WO2019170743A1

WO2019170743A1 - Lyocell fibers without mannan

Info

Publication number: WO2019170743A1
Application number: PCT/EP2019/055568
Authority: WO
Inventors: Verena Silbermann; Martina OPIETNIK; Gabriele Schild; Susanne MÖDERL; Magdalena Körbler
Original assignee: Lenzing Aktiengesellschaft
Priority date: 2018-03-06
Filing date: 2019-03-06
Publication date: 2019-09-12
Also published as: EP3536833A1; TW201942428A

Abstract

The present invention relates to cellulose pulp having an increased hemicellulose content and a reduced proportion of mannan, to a lyocell fiber produced therefrom and its use and to a method for the production thereof.

Description

Lyocell fibers without mannan

[0001] The present invention relates to a pulp having an increased content of hemicelluloses, wherein the proportion of mannan is reduced, a lyocell fiber produced therefrom and the use and production method thereof.

background

Wood is gaining more and more importance as a sustainable and natural raw material for all types of materials. Chemically, it has three main components: cellulose, hemicellulose and lignin. For many applications, only a single component is still used, such as For example, cellulose for regenerated cellulosic fibers. However, cellulose accounts for only 40 to 47% of the raw material wood. Less than 50% of the starting material gets into the finished fiber. Over the course of the production process from wood to fiber, a large part of the raw material is mined, lost or used for the energy supply of the production. From the process streams are also minor by-products such. As furfural, acetic acid, vanillin or T allöl won. On the other hand, the demand for cellulosic fibers is increasing worldwide due to population growth and increasing prosperity. Therefore, it would be desirable if a larger proportion of the raw material, namely the other components such. B. the micelle celluloses could be used in the final product. Higher yields achieved thereby can lead to an economic advantage and at the same time improved sustainability.

[0003] Hemicellulose in the sense of the present invention are components present in wood in the form of short-chain polymers of C5 and / or C6 sugars. In contrast to celluloses, they have side groups and can therefore form crystals only to a much lesser extent. Their basic building blocks are mannose, xylose, glucose, rhamnose, galactose. The side groups preferably consist of arabinose groups, acetyl groups and galactose esters as well as O-acetyl groups and 4-O-methylglucuronic acid side groups. It is known that mannans are preferably associated with cellulose, while xylans are more likely to associate with lignin. The composition of hemicelluloses varies greatly depending on the type of wood used. In the course of the pulping process, side chains are partially separated and the polymer chains split. In the context of this invention, the term hemicelluloses includes those in their native structure as well as those modified by their processing and also those which have been adjusted by specific chemical modification for the particular application. Also included are short chain celluloses and other polyoses with a DP of up to 500.

Mannan and xylan as prominent examples of hemicelluloses are plant polysaccharides which contain branched chains with a skeleton of mannose and glucose or Represent xylose. They are based on cellulose, an unbranched homopolysaccharide of anhydro-glucose units, for the largest proportion of polysaccharides in wood and cellulose. Mannan is thus a heteropolysaccharide composed of ß (1 -4) linked anhydro-mannose and glucose units each composed of 6 C-atoms. They form a ring structure, the so-called pyranose form. They are only slightly branched with acetyl groups and galactose residues. They are therefore most closely resembling completely unbranched cellulose, with both sugar monomers being called hexoses because of their 6 C atoms. It is known that cellulose and mannan are already associated in the tree and pulp. Mannan accounts for the largest proportion of hemicelluloses in conifers in terms of quantity and only occurs there with 15-20% by weight of wood.

In contrast, xylose monomers have only 5 C atoms. Therefore, xylan is one of the pentosans. In contrast to mannan, xylan is a homo- polymer whose basic structure is composed exclusively of β (1 -4) bonded anhydro-xylose units. The xylans of softwoods and deciduous trees differ fundamentally distinctively from each other. Hardwood consists of 10-35% by weight of xylan wood. They do not contain mannan, unlike softwood. The deciduous xylan has at irregular intervals 4-O-methylglucuronic acid side groups and is frequently substituted at the C2 and C3 positions of the xylose units with O-acetyl groups. Hardwood xylans still contain small amounts of rhamnose and galacturonic acid. As an exact name for deciduous xylan, therefore, O-acetyl-4-O-methylglucuronoxylan is used. On the other hand, softwoods contain on the one hand a markedly low proportion of xylan of 10-15% based on wood. On the other hand, they lack the acetyl side groups and at the same time contain additional arabinose side groups. They are therefore referred to as arabino-4-O-methylglucuronoxylan.

