WO2019170667A1

WO2019170667A1 - Dissolving pulp

Info

Publication number: WO2019170667A1
Application number: PCT/EP2019/055436
Authority: WO
Inventors: Gabriele Schild; Verena Silbermann
Original assignee: Lenzing Aktiengesellschaft
Priority date: 2018-03-06
Filing date: 2019-03-05
Publication date: 2019-09-12
Also published as: TW201938591A

Abstract

The present invention relates to a dissolving pulp which is characterised by a combination of properties: the pulp is produced using a sulphite pulping process; - the pulp has a bimodal molar mass distribution, wherein a first maximum of the molar mass distribution is in the range of (on the basis of g/mol) 4.2 to 6.0 log M, preferably 4.3 to 5.7, particularly preferably 4.5 to 5.5, and a second maximum of the molar mass distribution is in the range of 3.0 to 4.2 log M, preferably 3.5 to 4.0, particularly preferably 3.6 to 3.9; - the pulp has a mass average of the molar mass of log Mw 5.0 to 5.5, preferably 5.2 to 5.5; - the pulp has a cellulose content of less than 95 wt.%.

Description

Chemical pulp

The present invention relates to a chemical pulp, its use for the production of cellulose fibers, in particular lyocell fibers, and lyocell fibers which are produced by the

Spinning the inventive chemical pulp are available.

background

The predominant processes for producing chemical pulps are the Kraft process and the sulfite process. For subsequent processing in the viscose or lyocell process, a significantly lower viscosity is required than for papermaking and a higher purity, that is, the cellulose chains must be further split and low molecular weight carbohydrates, extractives and transition metals

as far as possible.

When using the alkaline Kraft method, this is achieved by combining the digestion with acid prehydrolysis and / or cold-alkali upgrading (CCE). In the prehydrolysis, a removal of the low molecular weight fractions is carried out before the actual boiling.

When using hardwood can be worked with the addition of pure water. The acetyl side groups of xylan split off under elevated temperature and form acetic acid with the water. This in turn accelerates the autocatalytic cleavage of the hemicelluloses, thus accelerating the degradation of the low molecular weight constituents and their solution in the aqueous phase, in the prehydrolysate.

When using softwood, a large proportion is present as mannan and only a small proportion in the form of xylan. The cleavage of the pendant acetyl groups is not sufficient to lower the pH so much that the acidic catalytic cleavage proceeds. As a catalyst, mineral acids are usually added. At a typical ratio of water to wood of 3 to 4.5: 1, a large amount of acidity falls

Pre-hydrolyzate for further processing. It not only contains dissolved low molecular weight carbohydrates but also small amounts of dissolved lignin. Upon relaxation of the container and emptying of the pre-hydrolyzate these Ligninbruchstücke fall out, condense and lead to significant sticking to pumps, valves and piping. This problem has so far been bypassed industrially so that chemical pulps with the

Prehydrolysis Force Procedures are only produced on a campaign basis and mainly Be cooked paper pulps that do not require prehydrolysis. With the alkaline cooking liquor for the production of paper pulp, therefore, in between all

Equipment rinsed and cleaned. The deposited and condensed lignin molecules then dissolve again.

As a result, the production capacity for chemical pulps is extremely limited. Furthermore, there is currently no technology for processing the prehydrolysate, for the recovery of mineral acids and for the production and use of low molecular weight

Carbohydrates in industrial use.

Another possibility for producing chemical pulps by the Kraft process without capacity limitation is the use of steam prehydrolysis. The removal of low molecular weight carbohydrates takes place using steam. The vapor phase with the dissolved carbohydrates is then displaced later with the alkaline cooking liquor. This method is limited to hardwood and prevents the preparation of the

Hemicelluloses completely, because the additional product stream is evaporated and burned with the cooking liquor, but allows a production of chemical pulps without

Interruptions with high capacities. This technology is known under the name VisCBC and finds industrial application (WO 94/12719).

Beyond that, in the literature (WO 2007/128026 and EP 2 855 765 B1)

Process possibilities described, which manage with a very short prehydrolysis in the vapor phase or without prehydrolysis. The pulp is subjected to cold or alkali upgrading (CCE) after or before the first bleaching stage. At low

Temperatures <50 ° C, the pulp is treated with pure caustic soda or white liquor from the recovery of the power process to remove the low molecular weight fraction of carbohydrates. The CCE liquor with the dissolved carbohydrates is pressed off. With ultra or nanofiltration these carbohydrates can then be removed from the

Press liquor are separated.

In the case of acid sulfite digestion, cooking for chemical pulps is carried out under harsher conditions than in the production of paper pulps, ie a longer cooking time and an increased use of chemicals. Most of the raw pulp still has a proportion of low molecular weight carbohydrates. This is partially removed in the bleach. For high-purity pulps, even a hot-alkali process (HCE) is used in bleaching. An HCE stage has a high energy requirement and is very unselective, ie Significant proportions of high molecular weight cellulose are degraded, which in turn comes at the expense of the yield.

