JP2011500984A - Methods for improving pulp properties - Google Patents

Abstract

  The present invention relates to a method for improving the properties of non-wood pulp by utilizing the selective removal of fines.

Description

  The present invention relates to improving the properties of pulp, particularly non-wood pulp, by selectively removing fines from the pulp.

Pulp fines generally refer to the fraction of pulp that passes through the 200-mesh screen of a McNett device, or fibers shorter than 0.2 mm. The pulp fines are not uniform but can be divided into flake-like and fibrillar particles, both of which are known to affect pulp properties in various ways (Brecht & Klemm 1953). The pulp fines are known to have many effects on pulp and paper properties.
Chemical wood pulp fines are generated mainly as a result of refining and are called secondary fines. In particular, the fine powder clearly affects the strength properties of the pulp, such as tensile strength.
In contrast, chemical non-wood pulp is used primarily without refining because of its good binding properties and because of the large amount of fines that limit its dehydration properties that are further reduced in refining. Is done. The content of the fine powder is inherently extremely high, especially in straw fibers, and straw fiber pulp also has low dewatering properties. Non-wood pulp fines are primarily primary fines and they have been found to have a pronounced effect on both tensile strength and opacity (Rousu & Niinimaki 2007).

  The non-wood pulp fines reduce the dewaterability of the pulp, so by removing the fines, for example by reducing the amount of leaf-derived material when pre-processing the raw material, Many attempts have been made to limit the amount of fines. Pre-processing of the raw material, for example wheat wheat straw, enables the removal of the fine powder, and the pre-processing reduces the content of inorganic components such as silicon in the pulp, high content of holocellulose in the pulp It is known to be able to achieve rates and increase in fiber length (Ma et al., 1992; Papatheofanous et al., 1995; Petersen, 1988; Paavilainen & Tulppala, 1996). In addition to these, it has been found that removal of the fine powder improves the dewatering properties, bulk, breathability and strength of the pulp (Ma et al., 1992; Paavilainen & Tulppala, 1996; Paavilainen et al., 1999). Dehydration is particularly slow in straw pulp. In fact, it has been suggested that the optimum amount of fines removal in wheat and wheat straw pulp would be 10%, calculated on the total pulp (Ma et al., 1992).

According to the above prior art, it has been suggested that fines should generally be removed in a relatively large amount with the pre-processing of the raw material, but this has resulted in loss of pulp and the May adversely affect other properties. Typically, the raw material of the pulp is subjected to pre-processing as a multi-stage pre-processing, often involving first dry processing followed by wet processing. Furthermore, one disadvantage of multi-stage pre-processing is that in dry processing, many desirable materials and fibers are removed along with the fines, and further wet processing results in large amounts of wastewater. Furthermore, wet processing is not suitable for all pulp manufacturing processes because an excessive amount of water is introduced into this step. In addition, these processing steps require special invested capital.
Nevertheless, in order to be able to improve the important pulp properties without substantially compromising other pulp properties other than the important pulp properties and while keeping the process arrangement as simple as possible, No method has been described or suggested in the art for selectively removing as little pulp dust as possible.

  Unexpectedly, removal of very small amounts of fines in pulp drainage characteristics and whiteness without significantly reducing other pulp properties such as tensile strength and opacity of the pulp We found significant improvements. It has also been found that the performance and composition of the pulp fines has a significant effect on various pulp properties. The fines to be removed are mainly composed of epidermal cells, small parenchymal cells, silicate and cork cells, and various fragments of ductal cells and corresponding non-fibrous cell types. These particles are characterized by their small size and their small width-to-length ratio and their flake-like nature. A similar improvement effect is achieved by removing only a very small portion of the fines component from the whole pulp as compared to the effect achieved by removing only the fines fraction itself, for example in dewaterability. I found out. Thus, by removing only a predetermined portion of the fines, a high pulp yield ratio is achieved with corresponding pulp and paper properties.

The present invention relates to a method for improving the properties of the non-wood pulp, in particular the drainage and / or whiteness of the pulp. This method is characterized by removing fine particles from the pulp having an average length of at most 0.18 mm (average maximum dimension) and a width of at most 0.05 mm (average minimum dimension).
In the context of the present invention, non-wood pulp means pulp made from grass-stemmed plants fibers (Poaceae fibers), bast fibers, leaf fibers or fruit fibers. To do. Examples of useful fibers based on stalked gramineous plants include cocoons, such as cereals (wheat, rye, oats, barley, rice), reeds, eg, reeds, common reed, papyrus, sugarcane. Or fiber of bagasse, bamboo, and herbs such as esparto, sabai, and lemongrass. Examples of bast fibers include flax, for example common flax stems and oil flax stems, cannabis, East Indian cannabis, kenaf, jute, ramie, banquet, ganpi fibres and mitsumata fibres. Examples of leaf fibers include, for example, abaca and sisal. Examples of fruit fibers include cotton seed hair, cotton seed skin fibers (linters), kapok, and coconut husk fibers.

