Patent Application
20210002825
The present invention describes special cellulose compositions which allow the large-scale stable production of a lyocell fiber with a reduced cellulose content, as well as the lyocell fiber produced from it.
Lyocell fibers are used in a variety of applications. Purified cellulose is often used as a raw material, with a very small proportion of various end parts made of cellulose.
Pulp is obtained from wood consisting only of 40-44% cellulose by weight. Since a high cellulose content of over 95% by weight is generally required in pulp for the production of lyocell moldings, a large proportion of the raw material for material use is lost during cooking and bleaching. There are a number of known ways of reducing the proportion of hemicelluloses in particular, both in pulp production on the way from wood to pulp or to the lyocell end product:
There are indeed strong efforts to use these other components as by-products. However, implementation is only carried out in small quantities due to known technical restrictions. In the waste liquors from pulp production, these further wood components are present in the form of a large number of different degradation products, in addition mixed with strong acids or bases, which makes separation and further processing extremely difficult. WO 98/16682 describes a production process for a cellulose composition suitable for fiber production. A starting mixture which is not considered suitable for fiber production (but only for paper production) is processed in such a way that the hemicellulose content, in particular the xylan content, is reduced. The WO 99/47733 describes Lyocell fibers and the WO 2010/132151 A2 reveals a pulp with a cellulose with a low degree of polymerization.
Nevertheless, efforts have been made in recent years to broaden the raw material base for Lyocell products through the use of celluloses with increased levels of lignin and/or hemicelluloses.
U.S. Pat. Nos. 6,440,523 and 6,444,314 describe such approaches as examples:
The approach taken in these papers is essentially to describe either the pulp and/or the lyocell products made from it, which, in addition to the cellulose content, also have a hemicellulose content of more than 5% by weight. However, it is considered essential in all these writings that the higher hemicellulose contents described there are only possible if a number of other essential conditions are fulfilled at the same time. These are, for example, a certain viscosity of the pulp, a maximum copper number and/or a maximum kappa number.
Although lyocell products are described in these papers, it is remarkable that the developments based on these intellectual property rights have not yet been realized on a large scale, although the use of cellulose with a higher hemicellulose content in particular should bring significant cost and thus competitive advantages. This may well be due to the difficulties in up-scaling from laboratory scale and the achievable fiber properties, which do not meet the expectations of the textile and nonwovens market. The US 2015/0184338 A1 reveals force pulp with a low content of hemicelluloses.
In the interests of maximum resource utilization, it would be desirable to be able to use as many material components as possible from the raw material wood to produce a lyocell fiber. The primary goal in the quest for the most comprehensive sustainability possible and a truly effective biorefinery concept must be to use the natural raw material wood as comprehensively as possible for the main product, namely Lyocell molded bodies, from the outset. The extraction of by-products remains of great importance, but overall this remains of secondary importance. The previous efforts to this end have failed because the reduction of the cellulose content in the fiber either led to a massive change in the material and property parameters of the resulting (Lyocell) fiber (or other variants of molded bodies) or, on the other hand, no stable large-scale production was possible. On the contrary, a large number of patents and publications require that the content of lignin, hemicelluloses and accessory components should be extremely low for the large-scale application of a chemical pulp in the Lyocell process.
For these reasons, it is desirable to provide technologies that can be used on a large scale to reduce the proportion of cellulose in the finished fiber by increasing the proportion of other wood components, in particular hemicelluloses, but also lignin, without significant restrictions with regard to the resulting material parameters. Despite the large number of state-of-the-art approaches, there are currently no known processes that can be used on a large scale to manufacture such Lyocell products with a reduced cellulose content.
The aforementioned prior art problems are overcome by this invention. The present invention provides a pulp according to claim 1, a lyocell product according to claim 9, and the methods according to claims 16 and 18. Preferred forms of the invention are indicated in the subclaims and the following detailed description of the invention.
In particular, the present invention provides the following aspects, as well as the preferred embodiments cited in the subclaims and the description.