These pulps are very reactive in the viscose and lyocell process, but usually have a lower degree of purity than alkaline pulps produced, or at the same degree of purity significantly lower yield. For this reason, new factories are no longer built according to this procedure, but according to the Kraft process. However, the sulphite process still has some importance as it accounts for a large proportion of existing capacity.

Conventional processes for the production of chemical zeolites mean that the yield is considerably reduced by the removal of the low molecular weight fraction, and there are clear problems in terms of cycle closure and environmental compatibility. Chemicals are further processed into a wide variety of cellulosic products. After the viscose z. For example, textile fibers or non-wovens products are manufactured. The viscose process is currently the most important process in the industry. The pulp is after a pre-ripeness in caustic soda, which is used to adjust the

Degree of polymerization, d. H. the chain length of the cellulose is used, xanthogeniert and precipitated after dissolution in sodium hydroxide in an acidic spin bath. Here are different

Process steps on each other, which allow a subsequent purification of the cellulose and a breakdown and removal of by-products. With this method, therefore, certain unfavorable pulp qualities can be compensated to a small extent.

On the other hand, it is quite different with the direct-release methods. The pulp is treated directly in a suitable solvent, e.g. As NMMO or ionic liquids, without the

Intermediate step of derivatization dissolved and then spun directly as a thread. These procedures are much more environmentally friendly. However, neither the degree of polymerization of the cellulose can be adjusted, nor can impurities be discharged to any appreciable extent. In the large-scale lyocell process, the cycle closure is very close. It is therefore well known that especially the direct dissolving processes place high demands on the quality of the used chemical pulp.

According to the state of the art, a chemical pulp to be used should have a low viscosity of 250 to 430 ml / g. In addition, it should have a very low proportion of low molecular weight carbohydrates. The proportion of low molecular weight

Carbohydrates are determined in practice over industry standard values such as R18, S18, alpha content or the like. In addition, the degree of polymerisation of the carbohydrates can be represented by SEC (size exclusion chromatography) as molecular weight distribution.

Chemical pulps vary according to the manufacturing process

Molar mass distributions on. For sulfite pulps (acid digestion) a distribution with a low molecular weight shoulder is described for kraft pulps (alkaline

On the other hand, a unimodal distribution (Sixta 2006, 11.3 Dissolving Grade Pulp p. 1035). In documents US 6,514,613, US 6,210,801 and US 6,331,354 a unimodal distribution of the degree of polymerization is described as advantageous. As far as in these documents of pulps with multimodal distribution of the degree of polymerization is mentioned, this is achieved by mixing pulps with unimodal distribution. Also, a low content of transition metals (<20 ppm), residual lignin (kappa number <2.0), carbonyl groups (copper number <2) and extractives is regarded as a prerequisite for good processability and sufficient stability in the lyocell process. For alkaline chemical pulps, these needs were also shown in the following documents: US 6,440,523; US 6,444,314; US 6,528,163; US 6,686,040; US 6,685,856;

6,605,350.

The typical molecular weight distributions of a commercially available pulp ("Comparative Pulp # 1") prepared by a prehydrolysis Kraft pulping process and a commercially available pulp prepared by a sulfite process ("Control # 2") are shown in FIG.

As a result, pulps produced by a kraft process are referred to as "kraft pulps" and pulps produced by sulfite processes are referred to as "sulfite pulps".

Paper pulps, that is, high yield pulps, have a bimodal molecular weight distribution when made from hardwood, or at least one additional low molecular weight shoulder when made from softwood (Sixta 2006, 11.2 Paper-Grade Pulp p. 1018). ,

The term "bimodal" here and below denotes a molecular weight distribution which has more than one maximum, in particular two maxima.

J. Oberlerchner et al., "OverView of Methods for the Direct Molar Mass Determination of Cellulose", Molecules 20 (6), 2015, 10313-10341 shows in Figure 5 the Molar mass distribution of a pulp of hardwood, which has a low molecular weight shoulder, but no second maximum.

Other pulps whose molecular weight distribution has a low molecular weight shoulder but no second maximum are

- K. Fischer et ab, "Hemicellulose in Dissolving Pulp and its Behavior during its Processing to Viscose", Macromolecular Symposia, 262 (1), 2008, 85-88) (Figures 1 and 3) and

H. Sixta et al., Evaluation of new organosolv dissolving pulps. Part I: Preparation, analytical characterization and viscose processability ", Cellulose 11 (1), 2004, 73-73 (Figures 1 and 11).

