ES2622567T3 - Procedure for the production of a cellulosic molded body - Google Patents

Abstract

Process for the production of a cellulosic molded body according to the viscose process by forming a spinning mass containing cellulose xanthogenate, characterized in that xylan is added to the cellulose xanthogenate in a percentage of at least 1% by weight , based on cellulose, preferably from 1% by weight to 20% by weight, especially preferably from 3% by weight to 15% by weight.

Description

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DESCRIPTION

Procedure for the production of a cellulosic molded body

The invention relates to a process for the production of cellulosic molded bodies according to the viscose process.

In particular, the invention relates to the production of fibers and filaments.

The production of viscose fibers according to the viscose process comprises the following steps

alkalize a cellulose starting material, in particular paste (macerated dough, matured dough)

convert the starting material of alkaline cellulose ("alkaline cellulose") into cellulose xanthogenate

dissolve the cellulose xanthogenate with alkali, obtaining the so-called viscose as spinning dough

if necessary add viscous modifying agents for the production of spinning dough for modal fibers

spin the viscose to give endless molded bodies

regenerate cellulose in a precipitation bath from the endless molded bodies subsequently treat as well as dry

if necessary cut the endless molded bodies to give cut fibers.

The fibers produced with this procedure are known by the generic term of (conventional) fibers and modal fibers. The modal procedure differs from the conventional procedure by a modified composition of the dough for spinning, additional modifying agents for spinning and a composition of the modified spinning bath.

The paste used in the viscose process has to meet certain criteria, to enable corresponding fiber qualities.

The paste used in the viscose process has an alpha-cellulose content of more than 90% and has only reduced percentages of secondary compounds, such as xylan and other hemicelluloses (such as, for example, mannan). These compounds degrade and are removed by dissolution for the most part during the alkalization of the paste at the beginning of the viscose process (Figure 1). The hemicelluloses that remain in the pulp are depolymerized in the matured mass together with the cellulose and therefore have a much lower average molecular weight than in the starting pulp. This is valid both for the use of chemical pastes and for the use of paper pulps.

Figure 2 explains the clearly lower molecular weight of the hemicelluloses, which are incorporated with the paste in the viscose process and then experience degradation in macerated mass and matured mass. In contrast to this, the molar mass distributions of hemicelluloses are represented, which were extracted from a pulp of wood of comifers and one of hardwood of wood without degradation.

WO 95/00698 describes a process, in which during the production of Kraft pulp, first a considerable percentage of hemicellulose is removed from the production stream and at a later stage it is again deposited in the pulp.

From US 7,390,566 B2 as well as from WO 2007/128026 it is known to use pulp with a relatively high percentage of xylan for the production of viscose fibers. The use of hemicellulose-rich raisin for the production of Lyocell fibers is known from WO 99/47733 A1 as well as WO 01/88236 A2.

WO 2005/118950 describes the separation of beta-cellulose from a bleach that is produced by pressing after hot or hot alkaline extraction (CCE, HCE) of a paste.

There is still a need to increase the performance of the viscose process with a constant quality of the final products. There is also a need to make available novel viscose fibers with modified properties, in particular an increased absorption capacity.

The objective of the present invention is achieved in one aspect by means of a process for the production of a cellulosic molded body according to the viscose process by forming a spinning mass containing cellulose xanthogenate, characterized in that cellulose xanthogenate Xylan is added in a percentage of at least 1% by weight, with respect to cellulose, preferably from 1% by weight to 20% by weight, especially preferably from 3% by weight to 15% by weight.

viscose viscous dough

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In a further aspect the invention relates to a cellulosic molded body obtained according to the viscose process with a percentage of high molecular weight xylan with an average degree of polymerization (DP) of from 75 to 350, preferably from 110 to 220, at least 0.5% by weight with respect to cellulose, preferably from 2% by weight to 8% by weight.

Brief description of the figures

Figure 1 shows the degradation in low molecular weight components in the viscose process.

Figure 2 shows the molar mass distributions of high molecular weight hemicelluloses from pastes as well as degraded hemicellulose from the macerated mass in the viscose process.

