AT514001B1 - Process for the preparation of a cellulosic molding - Google Patents

Abstract

The invention relates to a V experienced for producing a cellulosic molded article by the viscose process by shaping a dope containing cellulose xanthate, which is characterized in that the cellulose xanthate xylan in a proportion of at least 1 wt.%, Based on cellulose, preferably 1 wt 20 wt.%, Particularly preferably 3 wt.% To 15 wt.% Is added. The invention further relates to cellulosic molded articles obtained by the viscose process with a proportion of high molecular weight xylan having an average degree of polymerization (DP) of from 75 to 350, preferably from 110 to 220, of at least 0.5% by weight, preferably from 2% by weight to 8% by weight. %.

Description

description

METHOD FOR PRODUCING A CELLULOSIC FORM BODY

The invention relates to a process for the preparation of cellulosic molded bodies by the viscose method.

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,

Premature). [0005] Reaction of the alkalized cellulose starting material ("alkali cellulose") to cellulose xanthogenate. Dissolution of the cellulose xanthate with alkali, the so-called viscose being known as

If desired, addition of modifiers to the viscose for the production of

Dyestuff for Modal Fibers: Spinning the Viscose into Continuous Moldings Regenerating the Cellulose in a Precipitation Bath from End-Use Molded Articles. Post-treatment and Drying.

If appropriate, cutting the continuous molded body into staple fibers.

The fibers produced by this process are known by the generic term (standard) viscose fibers and modal fibers. The modal process differs from the standard viscose process in that the composition of the spinning dope is changed, additional dope in the dope and modified dope composition.

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

The pulp used in the viscose process has an alpha-cellulose content of greater than 90% and has only small proportions of secondary compounds, such as xylan and other hemicelluloses (such as, for example, 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 (Figure 1). Hemicelluloses remaining in the pulp are depolymerized in the pre-ripeness together with the cellulose and therefore have a much lower 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 apparent, which are incorporated with the pulp in the viscose process and then subject to degradation into mash and ripeness. In contrast, the molecular weight distributions are represented by hemiceluloses 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 portion of hemicellulose is removed from the production stream and is re-deposited on the pulp in a later stage.

From US 7,390,566 B2 and WO 2007/128026 the use of pulp with a relatively high proportion of xylan for the production of viscose fibers is known. The use of hemicellulose-rich pulp for producing lyocell fibers is known from WO99 / 47733 A1 and WO 01/88236 A2.

[0018] WO 2005/118950 describes the separation of beta-cellulose from liquor obtained by pressing after a cold or hot alkaline extraction (CCE, HCE) of a pulp.

Documents US 2008/001325 A1, AT 503610 B1, DE 3000306 A1, Östberg, L et al, BioResources 7 (1), 743-755, Published 2012-01-05 and Dominiak, K. 13-C- NMR spectroscopic investigations on the distribution of substituents in cellulose xanthogenates, PhD thesis III of the Technische Universität Berlin, Berlin 2010, deal with the content of hemicelluloses or xylan in pulps or in the viscose process.

There is still a need to increase the yield of the viscose process while maintaining the quality of the end products. There is also a need to provide novel viscose fibers having modified properties, particularly increased absorbency.

The object of the present invention is in one aspect solved by a process for the preparation of a cellulosic shaped body according to the viscose method by shaping a spinning mass containing cellulose xanthate, 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 cellulosic molded article obtained by the viscose method with a proportion of high molecular weight xylan having a 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 2 wt.% To 8 wt.%.

BRIEF DESCRIPTION OF THE FIGURES

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

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

Pulps and degraded hemicellulose from the mash in the viscose process Figure 3 shows fiber strengths of viscose fibers with an increased content of high molecular weight xylan compared to a standard fiber without additional xyl addition. Figure 4 shows the development of the water retention capacity (WRV) of Viscose fibers by the addition of high molecular weight xylan in the Löselauge [0027] 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 arithmetic removal of the high molecular weight xylan content.

DETAILED DESCRIPTION OF THE INVENTION

Unless otherwise indicated, percentages below mean in each case statements in percent by weight.

It has surprisingly been found that with an addition of xylan to Cellulo¬sexanthogenat in the viscose process, an increase in the production yield can be achieved at gleichbleiben¬ or even improved properties of the resulting cellulose moldings.

In contrast to the prior art, in which the xylan contained in the pulp are largely dissolved out during the alkalization of the pulp and incurred as a waste product, according to the invention the xylan is added to the cellulose xanthate. In the subsequent steps of the viscose process (spinning, regeneration, etc.), no substantial degradation or dissolution of the xylan takes place, so that this remains largely intact in the formed body.

Preferably, according to the invention, the xylan is 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 may be added to the cellulose xanthate as part of an alkaline solution.

When dissolving the cellulose xanthogenate to prepare the spinning solution, it is known to use an alkaline solution. In this, according to the preferred embodiment of the present invention, the xylan to be added may be contained.

