A spinning solution for producing regenerated cellulosic material

Abstract

The invention relates to a spinning solution for producing regenerated cellulosic material The spinning solution has improved stability. The spinning solution comprises cellulose material, aqueous alkaline solution and ammonium ions. The invention also relates to a method for producing the spinning solution. Further, it relates to a method for producing regenerated cellulosic material.

Description

[0001] A spinning solution for producing regenerated cellulosic material

[0002] Technical field

[0003] This specification relates to a spinning solution for producing regenerated cellulosic material as well as to a method for producing the spinning solution. It also relates to a method for producing regenerated cellulosic material.

[0004] Background

[0005] Regenerated cellulosic material refers to cellulosic material manufactured by dissolution or suspension of cellulose material or its conversion to a soluble cellulosic derivative and subsequent regeneration of cellulosic material for example as fibers, e.g., for textile industry purposes, or films.

[0006] Long-term stability of the alkaline spinning solution comprising the dissolved or suspended cellulose material can be a problem. At present, spinning solution stability of only up to 5-6 days has been achieved. After this period of time, the cellulose material contained in the spinning solution forms a gel, thereby preventing utilization of the spinning solution for extrusion. Thus, there is a need for improving the spinning solution stability.

[0007] Summary

[0008] It is an aim of this specification to provide a new spinning solution with improved stability for producing regenerated cellulosic material suitable for example for use in textile applications. The spinning solution comprises cellulose material, aqueous alkaline solution and ammonium ions. The ammonium ions function as stabilization agents to delay or even avoid gelation within the spinning solution.

[0009] The improved stability of the spinning solution provided by the addition of the ammonium ions enables production of larger volumes of the spinning solution at one go, as it is not necessary to use all the prepared spinning solution immediately after the preparation. Further, longer storage times enabled by the improved stability are a remarkable logistical improvement. Also, a method for producing a spinning solution as described herein is provided. The method comprises providing an aqueous alkaline solution comprising ammonium ions, cooling the aqueous alkaline solution comprising ammonium ions to a lowered temperature, and dissolving cellulose material into the alkaline solution comprising ammonium ions at temperature ranging from -30 degrees C to 50 degrees C so as to form the spinning solution.

[0010] Further, a method for producing regenerated cellulosic material is provided. The method comprises providing the spinning solution as described herein and extruding the spinning solution into a regeneration solution so as to form regenerated cellulosic material.

[0011] Brief description of the drawings

[0012] Fig. 1 shows a graph illustrating the spinning solution stability for various samples.

[0013] Detailed description

[0014] The solution is described in the following in more detail with reference to some embodiments, which shall not be regarded as limiting.

[0015] In this description and claims, the percentage values relating to an amount of a material are percentages by weight (wt.%) unless otherwise indicated. Unit of thickness expressed as microns corresponds to pm. Unit of temperature expressed as degrees C corresponds to °C.

[0016] Cellulose is a polysaccharide consisting of a linear chain of several hundred to many thousands of 0(1— >4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall of green plants, many forms of algae and the oomycetes. Natural cellulose is cellulose I, with structures laand Ip. Regenerated, i.e. man-made, cellulose is cellulose II. Conversion of cellulose I to cellulose II is irreversible.

[0017] Cellulose may be obtained from pulp. Pulp refers to lignocellulosic material separated chemically and / or mechanically from wood, fiber crops, waste paper or rags. Wood and other plant materials for pulp-making contain cellulose fibers, lignin and hemicelluloses. Feedstock for wood pulp may originate for example from birch, bamboo, beech, eucalyptus, softwood (i.e., spruce or pine), maple or aspen. Pulp may be pre-treated. For example, the pulp may be hydrolyzed pulp.

[0018] Regenerated cellulosic material may be made from cellulose material that is extracted from pulp. Alternatively or additionally, cellulose material may originate for example from hemp, flax, sisal, jute, kenaf, bamboo, agricultural fibers, or recycled fibers (e.g., recycled cotton and cotton linter). Cellulose material may be with or without hemicellulose. Cellulose material is chemically dissolved to form a colloidal suspension, i.e. the spinning solution, and subsequently extruded for example as a continuous filament or film.

[0019] Within context of this specification, term “spinning solution” refers to cellulose material or cellulosic material in aqueous alkaline solution, i.e., in dissolved form. The spinning solution may also be called a dope. The spinning solution is suitable for coagulation in a regeneration solution into regenerated cellulosic material (cellulose II type structure).