A. Potthast et al., Cellulose 22 (3), 2015, 1591-1613 discloses pulp "Pulp 3" containing xylose. "Comparative testing of methods for gel permeation chromatography of cellulose: coming closer to a standard protocol" and mannose of significantly less than 5% by weight (Table 2). An unbleached Pulp 4 pulp, also disclosed in this document, has a DP of 4401.

Further prior art is known from EP 1 362 935 A1 and US 2009/004473 A1.

So far, it is state of the art that chemical pulps for use in a large scale lyocell process of at least one ton of fiber

Production capacity per year (semi-commercial scale) up to 30,000 tons of fiber production capacity per year and more none to a very small one

may have low molecular weight carbohydrates. At the same time, their content of residual lignin and extractives (preferably <0.1%) must be very low so that they can be processed without difficulty, such as foaming in the process or deposits,

Filter clogging or thread breaks on the spinneret are processed further.

The present invention has set itself the task of a new chemical pulp for

To provide, despite a significantly increased content of low molecular weight carbohydrates is well suited for use in a large-scale process for the production of Fyocellfasem.

This object is achieved by a chemical pulp according to claim 1. Preferred embodiments are given in the subclaims. Brief description of the figures:

FIG. 1 shows a comparison of the typical molecular weight distribution of a commercially available prehydrolysis kraft pulp and of a commercially available sulphite pulp. Figure 2 shows the molecular weight distribution of an embodiment of the pulp according to the invention, compared with the molecular weight distribution of two kraft pulps.

FIG. 3 shows the molar mass distribution of two further embodiments of the invention

Pulp according to the invention, compared with the molecular weight distribution of a commercially available sulfite pulp.

FIG. 4 shows the molecular weight distribution of a further embodiment of the invention

Pulp according to the invention, compared with the molecular weight distribution of a commercially available sulfite pulp

Detailed description of the invention:

Surprisingly, it was found that a bimodal-distributed pulp with a significantly increased content of low molecular weight carbohydrates in Lyocell process can be used on an industrial scale. The significantly increased content of low molecular weight carbohydrates is reflected in the second maximum of the curve of the molecular weight distribution of the pulps according to the invention in the range of lower molecular weights. This

Chemical pulp may be produced by a conventional acid sulfite process followed by TCF or ECF bleaching. The increased yield of low molecular weight carbohydrates in the pulp significantly increases the yield. This leads to an overall higher use of the raw material wood and thus to an improved

Sustainability and thus LCA of the entire process and the products from this.

For the purposes of the present invention, the term "a bimodal molecular weight pulp pulp" is to be understood as meaning a single pulp which is produced by boiling from a single starting material and not by mixing a plurality of pulps having a different molecular weight distribution.

This is evident from the fact that in a bimodal pulp obtained by mixing several pulps, a maximum in the low molecular weight range

low molecular weight cellulose is formed, while it is formed in the bimodal pulp according to the invention from hemicelluloses and a low proportion of low molecular weight cellulose. From a paper pulp, a chemical pulp already differs by its overall lower average molecular weight. For hardwood paper pulp, Sixta indicates in 2006 an average degree of polymerization (DP) between 2636 and 4050 - which corresponds to a log M _w of 5.6 to 5.8 -, for chemical pulps for the viscose process only a DP of up to 1790 - this corresponds to one log M _w of 5.4, since it is a logarithmic scaling, so they are much lower viscous. The DP of chemical pulps for the lyocell process is approximately between 600 and 2000 (log M _w 5.0 to 5.5).

Here and in the following, the data from log M are based on the (if appropriate average) molar mass in g / mol.

The pulp according to the invention is produced by a sulfite pulping process.

Pulps produced by a sulfite pulping process differ in the same parameters as DP, viscosity and the like. from one to a force method

produced pulp in particular by

A significantly higher content of carbonyl groups

A higher proportion of high molecular weight cellulose chains (with a DP of 2000 or more) and

Differences in cell wall morphology due to different

chemical and physical processes in the kraft process or in the sulfite process.

In particular, the inventive chemical pulp may be prepared by a magnesium bisulfite process.

The inventive chemical pulp is characterized by a first maximum of

Molar mass distribution in the range of 4.2 to 6.0 log M, preferably 4.3 to 5.7, more preferably 4.5 to 5.5 characterized.

Furthermore, the inventive chemical pulp is characterized by a second

Maximum molecular weight distribution in the range of 3.0 to 4.2 log M, preferably 3.5 to 4.0, particularly preferably 3.6 to 3.9. The inventive chemical pulp has both maxima in the above-described ranges of molecular weight.

Between these two maxima lies a minimum of the molecular weight distribution.

Apart from the fundamental differences between a chemical pulp and paper pulps already described above, these maxima also differ fundamentally from the maxima of a bimodal molar mass distribution in hardwood pulp pulps.