Particularly preferably, the xylan is derived from a pressing liquor produced during the pressing off of alkalized pulp at the beginning of the viscose process. In particular, the cellulose xanthogenate may be added with the press liquor resulting from the pressing of alkalized pulp.

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

If this press liquor is used as the dissolving liquor to dissolve the cellulose xanthogen, the xylan previously dissolved out of the pulp is recycled 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 of the same strength properties is possible.

According to a particularly preferred embodiment of the method according to the invention, 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.

As already mentioned, in the embodiment described above, the xylan derived from the press liquor from the alkalization of the pulp in the viscose process is comparatively low molecular weight due to degradation during the alkalization (see FIG. 2).

It has been found that viscose fibers obtained by adding such low molecular weight xylans have properties such as e.g. Strength and elongation do not fall behind conventional viscose fibers.

Surprisingly, it has been found that the addition of high molecular weight xylan to the cellulose xanthogenate results in comparable strength values and, in addition, an increased water retention capacity as well as 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 consist of 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. an alkaline pre-extraction directly from the wood chips before a wood pulp or a cold oil feed extraction (CCE) are known. Also, non-alkaline method for extraction with complex bildnem such. As nitrenes or organic solvents such. B. DMSO be in the

Literature presented. In contrast to the alkalization of the (finished) pulp at the beginning of the viscose process, in these extraction processes the xylan is released from the pulp but substantially not degraded.

When the pulp obtained by pressing the pulp after extraction is removed by appropriate methods, e.g. Membrane filtration as in WO 2005/118050 aufkon¬zentriert, so it produces a stream with a high proportion of high molecular weight xylan. again be added directly as Löselauge or as part of the cellulose xantho-genate.

This means in particular in an integrated viscose, in which the Aus¬gangs pulp is produced for viscose itself, an increase in yield, because otherwise as waste stream resulting xylan is fed back into the process.

The present invention also relates to a cellulosic molded article obtained by the viscose process, having a high molecular weight xylan content with an average degree of polymerization (DP) of from 75 to 350, preferably from 110 to 220, of at least 0.5%, based on cellulose 2% to 8%.

The molding according to the invention is new, since - without the invention vorgesehe¬ne addition of high molecular weight xylan to cellulose xanthate - in the conventional Visko¬severfahren due to the degradation and leaching of xylan no high molecular weight xylan is more contained in the resulting molded body.

The cellulosic molding 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 the cellulosic shaped body according to the invention in absorbent products.

EXAMPLES

The invention will be further illustrated by the following examples: [0053] 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.

When an alkali with only low molecular weight xylans is used, the liquor may be added together with any dissolving water also used.

In the case of a lye containing high molecular weight xylans, in order to avoid precipitation of the xylans, it should first be added to the cellulose xanthate and any additional release water should be added separately.

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

To obtain the lye used in these examples of high-molecular-weight xylan, a paper pulp made of eucalyptus wood, which had been prepared by the kraft process, was treated with 90 g / l NaOH for 30 minutes at a consistency of 10%. The resulting liquor was unchanged and after an enrichment process z. B. by Membranfiltrati¬on, used as Löselauge.

The Löselauge contained between 1 and 66 g / l dissolved xylan. The xylan was added to the xanthogenate after the xanthogenation with the alkaline solvent solution and mixed homogeneously. The xylan had the following molecular weight distribution:

Mw Mn PDI DPkg / mol kg / mol

Xylan 22 13 λϊ Ϊ67

Table 1: 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 of coniferous or hardwood pulps. It can be clearly seen that the xylan recovered 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 was therefore not present during the sulfidation, but only in the subsequent process step, the dissolution of the xanthate. The xylan is thus not xanthoge-ned, 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 treated with about 18% NaOH, squeezed, and pre-ripened at about 34 ° C for 19 hours. A dope having the base composition 32% CS2, 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 spun in a conventional manner into fibers having the properties shown in Table 2, Example 1. The (low molecular weight) xylan present in the fibers of 0.6 or 0.7% is derived from the pulp used. EXAMPLE 2 To a xanthate according to Example 1, a Löselauge with 8.5 g / l hochmoleku¬larem 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 solution, corresponding to a high molecular weight xylan content of 0.7% relative to the fiber. EXAMPLE 3 To a xanthate according to Example 1, a Löselauge with 22.0 g / l hochmole¬kularem xylan was 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 solution, corresponding to a high molecular weight xylan content of 2.7% of the fiber. EXAMPLE 4 To a xanthate according to Example 1, a Löselauge with 39.0 g / l hochmole¬kularem xylan was 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 solution, corresponding to a high molecular weight xylan content of 4.8% relative to the fiber.