Examples of the stalked gramineous plants useful in the present invention and growing in Finland include the following: reed (common reed), kusayoshi, timothy, camogaya, shrimp, rice Smooth brome, red fescue, white-faced spider, red clover, goat's rue and alfalfa.
According to the invention, pulps produced from stalked gramineous plants, such as straw pulp, are particularly preferably used. In one embodiment, pulp made from annual plants with annual stems is used. In other embodiments, pulp made from perennial non-woody plants is used. According to the present invention, it is also possible to use agricultural waste materials containing, for example, the above-mentioned cereal meal.
Among non-wood pulps, the fines content of wheat straw pulp, for example, is typically in the range of 20-25% of total pulp, calculated on dry pulp.

The pulp can be any non-wood pulp made by any conventional pulp making method, for example, a pulp made by the sulfate method, sulfite method or soda method. The pulp may also be a pulp produced by a solvent-based method, for example a formic acid-based and / or acetic acid-based method, an alcohol-based method or an ionic method. The pulp can be bleached pulp or unbleached pulp.
According to the present invention, fine particles of a size having a length of at most 0.18 mm and a width of at most 0.05 mm are removed from the non-wood pulp. Preferably, the average length of the particles is at most 0.10 mm and the width is at most 0.04 mm.

In the present invention, the definition of the particle size, that is, “size having a length of 0.18 mm at the longest or 0.10 mm at the longest” means an average length in the particle size distribution of the particles to be removed (average Mean maximum dimension) is 0.18 mm at most or 0.10 mm at most. Furthermore, the width (average minimum dimension) of the particles is 0.05 mm or 0.04 mm at the most, respectively.
The shape of the particles to be removed is preferably flake-like. In a particularly preferred embodiment, the ratio of the width of the particle to its length is equal to or greater than 1:10, even more preferably equal to or greater than 1: 5 and in particular equal to 1: 2. Or more, up to the value of 1: 1.
The fine particles to be removed are mainly non-wood type plant epidermal cells, parenchymal cells, silicate cells, duct cell fragments, cork cells and / or corresponding non-fibrous cells and / or of these cells. It consists of a part or a combination of these cells and / or cell parts. Here, parenchymal cells mean small parenchymal cells having a length (maximum dimension) of at most 0.18 mm in accordance with the definition presented above. The fine particles to be removed constitute at least 50%, preferably at least 75% of the cell type.

The amount of fine particles to be removed is typically less than 8%, preferably less than 5% of the total pulp, calculated on dry pulp.
For example, the fines can be removed using a device based on filtration, sieving, classification or mass difference. Industrial devices suitable for this purpose include, for example, filters, screens, classifiers (eg, pressure classifiers), and hydrocyclones (vortex cleaners).
In a preferred embodiment, sieving is used, the opening of the sieve being in the range of 180-40 μm, preferably in the range of 100-40 μm, in particular in the range of 60-40 μm.
The fines can be removed from the raw material of the pulp, prior to pulp manufacture, with pulp manufacture, or from the final pulp obtained after pulp manufacture.
In a preferred embodiment, the fine particles are removed directly from the finished pulp after the pulp is produced and the concentration is reduced to the range of 0.1-5%. This separation can be done from the pulp washer filtrate, the paper machine and the dryer, from the disk filter, for example from 0.05 to 0.2 mm mesh, from the acceptance of the pressurized screen when using slot screens or perforated screens. Or a vortex cleaner with an appropriate pressure differential or various combinations thereof.

The following examples are for illustrative purposes and are not limiting examples of the invention.
The percentage values (%) in the examples below and throughout the specification and claims mean percentages on a mass basis.
The criteria used in the following examples are as follows:
SR number: SCAN-CM 19:65;
Manufacture of paper sheets: SCAN-P 26:76;
Tensile strength: SCAN-P 38:80;
Extinction coefficient, opacity and whiteness: ISO 2467;
Copper number: SCAN-C 1:00

Example 1:
Wheat wheat straw pulp produced using a mixed acid composed mainly of formic acid and acetic acid and bleached by EPP sequence was used as a starting material. The pulp was fractionated by using a screen having a 40 μm sieve opening and removing the fine powder portion that passed through the screen. The amount of fines thus removed corresponded to 2.34% of the total pulp. From this pulp, the drainage time is measured using a Shopper Riegler device, the free dewatering time is measured in a sheet mold at 13 ° C., and a paper sheet is produced, which is used to The tensile strength of the pulp was tested. These measurements were performed on both the untreated pulp as starting material and the fine powder-removed pulp (the pulp from which the portion that passed through the 40 μm screen was removed).