According to Sixta 2006, the low molecular weight fraction of hardwood pulp has a maximum of about log M 4.2 for sulfite and 4.7 for kraft pulps. There is about the minimum for the inventive chemical pulps. The low molecular weight maximum of

On the other hand, preference is given to significantly lower chemical celluloses according to the invention between log M of 3, 6-3, 9.

The inventive chemical pulp is further characterized by a weight average molecular weight of log M _w 5, 0-5, 5 g / mol, preferably 5, 2-5, 5 g / mol. This is below the weight average molecular weight of paper pulps.

In the pulp according to the invention, the proportion of cellulose is below 95% by weight. Accordingly, it means that the content of hemicelluloses is 5% by weight or more.

In a preferred embodiment, the inventive chemical pulp is characterized by a proportion (% by weight) of polymer chains with a log M _w of 5.5 (corresponds to a DP of 2000) or more of 25% or less, preferably <22%, more preferably <19%. This proportion is significantly lower than that of

Paper pulps.

The pulp of the invention may be made of hardwood, softwood or a mixture of both.

The chips used to make the pulp may be made from logs, sawdust, waste wood or any mixture thereof.

The bark content should not exceed 2%, preferably 1%. The pulp according to the invention is preferably characterized in that it has a

Whiteness of 75 [% ISO] and more, preferably 85 [% ISO] and more, more preferably 90 [% ISO] and more.

Such degrees of whiteness can only be obtained if the pulp has been bleached.

The pulp according to the invention may preferably be bleached totally chlorine-free (TCF).

The pulp according to the invention may have an acetone extractant content of> 0.1%.

As extractant groups, the following groups with typical amounts were found in embodiments of the pulp according to the invention:

Fatty acids / resin acids> 0.19 mg / g

- Sterols> 0.082 mg / g

Steryl ester> 0.072 mg / g

Triglycerides> 0.013mg / g

The pulp according to the invention may have a copper number of> 2.0%.

The pulp according to the invention can be produced by a kraft or sulfite pulping process, in particular by the magnesium bisulfite process.

The magnesium bisulfite process is well known to the person skilled in the art and goes back to the Swedish researcher Ekman, who in 1872 became the first wood to dig for paper pulp (Ingruber in Ingruber et al., 1985). The production of

Chemical pulp for further processing in the viscose or lyocell process is state of the art in itself and is described in detail by Sixta in Sixta 2006. The production of the new bimodal chemistry pulp was similar for all following examples

Modifications of a per se conventional method can be achieved. The great advantage of the sulphite process is that, unlike alkaline processes in the cooking phase, delignification, ie the removal of lignin from the raw material wood, is favored over a long period of time over the breakdown of carbohydrates (Rydholm 1985 p. 505).

In addition, the glucomannan, which accounts for the majority of hemicelluloses in softwood, can be stabilized by a lower temperature regime and thus preserved in the pulp (Rydholm 1985, p. 512). Thus, the setting of the

Process parameters in the delignification of the process, ie during the cooking and Oxygen bleaching or alkaline extraction take place. This can be z. B. with the help of a change of the SCk offer in the cooking acid or with the lowering of the H-factor happen. The H-factor is a factor known from the literature (Sixta 2006), which describes the intensity of the digestion process on the basis of the variables temperature profile and time.

The present invention also relates to the use of an inventive

Chemical pulp for the production of Cellulosischen Formkörpem, in particular fibers, in particular for the production of Lyocellfasem or viscose fibers, preferably for

Production of Lyocell fibers.

Accordingly, the present invention also relates to a cellulosic molded body, in particular a lyocell fiber, obtainable by spinning an organic solution of a chemical pulp according to the invention, in particular a solution of the pulp in an aqueous tertiary amine oxide.

A molded body according to the invention, in particular a lyocell fiber according to the invention, is characterized in that the proportion of cellulose is less than 95% by weight. That is, conversely, the content of hemicelluloses is 5% by weight or more.

Examples:

The abbreviations used in the following examples are referred to

List of abbreviations at the end of the description section.

Analysis Methods:

Determination of molecular weight distribution

The molecular weight distribution is determined by size exclusion chromatography (SEC) in DMAc-LiCl solution. A multi-angle laser light scattering (MALLS) detector is used. The method was described by Schelosky et al. (1999). To determine the low molecular weight fraction, the proportion of the total molar mass, which is smaller than the molecular weight of the minimum, stated as a percentage of the total molar mass, was determined.

Analysis of the extract substance groups The extract substance groups are based on Ösa et al. (1994). 10 g of sample are extracted in the Soxhlet extractor with cyclohexane / acetone (9: 1). The extract is made up to 100ml lml extract is added lml standard and at 40 ° C in

Dryed vacuum oven. The standard is a multistandard of heneicosanic acid, cholesterol, cholesteryl palmitate and 1,3-dipalmitoyl-2-oleyl-glycerol. By adding 160 mM BSTFA: TMCS (9 + 1), the sample is derivatized at 70 ° C for 20 min. This solution is injected directly into GC 6890 from Agilent using the Zebron ZB-5HT Inferno column from Phenomenex and an FI detector.