[0006] During the cooking and bleaching in pulp production, acidic and alkaline process steps alternate, causing a change in the chemical structure of the hemicelluloses. There is a cleavage of the acetyl side groups in xylan and mannan. In addition, a reduction in the degree of polymerization takes place in the alkaline and acidic medium which leads to a shortening of the basic structure of the hemicelluloses. The chains of native hemicelluloses are significantly shorter than those of cellulose. This can lead to a detachment of short-chain hemicelluloses, which in turn can agglomerate in the aqueous phase and then precipitate on the surface of the pulp. However, the basic structure of hemicelluloses from glucose, mannose and xylose units remains intact.

So far, hemicelluloses are largely removed from the chemical pulps in order to produce from the purified materials then later Regeneratfasern can. For technical and economic reasons is a complete removal of xylan and Mannans, however, not possible or useful. The limits for hemicelluloses are very low and for chemical pulps for the viscose and for the lyocell process significantly below 5% (wt .-%). The effects of mannan on fiber formation and fiber properties have not been studied so far. Investigations on the production of cellulosic fibers with xylan as an additional natural polymer are known to a limited extent from the literature both for the lyocell process and for the viscose process in laboratory and pilot plant scale. The statements in the literature are contradictory. The large-scale implementation has not been done because of serious deficiencies, such. B. reduced fiber strength, contamination of the process cycles, poorer processability s etc.

Experiments for admixing high molecular weight hardwood xylan in the viscose process have been described on a pilot scale in the literature (WO2014086883, Shield G, Liftinger E, xylan enriched viscose fibers, Cellulose 21: 3031-3039). Regardless of the origin of the cellulose, despite good mixing of high-molecular-weight xylan, segregation over the entire fiber cross-section was evident, with a marked accumulation of xylan in the outer fiber layer with a strongly decreasing concentration towards the fiber center. Agglomerations of xylan even became visible as lumps on the fiber surface. WO 98/16682 describes a process for the production of pulp compositions for papermaking. It is important that levels of xylan and mannan be set to specific values. Furthermore, the pulp compositions described there are considered to be unsuitable for fiber production. US 2003/0186055 A1, US 2008/0241536 A1 and US 2010/0162542 A1 disclose pulp compositions.

[0009] For the lyocell process, it has repeatedly been found in the literature that a reduced cellulose content has negative effects on the spinnability and fiber qualities in the lyocell process. Fink et al. Part II: Structure and NMMO processability of the pulps. Cellulose 1: 85-98 ) observed in unbleached organosolv cells, which had an increased content of hemicelluloses and lignin, as a result of which the spinning behavior in the lyocell process was extremely poor. Pulps from different pulping processes were tested, mainly using hardwood as raw material. An influence on the crystallinity and the orientation of the polymer chains in the amorphous and crystalline range he did not notice.

Chen et al. (Chen JH, Wang K, Xu F, Sun R (20 '\ 5) \ Zhang et al. (Zhang H, Tong M (2007): Influence of Hemicelluloses on the Structure and Properties of Lyocell Fibers.) Polym Eng. Zhang H, Zhang H, Tong M, Shao H and Hu X (2008): Comparison of the Structured and Properties of Lyocell Fibers from High Hemicellulose Pulp and Hich a-cellulose Pulp. J of Appl Polym. 107: 636-641) made Lyocell fibers from a softwood pulp with increased hemicellulose content and a low hemicellulose hardwood pulp in the laboratory. Although xylan concentrations of pulp were 9.8 and 20.8%, the differences were marginal and can not be considered scientifically meaningful. The working group presented z. B. a collapsed by only 2% crystallinity firmly at the same time increased orientation in the crystalline and amorphous region. The fiber strengths obtained were the same, the dyeability lower. However, it is the study of only two samples, the samples differing greatly in the composition of the hemicelluloses because they are made from different species of wood. The pulp with the higher hemicellulose content was produced from softwood, mainly pine, and therefore contained mainly mannan and only small amounts of softwood xylan. The hemicelluloses of the other sample consisted of hardwood xylan as they were made from eucalyptus.