If the proportion of cellulose in the lyocell process is reduced, this means that the savings are to be offset by other substances from the wood raw material. This poses the problem of process stability or property change when the cellulose content is reduced, as explained above. The main components of non-cellulosic material in the raw material wood are hemicelluloses (essentially polyoses from the sugar monomers xylose, arabinose, mannose, galactose, glucose and rhamnose), lignin and accessory components.
Cellulose: It is the structural substance of the cell walls in wood and is mainly used for tensile strength. The long molecule chains of glucose units are stored together in so-called fibrils several times in a helical structure. This helical arrangement in the cell wall ensures good bending strength of the tree, e.g. in the event of wind loading or of the wood, e.g. in a roof construction. Cellulose is hydrophilic, but not water-soluble due to its high crystallinity.
Lignin: binder for the solid bond of cellulose in the form of an amorphous matrix. Thus, lignin is mainly responsible for the compressive strength, on the other hand it is less flexible and in contrast to cellulose hydrophobic. It is responsible for the stamina of the tree. Plants that do not store lignin reach only low growth heights. Lignin is biologically relatively stable and biodegradable only slowly.
Hemicellulose in the sense of the present invention means components present in wood in the form of short-chain polymers of C5 and/or C6 sugars. In contrast to cellulose, they have side groups and can therefore only form crystals to a much lesser extent. Their basic building blocks are mannose, xylose, glucose, rhamnose and galactose. The side groups preferably consist of arabinose groups, acetyl groups and galactose residues as well as 0-acetyl groups and 4-O-methylglucuronic acid side groups. It is known that mannans prefer to be associated with cellulose, while xylans tend to associate with lignin. The composition of hemicelluloses varies greatly depending on the type of wood used. During the manufacturing process of pulp, 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 which have been altered by their processing and also those which have been adjusted for their intended use by specific chemical modification. Also included are short-chain celluloses and other polyoses with a DP of up to 500.
Accessory components: Accessory constituents are organic and inorganic wood components other than lignin, cellulose and hemicellulose, and usually include salts and low molecular organic compounds of up to about 100 atoms, such as tannins, resins, fats and waxes, tannins and humins, terpenes, terpenoids and phenolic compounds, pectins, suberins, polyphenols and polyoses.
If the cellulose content in a cellulose material is to be reduced as desired and other components of the raw material wood are to compensate for this reduction, it has surprisingly been shown that only the combination of different types of sugar in a certain ratio makes it possible to indicate a cellulose which, despite its reduced cellulose content, allows the safe large-scale production of lyocell products, whereby these products also have a reduced cellulose content, but nevertheless have satisfactory product properties.
According to the invention, it is essential that a reduced cellulose content in the pulp of less than 90% by weight has a hemicelluloses content of at least 7% by weight, the ratio of sugars with five carbon atoms such as xylan to sugars with six carbon atoms such as mannan (hereinafter referred to as C5/C6 ratio) being in the range from 125:1 to 1:3.
Surprisingly, the large-scale production of lyocell products can be safely realized with such a pulp, even though the cellulose content in the pulp is lowered.
The cell materials used here, which are preferably used in the context of the present invention, show, as already explained, a relatively high content of hemicelluloses with the composition defined here. In comparison with standard pulps with a low hemicellulose content, used especially in the state of the art for the production of standard lyocell fibers, the preferred pulps used in the context of this invention also show further differences, which are listed below.
In comparison with standard cell materials, the cell materials preferably used in the present invention show a rather fluffy view. After grinding (during the production of starting materials for the production of spinning solutions for the Lyocell process), this results in a particle size distribution with a high proportion of larger particles. As a result, the bulk density is much lower compared to standard pulps with a low hemicellulose content. Such a low bulk density requires adaptations with regard to dosing parameters (e.g. dosing using at least two storage tanks) during the production of the spinning solutions. In addition, the cell materials preferably used in the present invention show an impregnation behavior towards NMMO, which in comparison with standard cell materials shows that impregnation is more difficult here. This can be checked by evaluating the impregnation 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 for 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 approximately 2.3 g/g. This requires adaptations during the preparation of spinning solutions, such as increased solution time (e.g. explained in WO 94/28214 and WO 96/33934) and/or temperature adaptation and/or increased shear during dissolution (e.g. WO 96/33221, WO 98/05702 and WO 94/8217). This makes it possible to produce spinning solutions that allow the pulp described here to be used in a standard lyocell process).
