WO2014086883A1 - Method for producing a cellulosic molded body - Google Patents

Abstract

The invention relates to a method for producing a cellulosic molded body in accordance with the viscose method by shaping a spinning mass containing cellulose xanthate. The method is characterized in that xylan is added to the cellulose xanthate at a fraction of at least 1 wt%, with respect to cellulose, preferably 1 wt% to 20 wt%, especially preferably 3 wt% to 15 wt%. The invention further relates to cellulosic molded bodies, obtained in accordance with the viscose method, having a fraction of high-molecular-weight xylan having an average degree of polymerization (DP) of 75 to 350, preferably 110 to 220, of at least 0.5 wt%, preferably 2 wt% to 8 wt%.

Description

 Process for the preparation of a cellulosic molding

The invention relates to a process for producing cellulosic shaped bodies by the viscose process.

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

The production of viscose fibers by the viscose process comprises the following steps

 Alkalizing a cellulosic starting material, in particular pulp (mash, pre-maturity)

 • Reacting the alkalized cellulose starting material ("alkali cellulose")

 cellulose xanthate

 Dissolving the cellulose xanthate with alkali, whereby the so-called viscose is obtained as a dope

 Optionally, adding modifiers to the viscose to make dope for modal fibers

 Spinning the viscose into continuous shaped articles

 Regenerating the cellulose in a precipitation bath from the continuous moldings

 • After-treatment, as well as drying.

 If necessary, cutting the continuous tablets into staple fibers.

The fibers produced by this process are under the generic term

(Standard) viscose fibers and modal fibers known. The modal process differs from the standard viscose process by changing composition of the dope, additional modifiers in the dope and modified

Spinnbadzusammensetzung.

The pulp used in the viscose process must meet certain criteria to allow appropriate fiber qualities.

The pulp used in the viscose process has an alpha-cellulose content of greater than 90% and has only low levels of secondary compounds, such as xylan and others

Hemicelluloses (such as mannan). These compounds are for the most part degraded and leached out during the alkalization of the pulp at the beginning of the viscose process (FIG. 1). Hemicelluloses remaining in the pulp are depolymerized in pre-maturity together with the cellulose and therefore have a much lower content average molecular weight than in the starting pulp. This applies both to the use of chemical pulps and to the use of paper pulps.

In Figure 2, the significantly lower molecular weight of the hemicelluloses becomes clear, which are introduced with the pulp in the viscose process and then subject to degradation in mash and pre-maturity. In contrast, the molecular weights are represented by distributions of hemicelluloses extracted from a softwood and a hardwood pulp without degradation.

WO 95/00698 describes a process in which, during the production of Kraft pulp, initially a substantial amount of hemicellulose is removed from the production flow and is deposited again on the pulp in a later stage.

US Pat. No. 7,390,566 B2 and WO 2007/128026 disclose the use of pulp with a relatively high proportion of xylan for producing viscose fibers. The use of hemicellulose-rich pulp for the production of lyocell fibers is known from WO 99/47733 A1 and WO 01/88236 A2.

WO 2005/118950 describes the separation of beta-cellulose from lye obtained by pressing after a cold or hot alkaline extraction (CCE, HCE) of a pulp.

There is still a need to improve the yield of the viscose process

to increase the consistent quality of the end products. There is also a need for novel viscose fibers with modified properties, in particular elevated

To provide absorption capacity.

The object of the present invention is in one aspect by a method for producing a cellulosic molded body by the viscose method

Forming a spinning mass containing cellulose xanthate dissolved, which is characterized in that the cellulose xanthate xylan in a proportion of at least 1 wt.%, Based on cellulose, preferably 1 wt.% To 20 wt.%, Particularly preferably 3 wt.% To 15 wt .% is added.

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

Brief description of the figures

FIG. 1 shows the degradation of low-molecular constituents in the viscose process.

FIG. 2 shows the molecular mass distributions of high-molecular hemicelluloses

Pulps and degraded hemicellulose from the mash in the viscose process

Figure 3 shows fiber strengths of viscose fibers having an increased content

high molecular weight xylan compared to a standard fiber without additional xylan addition Figure 4 shows the evolution of the water retention capacity (WRV) of viscose fibers by the addition of high molecular weight xylan in the solution liquor

 FIG. 5 shows the molecular weight distribution of xylan precipitated after CCE treatment of a eucalyptus kraft pulp and the molecular weight distribution of a viscose fiber after addition of this high molecular weight xylan.