Another reference (Wendler F, Persin Z, Stana-Kleinschek K, Reischl M, Rijitsch V, Bohn A, Fink HP, Meister F (201 1): Morphology of polysaccharide blend fibers shaven from NaOH, Cellulose N-oxide and 1-ethyl-3-methylimidazolium acetate., Cellulose 18: 1 165-1 178) notes that a blended short-chain xylan hardly affects the lyocell fibers. The xylan comes from the hardwood birch. The crystalline orientation sinks slightly, which contradicts the previous publication. The water retention capacity and the contact angle of water remain constant. The zeta potential also remains almost the same. The experiments were carried out on a laboratory scale. Therefore, hardly any industrial conditions could be adjusted at the spinnerets and in the air gap.

However, these basic experiments are not very meaningful in terms of the organization of the thread structure in large-scale production scale.

Various patents allow the use of hemicelluloses in an amount of more than 5% or 7% for lyocell fibers (EP1441050, US6528163, US6686040, US6685856, EP1435404, US6514613, US6440523, US6444314, US6605350, EP1068376, EP1311717, EP1362935 , US6210801, DE69913117). It is noteworthy, however, that lyocell products based on these intellectual property rights have not yet been realized on a large scale, although the priority dates date back to 1998. This is probably due to the lab scale upscaling and fiber properties difficulties that do not meet market expectations. In these patents, no distinction is made with regard to the hemicellulose content with regard to the composition of the hemicelluloses. In the processing industry, it is therefore still required that the proportion of xylan in the pulp and thus in the finished fiber is less than 5% by weight, preferably less than 3% by weight. Since xylan and mannan per se and in addition to different types of wood differ greatly from one another, it can be assumed that the influences on the fibers produced therefrom vary accordingly. So far, however, this has not been taken into account in any way, and therefore the generally available conclusions can be drawn from the few published results, nor can the results be transferred to large-scale production.

[0015] The poor spinning behavior of pulps with increased lignin and / or hemicelulose content is attributed in the literature to the fact that so-called lignin-carbohydrate complexes are formed. These dissolve in Direktlöseverfahren such. B. with NMMO or ionic liquids are not complete, but form gel-like structures. This in turn leads to inhomogeneity of the spinning solution, to a change in its viscous behavior and finally to a reduced mechanical strength of the fibers. The same is generally known from the viscose process. These precipitates are pH- and temperature-dependent. Xylan is soluble in alkali and precipitates when the pH drops. This phenomenon is also known from alkaline boiling (Potthast A (2006): 4.2.4.2 Reactions of Carbohydrates and 4.3.4.2 Reactions of Carbohydrates: Acid Hydrolysis. In Sixta (ed.): Handbook of Pulp Volume 1, 174-181 and 416-421). In the final stage of the cooking, the pH drops when the digestion chemicals are consumed, and precipitations of already dissolved xylan on the surface of the pulp fibers occur. This is undesirable for the production of chemical pulps. Precipitated xylan can not be completely dissolved again. It forms in the solvent gel-like aggregates o- remains completely unsolved. Also, such lumps from the pulp in the lyocell process can not be solved again.

Up to now, the problem of lignin-carbohydrate bonds could only be circumvented by ionic liquids in a direct dissolving process by treating the pulp with electron radiation prior to the dissolving process Ma Y, Stubb J, Contra I, Nieminen K, Hummel M, Sixta H (2017b): Filament spinning of unbleached birch kraft pulps: Effect of pulping intensity on the processability and the fiber properties. Carb Polym 179: 145-151). Thus, the lignin-carbohydrate bonds could be broken and the pulps were successfully dissolved in ionic liquids and spun out. In the case of fibers with a low cellulose content, however, strength losses also occurred here again. Here, too, hardwood, namely birch, was used as a raw material, which in turn indicates a problem with xylan.

Ma et al. (Ma Y, Stubb J, Contra I, Hummel M, Sixta H (2017a): High performance man-made cellulosic fibers from recycled newsprint. Green Chem. Ahead of print) In this context, the mixing of the dissolved macromolecules in the polymer matrix is the most important point for further processing in the lyocell process. Presumably, this can not happen if only xylan is present next to the cellulose. For a good mixing with the cellulose, the assumption that xylan and mannan must be found in the raw material. The mannan could serve as a solubilizer for the xylan in this polymer matrix.