[0020] Within context of this specification, term “regenerated cellulosic material” comprises fibers, filaments, films, cellulosic beads, and 3D objects. Regenerated cellulosic fibers / filaments disclosed herein may particularly find use as cellulosic textile fibers in textile industry.

[0021] Within context of this specification, term “extrusion” refers to a process for forming objects of a fixed cross-sectional profile by pushing material through a die or nozzle of the desired cross-section. Extrusion also covers spinning, which is a specialized form of extrusion.

[0022] Within context of this specification, terms “fiber”, “filament”, “staple fiber” and “filament fiber” are used interchangeably to refer to natural or man-made substances that are significantly longer than they are wide. Cellulose fibers or cellulosic fibers refer to fibers predominantly consisting of cellulose.

[0023] Within context of this specification, term “regeneration solution” refers to a solution by which the cellulosic material is coagulated or formed in the aimed shape or physical form. The regeneration solution can also be called a regeneration bath, a coagulation bath or a spinning bath.

[0024] Typically, the method of producing regenerated cellulosic material comprises providing cellulose material and dissolving the cellulose material in an aqueous alkaline solution, preferably at lowered temperature, so as to form a suspension. The process of forming the suspension may also be called a cold alkali process.

[0025] As mentioned, as a result of dissolving step a suspension is formed. Particularly, the suspension may be a colloidal suspension. Colloidal suspension refers to a heterogeneous mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. In other words, the colloidal suspension is composed of solid particles uniformly dispersed in a liquid. Thus, as a result of the dissolving step, cellulose is uniformly dispersed in the aqueous alkaline solution.

[0026] Spinning solution stability, especially long-term stability is often a problem. The spinning solution stability may be expressed by Brookfield viscosity. Increased Brookfield viscosity is caused by gelation of the cellulose / cellulosic material. Spinning solutions having Brookfield viscosity values above 6500 mPa s are considered to be non-stable or not suitable for extrusion. Within context of this disclosure, Brookfield viscosity may be measured at a temperature of from 4 to 6 degrees C using a spindle having a capacity up to 10 000 mPa s (theoretical error ± 100, measured error ± 147.87). Speed of rotation is 100 rpm and duration of the measurement is 30 seconds. Spindle must be separated by at least 2 cm from wall of the container holding the sample. Amount of the sample is from 60 g to 200 g. Viscometer used may be of model “Brookfield digital viscometer DV1 MRVMB0”.

[0027] A spinning solution for producing regenerated cellulosic material, the spinning solution having improved stability is provided. The spinning solution comprises cellulose material, aqueous alkaline solution and ammonium ions. The ammonium ions function as stabilization agents to delay or even avoid gelation within the spinning solution. Ammonium ions are ideal for stabilization of spinning solution, since they are safe to use and inexpensive. Further, they are soluble in alkaline aqueous conditions and are soluble in their salt forms. It is supposed that the bulky enough size of the ammonium ions helps in keeping the cellulose polymers separated in the aqueous alkaline solution, thereby enabling delaying or avoiding the gel formation. Further, the cationic ammonium ions are able to interact with the deprotonated carboxylic acid groups, i.e., the carboxylate groups of the cellulose in aqueous alkaline conditions. This may have effect in enhancing the hydrophilicity of the cellulose, thereby preventing the hydrophobic interaction of the cellulose polymers.

[0028] The cellulose material may comprise or consist of at least one of the following: cellulosic pulp, pre-treated cellulosic pulp, hemp fibers, flax fibers, sisal fibers, jute fibers, kenaf fibers, bamboo fibers, agricultural fibers, and recycled fibers.

[0029] For dissolving the cellulose material in aqueous alkaline solution, the degree of polymerization (DP) of the cellulose material preferably is at most 300, such as between 200 and 300.

[0030] Amount of the cellulose material may be from 5 to 15 wt.% of the weight of the spinning solution.

[0031] The aqueous alkaline solution may comprise as an alkaline component at least one of the following: sodium hydroxide (NaOH), potassium hydroxide (KOH), or lithium hydroxide (LiOH). NaOH may be preferred over the more expensive KOH and LiOH. Amount of the alkaline component may be from 5 to 10 wt.% of the weight of the spinning solution.

