FI123344B - A method for bleaching a fibrous material - Google Patents

Abstract

The invention relates to a method for bleaching a material that comprises fibres made of a cellulose-containing raw material, in which method the fibres are treated with a bleaching solution that contains a peracid.

Description

FIELD OF THE INVENTION The present invention relates to a process for bleaching a fibrous material comprising cellulose-based conversion fibers and modified conversion fibers.

BACKGROUND OF THE INVENTION Transformation fibers, also called regenerated fibers, can be made by chemical process from naturally occurring high molecular weight raw materials such as cellulose. Such cellulose-based conversion fibers, i.e. cellulosic conversion fibers, include, for example, viscose, modal, cupro, carbamate, biocelsol and lyocell fibers. The conversion fibers can also be further modified, for example, by chemical treatments. For example, specialty fibers having various functional properties such as flame retardant properties, electrical conductivity, or antibacterial properties can be obtained by customization. Such modified synthetic fibers (specialty fibers) include, for example, cellulose-based hybrid fibers, such as silicate-containing viscose fibers, which are poorly or not at all flammable.

Conventionally, fiber manufacture also includes post-treatment steps, such as bleaching, for example to increase the brightness of the fiber or to improve its stability. Bleaching is accomplished by either removing or bleaching the chromophoric compounds of the fiber. One way to bleach various textile fibers, such as cellulose-based conversion fibers, is by bleaching with oxygen peroxide (H 2 O 2). Such a method is disclosed, for example, in US 5071439.

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BRIEF SUMMARY OF THE INVENTION The object of the present invention is to provide an improved process for bleaching fibrous material comprising cellulosic conversion fibers. It is an object of the invention to provide a bleaching process in which cellulose conversion fibers made from a plurality of cellulosic raw materials can be used. A further object of the invention is to improve the fiber material

Quality, such as lightness, while retaining functional properties such as strength and / or flame retardancy of the cellulosic conversion fiber.

To accomplish this, the process 5 according to the invention is essentially characterized in that the fibrous material comprising a cellulosic conversion fiber made from an atypical cellulosic raw material is bleached by a process using a bleach solution containing peracid. Atypical cellulosic raw materials include, for example, natural fiber-containing biomasses and / or cellulosic materials such as so-called "cellulose". 10 paper pulp. These atypical raw materials differ from soluble pulp, which is, for example, a typical raw material for the viscose process. Atypical raw materials generally contain impurities such as lignin residues, high hemicellulose content and / or other impurities. They may also have lower brightness, higher molecular weight, broader molecular weight distribution, better viscosity dispersion at mouth, or they may be more cost effective.

The dependent claims disclose some preferred embodiments of the process of the invention.

The atypical feedstock may be a cellulosic feedstock that has a high hemicellulose content and / or other impurities and has been treated, for example, with an alkali solution treatment and / or enzymes. The treatment may also be carried out by another method which improves the suitability of the raw material for the production of cellulosic conversion fibers. The treatment can be carried out either as a separate treatment step before or during the manufacture of the cellulosic conversion fiber.

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Cellulose-based conversion fibers to be bleached by the process of the invention may be ionic solvent-based fibers, viscose fibers, modal fibers, carbamate fibers or Q_ fibers produced by enzymatic treatment, such as so-called. biocelsolkuituja. Cellulose-based conversion fibers may also be modified synthetic fibers (specialty fibers), such as cellulose-based

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those hybrid fibers containing silicate, δ

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The bleaching solution of the invention may contain, for example, one of the following peracids: peracetic acid, permic acid or perric acid (Caron 3 acid). The concentration of peracid in the bleaching solution may range from 0.06 to 2000 mmol / l. The bleaching solution may additionally contain 2,2'-bipyridine. The bleaching solution may also contain transition metal chelators and / or other stabilizers compatible with peracids. The bleaching solution may have a pH in the range of from 1 to 11, preferably from 5 to 11, most preferably from 5 to 7. The temperature of the bleaching solution may range from 20 to 100 ° C, preferably from 50 to 70 ° C.

The pH of the fibrous material to be treated prior to bleaching may be in the range of 1-14, preferably 7-14, most preferably 8-9.

The bleaching process of the invention can be carried out in a continuous process.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described with reference to the accompanying drawing, which is a diagram illustrating an embodiment of the method of the invention.