In order to detect the high molecular weight xylan on the fiber, the molecular weight distributions of the xylan-enriched fiber and that of the CCE-xylan used were determined by size exclusion chromatography (FIG. 5). In the area of the xylan peak, there is clearly a shoulder on the fiber which suggests an accumulation of the added xylan in the fiber. When this xylan content is calculated, a curve is obtained from 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 added plus added high molecular weight xylan). EXAMPLE 5 To a xanthate according to Example 1, a Löselauge was added with 31.7 g / l of xylan. The resulting dope was spun into fibers having the properties shown in Table 2, Example 5. 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 was added a Löselauge with 66.3 g / l of xylan. 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 proportion of high molecular weight xylan of 10.0% based on the fiber.

In this example, the xylan-containing Löselauge was added to the cellulose xantho-genate together with solvent water. Obviously as a result, there was a partial precipitation of xylan in the spinning mass, so that the quality of the spinning solution (Fil¬terwert etc.) and also those of the spun fibers behind those of Examples 2 to 5 zuberrückblieben. EXAMPLE 7 (COMPARATIVE EXAMPLE) In a pilot plant, the same beech sulphite pulp was used for the production of viscose fibers. After the mash of the pulp, a pressed liquor enriched with low-molecular-weight xylan was obtained by pressing off. 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.

Due to the low availability 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. As Löselauge the low molecular weight xylan rich 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 SUGAR IN FIBER: After a two-stage total hydrolysis with sulfuric acid H 2 SO 4, the sugar monomers were determined by means of anion exchange chromatography (AEC) with a pulsed amperometric detector (PAD). The method has been described in the following publication: SixtaH, Schelosky N, Milacher W, Baidinger T, Röder T (2001) Characterization of alkaline-soluble pulp fractions by chromatography. Proceedings of the Nth ISWPC, Nice, France: 655-658. DETERMINATION OF MOLECULAR WEIGHT DISTRIBUTION IN 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 have been published by Schelosky N, Röder T, Baidinger T (1999), Molar Mass 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 to determine the beta and gamma fraction. Subsequently, as for the determination of the molecular weight distribution of Fibers continued with the SEC method. LIST OF ABBREVIATIONS: CCE cold caustic extraction, cold-alkali upgradingCS2 carbon disulphide DP Degree of Polymerization, degree of polymerizationMW molecular weightMw weight-average molecular weightMe-number average molecular weight SEC size exclusion chromatography, size exclusion chromatographyWRV water retentionPDI polydispersity index Mw / Mn The properties of the respective viscose spinning compositions obtained as well as obtained fibers according to Examples 2 to 5 are summarized in the following Table 2:

Table 2: Properties of viscose fibers of beech sulfite pulp with spun xylan from a CCE stage as a co-polymer. The high molecular weight xylan was taken up to an unexpectedly high level by the fiber. Intake into the viscose fiber was from 63% to 79% of the xylan offered in the release leach. From the filter value and the number of particles it becomes clear that the quality of the dope and the processability by no means suffer 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 consequently removed by 63 to 80% during the mash and in the spinning bath (see the following Table 3). The filter value and particle content of the viscose spinning mass are also markedly reduced, in particular with a high input of xylan from a paper pulp.

It has surprisingly been found that the textile mechanical properties of the fibers produced remain virtually constant (see FIG. 3). Again, the xyl levels indicated in Figure 3 refer to the total content of xylan in the fiber (i.e., xylan from pulp used plus any xylan).

The water retention capacity WRV could also be significantly increased by the incorporation of xylan into the viscose fiber (see Table 2 and Figure 4). That the uptake of water and the ability to adsorb water could not only be increased, but also be targeted via the xylan content of the fiber. This is z. B. for the application of 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 (content of high molecular weight xylan: 10.0%). This was 106.0%.

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

Table 4. Properties of viscose fibers prepared with the addition of xylan from Visko¬seproduktion

Claims (11)

1. A process for producing a cellulosic shaped body by the viscose method by shaping a spinning mass comprising cellulose xanthate, characterized gekenn¬zeichnet that the cellulose xanthate in a proportion of at least 1 wt.%, Based on cellulose, preferably 1 wt.% To 20 wt. %, more 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 an ingredient of an alkaline Löselauge. 4. The method according to any one of claims 2 or 3, characterized in that the xylan comes from a obtained during the pressing of alkalized pulp at the beginning of Viskoseverfah¬rens pressing liquor. 5. The method according to claim 4, characterized in that the Zellulosexanthogenateine is added during the pressing of alkalized pulp at the beginning of the viscose process anfallen¬de pressing liquor. 6. The method according to any one of claims 1 to 5, characterized in that zumin¬dest part of the added xylan is a high molecular weight xylan having a average degree of polymerization (DP) of 75 to 350, preferably 110 to 220, is. 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.%, Bezo¬gen on cellulose, is added. A process according to claim 6 or 7, characterized in that the high molecular weight xylan is derived from a hemicellulose-rich material stream occurring in the course of an extraction step in the production of a pulp. 9. A cellulosic molded body obtained by the viscose process with a proportion 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% by weight, based on cellulose, preferably 2% 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 absorbent products. For this 6 sheets of drawings