For the use of pulps without mannan z. For example, from hardwood such as eucalyptus, birch, beech, etc., the skilled man would therefore expect that the mixture of xylan and cellulose in the absence of mannan in Lyocell process results in a completely different process behavior and fibers are obtained with significantly different properties , It is therefore currently assumed that the processability deteriorates severely and that the fiber strengths decrease significantly. Raw materials with an increased hemicellulose content without mannan are thus hitherto regarded as completely unsuitable for the production of moldings in the lyocell process.

problem

Since the purification of cellulose is complicated and energy-intensive, it would be advantageous if cellulose materials were also suitable for producing lyocell products, in particular fibers, which on the one hand have a reduced cellulose content and, on the other hand, the specifications hitherto demanded on the market for hemicellulose levels. It would also be advantageous if it were also possible to use starting materials which, due to their composition, have hitherto not been considered suitable for the production of lyocell products. The object of the present invention is therefore to specify such materials and associated technologies, in particular in the field of lyocell fiber production.

Brief summary of the invention

Surprisingly, it has been found according to the invention that a lyocell fiber having good properties can be produced from a xylan-rich pulp despite a very low content of mannan. The fibers could be produced directly from the celluloses, whose micellar materials consisted largely of xylan, and showed no industrial effect on the spinning behavior or the fiber strengths. In contrast to the literature, no pretreatment of the pulp was necessary for the new lyocell fibers described here. [0021] Thus, the present invention provides the pulp of claim 1, the processes of claims 2 and 4, and the fiber of claim 3, as well as the embodiments listed below. Preferred embodiments of the invention are specified in the subclaims and the description below.

1. Pulp suitable for producing a lyocell fiber, the pulp having a hemicellulosity content of at least 7% by weight, the proportion of xylan, based on said hemicellulose, being at least 90%, and furthermore the content being Mannan in the pulp is less than 0.2 wt .-%.

2. A process for the production of a pulp, suitable for the production of a lyocell fiber, wherein the pulp has a hemicellulose content of at least 7 wt .-%, where in the proportion of xylan, based on this Hemicellulosengahlt is at least 90%, and wherein further the content mannan in the pulp is less than 0.2% by weight, the process comprising at least one of the following steps:

a) mixing a pure pulp with xylan to achieve the stated xylan content;

b) treating a pulp with a hemicellulose moiety including mannan by chemical and / or physical means to reduce the mannan content;

c) production of a pulp using hardwoods;

d) mixing a mannan-free pulp with a hemicellulose-rich pulp and / or subsequent chemical and / or physical treatment of the mixture to adjust the hemicellulose content and the composition of the hemicellulose fraction.

3. lyocell fiber, with a hemicellulose content of at least 5% by weight, the proportion of xylan relative to this hemicellulose layer being at least 90%, and furthermore the content of mannan in the fiber being less than 0.2% by weight. -% is.

4. A process for producing a lyocell fiber, characterized in that the spinning composition is prepared from a pulp having a hemicellulose content of at least 7 wt .-%, wherein the proportion of xylan, based on this Hemicellu- losengahlt at least 90%, and further wherein the content of mannan in the pulp is less than 0.2 wt .-%. 5. pulp, lyocell fiber or method according to one of the preceding embodiments, wherein the hemicellulose content is at least 10 wt .-% and the xylanan part, based on the hemicellulose content is at least 98%.

6. Pulp, lyocell fiber or method according to one of the preceding embodiments, wherein the hemicellulose content is at least 1 1 wt .-% and the xylanan part, based on the hemicellulose content is at least 99%.

7. pulp; Lyocell fiber or method according to one of the preceding embodiments, wherein the pulp has a SCAN viscosity of 300 to 440 ml / g.

8. Lyocell fiber according to any one of embodiments 3, 5, 6 and / or 7, with a fiber titer in the range of 0.5 dtex to 10 dtex.

9. lyocell fiber according to any one of embodiments 3, 5, 6, 7 and / or 8, wherein the fiber is a staple fiber.

10. A process for producing a pulp according to any one of embodiments 2, 5, 6 and / or 7, comprising the step of pulp production using deciduous trees, preferably eucalyptus.

1 1. A process for producing a lyocell fiber according to any one of embodiments 4, 5, 6 and / or 7, wherein the dope comprises as solvent aqueous tertiary amine N-oxides.

Detailed description of the invention

The present invention thus provides a pulp suitable for the production of a lyocell fiber, the pulp having a hemicellulose content of at least 7% by weight, the proportion of xylan, based on said hemicellulose, being at least 90% %, and further wherein the content of mannan in the pulp is less than 0.2 wt .-%.