Detailed Description of the Invention

It has been found in the invention that cellulosic conversion fibers made from atypical raw materials and the fibrous material comprising them have the problem of insufficient bleaching efficiency of conventional hydrogen peroxide bleaching. In addition, the invention has found that the problem of hydrogen peroxide bleaching of such cellulosic conversion fibers and specialty cellulose-based fibers is the loss of fiber properties during the bleaching process. For example, the strength of viscose fibers made from atypical raw materials for textile use is diminished in hydrogen peroxide bleaching. In addition, silicate-containing synthetic fibers, such as viscose fibers, have a problem with silicate

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solubilization of fibers during bleaching treatment under hydrogen peroxide bleaching conditions under op-g conditions. The dissolution of the silicate is shown in e.g. fiber inferior

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a fire. The bleaching process according to the invention can be used to bleach various fibrous materials, in particular fibrous material comprising cellulose conversion fibers. Such cellulose conversion fibers include, for example, viscose, modal and carbamate fibers. The method is also suitable for bleaching fibers, such as biocelsol fibers, by processes based on N-4 methylmorpholine oxide or other ionic solvents or by enzymatic treatment.

Soluble pulp may be used as a raw material for cellulosic conversion fibers. Soluble pulp is characterized by so-called. low viscosity, high brightness, and low levels of impurities, such as residual lignin, hemicellulose, pitch and resin, compared to paper pulp.

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The process according to the invention is most advantageous when it is used for bleaching of modified fibers which have been used as raw material from biomass containing natural fibers and / or from pulps such as so-called pulp. paper pulp. Such raw materials may also be referred to as atypical raw materials or atypical cellulosic raw materials such as, for example, atypical raw materials for the viscose process. Natural fibers may be derived, for example, from hardwoods and / or conifers, sugarcane bagasse, straw, other agricultural by-products of fiber, reeds such as lake reed, reed, bamboo or other useful biomass sources. Such atypical raw materials generally contain impurities, a higher soluble cellulose hemicellulose content, a wider molar mass distribution and a higher viscosity dispersion. For example, the R18% alkali resistance of atypical raw materials may be less than 93%. By R18, here is meant the 18% undiluted fraction of Liu-25 in 18% NaOH pulp solution at + 20 ° C. For example, the viscosity may be greater than 900 ^ kg / dm3.

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o Atypical cellulosic raw materials may be pretreated, for example, with a cv alkaline solution treatment prior to the raw material being subjected to a process for producing cellulosic synthetic fibers, such as viscose. Alkali-

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the solution treatment can be carried out either in a separate step before the production of the cellulose-g-containing conversion fiber or in the manufacture of the conversion fiber.

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^ at. The atypical raw material may also be treated with enzymes or other methods that improve the suitability of the raw material for the production of cellulose-based conversion fibers. For example, the treatment can remove impurities from the raw material, increase the alpha cellulose content of the raw material 5 and / or reduce the hemicellulose content. Pulp pulps may be pulps made by chemical manufacturing processes known as raw materials for papermaking, such as sulphate cellulose and / or sulphite cellulose. If bleached pulp is used as a raw material, it may be, for example, ECF (ele-5 mental chlorine free) or TCF (total chlorine free) pulp. Mixtures of two or more different cellulose-containing raw materials may also be used as a raw material for a fibrous material comprising a cellulosic conversion fiber.

Atypical raw materials that have been pretreated prior to the process of making the fibrous fiber typically contain chromophoric compounds that cannot be removed efficiently under the optimum conditions of hydrogen peroxide bleaching. These hydrogen peroxide bleach resistant (chromophore) compounds can be formed, for example, from impurities in the cellulosic material during the pre-treatment and / or the alkali treatment (mercerization) step. Therefore, the use of such atypical raw materials can lead to low brightness of the fiber material and thus also cause a significant quality problem. The low brightness of the fibrous material may also be due to the lower brightness level of the paper pulp than the soluble pulp.

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The bleaching process is also particularly suitable for bleaching modified synthetic fibers, such as specialty alkali-stable fibers. Such fibers include cellulose-based hybrid fibers, for example, silicate-containing conversion fibers, such as silicate-containing viscose, modal and carbamate fibers, and those based on ionic solvents or prepared by enzyme treatment. Silicate-containing viscose fibers are cellulosic products made by a viscose process.

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Silica hybrid fibers with added water glass during the manufacture of the viscose fiber to provide flame retardant properties, i.e., the fibers are poorly or non-flammable. Such fibers may also be referred to as mo-nic component products or fibers. The amount of silica (SiO 2) may be in the range of 5 to 50% by weight and preferably about 20 to 40% by weight based on the dry weight of the fiber. For example, shaping can be accomplished with agents added prior to regeneration, such as water glass, which provide the fiber with a flame retardant property.

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In addition to bleaching the fibrous material, the process of the invention can also be used to bleach other regenerated cellulose-based products, such as films, granules or other solids, which are manufactured using atypical cellulosic feedstock. Also, these products may be further chemically modified, for example to provide flame retardant properties.