In a preferred form of the present invention, the pulp used for the manufacture of lyocell products, preferably fibers as described here, shows a SCAN viscosity in the range 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 cupriethylenediamine solution, a method known to the professional and which can be performed with commercially available devices, such as the Auto PulpIVA PSLRheotek device, available from PSL-Reotek. The SCAN viscosity is an important parameter which influences the processing of pulp during the production of spinning solutions. Even if two pulps show a large agreement in terms of composition etc., different SCAN viscosities lead to a 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 maturing step, comparable for example with the viscose process, where the degree of polymerization of the cellulose can be adapted to the needs of the process. Therefore, the viscosity specifications of a raw pulp are typically for the lyocell process in a small target window. Otherwise, problems may occur during production. In accordance with the present invention, it was found that the pulp viscosity is preferably as described above. Lower viscosities lead to a deterioration of the mechanical properties of the Lyocell products. Higher viscosities can in particular lead to an increased viscosity of the spinning solution, so that spinning becomes slower overall. Lower spinning speeds also result in lower tensile ratios, which again can have a significant influence on the fiber structure and fiber properties (Carbohydrate Polymers 2018, 181, 893-901). This would require procedural adaptations leading to a capacity reduction. The use of cellulose with the viscosities defined here, on the other hand, enables simple processing and the manufacture of high-quality products.
The term “lyocell process”, or the terms “lyocell technology” and “lyocell process” as used herein, designate a direct dissolution process of wood cellulose pulp or other cellulose based starting materials in a polar solvent (e.g. N-methylmorpholine-n-oxide (NMMO, NMO) or ionic liquids). Commercially, this technology is used to produce a group of cellulose staple fibers commercially available from Lenzing AG, Lenzing, Austria under the brand names TENCEL® or TENCEL™), which are widely used in the textile industry or the nonwoven industry. Other shaped cellulose bodies obtained by lyocell technology have also already been produced. In accordance with this process, the cellulose solution is usually extruded in a so-called dry wet spinning process using a forming tool and the formed solution is obtained e.g. after passing an air gap into a precipitation bath where the formed body is obtained by precipitating the cellulose. The molded body is washed and optionally dried after further treatment steps. A process for the production of lyocell fibers is described in U.S. Pat. No. 4,246,221, WO 93/19230, WO 95/02082 or WO 97/38153. As far as the present invention discusses the disadvantages of the state of the art and discusses the unique properties of the new products, disclosed and claimed here, in particular in the context of the use of laboratory equipment (especially in the state of the art) or in the context of (semi-commercial) pilot plants and commercial fiber spinning units, the present invention is to be understood as referring to units which can be defined as follows with respect to their respective production capacities:
In the context of the present invention, it has been shown that, especially in fiber production in the context of a lyocell process, orientation in the direction of production and stretching of the fibers takes place. From an initial more or less orientationless mix of different polymers and other components in the dope
The fiber properties are strongly influenced by the type and composition of the polymers. It is also known that cellulosic fibers produced by the Lyocell process have a very high crystallinity of about 44 to 47%, while fibers from the viscose process have a crystallinity of about 29 to 34%. The crystallinity describes the orientation of the cellulose polymers towards each other and thus, for example, their ability to absorb, swell and store water. In addition, the polymer chains in the non-crystalline areas of the lyocell fibers are more ordered than in the viscose fibers. As a result, ordinary lyocell fibers swell less and are less suitable for highly absorbent products than viscose fibers.
The use of cellulose with a reduced cellulose content in accordance with the invention unexpectedly enables a completely different type of aggregation of the polymers and thus a different structure of the lyocell fibers. Their crystallinity is significantly lower, typically 40% or less, such as 39% or less, and for example in the range 38% to 30%, such as in the range 37% to 33%.