Figure 3 shows fiber resistance of viscose fibers with an increased content of high molecular weight xylan compared to a conventional fiber without additional xylan addition.

Figure 4 shows the development of water retention capacity (ARC) of viscose fibers by the addition of high molecular weight xylan in the solution solution.

Figure 5 shows the distribution of molar masses of precipitated xylan after a CCE treatment of a Kraft eucalyptus raisin and the distribution of molar masses of a viscose fiber after the addition of this high molecular weight xylan.

Figure 6 shows the distribution of molar masses of a viscose fiber with a percentage of 4.8% high molecular weight xylan and its distribution of molar masses after the computational elimination of the percentage of high molecular weight xylan.

Detailed description of the invention

As long as the opposite is not indicated, the data in percentages means in each case data in percentage by weight.

It was surprisingly found that with an addition of xylan to cellulose xanthogenate in the viscose process, an increase in production yield with constant or even improved properties of the resulting cellulose molded bodies can be achieved.

Unlike the state of the art, in which the xylans contained in the pulp are removed by dissolution for the most part during the alkalization of the pulp and are produced as a waste product, according to the invention the xylan is added to the cellulose xanthogenate . In the following stages of the viscose process (spinning, regeneration, etc.), no degradation or elimination by substantial dissolution of the xylan takes place, so that it is mostly conserved in the generated molded body.

Preferably, according to the invention, the xylan is added in the form of an alkaline solution. The alkaline solution may have a ratio of xylan from 1 to 60 g / l.

In particular, xylan can be added to cellulose xanthogenate as a component of an alkaline solution.

During the dissolution of the cellulose xanthogenate for the production of the spinning solution, an alkaline solution bleach is known. In this, the xylan to be added may be contained according to the preferred embodiment of the present invention.

Especially preferably, the xylan comes from a press bleach that is produced during the pressing of alkaline paste at the beginning of the viscose process. In particular, cellulose xanthogenate can be added to the press bleach produced during the pressing of alkalized pulp.

As mentioned at the beginning, at the beginning of the viscose process the paste is alkalized. An alkaline press bleach is produced during pressing of the alkalized paste, which contains a high percentage of xylan removed by dissolving the paste by alkalization.

If this press bleach is now used as a solution bleach to dissolve the cellulose xanthogenate, then the previously removed xylan is dissolved by dissolving the paste back to the process and its yield is therefore increased.

This xylan has a relatively low molecular weight. The person skilled in the art expects that a low molecular weight xylan addition would have a negative influence on the strength properties of the resulting fiber. However, it has been shown that the addition of low molecular weight xylan does not negatively influence the strength of the fibers and therefore an increase in yield with constant strength properties is possible.

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According to a particularly preferred embodiment of the process according to the invention, at least a part of the xylan added is a high molecular weight xylan with an average degree of polymerization (DP) of from 75 to 350, preferably from 110 to 220.

As already mentioned, the xylan originating in the embodiment described above from the pressing alkali of the paste alkalization in the viscose process is due to the degradation during the comparatively low molecular weight alkalization (see figure 2). It has been shown that viscose fibers, which are obtained by the addition of such low molecular weight xylan, in terms of their properties such as strength and extension, do not lie behind conventional viscose fibers.

Surprisingly, it has been shown that during the addition of high molecular weight xylan to cellulose xanthogenate, comparable resistance values and additionally an increased water retention capacity are obtained as well as an improved stability of the xylan content with respect to additional process steps .

In this regard, high molecular weight xylan is also added in a percentage of from 1% to 20%, preferably from 3% to 15%, with respect to cellulose.

The high molecular weight xylan can preferably come from a stream of hemicellulose-rich substance that is produced in the course of an extraction stage during the production of a paste.

Procedures are known for the extraction of pastes in the course of their production, such as an alkaline pre-extraction directly from wood chips before a wood disintegration or an alkaline extraction in fno (CCE). Non-alkaline procedures for the extraction with complexing agents such as nitrenes or organic solvents such as for example DMSO are also presented in the literature. Unlike the alkalization of the paste (finished) at the beginning of the viscose process, in these extraction procedures the xylan is removed by dissolving the paste, but it does not degrade substantially.