Bleaching of the fiber material, which is one of the post-treatment steps of fiber preparation, can be carried out after spinning the fibers. Figure 1 shows a 10 diagram of viscose spinning and fiber production. The manufacture of the fibrous material begins by preparing a multi-component solution 2 mixed with a base solution of silica and a viscose which is dissolved, and preferably after maturation and filtration. The production continues either from route A to filaments, or continuous fiber, or from route B to staple fibers. For example, the multicomponent solution 2 may be pressed through a die into one or more fibers in a spinning bath 4.25 in an acidic regeneration solution, i.e. a spinning solution used as a spinning bath, whereby, for example, solid silica-containing cellulose fibers are formed. The nozzle may be selected such that it is also possible to manufacture films or other multi-component components. The solidification of the fibers or other products is then carried out automatically so that the acidic regeneration solution is immediately at the outlet of the nozzle. The products formed in the spinning bath, most preferably filament fibers, are collected through a die around the drawing rolls and drawn 27. By stretching, the strength of the fibers 25 can be increased. The fibers can also be washed at or after the draw 6. In the manufacture of staple fibers, the fibers are cut to the desired length after 29 draws.

Next, the fibers are bleached at 8.31 using the bleaching process of the invention.

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o method. Prior to bleaching, the pH of the fibrous material is adjusted to the desired value. After bleaching, the fibers can also be treated with various finishing agents 30, followed by drying at 10.35 and collecting, for example,

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in blades 12 or staple fibers 37.

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In the fiber bleaching process of the invention, peracid such as peracetic acid (CH3COOOH) is used as the bleaching chemical in the bleaching solution. Other peracids, such as permic acid or perric acid (Caron 7 acid), also give the same result. The concentration of peracid such as peracetic acid in the bleaching solution may be, for example, 0.06-2000 mmol / l.

The bleaching solution may contain distilled peracetic acid or an equilibrium mixture of peracetic acid containing hydrogen peroxide and acetic acid. Peracetic acid used as a bleaching chemical can also be prepared enzymatically or by means of Activators chemicals such as tetraacetyl ethylenediamine (TAED) or Pentaacetylglucose, or hydrogen peroxide and acetic anhydride in situ. The bleaching can also be carried out, for example, as 2,2'-bipyr-10 din-catalyzed peracetic acid bleaching. In addition, peracetic acid-containing bleaching solution may use stabilizing agents compatible with peracids, such as transition metal chelators or other stabilizers. The bleaching solution may contain, for example, chelators of transition metal ions that catalyze the decomposition of peracetic acid and hydrogen peroxide and / or other stabilizers such as tetrasodium pyrophosphate or a preparation containing aspartic acid diethoxysuccinate (AES). The chelating agents may also be added in a separate pre-chelating step prior to the actual bleaching treatment.

In the process of the invention, the pH of the bleaching solution may be between 1 and 11. Preferably, the pH of the solution is between 2 and 11, most preferably between 5 and 7. For example, the pH of the solution may be in the range of 5.0 to 5.5. The temperature of the bleaching solution may be, for example, between 20 and 100 ° C, preferably between 50 and 70 ° C.

The fiber bleaching end result may also be affected by one or more of the following parameters: a fiber mat such as a fiber mat consisting of a plurality of individual ™ fibers, e.g.

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9 suspension, at pH before bleaching, by bleaching solution peracid concentration or by interaction of hydrogen peroxide and peracid concentrations, fiber temperature of material before bleaching, bleaching residence time, bleaching

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the amount of chelating agent o 0 S and / or the stabilizer. For example, the pH of the fibers to be treated, such as the fibrous non-fibrous fiber, prior to bleaching may be in the range of 1 to 14, preferably 7 to 14, and most preferably 8 to 9. The pH of the fiber material to be treated can be adjusted to the target value, for example, with sodium hydroxide or 8 sodium carbonate. For example, the peracetic acid content of the bleaching solution may be about 6 mmol / l. The non-fibrous temperature may be, for example, about 80 ° C.

The bleaching method of the invention has the advantage, for example over hydrogen peroxy-5 bleaching, that without reducing the bleaching efficiency of the solution, the pH and temperature of the solution can be adjusted to maintain the fiber strength and functionality, such as flame retardant property, at the desired level. It has been found that under optimal bleaching conditions, such as in the neutral pH range, peracetic acid does not react with the carbohydrate structures of the fibers. In addition, according to the method, the bleached fiber has no significant need for neutralization, such as neutralization after hydrogen peroxide bleaching with organic acid. Thus, the method can also provide cost savings.

The overall cost savings can also be achieved by the process being able to produce high quality synthetic fibers, such as viscose fibers, from atypical raw materials with substantially lower raw material costs than, for example, soluble pulp.