Lyocell application test

The pulp is dissolved in NMMO and then tested by a standard method as described in Schild et al. (2011). The dope is with a constant

Speed pressed through a filter. The filter value is the time in minutes until the initial pressure is doubled. To numerical values of the order of

Viscose filter value, the value is multiplied by 10.

example 1

From industrial Eucalyptus globulus chips, a Mg bisulfite chemical cell stock ("pulp # 1") was made in a 10L pilot cooker. The boiling was carried out at a temperature of 45 ° C and a H-factor of 75. The total SCk was dosed with 200g / kg of dry wood. For comparison, a prehydrolysis kraft pulp was used

("Comparative Pulp # 3") also prepared on a pilot scale using conventional VisCBC (continuous batch cooking with steam prehydrolysis) conditions. The steam prehydrolysis was carried out at a temperature of l70 ° C and a P-factor of 600. The boiling took place at an H-factor of 300 at 150 ° C. The effective potassium concentration was 30 g / l.

Both pulps were end-bleached with a uniform O-Z-P sequence. The

Oxygen bleaching O was carried out at a temperature of 90 ° C, a consistency of 12% and a NaOH addition of 20kg / t pulp over a period of 60min. The

Ozone dosage in the Z-stage was adjusted to reach the final viscosity. The reaction temperature was 50 ° C. The P-stage was carried out at 70 ° C and lasted for l20min. At this stage, the following bleaching chemicals were added per ton of pulp: 6.0 kg NaOH, 5.0 kg H ₂ O ₂ , 5.0 kg MgS0 ₄ . In the following, the two pulps are additionally compared with a commercially available prehydrolysis kraft pulp (the "comparative stock # 1" of Fig. 1).

Table 1: Grades of the final bleached bimodal sulphite pulp from pilot cooks as compared to a prehydrolysis Kraft pulp

The kappa number is comparable for # 1 pulp and # 3 comparative pulp. By using the same bleaching conditions, # 1 pulp is clearly superior to # 3 in terms of whiteness. Also, the water retention as a measure of the

Pore volume and thus the absorbency and accessibility of the pulp for further processing is higher in pulp # 1 than in comparison # 3. The R18 value is lower due to the greatly increased low molecular weight portion of the carbohydrate chains. This is also in the low molecular weight fractions DP <50 or <100 and at a high PDI visible. The values for pulp # 1 are very high compared to the comparative pulp # 3.

Similar trends are also apparent in comparison to the market

Comparative pulp # 1.

FIG. 2 shows the molecular weight distribution of the pilot samples of the new bimodal

Sulphite pulp # 1 compared to Comparative # 3 and # 1 pulp.

For the graphic representation of the molecular weight distribution, the mass fraction of the dissolved sample in mol / g, which elutes at a specific point in time after separation on the GPC, is plotted against the molecular weight M. For better clarity, the X-axis

logarithmized, that is log M based on g / mol. It can therefore be deduced from this, how large the fraction of the sample, which has a certain molecular weight and thus a certain chain length - so a distribution of the chain lengths in the pulp examined.

While the molecular weight distribution of the new pulp # 1 is bimodal, both comparative pulp # 1 and comparative pulp # 3 show a unimodal distribution. This low molecular weight second maximum of the pulp according to the invention with a log molecular weight of 3.78 shows the retention of the low molecular weight constituents of the wood in the pulp to a large extent even after bleaching, while comparative pulp # 1 and # 3 have no second maximum. This naturally suggests itself in a yield advantage. After cooking, the yield of the pulp of the invention is 8.5% higher than that of the comparative pulp # 1. In bleaching, the pulp according to the invention degrades more strongly than the comparative pulp # 1, but retains, as the end product, a clear yield advantage of 2.9%. Pulp # 1 has a high whiteness of 94.2% after uniform bleaching. Here, by optimizing the bleaching conditions matched to the particular cooking process, bleaching chemicals can be saved, thereby reducing the degradation of the pulp during bleaching, which further increases the yield.

Example 2

Production experiments were carried out with Fagus sylvatica woodchips to produce the new bimodal sulfite wood pulp. Here, the viscosity was adjusted so that the products are suitable for further processing in the Lyo cell process. The values of two pulps of the invention ("pulp # 2" and "pulp # 3") are compared with a sulfite market pulp of the same viscosity (the "comparative pulp # 2" of Figure 1). Both pulps were commercialized with the same

Digestion process namely made with the acidic magnesium bisulfite process and then with a comparable TCF sequence end bleaching consisting of oxygen, ozone and peroxide bleach.

