mesh wire__3,1

The proportion of the fines by removing the 4.2 mass fraction passed through the 50 pm wire_____

The part of the fines which has passed the 50 µm wire and the 6.2% of which has passed the 40 µm wire___

The percentage of fines that has passed a 40 μπν.η wire__6.7 20

It was found that different portions of the fines had different kappa numbers, all of which were higher than the fiber fraction. The highest kappa number was on the finest section of fines.

Example 4.

The wheat pulp was fractionated to remove a portion of the 40 µm wire and 50 µm wire. The fines removed corresponded to 2.34% and 3.87% respectively of the total mass. From the original pulp as well as from the pulps deprived of the aforementioned 8 fines fractions, sheets were prepared with light absorption coefficient, opacity and brightness determined.

Mass fraction studied Light absorption sugar Opacity,% roin, m2 / kg

Removed 50 µm fraction__0.66__77.48

Removed 40 µm fraction__0.72__77.83

Reference, no fractions removed 0.80 78.32 no fractions______ 5 It was observed that the light absorption coefficient was improved by 9.4% after removal of the particle size of the pulp which had passed the 40 µm wire and 17.6% after removal of the particle size a section that had passed a 50 μητ.η wire. Correspondingly, the opacity decreased only by 0.6% and 1.1%, but the brightness of the masses improved by 1.0 and 1.9 units.

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Literature Reference List

Brecht, W. & Klemm, K., Pulp Paper Mag. Can. 54 (1), 72, 1953.

Rousu, P. & Niinimäki, J., Nonwood pulp constituents Part I - The effect of 5 on pulp and paper properties. Appita Journal 60 (3), 217-221,2007.

Ma, J.-H., Xie, L.-S. & Zhang, S.-Z., Characteristics of various fractions of bisulfite reed and amur silver grass pulp and effects of fines on paper and papermaking properties. Proc., Second International Nonwood Fiber Pulping and Papermaking Conference, Shanghai, P.R. China, 2: 834-10843, 1992.

Papatheofanous, M.G., Koullas, D.P., Koukios, E.G., Fuglsang, H. & Schade, J.R., Biorefining of agricultural crops and residues: effect of pilot plant fractionation on properties of fibrous fractions. Biomass and Bioenergy 8 (6): 419-426, 1995.

15 Petersen, P.B., Separation and characterization of botanical com ponents of straw. Agricultural Progress 63: 8-23, 1988.

Paavilainen, L. & Tulppala, J. (1996) TOP-quality agro-based fine paper produced on pilot scale. Proc 1996 Pulping Conference, Nashville, TN, 2: 577-582.

20 Paavilainen, L, Tulppala, J., Finell, M. & Rehnberg, 0. Reed ca nary grass pulp produced on mill scale. Proc. Pulping Conference, Orlando, Florida, 1: 335-341, 1999.

Claims (14)

A process for improving the properties of the nonwood pulp, such as dewatering and / or the brightness of the pulp, wherein the nonwood pulp is produced by sulfate, sulfite or soda processes, solvent-based or ionic processes, characterized in that finished with an average length of not more than 0.18 mm and a width of not more than 0.05 mm is removed from the pulp. 2. A method according to claim 1, characterized in that the particles have an average length of not more than 0.10 mm and a width of not more than 0.04 mm. 3. A method according to claim 2, characterized in that the particles have a disc-like shape. 4. A method according to claim 3, characterized in that the ratio of the width of the particles to their length is equal to or greater than 1:10. 5. A method according to claim 4, characterized in that the ratio is equal to or greater than 1: 5. 6. A method according to claim 5, characterized in that the ratio is equal to or greater than 1: 2. 20 Method according to Claim 1, characterized in that the amount of fine substance particles to be removed is below 8%, preferably less than 5% of the total mass, calculated on dry mass. Method according to claim 1, characterized in that the particles to be removed consist mainly of epidermal cells, parenchyma cells, silicate cells, fragments of tube cells, cork cells and / or corresponding non-fibrous cells and / or parts thereof. cells or combinations of these cells and / or portions of these cells. Method according to claim 1, characterized in that the removal of the fine substance particles is carried out by filtration, screening, classification or by a method based on pressure difference. 10. A method according to claim 9, characterized in that screening is used, wherein the screen has an opening size of 180 - 40 µm, preferably 100 - 40 µm. 11. A process according to claim 1, characterized in that the removal of the fine substance particles is carried out from the pulp material prior to the production of the pulp, in connection with the preparation of the pulp or after the pulping process. Method according to claim 1, characterized in that the non-wood pulp is made up of pulp made from grass-stalk plants. 5 13. A process according to claim 1, characterized in that the non-wood pulp is pulp made from agricultural waste. 14. A method according to claim 12 or 13, characterized in that the nonwood pulp is made of wood cellulose pulp.