When the portion that passed through the 40 μm screen was removed (ie 2.34% of the pulp), the SR number was improved by 7.2%, and correspondingly, the dewatering time in the sheet mold was improved by 9.1%. I found out that In these tests, no substantial change in tensile strength was found.
The separated fine powder was analyzed microscopically. The fines were found to be mainly epidermal cells, small parenchymal cells, silicate cells, ductal cell fragments, cork cells and corresponding non-fibrous particles and parts thereof. The particle shape was flake-like and the ratio of its width to its length was typically greater than 1: 5.

Example 2:
The wheat wheat straw pulp of Example 1 was fractionated by using a screen having a sieve opening of 50 μm and removing the fine powder portion that passed through the screen. The amount of fines removed was equivalent to 3.87% of the total pulp. The drainage time was measured from this pulp using a Shopper Riegler device, and the free dewatering time was measured in a sheet mold at 13 ° C. These measurements were performed on both the untreated pulp as a starting material (reference) and the fine powder-removed pulp described above. In addition to the reference, a pulp from which various proportions of fine powder were removed, which passed through a 200 mesh standard screen (screen opening: 74 μm), was used as a comparative example.

When the portion that passed through the 50 μm screen was removed (ie 3.87% of the pulp volume), the SR number was improved by 11.6%, and correspondingly, the dewatering time in the sheet mold was only 18.4%. I found it to be improved. Comparing the effect of removing 3.87% of the fraction that passed through the 50 μm screen with the effect of removing all fines, it can be seen that the same dewatering efficiency requires about 35% reduction in the amount of fines. .
In connection with the separated fines, the average length of the particles, measured using an optical analyzer, was 0.18 mm. In the microscopic analysis, particles of the same type as in Example 1 were detected. The shape of the particles was similarly flake-like, but the ratio of its width to its length typically exceeded 1:10.

Example 3:
The wheat wheat straw pulp is divided into three parts as follows: the fine powder (obtained by separating with a standard mesh screen with a sieve opening of 74 μm and collecting the part that passed through the screen) (1) The fine powder that passed through the 50 μm mesh screen was removed from the fine powder; (2) The fine powder that passed through the 40 μm mesh screen was removed from the fine powder that passed through the 50 μm mesh screen; and (3) 40 μm The fine powder that passed through the mesh screen was collected.

該微粉の様々な部分は、様々なカッパー価を持つが、その全てが、該繊維画分のカッパー価よりも高いことが分かった。該微粉の最も微細な部分が、最大のカッパー価を有していた。

Various parts of the fine powder have various kappa numbers, all of which have been found to be higher than the kappa number of the fiber fraction. The finest part of the fine powder had the largest kappa number.

Example 4:
Wheat wheat straw pulp was fractionated by removing the fine part that passed through the 40 μm mesh screen and the fine part that passed through the 50 μm mesh screen. The amount of fines removed corresponded to 2.34% and 3.87% of the total pulp, respectively. Sheets were made from the original pulp and from the pulp from which the fines fraction had been removed, and the extinction coefficient, opacity and whiteness of the sheet were measured.

  The extinction coefficient was improved by 9.4% when the fine powder portion that passed through the 40 μm mesh screen was removed from the pulp, and correspondingly, the fine powder portion that passed through the 50 μm mesh screen was removed from the pulp. In the case, it was found to improve by 17.6%. Similarly, the opacity decreased by only 0.6% and 1.1%, but the whiteness of the pulp was improved by 1.0 and 1.9 whiteness units.

References

Claims (14)

  Characteristics of the non-wood pulp, for example drainage of the pulp, characterized by removing fine particles having a mean length of at most 0.18 mm and a width of at most 0.05 mm from the non-wood pulp And / or methods to improve whiteness.   The method of claim 1, wherein the average length of the particles is at most 0.10 mm and the width is at most 0.04 mm.   The method of claim 2, wherein the particle shape is a flake-like shape.   4. The method of claim 3, wherein the ratio of the particle width to the particle length is equal to or greater than 1:10.   The method of claim 4, wherein the ratio is equal to or greater than 1: 5.   The method of claim 5, wherein the ratio is equal to or greater than 1: 2.   The method according to claim 1, wherein the amount of the fine particles to be removed is less than 8%, preferably less than 5% of the total pulp, calculated on the basis of dry pulp.   The particles to be removed are epidermal cells, parenchymal cells, silicate cells, vascular cell fragments, cork cells and / or corresponding non-fibrous cells and / or parts of these cells or of these cells and / or cell parts The method of claim 1, consisting primarily of combinations.   The method according to claim 1, wherein the fine particles are removed by a method based on filtration, sieving, classification or mass difference.   10. The method according to claim 9, wherein the sieving method is used and the opening of the used sieve is in the range of 180 to 40 [mu] m, preferably in the range of 100 to 40 [mu] m.   The method of claim 1, wherein the fine particles are removed from the pulp raw material before or after pulp manufacture.   The method of claim 1, wherein the non-wood pulp is a pulp made from a stalked gramineous plant.   The method of claim 1, wherein the non-wood pulp is pulp made from agricultural waste.   14. The method of claim 12 or 13, wherein the non-wood pulp is straw pulp.