Table 2: Results of the production experiments for the production of two bimodal sulfite chemical pulps compared to a sulfite market pulp

The bimodal pulps of the present invention are well comparable to the market pulp, although the market pulp is from spruce wood and the pulps from the production trials are from beechwood. The viscosities are almost identical. The pulp # 2 attains a high degree of whiteness like the comparative pulp # 2. The whiteness of pulp # 3 at 90.9% is also sufficient. R10, R18 and the ash content are at the same level. The pulps according to the invention from the production experiments differ only by the high acetone extracts of 0.22% and 0.26% and the second low molecular weight maximum in the molecular weight distribution.

FIG. 3 shows the molar mass distribution of the sulfite pulps according to the invention in comparison to a sulfite market pulp of comparative pulp # 2. The log values of the low molecular weight maxima of pulps # 2 and # 3 are 3.80 and 3.86, while comparative pulp # 2 has no second low molecular weight peak. The proportion of carbohydrates with a DP <100 is slightly increased, the proportion DP <50 is 2.5 to 3 times. As a result, the molecular weight distribution is slightly wider. The polydispersity index for the pulps of the present invention is 5.3 and 5.5 while that of the comparative pulp is 4.1. By contrast, the high molecular weight fraction is the same for all pulps (compare FIG. 3).

The kappa number determination method is generally used to characterize a pulp. It describes the residual content of lignin. In endgebleichten chemical pulps lignin is hardly, so here are more oxidizable

Ingredients recorded. In order to better characterize these groups of substances, the extractives were additionally determined by means of acetone extraction and then analyzed with the aid of gas chromatography individual extract groups. Here was another significant difference of the pulps of the invention compared to

Market pulps. The inventive chemical pulps are suitable for the lyocell process, despite an increased content of extractives, specifically throughout all extractant groups (see Table 3). Three market pulps, the softwood sulfite pulp comparison pulp # 2 and additionally a sulphite pulp from hardwood, serve as comparison

(Comparative pulp # 4) and another hardwood prehydrolysis kraft pulp

(Comparative pulp # 5). The extracts of the new bimodal pulps amount to 2 to 3 times the market pulp, thus far exceeding the previously required limits for use in direct dissolving processes. All pulps were successfully processed on an industrial scale in the Lyocell-V experience into fibers.

Table 3: Extract substance groups of the new bimodal sulfite chemical pulp compared to market pulps

Example 3

A sulphite pulp made of spruce wood was removed from production after cooking and the first bleaching stage. This pulp was finally bleached with ozone and hydrogen peroxide. The ozone stage was carried out at medium consistency and at 50 ° C.

1 lkg of ozone was metered per ton of pulp. The subsequent P-stage was carried out at 65 ° C for 180min. There were added 5.0 kg of NaOH and 4.0 kg of H ₂ O ₂ per ton of pulp.

The resulting pulp of the invention is referred to as "pulp # 4".

For comparison, again the sulfite market pulp ("Comparative Pulp # 2") from Example

2 used. Both pulps were made from spruce wood, thus excluding the influence of the wood species. Both pulps were produced using the Mg sulphite process, which also neglected the influence of the pulping process. After final bleaching, the bimodal sulfite chemical pulp of the present invention has comparable properties to the market pulp of Comparative Pulp # 2 (see Table 4). Also, a similar level of kappa and whiteness was achieved. Also acetone extract and ash are comparable. Surprisingly, the pulp according to the invention could also be further processed with a high copper number of> 2%. The viscosity of the pulp according to the invention is slightly higher than that of the market pulp in the range required for the lyocell process. Table 4: Properties of the sulfite chemical pulp according to the invention in comparison with a market pulp made of spruce wood

The bimodal distribution of the pulp according to the invention becomes clear in comparison to the comparative pulp # 2 both from FIG. 4 and from FIG

Low molecular weight maximum of the inventive pulp # 4 is at a log molecular weight of 3.81 g / mol. The low molecular weight fractions PD <50 and <100 are significantly higher, while the high molecular weight fraction DP> 2000 is greatly increased. This results in a much broader molecular weight distribution (PDI) for the bimodal pulp. It is 7.3 versus 4.1 for the market pulp # 2 comparative pulp. At the same time, the maxima of the high molecular weight carbohydrates are very close to each other for the investigated pulps. Characterization of the low molecular weight maximum

The bimodal chemistry pulps of the invention were prepared from various hardwood and softwoods on a pilot scale and in production trials by means of TCF bleaching. The raw material thus has a different carbohydrate composition. The experimental conditions also vary. In addition, the middle soft

logarithmic molar masses (log M) strongly from each other. They range between 5.23 for pulp # 2 and 5.60 for pulp # 1. Since this is a logarithmic evaluation and presentation, the difference is very clear and is also reflected in the viscosity, which varies between 405 ml / g for pulp # 2 and 580 ml / g for pulp # 1. The differences are extremely evident in the molecular weight of the high molecular weight maximum.