Furthermore, the present invention provides a lyocell fiber having a hemicellulose content of at least 7% by weight, wherein the proportion of xylan, based on the sen Hemicellulosengahlt is at least 90%, and further wherein the content of mannan in the Fiber less than 0.2 wt .-% is.

[0024] In addition, the present invention provides a process for producing a lyocell fiber, characterized in that the dope is made from a pulp having a hemicellulose content of at least 7% by weight, the The proportion of xylan, based on this Hemicellulosengahlt is at least 90%, and further wherein the content of mannan in the pulp is less than 0.2 wt .-%.

The preferred embodiments described below relate in each case to the three abovementioned aspects of the present invention, even if only one of the preceding aspects is explicitly mentioned in the corresponding passages.

Preferably, the hemicellulose content in the pulp is at least 10 wt .-%, in embodiments also at least 12 wt .-% or at least 14 wt.%. Since the hemicellulose content in a spun fiber is usually somewhat lower in comparison with the starting pulp, the hemicellulose contents may be slightly lower for the fiber according to the invention, e.g. at least 10% by weight, such as at least 11% by weight, or at least 12% by weight.

According to the invention, the proportion of xylan in the hemicellulose content is at least 90%, in embodiments at least 95%, preferably at least 98%, such as at least 99%. In embodiments, xylan is the only hemicellulose component. This means that all other hemicellulose components are present in each case in an amount of less than 0.2% by weight, preferably in each case less than 0.1% by weight.

The Mannangehalt is less than 0.2 wt .-%, preferably less than 0.1% by weight. A male content of less than 0.1% by weight corresponds to a male content below the detection limit of the method for determining the composition of cellulose / lyocell fibers described in this application. Such Mannangehalte can be achieved, for example, that are selected as starting material for the production of the pulp species of wood, which have a very low or practically negligible Mannangehalt. This is the case with hardwoods, for example. The present invention thus makes it possible to use this class of renewable raw materials for lyocell fiber production.

However, it is also possible to adjust the hemicellulose content (and its composition in accordance with the present invention) according to the invention by combining individual components and / or by chemically treating pulps. Mannan-containing pulps can be treated in such a way that the mannan fraction is specifically degraded and removed. The adjustment of the Xylangehalts invention can be done accordingly by mixing isolated Xylanfraktionen.

Thus, the present invention again allows the use of materials that would otherwise have been discarded as unwanted by-products of pulp production otherwise. Preferred embodiments of the pulp according to the invention have a micellulose content of at least 10% by weight, with a mannan content of 0.1% by weight or less and a xylan content in the hemicellulose fraction of at least 98%.

The lyocell fibers according to the invention can be prepared from the pulp disclosed here by the lyocell method. Contrary to expectation, there are no problems with processing, neither in the production of a homogeneous spinning solution nor in the fiber produced from it. These can be produced with different fiber titers, depending on the respective desired application areas. Suitable fiber titers are in the range of about 0.5 dtex to 10 dtex, in particular 1, 3 dtex to 7 dtex. According to the invention, both staple fibers and filaments can be produced; the apparatuses and general process parameters necessary for this purpose are familiar to the person skilled in the art.

The pulps used here, which are preferably used in the context of the present invention, as already stated, have a relatively high content of hemicelluloses with the composition defined here. In comparison with standard hemicellulosic pulps used in the prior art for the production of standard lyocell fibers, the pulps preferably used in the context of the present invention also exhibit further differences, which are listed below.

In comparison with standard pulps, the pulps preferably used in the context of the present invention show a rather fluffy view. This results after the grinding (during the production of starting materials for the production of spinning solutions for the lyocell process) in a particle size distribution with a high proportion of larger particles. As a result, the bulk density is much lower when compared to standard hemicellulose content. Such a low bulk density requires adaptations with regard to metering parameters (eg metering using at least two storage tanks) in the preparation of the spinning solutions. In addition, the pulps preferably used in the context of the present invention show an impregnation behavior with respect to NMMO, which, in comparison with standard pulps, shows that impregnation is more difficult here. This can be verified by evaluating the imprint behavior with the Cobb evaluation. While standard pulps typically show a Cobb value of more than 2.8 g / g (determined in accordance with DIN EN ISO 535 with adaptations with respect to the use of an aqueous solution of 78% NMMO at 75 ° C. with an impregnation time of two minutes), the pulps preferably used in the present invention show Cobb values of about 2.3 g / g. This requires adaptations during the production of spinning solutions, such as increased solubility. time (eg explained in WO 94/28214 and WO 96/33934) and / or temperature adaptation and / or increased shear during dissolution (eg WO 96/33221, WO 98/05702 and WO 94/8217). This makes it possible to produce spinning solutions which make it possible to use the pulps described here in a standard lyocell process).