The values for WRV for fibers in accordance with the present invention, isolated or in combination with the other preferred designs described here, preferably in combination with the values for the crystallinity of the fiber described here, are preferably 70% or more, in particular 75% or more, such as 80% or more, e.g. from 70 to 85%.
It is known from literature that xylans also form a crystal structure if their side chains have been split off during the production process and they are precipitated from a pure xylane solution (Fengel, Wegener p. 113; Fengel D, Wegener G (1989): Wood, Chemistry, Ultrastructure, Reactions; Walter de Gruyter Verlag). The same applies to Mannan (ibid.; p. 119). In the present invention, however, opposite effects can be seen. The polymers including the cellulose are present in dope in a mixture and are thus also spun out and precipitated. Furthermore, the hemicelluloses still have side groups, since the glucuronic acid side groups of xylans are comparatively stable under the conditions of acid digestion (Sixta H (Ed.) (2006): Handbook of Pulp Vol. 1; Wiley VCH p. 418). The hemicelluloses thus fulfil all the conditions required to disrupt the crystallization of the cellulose and thus form a more disordered structure than standard Lyocell fibers. Thus, the expert would expect that with a higher hemicellulose content and reduced cellulose content, useless products, in particular fibers, would result. However, it has been shown unexpectedly that the hemicelluloses content in combination with the C5/C6 ratio can be used to selectively control product properties. This mixture of different sugar polymers still achieves crystallinity values above those of viscose fibers, but the overall accessibility of the fiber to water is now increased, so that the water retention capacity (WRV) can be significantly increased. This improved absorbency is a decisive advantage for various applications, e.g. nonwovens. This relationship between decreasing crystallinity and increasing water retention capacity for Lyocell fibers is shown in
As shown in the examples, the qualities of the new Lyocell fibers with reduced cellulose content are similar to those of conventional TENCEL® fibers. It becomes clear that the fiber strengths are slightly below those of TENCEL® fibers, measured in the examples as strength and working capacity. At the same time, the cellulose content could be significantly reduced, recorded in the examples as a glucan value. By absorbing other wood components, the crystallinity decreases by up to 21% and the absorbency increases significantly by up to 27%, measured in the examples as crystallinity index and water retention capacity. Interestingly, the crystallinities of the new Lyocell fibers according to the invention lie between those of conventional TENCEL® fibers and nonwovens Lenzing Viscose® fibers; at the same time, the WRV is in the range of Lenzing Viscose®. The WRV thus rises more strongly than it could be explained by the decreasing crystallinity of the fibers. This is a clear sign of the unexpected properties that can be realized with this invention. The other components such as in particular hemicelluloses, but also lignin and accessory components from the wood not only provide a significant increase in yield, i.e. improved sustainability, but also a significant improvement in product properties such as water retention capacity.
As defined in claim 1, the pulp according to the invention is characterized by a reduced cellulose content, a minimum of hemicelluloses and a certain C5/C6 ratio with respect to the composition of the hemicellulose.
In a preferred form, the pulp, which may also be a mixture of different pulps (as long as the essential conditions are met), is a pulp having a hemicellulose content of from 7 to 50% by weight, preferably from 7 to 30% by weight, more preferably from 15 to 25% by weight, such as from 10 to 20% by weight.
The pulp to be used in accordance with the invention is also preferably a pulp containing at least 9% xylan by weight, preferably at least 10% xylan by weight. The proportion of mannan can be chosen, in combination or independently, in a wide range, as long as the ratio defined in the invention is fulfilled. Suitable man contents lie in the range from 0.1 to 10 wt. %, such as from 0.1 to 9 wt. %, and in the form of 0.1 to 6 wt. %, from 0.1 to 4 wt. %, from 5 to 10 wt. %, from 6 to 10 wt. %, etc., from 0.1 to 9 wt. %. In forms of execution, the mannan content is in the range from 0.1 to 1 wt. %, preferably in combination with a xylan content of at least 9 wt. %, preferably at least 10 wt. %. In other designs, the manganese content is higher, preferably in the range of 6% or more by weight.