If the press bleach obtained by pressing the paste after extraction is concentrated by corresponding procedures, for example membrane filtration as in WO 2005/118050, then a stream of substance with a high percentage is generated in this respect of high molecular weight xylan. This bleach can be added, for example, directly as a solution bleach or as part thereof to cellulose xanthogenate.

This means in particular in an integrated viscose unit, in which the starting paste is produced for the viscose process itself, an increase in yield, because xylan, which is otherwise produced as waste stream, is supplied back to the procedure.

The present invention also relates to a cellulosic molded body obtained according to the viscose process with a high molecular weight xylan percentage with an average degree of polymerization (DP) of from 75 to 350, preferably from 110 to 220, of at minus 0.5% with respect to cellulose, preferably from 2% to 8%.

The molded body according to the invention is new, since (without the planned addition according to the invention of high molecular weight xylan to cellulose xanthogenate) in the conventional viscose process due to degradation as well as removal by dissolution of xylan and There is no high molecular weight xylan content in the generated molded body.

The cellulosic molded body according to the invention is preferably in the form of a fiber, for example cut fiber or filamentous fiber.

The invention also relates to the use of the cellulosic molded body according to the invention in products with absorbent power.

Examples

The invention will be explained in more detail by the following examples:

Until the production of cellulose xanthogenate, the production process follows the conventional viscose procedure. According to the invention, as a solution bleach a pure bleach is used, which was enriched with xylan or a bleach that already contains xylan.

The lye may contain low molecular weight and / or high molecular weight xylanes.

When a bleach with only low molecular weight xylanes is used, the bleach can be added together with a solution water used if necessary.

In the case of a bleach with high molecular weight xylanes, in order to avoid a precipitation of the xylanes, this must first be added to the cellulose xanthogenate and a possible addition of water from

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dissolution.

In the following examples 2 to 6 a ^ a containing high molecular weight xylanes was used.

To obtain the high molecular weight xylan rich bleach used in these examples, a eucalyptus wood pulp was treated, which was produced according to the Kraft procedure, 30 min with NaOH 90 g / l and a substance density of 10 %. The bleach that was produced was used without alteration and after an enrichment process for example by means of membrane filtration, as a solution.

The solution solution contains between 1 and 66 g / l of dissolved xylan. The xylan was poured after xanthogenization with the alkaline solution solution to the xanthogenate and mixed homogeneously. Xylan had the following molecular weight distribution:

 Mw Mn PDI DP

 kg / mol kg / mol

 xylan

 22 13 1.7 167

Table 1: Molecular weight of xylan used from a CCE bleach

Figure 2 shows the distribution of molecular weights of high molecular weight xylan, as produced from a CCE bleach of wood pulp from wood or hardwood. It can be clearly recognized that the xylan, which is obtained after the application of a CCE stage, has a molecular weight much greater than the xylene already degraded in the macerated mass of the viscose process.

The xylan was added to the xanthogenate from a conventional beech sulphite paste and therefore it is not present during the sulfuration, but not until the next procedure step, the dissolution of the xanthogenate. Therefore, xylan is not xanthogenated, but dissolved in NaOH. The fibers are spun in the laboratory. Thus fibers with a clearly higher content of xylan were produced (see table 2 below).

Example 1 (comparative example):

A paste (beech sulphite paste) was mixed with approximately 18% NaOH, pressed and matured at approximately 34 ° C over 19 hours. A spinning mass was produced with the basic composition of 32% of CS2, 8.6 to 8.9% cellulose and 5.2 to 5.6% alkali. The test was repeated with the same distribution (examples 1-1 or 1-2).

The solution solution contains 0% xylan. The spinning mass thus obtained is yarn in the conventional manner to give fibers with the properties shown in Table 2, example 1. The xylan (of low molecular weight) present in the 0.6 or 0.7% fibers proceeds of the paste used.