 FIG. 6 shows the molecular weight distribution of a viscose fiber with a proportion of 4.8% high molecular weight xylan and its molecular weight distribution after mathematical removal of the high molecular weight xylan content.

Detailed description of the invention

Unless stated otherwise, percentages in each case below mean percentages by weight.

It has surprisingly been found that with the addition of xylan for

Cellulose xanthogenate in the viscose process an increase in the production yield with the same or even improved properties of the resulting

Cellulose molding can be achieved.

In contrast to the prior art, in which the xylans contained in the pulp are largely dissolved out during the alkalization of the pulp, and as

Incurred waste product, the xylan is added to the cellulose xanthate according to the invention. In the subsequent steps of the viscose process (spinning, regeneration, etc.), no significant degradation or dissolution of the xylan takes place more, so that it remains largely in the resulting molded body. According to the invention, the xylan is preferably added in the form of an alkaline solution. The alkaline solution may have a xylan content of 1 to 60 g / l.

In particular, the xylan can be added to the cellulose xanthate as a constituent of an alkaline solution.

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

Particularly preferably, the xylan originates from a pressing liquor produced during the pressing off of alkalized pulp at the beginning of the viscose process. In particular, the

Cellulose xanthogenate which are added during pressing of alkalized pulp caustic.

As mentioned above, the pulp is alkalized at the beginning of the viscose process. When the alkalized pulp is pressed off, an alkaline press liquor is obtained which contains a high proportion of xylan dissolved out by alkalization from the pulp.

If this press liquor is used as the dissolving liquor to dissolve the cellulose xanthogenate, the xylan previously dissolved out of the pulp is returned to the process, thus increasing its yield.

This xylan is relatively low molecular weight. One skilled in the art would expect that addition of low molecular weight xylan would adversely affect the strength properties of the resulting fiber. However, it has been shown that the addition of low molecular weight xylan does not adversely affect the strength of the fibers and thus an increase in yield with constant strength properties is possible.

According to a particularly preferred embodiment of the inventive method, at least a portion of the added xylan is a high molecular weight xylan having an average degree of polymerization (DP) of 75 to 350, preferably 110 to 220.

As already mentioned, in the embodiment described above, the xylan derived from the caustic liquor of the alkalization of the pulp by the viscose process is comparatively low in molecular weight during the degradation in the alkalization (see FIG. 2). It has been shown that viscose fibers by adding such low molecular weight xylans in their properties such as strength and elongation do not fall behind conventional viscose fibers.

Surprisingly, it has been found that the addition of high molecular weight xylan to cellulose xanthate results in comparable strength values and, in addition, an increased water retention capacity and also a better resistance of the xylan present to further process steps.

The high molecular weight xylan is added in a proportion of 1% to 20%, preferably 3% to 15%, based on cellulose.

The high molecular weight xylan may preferably originate from a hemicellulose-rich material stream obtained in the course of an extraction step in the production of a pulp.

Process for the extraction of pulps in the course of their production, such as e.g. Alkaline pre-extraction directly from the wood chips before wood pulping or cold caustic extraction (CCE) are known. Also, non-alkaline method for extraction with complexing agents such. As nitrenes or organic solvents such. B. DMSO are presented in the literature. Unlike the alkalization of the (finished)

Pulp at the beginning of the viscose process, the xylan is indeed dissolved out of the pulp in these extraction process, but not degraded substantially.

If the press liquor obtained by pressing off the pulp after extraction is removed by appropriate methods, e.g. Membrane filtration as in WO 2005/118050,

concentrated, so it creates a stream with a high proportion of

high molecular weight xylan. This liquor may e.g. be added again directly as Löselauge or as part of the cellulose xanthate.

This means in particular in an integrated viscose factory, in which the starting pulp is made to the viscose process itself, an increase in yield, because the otherwise obtained as a waste stream xylan is fed back into the process.

The present invention also relates to a cellulosic molded body obtained by the viscose process with a high molecular weight xylan content having an average degree of polymerization (DP) of 75 to 350, preferably 110 to 220, of at least 0.5% based on cellulose, preferably 2% to 8 %. The molding according to the invention is new, since - without the fiction, according to the proposed addition of high molecular weight xylan to cellulose xanthate - in the conventional viscose process due to the degradation and leaching of xylan no

high molecular weight xylan is more contained in the resulting molded body.

The cellulosic shaped body according to the invention is preferably in the form of a fiber, e.g. Staple fiber or filament fiber.

The invention also relates to the use of fiction, contemporary cellulosic

Shaped body in absorbent products.