In a preferred form, isolated or in combination with the forms described above and below, the cellulose content in the pulp is in a range of equal to or less than 90 wt. % to 50 wt. %, preferably in a range of 90 wt. % to 60 wt. %, such as from 85 wt. % to 70 wt. %.
The weight ratio of cellulose to hemicellulose may range from 1:1 to 20:1. The proportion of accessory components can be more than 0.05 wt. %, preferably more than 0.2 wt. %, more preferably more than 0.5 wt. %. Unexpectedly, it has been shown that with such proportions of accessory components in the pulp according to the invention, the effect can be supported that the C5/C6 ratio in the produced lyocell products, especially fibers, is stable and the hemicellulose content does not change significantly (i.e. the content in the lyocell product does not decrease or only decreases to a minor extent compared to the pulp).
In another preferred design, the C5/C6 ratio in accordance with the invention achieves such a high retention capacity that at the same time a proportion of metal compounds, usually present as their oxides and hydroxides, of up to 25% by weight, based on the weight of the lyocell product (e.g. Mg(OH)2 or Al(OH)3 for flame retardant purposes) is made possible, which further substantially reduces the cellulose proportion. Such metal compounds are in particular TiO2, Al2O3, MgO, SiO2, CeO2, Mg(OH)2, Al(OH)3, BN, ZnO and originate partly from the mineral components of the wood or can be added to the cellulose solution as functional additives (flame retardants, matting agents, biocides . . . ).
In another preferred design, lyocell fibers with a cellulose content reduced to less than 70% can be produced, which not only meet the practical requirements compared with the known lyocell fibers (mechanical strength etc.), but are also even more suitable for some applications due to the new properties resulting from the invention. The relevant studies have shown that fibers in the proposed composition show in particular an increased water retention capacity and rapid biodegradability during composting.
According to the invention, the ratio of C5/C6 sugars of non-cellulosic polymers has been shown to be an important factor in adjusting the fiber composition and its resulting properties. By adjusting this ratio, also in combination with the content of hemicelluloses, the desired product properties can be adjusted.
In this context, the expert knows how to control or adjust the C5/C6 ratio. This can be achieved by mixing various pulps such as softwood pulps with a higher mannan content with hardwood pulps with a higher xylan content. Trials have confirmed another very effective way to adjust the setting. The ratio of C5 to C6 sugars can be controlled by setting specific cooking parameters such as the H factor. This is illustrated in
When using softwood, the hemicellulosis ratio is the other way around. The proportion of mannan in wood and pulp is higher. Here, contrary to expectations, Mannan is dismantled faster than Xylan as can be seen in
Another way to adjust the pulp composition according to the invention is to add C5 and/or C6 sugars previously obtained in other processes or process steps, such as an alkaline extraction, be it a cold alkaline extraction or an E step or the like. For the production of viscose, the addition of hemicelluloses in dissolved form to the spinning mass and the subsequent joint spinning are known (WO2014086883). This allows viscose fibers with a reduced cellulose content to be produced. This is only possible because the viscose process takes place in an aqueous medium and the hemicelluloses are correspondingly alkali-soluble, so the cellulose exanthate and the dissolved hemicelluloses can be mixed together and spun out together. In contrast, the pulp is dissolved in NMMO or similar solvents in the Lyocell process, which means that no alkaline or aqueous solutions can be added. They would dilute the solvent and reduce solubility or even lead to unwanted precipitation. Hemicelluloses cannot therefore be added in the form of solutions in the production of spinning solutions but must be introduced differently into the process. One possibility is the addition in the pulp production process, so that the mixture can then be dried with the pulp.
Surprisingly, it was found that close attention to the hemicellulose composition is a crucial point for the technical production of lyocell moldings, in particular fibers. A large-scale use of hemicellulose in the fiber structure is only possible if the proportion of the C5 fraction is correlated with the proportion of the C6 fraction. The ratio of xylan to mannan is preferred between 18:1 to 1:3, preferably 9:1 to 1:2. At the same time such a mixing ratio allows the incorporation of 0.5-5 wt. % lignin (and/or other accessory components) into the fiber structure without impairing the desired properties to an adverse extent.