Example 2

To a xanthogenate according to example 1, a solution solution with 8.5 g / l of high molecular weight xylan was added. The spinning mass thus obtained is fused to give fibers with the properties shown in Table 2, example 2. The absorption of xylan amounted to 63% of the high molecular weight xylan present in the solution solution, which corresponds to a percentage of high molecular weight xylan of 0.7% with respect to fiber.

Example 3

To a xanthogenate according to example 1 was added a solution solution with 22.0 g / l of high molecular weight xylan. The spinning mass thus obtained was fused to give fibers with the properties shown in Table 2, example 3. The absorption of xylan amounted to 79.2% of the high molecular weight xylan present in the solution solution, which corresponds to a percentage of high molecular weight xylan of 2.7% with respect to fiber.

Example 4

To a xanthogenate according to Example 1, a solution solution with 39.0 g / l of high molecular weight xylan was added. The spinning mass thus obtained is fused to give fibers with the properties shown in Table 2, example 4. The absorption of xylan amounted to 77.2% of the high molecular weight xylan present in the solution solution, which corresponds to a high molecular weight xylan percentage of 4.8% with respect to fiber.

To determine the high molecular weight xylan in the fiber, the molar mass distributions of the xylan enriched fiber and the CCE xylan used by means of molecular exclusion chromatography were determined (Figure 5). In the area of the xylan peak, a highlight can be clearly recognized in the fiber, which allows to deduce an enrichment of the xylan added in the fiber. When this percentage of xylan is subtracted computationally, a curve of a conventional viscose fiber is obtained, which is depicted in Figure 6. In this regard, the

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Xylan content indicated in Figures 5 and 6 of 5.5% refers to the total content of xylan in the fiber (ie xylan of the paste used plus the high molecular weight xylan added).

Example 5

To a xanthogenate according to example 1 was added a solution solution with 31.7 g / l of xylan. The spinning mass thus obtained is fused to give fibers with the properties shown in Table 2, example 5. The absorption of xylan amounted to 60.2% of the high molecular weight xylan present in the solution solution, which corresponds to a percentage of high molecular weight xylan of 6.9% with respect to fiber.

Example 6

To a xanthogenate according to example 1 was added a solution solution with 66.3 g / l of xylan. The spinning dough thus obtained is yarn to give fibers. The absorption of xylan amounted to 54.4% of the high molecular weight xylan present in the solution, which corresponds to a percentage of high molecular weight xylan of 10.0% with respect to the fiber.

In this example the solution bleach containing the xylan to the cellulose xanthogenate was added together with dissolution water. Evidently conditioned by this there was a partial precipitation of the xylan in the spinning mass, so that the quality of the spinning solution (filter value, etc.) as well as that of the spun fibers remained behind that of the Examples 2 to 5.

Example 7 (comparative example)

In a pilot installation, the same beech sulphite paste was used for the production of viscose fibers. After mashing the paste, a press bleach enriched with low molecular weight xylan was obtained by pressing. This bleach was subjected to nanofiltration. The nanofiltration permeate, which only has a reduced content of low molecular weight xylan, was then used as a solution solution in the pilot installation.

Due to the reduced amount of 0.38% xylan with respect to cellulose in the spinning mass and its low molecular weight, no additional xylan precipitate on the viscose fiber. The xylan content of the spun fiber was 0.5%. This xylan comes from the paste used.

Example 8

In a pilot installation, the same beech sulphite paste was used for the production of viscose fibers. As a solution solution, the low molecular weight xylan-rich retention of the nanofiltration described in example 7 was used.

The amount of xylan in the spinning mass amounted to 5.67% with respect to cellulose. Of this, 30.0% of the fiber is thread. A fiber with 2.2% xylan was obtained.

Test methods

Determination of sugar in fiber:

After a two-stage total hydrolysis with H2SO4 sulfuric acid, the sugar monomers were determined by means of anion exchange chromatography (AEC) with a pulsed amperometric detector (PAD). The method was described in the following publication: Sixta H, Schelosky N, Milacher W, Baldinger T, Roder T (2001) Characterization of alkali-soluble pulp fractions by chromatography. Proceedings of the 11th ISWPC, Nice, France: 655-658.