Examples

The invention will be explained in more detail with reference to the following examples:

Until the preparation of the cellulose xanthate, the manufacturing process follows the conventional viscose process. According to the invention, the solution solution used is a pure alkali which has been enriched with xylan or an alkali which already contains xylan.

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

If a lye with only low molecular weight xylans is used, the lye can be added together with a possibly also used dissolving water.

In the case of a lye containing high molecular weight xylans, it should first be added to the cellulose xanthate in order to prevent precipitation of the xylans and any addition of dissolving water should be carried out separately.

In the following Examples 2 to 6, a high molecular weight xylans-containing liquor was used.

To obtain the high molecular weight xylan rich liquor used in these examples, a pulp of eucalyptus wood made by the Kraft process was treated with 90 g / l NaOH at a stock consistency of 10% for 30 minutes. The resulting liquor was unchanged and after an enrichment process z. B. by membrane filtration, used as Löselauge. The Lösleauge contained between 1 and 66 g / 1 dissolved xylan. The xylan was added to the xanthogenate with the alkaline Löselauge after xanthogenation and homogeneously mixed. The xylan had the following molecular weight distribution:

Mw Mn PDI DP

 kg / mol kg / mol

 Xylan 22 13 1.7 167

 Table: Molecular weight of the xylan used from a CCE liquor

Figure 2 shows the molecular weight distribution of high molecular weight xylan as prepared from a CCE liquor from coniferous or hardwood pulps. It can be clearly seen that the xylan obtained after application of a CCE stage has a much higher average molecular weight than the xylan already degraded in the mash of the viscose process.

The xylan was added to the xanthate from a conventional beech sulfite pulp and therefore was not present during the sulfidation, but only in the subsequent process step, the dissolution of the xanthate. The xylan is thus not xanthogenated, but dissolved in NaOH. The fibers were spun out in the laboratory. Fibers were thus produced with a significantly higher content of xylan (see Table 2 below).

Example 1 (comparative example)

A pulp (beech sulfite pulp) was mixed with about 18% NaOH, pressed and subjected to a pre-ripeness at about 34 ° C for 19 hours. A dope having the base composition 32% CS ₂ , 8.6 to 8.9% cellulose and 5.2 to 5.6% alkali was prepared. The experiment was repeated with the same arrangement (Examples 1-1 and 1- 2, respectively).

The Löselauge contained 0% xylan. The resulting dope was conventionally spun into fibers having the properties shown in Table 2, Example 1. The present in the fibers (low molecular weight) xylan of 0.6 and 0.7% comes from the pulp used.

Example 2 To a xanthate according to Example 1, a Löselauge with 8.5 g / 1 high molecular weight xylan was added. The resulting dope was spun into fibers having the properties shown in Table 2, Example 2. The xylan uptake was 63% of the high molecular weight xylan present in the Löselauge, which corresponds to a proportion of high molecular weight xylan of 0.7% based on the fiber.

Example 3

To a xanthate according to Example 1 was a Löselauge with 22.0 g / 1

high molecular weight xylan added. The resulting dope was spun into fibers having the properties shown in Table 2, Example 3. The xylan uptake was 79.2% of the high molecular weight xylan present in the Löselauge, which corresponds to a high molecular weight xylan content of 2.7% based on the fiber.

Example 4

To a xanthate according to Example 1 was a Löselauge 39.0 g / 1

high molecular weight xylan added. The resulting dope was spun into fibers having the properties shown in Table 2, Example 4. The xylan uptake was 77.2% of the high molecular weight xylan present in the Löselauge, which corresponds to a high molecular weight xylan content of 4.8% based on the fiber.

To detect the high molecular weight xylan on the fiber, the

Molar mass distributions of the xylan-enriched fiber and that of the CCE-xylans used determined by size exclusion chromatography (Figure 5). In the area of the xylan peak, there is clearly a shoulder on the fiber that suggests an accumulation of added xylan in the fiber. If this xylan content is subtracted by calculation, the result is a curve of a standard viscose fiber, as shown in FIG. The xylene content of 5.5% reported in Figures 5 and 6 refers to the total content of xylan in the fiber (i.e., xylan from pulp used plus added high molecular weight xylan).

Example 5

To a xanthate according to Example 1, a Löselauge with 31.7 g / 1 xylan was added. The resulting dope became fibers having the properties given in Table 2, Example 5 Spun shown properties. The xylan uptake was 60.2% of the high molecular weight xylan present in the Löselauge, which corresponds to a high molecular weight xylan content of 6.9% based on the fiber.