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The method of the invention can enhance the bleaching of the fiber material and improve the brightness level of the fiber material. The brightness of the fibrous material, which can be measured, for example, as a ClE whiteness in IS011475 or an ISO brightness in accordance with ISO3688 / ISO2470, can increase by up to 25 to 10% units relative to the lightness of fiber obtained by conventional hydrogen peroxide bleaching.

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o The bleaching process of the invention can effectively destroy the hydrogen peroxide bleach resistant chromophoric compounds formed on the viscose fiber, for example. This may be due, for example, to the hydrogenation of peracids

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higher oxidation potential of peroxide or, under optimal bleaching conditions, the interaction of nucleophilic and electro-trophic peracids in the bleaching solution, δ

Door 35 The process also has the advantage of minimizing fiber damage during processing, whereby the fiber strength can be retained or even increased compared to the processing of the corresponding product in the optimum hydrogen peroxide bleaching process.

For example, a viscose fiber made from a non-abrasive raw material for the viscose process, such as paper pulp, is characterized by lower tensile strength compared to fiber made from soluble pulp. This may be due, for example, to a wider range of molecular weight distribution, higher viscosity dispersion or higher fiber-cellulose content, which is normally acceptable for a conventional use of a paper pulp. The lower tensile strength may also be due to the high particle content of the viscous cellulose xanthogenate solution, which impedes spinning of the fiber, and to the unfavorable particle size distribution. For example, by using a bleaching solution containing peracid, it is possible to reduce or prevent the degradation of the carbohydrate structures of the fibers and thus maintain sufficient fiber tensile strength. Non-selective bleaching such as hydrogen peroxide bleaching has been found to destroy the carbohydrate structures of the fibers.

The process bleaching can also reduce the residual sulfur content of the fibers, for example, in the manufacture of viscose fibers.

A further advantage of the process is the reduced swelling of the fibrous material compared to the H 2 O 2 bleaching, which results in a better wetting of the fibrous material and thus a more efficient interaction of the bleaching chemical with the fiber.

A further advantage of the bleaching process according to the invention is that, for example

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9 the solubility of the silicate in the modified synthetic fibers, such as the silicate-containing viscose fiber, is substantially prevented or reduced, thereby maintaining the functionality of the fiber, i.e., the flame retardant properties.

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00 § By limiting the solubility of silicate from fibers to bleaching solution can be

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also reduces the accumulation of precipitates in the bleaching cycle. The silicate load on waste water can also be reduced. This also contributes to the overall cost savings of Method 35.

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The bleaching process of the invention can be implemented with minor modifications to existing bleaching equipment. It can also easily be applied to existing converting fiber plants using the hydrogen peroxide bleaching process. Bleaching can also be carried out in 5 continuous processes. For example, the bleaching reaction time in a continuous process is about 4 minutes.

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Claims (12)

1. A process for bleaching fibrous materials comprising cellulose regenerate fiber made from atypical cellulose-containing raw material consisting of natural fibers containing biomass or cellulose pulp and not other than dissolving pulp, preferably such raw material whose alkali resistance R a bleaching solution containing peracid. 10 Process according to claim 1, characterized in that the atypical cellulose-containing raw material is a raw material with a high hemicellulose content and / or with other impurities, which is pretreated with alkali solution treatment and / or with the enzymes prior to the production of the cellulose regenerate fiber. 15 3. A process according to claim 1 or 2, characterized in that the cellulose regenerate fibers are fibers based on ionic solvents, fibers made with an enzyme treatment process, viscose, modal or carbamate fibers. 20 Process according to any of the preceding claims, characterized in that the cellulose regenerate fibers contain silicate. Process according to any of the preceding claims, characterized in that the bleaching solution contains at least one of the following acids: peracetic acid, peracetic acid or peracetic acid. CO δ A method according to any of the preceding claims, characterized in that the bleaching solution contains 2,2'-bipyridine. o CO g 30 Process according to any of the preceding claims, characterized by CL that the bleaching solution contains transition metals chelating agents cg and / or other stabilizers which are compatible with peracids. m ° 8. A process according to any of the preceding claims, characterized in that the peracid content is 0.06-2000 mmol / l. Process according to any of the preceding claims, characterized in that the pH of the bleaching solution is between 1 and 11, preferably between 2 and 11, preferably between 5 and 7. Process according to any of the preceding claims, characterized in that the pH of the fibrous material to be treated before bleaching is between 1 and 14, preferably between 7 and 14, preferably between 8 and 9. Process according to any of the preceding claims, characterized in that the temperature of the bleaching solution is between 20 and 100 ° C, preferably between 50 and 70 ° C. Process according to any of the preceding claims, characterized in that the bleaching is carried out in a continuous process. 15 CO δ c \ j i δ i o CO X cc CL CO CD CD LO δ C \ l