Determination of the molecular weight distribution in the fiber:

The molecular weight distribution in the fibers was determined by means of molecular exclusion chromatography (SEC). The samples were dissolved in DMAc-LiCl (dimethylacetamide / lithium chloride). A MALLS detector (multi-angle laser light scattering, multiple angle laser light scattering) was used. Additional details were published by Schelosky N, Roder T, Baldinger T (1999), Molmassenverteilung cellulosischer Produkte mittels GroUenausschlusschromatographie in DMAc / LiCl, Das Papier 53, 12: 728-738.

Determination of the molecular weight distribution of high molecular weight xylan added:

The xylan was precipitated from the CCE bleach under acidic conditions, analogously to the conventional Tappi T 203 om-93: 1993 method for the determination of the beta and gamma fraction. Thereafter, it was continued as for the determination of the molecular weight distribution of fibers with the SEC method.

List of abbreviations:

CCE cold caustic extraction, alkaline refining at fno

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CS2 carbon disulfide

DP degree of polymerization, polymerization degree MW molecular weight

Mw weight average molecular weight

Mn number average molecular weight

SEC size exclusion chromatography, molecular exclusion chromatography

CRA water retention capacity PDI polydispersity index Mw / Mn

The properties of the viscose spinning masses obtained in each case as well as the fibers obtained according to examples 2 to 5 are summarized in the following table 2:

 Example

   1-1 1-2 2 3 4 5

 Filter value

   358 374 353 330 372 364

 Particles

 ppm 14.7 17.7 22.0 13.6 15.3 15.6

 Xylan in the solution

 g / l 0.0 0.0 8.5 22.0 39.0 31.7

 Xylan Absorption

 % 0.0 0.0 63.0 79.2 77.2 60.2

 Low molecular weight xylan in the fiber

 % od 0.6 0.7 0.7 0.7 0.7 0.7

 High molecular weight xylan in the fiber

 % od 0 0 0.7 2.7 4.8 6.9

 Total Xylan in the fiber

 % od 0.6 0.7 1.4 3.4 5.5 7.5

 Molecular weight distribution of viscose fiber: Average in number Mn

 kg / mol 26.5 28.5 29.3 27.6 27.5 26.6

 Average in weight Mw

 kg / mol 63 65 66 66 63 61.5

 PDI polydispersity index (Mw / Mn)

 - 2.4 3.3 2.2 2.4 2.3 2.3

 Weight percentage of polymers

 % 5.6 5.0 4.8 5.2 5.1 5.6

 with DP <50

 Weight percentage of polymers

 % 11.7 11.7 11.5 12.8 13.0 13.8

 with DP <100

 Title

 dtex 1.30 1.29 1.34 1.37 1.34 1.34

 Conditional resistance, 60% of

 cN / tex 26.0 25.0 26.5 24.8 24.8 23.8

 stretching

 Conditioned extension, 60% of

 % 17.8 17.7 16.0 18.0 16.6 15.5

 stretching

 Working capacity

 % cN / tex 465 443 424 447 412 370

 CRA water retention capacity

 % 90.0 92.4 94.5 95.6 98.5 97.1

Table 2: Properties of viscose fibers from beech sulphite pulp with spun xylan of a CCE stage as copolymer

The fibers absorbed the high molecular weight xylan in an unexpectedly high percentage. The absorption in the viscose fiber amounted to 63% to 79% of the xylan present in the solution. From the filter value and 15 of the number of particles, it is clear that the quality of the spinning mass and the processability are not affected at all by the addition of this copolymer.

Unlike this, xylan is degraded, which is only incorporated into the process with a chemical or paper pulp, and as a result it is eliminated in 63 to 80% during maceration and in the spinning bath (see the following table 3). The filter value and the particulate content of the viscose spinning mass (especially in the case of a high contribution of xylan from a paper pulp) are also clearly reduced.