While pulp # 1 has a maximum at a M of 5.37, the lowest value of pulp # 2 is 4.75 (see Table 6). This corresponds to a degree of polymerization of 1456 or 345.

Surprisingly, this has very little effect on the low molecular weight fraction of the bimodal pulps according to the invention. The molecular weight distributions of the low molecular weight carbohydrates are very similar for all pulps investigated. The minimum for a DP is between 51 and 72. This corresponds to a log M of 3.91 and 5.07, respectively. The low molecular maximum lies between a DP of 28 and 44. This corresponds to a log M of 3.66 and 3.86, respectively.

The pattern of the new Zehstofftype pulp # 4 on spruce wood basis is exactly in the required range for lyocell application in terms of viscosity (440ml / g).

Characteristically, the molecular weight distribution again shows the clear minimum between the two maximum peaks, over which the bimodality is defined, and which allows the determination of the low molecular weight fraction.

The mass fraction of low molecular weight carbohydrates below the minimum is 6.1%. This fraction characterizes the increased yield by obtaining the low molecular weight carbohydrates. This results in a significant economic advantage and a more efficient use of the raw material wood and thus a better eco-balance for the entire production chain and the products.

The sum of the hemicelluloses differs significantly from the low molecular weight fraction of the pulps. Thus pulp # 1 has a low molecular weight content of 8.7% and a hemicellulose content of 5.2% in total. In this pulp so is the low molecular weight Peak significantly larger than the hemicellulose content, ie in the low molecular weight fraction are other polymers such as degraded short-chain cellulose.

It is different with pulp # 4. At 8.0%, the low molecular weight fraction is slightly below the sum of the hemicelluloses with 8.9%. H. Hemicelluloses, which have polymer chains so long that they can not be found in the low-molecular peak, also have a role in this sample. That means in summary that in the

low-molecular peak also degraded cellulose is to be found and that at the same time hemizelluloses in a longer-chained form can hold, so that they are not to be found in the low-molecular peak. The low molecular weight peak is thus by no means identical to the proportion of hemicelluloses in the pulp

Table 6: Comparison of the maxima of the new bimodal sulfite chemical pulps or of the low molecular weight fraction

Use of the Pulps According to the Invention for the Production of Lyocell Fibers:

It has been repeatedly stated in the literature that a reduced cellulose content has a negative impact on the spinnability and fiber qualities in the lyocell process. Fink observed in unbleached Organosolvzellstoffen, which thus had an increased content of hemicelluloses and lignin, that the spinning behavior in the lyocell process was characterized by extremely poor. Chen attributed the poor spinnability directly to increased hemicellulose content. At the same time he received lasers with significantly lower mechanical properties at elevated hemicellulose content. He calls that

Removal of branched hemicelluloses as the key to making better lasers.

The poor spinning behavior of high hemicellulose pulps is attributed in the literature to lignin, hemicellulose and cellulose in the pulp are associated with each other and form so-called lignin-carbohydrate complexes. 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. Up to now, this has only been possible by using ionic liquids in a direct dissolution process, since the pulp was additionally treated with electron radiation before the dissolution process (Ma et al., 2018). Thus, the lignin-carbohydrate bonds could be solved and the pulps were successfully dissolved in ionic liquids and spun out. However, fibers with a low cellulose content also occurred here

Loss of strength.

In contrast, however, no pretreatment of the pulp was necessary for the production of lyocell fibers from the pulps of the invention. Surprisingly, the fibers could be prepared directly from the pulps of the invention and showed no industrial effect on the spinning behavior or the

Fatigue strength.

Example:

The pulp # 4 according to the invention was subjected to a Lyo cell application test. For comparison, the prehydrolysis kraft pulp from Example 1 (comparative pulp # 3) and two market pulps (see Table 7) were used. Overall, it should be noted that the fibers produced from the inventive chemical pulps are very well comparable with the fibers produced from the market pulp. The fiber of the bimodal pulp # 4 of the present invention showed a good elongation of 9.4%. The textile strength is below that of the fibers made from the other pulps.

It is well known from polymer chemistry that a high proportion of low molecular weight

Polymers such as in this example adversely affected the strength. The filter value is sufficient. So this pulp is sufficiently easy to process in the application test. The pulps according to the invention are thus suitable for the production of a new fiber type by the fyocell method.