In a preferred embodiment of the present invention, the pulp used for the production of lyocell products, preferably fibers, as described herein, exhibits a SCAN viscosity in the range of 300 to 440 ml / g, in particular 320 to 420 ml / g, more preferably 320 to 400 ml / g. The SCAN viscosity is determined in accordance with SCAN-CM 15:99 using a Cupriethylendiaminlösung, a method which is known in the art and which can be carried out with commercially available devices, such as with the device Auto PulpIVA PSLRheotek, available from the company PSL Reotek. The SCAN viscosity is an important parameter which influences in particular the processing of the pulps in the production of spinning solutions. Even if two cell materials show a great match in terms of their composition, etc., different SCAN viscosities lead to completely different behavior during processing. In a direct solution spinning process, such as the lyocell process, the pulp is dissolved in NMMO as such. There is no maturation step, comparable for example with the viscose method, where the degree of polymerisation of the cellulose can be adapted to the needs of the process. Therefore, the specifications for the viscosity of a raw pulp are typically in a small target window for the lyocell process. Otherwise problems can occur during production. In accordance with the present invention, it has been found that the pulp viscosity is preferably as previously described. Lower viscosities lead to a worsening of the mechanical properties of the lyocell products. Higher viscosities may in particular lead to an increased viscosity of the spinning solution, so that spinning is slower overall. Lower spinning speeds also result in lower draw ratios, which again may have a significant impact on fiber structure and fiber properties (Cabohydrate Polymers 2018, 181, 893-901). This would require process adaptations that would lead to a reduction in capacity. The use of pulps with the viscosities defined herein, on the other hand, allows for easy processing and the production of high quality products.

The term "lyocell process", or the terms "lyocell technology" and "lyocell process", as used herein, refers to a direct dissolution process of wood cellulose pulp or other cellulose based feedstocks in a polar solvent (eg N-methylmorpholine-n oxide (NMMO, NMO) or ionic liquids). Commercially, this technology is used to make a group of cellulosic staple fibers, commercially available from Lenzing AG, Lenzing, Austria under the TENCEL® or TENCEL ™ brand, which are widely used in the textile industry or nonwovens industry. Other cellulose moldings obtained by the lyocell technology were also already manufactured. In accordance with this method, the cellulosic solution is usually extruded in a so-called dry-wet-spinning method, using a forming tool, and the molded solution, for example, after passing an air gap, reaches a precipitation bath where the molded body is obtained by the precipitation of the cellulose. The shaped body is washed and optionally dried, after further treatment steps. A process for the production of lyocell fibers is described, for example, in US 4246221, WO 93/19230, WO 95/02082 or WO 97/38153. Insofar as the present invention discusses the disadvantages of the prior art, and discusses the unique properties of the new products disclosed and claimed herein, particularly in the context of the use of laboratory equipment (in particular in the prior art) or in the context of the invention. In the case of (semi-commercial) pilot plants and commercial fiber spinning units, the present invention should be understood to refer to units that can be defined in terms of their respective production capacities as follows:

Semi-commercial pilot plant: about 1 kt / a

Commercial unit greater than 30 kt / a

The mechanical properties of the fibers according to the invention are also surprising in such a way that their use in the customary fields of application of lyocell fibers is possible without problems. The slight deviations from the mechanical characteristics of Lyocell fibers of pulp with a low hemicellulose content, which may possibly occur, do not impair the applicability of the fibers according to the invention.

Example

In the pilot plant, a kraft-wood pulp made of eucalyptus wood was produced according to the VisCBC process according to I A / 09412719. The H-factor was 1200, the effective alkali in the cooking liquor was 25 g / l. The bleaching was done after a total chlorine-free (TCF) sequence. Table 1 shows the progression of the sugar content from the wood to the finished lyocell fiber. A small proportion of manan results in the wood from the mannose of other polysaccharides. These polysaccharides are degraded during cooking and dissolved out. The finished pulp and the new lyocell fiber from it contain no mannan, but mainly xylan as hemicellulose. The glucan content largely reflects the cellulose content in the pulp and fiber.