The fibers provided by the invention have common fiber titers, such as 7 dtex or less, for example 2.2 dtex or less, such as 1.3 dtex, or less, or even less, such as 0.9 dtex or less, depending on the desired application. For applications in the nonwoven sector, titers of 1.5 to 1.8 dtex are typical, while lower titers such as 1.2 to 1.5 dtex are suitable for textile applications. This invention also includes fibers with even lower titers as well as fibers with significantly higher titers, such as 10 dtex or less, such as 9 dtex or less, or even 7 dtex or less. Suitable lower limits for fiber titers are values of 0.5 dtex or more, such as 0.8 dtex or more, and 1.3 dtex or more in the forms. The upper and lower limits revealed here can be combined and the resulting ranges, such as from 0.5 to 9 dtex, are also included. Surprisingly, the earth discovery at hand enables the production of fibers with titers that can be used in the entire spectrum of fiber applications, including textile applications as well as nonwoven applications.
If reference is made in this application to parameters, these are determined as described here. It is essential that these parameters are obtained with the fibers as such, comprising a maximum of 1% by weight of additives, such as matting agents, etc., and that the fibers are not affected by the process. However, the fibers described here can of course contain conventional additives in normal quantities, provided that this does not impair the production of spinning solutions and/or the production process of the fibers.
The following examples illustrate aspects of this invention.
Determination of the Crystallinity Index [%]
The crystallinity index is determined by Raman spectroscopy. This method is calibrated with data from the X-ray wide-angle method (WAX) and was published by Röder et al. (2009) (Roder T, Moosbauer J, Kliba G, Schlader S, Zuckerstätter G, and Sixta H (2009): Comparative Characterizations of Man-Made Regenerated Cellulose Fibers. Lenzing Reports Vol. 87, p. 98 ff.).
Allow the sample to swell overnight at 20±0,1° C. After further dilution, the sample is centrifuged in accordance with Zellcheming Leaflet IV/33/57 at 3000 times acceleration due to gravity. The water retention capacity is then calculated as follows:
WRV=(weight of wet sample−weight of dry sample)/weight of dry sample×100
Table 1 shows the results of the adjustment of the C5/C6 ratio, for two wood species, using the example of the variation of the H-factor in magnesium bisulphite digestion.
sylvatica
fagus
Picea
abies
In the pilot plant, a new Kraft chemical pulp was produced from eucalyptus wood using the VisCBC process in accordance with the invention. The H-factor was 1200, the effective alkalinity in the cooking liquor was 25 g/l. Bleaching was performed after a TCF sequence. Relevant process information and product properties are given in Table 2.
In this new chemical pulp with reduced cellulose content, the xylan-to-mannan ratio has been extremely increased to 121 in the finished fiber, while the cellulose content has been kept very low at about 85%. This new pulp fully meets the requirements of the Lyocell process for the production of the new Lyocell fiber with reduced cellulose content.
Table 3 summarizes the salaries of the sugar monomers of the starting pulps for the production of Lyocell fibers.
Table 4 shows mechanical properties for standard fibers (lyocell and viscose) compared to properties achieved with lyocell fibers produced with invention pulp. The results impressively demonstrate the advantages of this invention.
Both in pilot plant trials and in large-scale production of lyocell fibers in accordance with the present invention, it has been shown that acceptable values for strength and working capacity can be achieved for commercially relevant titers, despite a considerably lower cellulose content. At the same time, the WRV increases drastically, so that such fibers become interesting for new areas of application, which were previously occupied by viscose fibers. Compared to commercially available viscose fibers, however, significantly higher mechanical properties can be achieved with the Lyocell fibers invented.
The new, inventive lyocell fibers thus combine the advantageous properties of previously commercially available lyocell and viscose fibers.
| Number | Date | Country | Kind |
|---|---|---|---|
| 18160123.8 | Mar 2018 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/055593 | 3/6/2019 | WO | 00 |