Example 6

To a xanthate according to Example 1, a Löselauge with 66.3 g / 1 xylan was added. The resulting dope was spun into fibers. The xylan uptake was 54.4% of the high molecular weight xylan present in the Löselauge, which corresponds to a high molecular weight xylan content of 10.0% based on the fiber.

In this example, the xylan-containing solubilizer was added to the cellulose xanthate along with solvent water. Obviously due to this, there was a partial precipitation of the xylan in the spinning mass, so that the quality of the spinning solution (filter value etc.) and also those of the spun fibers lagged behind those of Examples 2 to 5.

Example 7 (comparative example)

In a pilot plant, the same beech sulphite pulp was used for the production of

Viscose fibers used. After the mash of the pulp, a low-molecular-weight xylan enriched press liquor was obtained by pressing. This liquor was subjected to nanofiltration. The permeate from the nanofilter, which has only a low content of low molecular weight xylan, was then used as Löselauge in the pilot plant.

Because of the low supply of 0.38% xylan based on cellulose in the dope and its low molecular weight, no additional xylan was precipitated on the viscose fiber. The xylan content of the spun fiber was 0.5%. This xylan is derived from the pulp used.

Example 8

In a pilot plant, the same beech sulphite pulp was used for the production of

Viscose fibers used. As Löselauge the rich low molecular weight xylan retentate from the nanofiltration described in Example 7 was used. The xylan supply in the dope was 5.67% based on cellulose. Of these, 30.0% were spun into the fiber. A fiber with 2.2% xylan was obtained.

Test Methods

Determination of sugars in the fiber:

After a two-stage total hydrolysis with sulfuric acid H ₂ S0 ₄ were the

Sugar monomers determined by anion exchange chromatography (AEC) using a pulsed amperometric detector (PED). The method has been described in the following publication: Sixta H, Schelosky N, Milacher W, Baldinger T, Röder T (2001)

Characterization of alkaline-soluble pulp fractions by chromatography. Proceedings of the II ^th ISWPC, Nice, France: 655-658.

Determination of the molecular weight distribution in the fiber:

 The molecular weight distribution in fibers was determined by size exclusion chromatography (SEC). The samples were dissolved in DMAc-LiCl (dimethylacetamide / lithium chloride). A MALLS detector (multi-angle laser light scattering) was used. Further details were published by Schelosky N, Röder T, Baldinger T (1999), Molecular Distribution of Cellulosic Products by Size-exclusion chromatography in DMAc / LiCl, Paper 53, 12: 728-738.

Determination of the molecular weight distribution of the added high molecular weight xylan: The xylan was precipitated from the CCE liquor under acidic conditions, analogous to the standard method Tappi T 203 om-93: 1993 for the determination of the beta and gamma fraction. It was then continued as in the determination of the molecular weight distribution of fibers by the SEC method.

List of abbreviations:

 CCE cold caustic extraction, cold-alkali finishing

CS ₂ carbon disulfide

 DP Degree of Polymerization, degree of polymerization

 MW molecular weight

 Mw weight average molecular weight

 Mn number average molecular weight

 SEC size exclusion chromatography, size exclusion chromatography

 WRV water retention

PDI polydispersity index Mw / Mn The properties of the respectively obtained viscose spinning compositions and the resulting fibers 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

Particle ppm 14.7 17.7 22.0 13.6 15.3 15.6

Xylan in the solvent g / i 0.0 0.0 8.5 22.0 39.0 31.7

Xylan uptake% 0.0 0.0 63.0 79.2 77.2 60.2

Low Molecular Xylan in

 fiber% od 0.6 0.7 0.7 0.7 0.7 0.7

High molecular weight xylan in

 fiber% od 0 0 0.7 2.7 4.8 6.9

Total xylan in fiber% od 0.6 0.7 1.4 3.4 5.5 7.5

Molecular weight distribution

 the viscose fiber:

 Number average Mn kg / mol 26.5 28.5 29.3 27.6 27.5 26.6

Weight average Mw kg / mol 63 65 66 66 63 61.5

Polydispersity index PDI

 (Mw / Mn) - 2.4 3.3 2.2 2.4 2.3 2.3

Weight fraction of the polymers

 with DP <50% 5.6 5.0 4.8 5.2 5.1 5.6

Weight fraction of the polymers

 DP <100% 11.7 11.7 11.5 12.8 13.0 13.8

Titer dtex 1.30 1.29 1.34 1.37 1.34 1.34

Strength conditioned,

 60% orientation cN / tex 26.0 25.0 26.5 24.8 24.8 23.8

Stretching conditioned,

 60% orientation% 17.8 17.7 16.0 18.0 16.6 15.5

Working capacity% cN / tex 465 443 424 447 412 370

What water retention assets

 WRV% 90.0 92.4 94.5 95.6 98.5 97.1

Table 2: Properties of viscose fibers of beech sulfite pulp with spun xylan from a CCE stage as co-polymer