Table 1: Proportions of the various sugar monomers from the raw material wood to the finished non-wovens fiber of eucalyptus wood

A comparison with other market pulps shows the unique composition of the new raw material (Table 2). The market pulp 1 is a conventional sulphite pulp made of hardwood, which clearly undercuts the required xylan content of not more than 5% with 2.6% xylan. He does not contain mannan. The market pulp 2 was produced from softwood and therefore contains xylan and mannan in a ratio of about 1: 1, 5. The new pulp BI438 has a high content of xylan of 14.0%, which is well above the required maximum of 3 to 5%, while the proportion of mannan is below the detection limit. It does not meet the conventional generally known conditions for further processing in the lyocell process with regard to the hemicellulose content and their relationship to each other in any way. It is well above the known limits and should therefore not be used.

Table 2: Sugar content of carbohydrates of mannan-free pulp compared to market pulps

The pulp with the high xylan content and without mannan BI438 was spun-out in comparison to market pulp 1 on a pilot plant scale. Contrary to expectations, a good processability turned out. There were no problems with further processing. The fiber strengths were determined. In contrast to all known deficiencies, the fibers without mannan showed an extremely small decrease in the strength properties (Table 3). Because of the extremely high xylene content of 12.1% compared to 1.7%, the skilled person would no longer expect acceptable fiber data at all. The fiber strength (FFk) and the fiber elongation (FDk) in a conditioned state only decrease by 10%. The value for the strain is even within the normal fluctuation range of the pilot plant.

Table 3: Fiber properties of the novel non-mannan fiber of the present invention as compared to fibers of low xylan and mannan market pulp

Methods

Determination of sugar monomers The determination of the neutral sugar monomers was carried out after total hydrolysis with H2SO4 by anion exchange chromatography. The method is well known to the person skilled in the art and is described by Sixta et al. Sixta H, Schelosky N, Milacher W, Baidinger T, Röder (2001): Characterization of alkaline-soluble pulp fractions by chromatography. In: Pro- grams of the 11th ISWPC, Nice, France. 655-658).

Claims

claims

1. Pulp suitable for producing a lyocell fiber, the pulp having a hemicellulosity content of at least 7% by weight, the proportion of xylan, based on this hemicellulose content, being at least 90%, and furthermore the content of mannan in the Pulp is less than 0.2 wt .-% is.

2. A process for producing a pulp, suitable for producing a lyocell fiber, wherein the pulp has a hemicellulose content of at least 7 wt .-%, wherein the proportion of xylan, based on this Hemicellulosengtt is at least 90%, and wherein further the content Mannan in the pulp is less than 0.2% by weight, the process comprising at least one of the following steps: a) mixing a pure pulp with xylan to achieve the stated xylan content;

c) production of a pulp using hardwoods;

4. A process for producing a lyocell fiber, characterized in that the spinning composition is prepared from a pulp having a hemicellulose content of at least 7 wt .-%, wherein the proportion of xylan, based on this hemicellulose content at least 90%, and further wherein the content of mannan in the pulp is less than 0.2 wt .-%.

5. pulp, lyocell fiber or process according to any one of the preceding claims, wherein the hemicellulose content is at least 10 wt .-% and the xylan content, based on the hemicellulose content is at least 98%.

6. pulp, lyocell fiber or process according to any one of the preceding claims, wherein the hemicellulose content is at least 1 1 wt .-% and the xylan content, based on the hemicellulose content is at least 99%.

A pulp, lyocell fiber or process according to any one of the preceding claims, wherein the pulp has a SCAN viscosity of 300 to 440 ml / g.

8. lyocell fiber according to any one of claims 3, 5, 6 and / or 7, with a fiber titer in the range of 0.5 dtex to 10 dtex.

The lyocell fiber according to any one of claims 3, 5, 6, 7 and / or 8, wherein the fiber is a staple fiber.

10. A process for producing a pulp according to any one of claims 2, 5, 6 and / or 7, comprising the step of pulp production using hardwoods, preferably eucalyptus.

1 1. A process for producing a lyocell fiber according to any one of claims 4, 5, 6 and / or 7, wherein the dope comprises as solvent aqueous tertiary amine N-oxides.