 Pasta

 Xylan procedure in the paste [%] Filter value [-] Particle content [ppm] Xylan in the spinning / fiber mass [%] Loss of xylan [%]

 Chemical paste

 To beech sulphite 3.1 364 15.6 0.6 80.6

 Paper pulp

 Eucalyptus Kraft 22.1 8 671 8.1 63.3

 Paste of

 Kraft 19.8 69 118 7.3 63.1

 paper

 poplar

Table 3: Loss of xylan incorporated with the paste in the viscose process

Surprisingly it has been shown that the textile mechanical properties of the produced fibers remain practically constant (see Figure 3). In this regard, the xylan contents indicated in Figure 3 refer in turn to the total xylan content in the fiber (ie xylan from the paste used plus the 5 xylan added).

The water retention capacity CRA could also be clearly increased by incorporating xylan in the viscose fiber (see Table 2 and Figure 4). That is, water absorption and the ability to absorb water could not only be increased, but also adjusted in a directed manner through the fiber's xylan content. This is a completely new possibility, for example for use in products with absorbent power, to design product properties. The axis of the abscissa (xylan content) in Figure 4 again refers to the total xylan content in the fiber.

Figure 4 also shows the water retention capacity of the fiber produced according to example 6 (high molecular weight xylan content: 10.0%). This amounted to 106.0%.

The properties of the spinning masses obtained in each case as well as the fibers obtained according to 15 examples 7 and 8 are summarized in the following table 4:

 Example

   7 8

 Filter value

   389 401

 Particles

   4.5 5.0

 Total Xylan Absorption

 % 0 30.0

 Total Xylan in the fiber

 % od 0.5 2.2

 Molecular weight distribution of viscose fiber:

 Average in number Mn

 kg / mol 22.1 22.0

 Average in weight Mw

 kg / mol 60.1 66.7

 PDI polydispersity index (Mw / Mn)

 - 2.7 3.0

 Weight percentage of polymers with DP <50

 % 7.1 8.0

 Weight percentage of polymers with DP <100

 % 15.3 15.1

 Title

 dtex 1.40 1.45

 Conditioning resistance, 60% stretch

 cN / tex 26.8 25.8

 Conditioned extension, 60% stretch

 % 17.0 15.9

 Working capacity

 % cN / tex 455.6 410.2

Table 4. Properties of viscose fibers produced with the addition of xylan from viscose production

Claims (11)

10 fifteen twenty 25 30 1. Procedure for the production of a cellulosic molded body according to the viscose procedure by forming a spinning mass containing cellulose xanthogenate, characterized in that the cellulose xanthogenate is added by a percentage of at least 1% by weight, with respect to cellulose, preferably from 1% by weight to 20% by weight, especially preferably from 3% by weight to 15% by weight. 2. Method according to claim 1, characterized in that the xylan is added in the form of an alkaline solution. 3. Method according to claim 1 or 2, characterized in that the xylan is added to the cellulose xanthogenate as a component of an alkaline solution bleach. 4. Method according to one of claims 2 or 3, characterized in that the xylan comes from a press bleach that is produced during the pressing of alkalized paste at the beginning of the viscose process. 5. Method according to claim 4, characterized in that a pressurized bleach which is produced during the pressing of alkaline paste at the beginning of the viscose process is added to the cellulose xanthogenate. 6. Method according to one of claims 1 to 5, characterized in that at least a part of the xylan added is a high molecular weight xylan with an average degree of polymerization (DP) of from 75 up to 350, preferably from 110 to 220. 7. Method according to claim 6, characterized in that the high molecular weight xylan is added in a percentage of 1% by weight to 20% by weight, preferably from 3% by weight to 15% by weight, with Regarding cellulose. Method according to claim 6 or 7, characterized in that the high molecular weight xylan is derived from a stream of substance rich in hemicellulose that is produced during an extraction stage during the production of a paste. 9. Cellulosic molded body obtained according to the viscose process with a high molecular weight percentage of xylan with an average degree of polymerization (DP) from 75 to 350, preferably 110 to 220, at least 0.5% by weight with respect to cellulose, preferably from 2% by weight to 8% by weight. 10. Cellulosic molded body according to claim 9 in the form of a fiber. 11. Use of a cellulosic molded body according to one of claims 9 or 10 in products with absorbent power.