The high molecular weight xylan was taken up to an unexpectedly high level by the fiber. The uptake into the viscose fiber was 63% to 79% of the xylan offered in the Löselauge. From the filter value and the particle number it becomes clear that the

Quality of the dope and processability by no means suffered from the addition of this co-polymer. In contrast, xylan, which is introduced into the process with only a chemical or paper pulp, is degraded and as a result is removed by 63 to 80% during the mash and spin bath (see Table 3 below). The filter value and particle content of the Viskosespinnmasse are - especially at a high input of xylan from a pulp - significantly reduced.

 Table 3: Loss of wood pulp entering xylan in the viscose process

Surprisingly, it has been found that the textile mechanical properties of the fibers produced remain virtually constant (see FIG. 3). The xylan contents indicated in Figure 3 again refer to the total content of xylan in the fiber (i.e., xylan from pulp used plus added xylan).

The water retention capacity WRV could also be significantly increased by the incorporation of xylan into the viscose fiber (see Table 2 and FIG. 4). That The uptake of water and the ability to adsorb water could not only be increased, but also selectively adjusted via the xylan content of the fiber. This is z. B. for use in absorbent products a whole new way to make product features. The abscissa (xylan content) in Figure 4 again refers to the total content of xylan in the fiber.

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

The properties of the respectively obtained viscose spinning compositions and the resulting fibers according to Examples 7 and 8 are summarized in the following Table 4:

Example 7 8

Filter value 389 401 Example 7 8

Particles 4,5 5,0

 Total xylan uptake% 0 30.0

 Total xylan in fiber% od 0.5 2.2

 Molecular weight distribution

the viscose fiber:

 Number average Mn kg / mol 22.1 22.0

 Weight average Mw kg / mol 60.1 66.7

 Polydispersity Index PDI 2.7 3.0

(Mw / Mn)

 Weight fraction of the polymers 7.1 8.0

with DP <50%

 Weight fraction of the polymers 15.3 15.1

 DP <100%

 Titre dtex 1.40 1.45

 Strength conditioned, 26.8 25.8

 60% stretch cN / tex

 Elongation conditioned, 17.0 15.9

 60% drawing%

 Working capital% cN / tex 455.6 410.2

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

Claims

Claims: 1. A method for producing a cellulosic molded article according to  Viscose process by shaping a dope containing  Cellulose xanthogenate, characterized in that the cellulose xanthate xylan in a proportion of at least 1 wt.%, Based on cellulose, preferably 1 wt.% To 20 wt.%, Particularly preferably 3 wt.% To 15 wt.% Is added. 2. The method according to claim 1, characterized in that the xylan is added in the form of an alkaline solution. 3. The method according to claim 1 or 2, characterized in that the xylan is added to the cellulose xanthate as part of an alkaline Löselauge. 4. The method according to any one of claims 2 or 3, characterized in that the xylan from a pressed in the pressing of alkalized pulp at the beginning of  Viscous process resulting caustic comes. 5. The method according to claim 4, characterized in that the cellulose xanthate is added to a pressing off of alkalized pulp at the beginning of the viscose process resulting caustic. 6. The method according to any one of claims 1 to 5, characterized in that  at least part of the added xylan is a high molecular weight xylan having an average degree of polymerization (DP) of 75 to 350, preferably 110 to 220. 7. The method according to claim 6, characterized in that the high molecular weight xylan in a proportion of 1 wt.% To 20 wt.%, Preferably 3 wt.% To 15 wt.%, Based on cellulose added. 8. The method according to claim 6 or 7, characterized in that the high molecular weight xylan from a in the course of an extraction step in the preparation of a  Pulp accumulating hemicellulose-rich stream comes. 9. A cellulosic molded body obtained by the viscose process and containing a high molecular weight xylan having an average degree of polymerization (DP) of 75 to 350, preferably 110 to 220, of at least 0.5% by weight, based on cellulose, preferably 2% by weight to 8% by weight. 10. Cellulosic molding according to claim 9 in the form of a fiber. 11. Use of a cellulosic molding according to one of claims 9 or 10 in absorbent products.