Table 5: Fyocell application tests of pulp # 4 compared to prehydrolysis kraft and market pulps

Abbreviations

CBC Continuous batch cooking

CCE cold alkaline extraction (cold caustic extraction)

DP degree of polymerization

EA effective alkali

ECF elemental chlorine-free bleach

HCE hot alkaline extraction (Hot caustic extraction)

IL ionic liquids

LH hardwood

M molecular weight, molar mass

MALLS multi-angel laser light scattering

M "number average molecular mass

MgS magnesium bisulfite pulp

M _{w is the} mass average of the molecular mass

NH softwood

NMMO N-methyl-morpholine-N-oxide

O oxygen bleach

odp Oven-dried pulp (oven dry pulp)

or Oven dried wood (oven dry wood)

P hydrogen peroxide bleaching (hydrogenperoxide bleaching stage)

PDI polydispersity index M _w / M _n (polydispersity index)

SEC size exclusion chromatography ssp. subspecies

R10 Alkali resistance at 10% NaOH

R18 Alkali resistance with! 8% NaOH TCF Total chlorine-free bleaching

VisCBC Continuous batch cooking for the production of chemicals

VH-K prehydrolysis kraft pulp

WRV water retention value

Z ozone bleaching

Non-patent literature

Ingruber OV in Ingruber OV, Kocurek MJ, Wong A (Ed.) (1985): Pulp and Paper

Manufacture Vol. 4 Sulfites Science & Technology, Historical Development, p VII et seq.

Örsa F, Holmbom B (1994): A Convenient Method for the Determination of Wood

Extractives in Papermaking Process Waters and Effluents. Journal of Pulp and Paper Science: Vol. 20, No 12

Rydholm SA (1985) Pulping Processes. 9 Chemical Pulping pp. 505 and 512. Wiley Verlag. Schelosky N, Röder T, Baldinger T (1999): Molar mass distribution of cellulosic products by size exclusion chromatography in DMAc / LiCl. Paper 53 (l2): 728-738 Shield G, Sixta H (2011): Sulfur-free dissolving pulps and their application for viscose and lyocell. Cellulose 18: 1113-1128

Sixta H (Ed.) (2006): Handbook of Pulp Vol. 1; 4.3 Sulfites Chemical Pulping, p. 432, 437, 452.

Sixta H (Ed.) (2006): Handbook of Pulp Volume 2; 11.3 Dissolving Grade Pulp, p. 1022 ff. Sixta H (Ed.) (2006): Handbook of Pulp Volume 2; 11.2 Paper Grade Pulp, p. 1010 ff.

Ma Y, Stubb J, Kontra I, Nieminen K, Hummel M, Sixta H; Filament spinning of unbleached birch kraft pulps: Effect of pulping intensity on the processability and the fiber properties, Carb Polym 179: 145-151, 2018.

Fink, H-P, Weigel P, Ganster J, Rihm R, Puls J, Sixta H and Parajo JC; Evaluation of new organosolv dissolving pulp. Part II: Structure and NMMO processability of the pulps, Cellulose 11: 85-98, 2004.

Chen, Jing-huan; Wang, Kun; Xu, Feng; Sun, Runcang; Properties of regenerated bamboo fibers prepared from raw materials with different hemicellulose content,

Abstracts of Papers, 249th ACS National Meeting & Exposition, Denver, CO, United States, March 22-26, 2015

Claims

Claims:

1. chemical pulp, characterized by a combination of the following features:

- The pulp is made by a sulfite pulping process

- The pulp has a bimodal distribution of the molecular weight, wherein a first maximum of the molecular weight distribution in the range of (based g / mol) 4.2 to

6.0 log M, preferably 4.3 to 5.7, more preferably 4.5 to 5.5 and a second maximum of the molecular weight distribution in the range of 3.0 to 4.2 log M, preferably 3.5 to 4 , 0, more preferably 3.6 to 3.9

- The pulp has a weight average molecular weight of log M _w 5.0 to 5.5, preferably 5.2 to 5.5 on

- The pulp has a content of cellulose of less than 95 wt.%.

2. A chemical pulp according to claim 1, characterized by a proportion (wt.%) Of polymer chains with a log M _w of 5.5 or more of 25% or less preferably <22%, particularly preferably <19%.

3. chemical pulp according to one of the preceding claims, characterized

characterized in that it has a brightness of 75 [% ISO] and more, preferably 85

[% ISO] and more, more preferably 90 [% ISO] and more.

4. chemical pulp according to claim 3, characterized in that it was totally chlorine-free (TCF) bleached.

5. Use of a chemical pulp according to one of the preceding claims for the production of cellulosic Formkörpem, in particular fibers.

6. Use according to claim 5 for the production of Lyocellfasem or

Viscose fibers.

7. Cellulosic shaped body, in particular lyocell fiber, obtainable by spinning an organic solution of a chemical pulp according to one of claims 1 to

4th

8. Shaped body according to claim 7, characterized in that the proportion of

Cellulose is below 95 wt.%.