[0032] The ammonium ions may originate from water-soluble ammonium salt. The water-soluble ammonium salt may be any commercially available water- soluble ammonium salt. In an example, the water-soluble ammonium salt is at least one of the following: ammonium hydroxide (NH4OH), ammonium chloride (NH4CI), ammonium bromide (NH4Br), ammonium iodide (NH4I) or ammonium nitrate (NH4NO3). The amount of the water-soluble ammonium salt may be from 0.1 to 20 wt.%, such as from 0.1 to 10 wt.%, or from 0.1 to 5 wt.%, or from 0.1 to 1 wt.% of the weight of the spinning solution. In case ammonium hydroxide is used, the amount of the alkaline component of the aqueous alkaline solution may be adjusted such that the hydroxide concentration is kept constant.

[0033] The spinning solution may further comprise additive(s), such as zinc oxide (ZnO), thiourea and / or urea. Purpose of the additive(s) is to enhance the cellulose dissolution / dispersion in the aqueous alkaline solution. Urea may also be used for forming cellulose carbamate. Amount of the additive(s) may be from 0.1 to 3 wt.% of the weight of the spinning solution.

[0034] For example, the spinning solution may comprise from 5 to 15 wt.% of alkaline component, from 0.1 to 20 wt.% of ammonium ions, from 0.1 to 3 wt.% of additive(s), and from 5 to 15 wt.% of cellulose material.

[0035] In a specific example the spinning solution may consist of from 5 to 15 wt.% of alkaline component, from 0.1 to 20 wt.% of ammonium ions, from 0.1 to 3 wt.% of additive(s), from 5 to 15 wt.% of cellulose material, and water.

[0036] In a further specific example the spinning solution comprises from 5 to 10 wt.% of NaOH, from 0.1 to 0.5 wt.% of ammonium hydroxide and / or ammonium chloride, from 0.1 to 3 wt.% of ZnO as an additive and from 5 to 15 wt.% of cellulose material. Remaining part of the spinning solution may consist of water.

[0037] The annual production of the spinning solution may for example be 50 kilotons per year. The improved stability of the spinning solution provided by the addition of the ammonium ions enables production of larger volumes of the spinning solution at one go, as it is not necessary to use all the prepared spinning solution immediately after the preparation. Further, longer storage times enabled by the improved stability are a remarkable logistical improvement.

[0038] A method for producing a spinning solution comprises providing an aqueous alkaline solution comprising ammonium ions. The aqueous alkaline solution may be provided by dissolving alkaline component in water so as to produce aqueous alkaline solution and subsequently dissolving ammonium ions in the aqueous alkaline solution. Alternatively, the ammonium ions may be dissolved in water prior to dissolving the alkaline component. Yet alternatively, it is also possible to introduce the alkaline component and the ammonium ions simultaneously into water. The method may further comprise dissolving additive(s) in the aqueous alkaline solution comprising ammonium ions.

[0039] The aqueous alkaline solution comprising ammonium ions is cooled to a lowered temperature, such as to a temperature of from 0 to 15 degrees C. After that, cellulose material is dissolved in the aqueous alkaline solution comprising ammonium ions at a temperature ranging from -30 degrees C to 50 degrees C, or at a temperature ranging from -30 degrees C to 30 degrees C, or at a temperature ranging from -30 degrees C to 15 degrees C, or at a temperature ranging from -30 degrees C to 10 degrees C, or at a temperature ranging from -30 degrees C to 5 degrees C, preferably at a temperature from -15 degrees C to 5 degrees C, so as to produce the spinning solution. If the produced spinning solution is not used for extrusion immediately after its production, it is preferably stored at a temperature ranging from 0 to 10 degrees C.

[0040] In the process of producing regenerated cellulosic material the spinning solution as described above is extruded into a regeneration solution so as to form regenerated cellulosic material. Temperature of the spinning solution at time of extrusion may be from 0 to 10 degrees C, such as from 4 to 6 degrees C. The regenerated cellulosic material forms by coagulation (i.e., regeneration) of the extruded suspension in the regeneration solution. During the coagulation, cellulose of the spinning solution is solidified into the desired forms of the regenerated cellulosic material (i.e., fibers, filaments, films, cellulosic beads or 3D objects). Terms “coagulation” and “regeneration” may refer to precipitation and / or crystallization of cellulose from the solubilized state. Cellulose may be crystallized at least partially into cellulose II. Typically, the coagulated cellulose is in the form of cellulose II.

[0041] The regeneration solution may be an acidic, alkaline or neutral aqueous solution. Only one regeneration solution may be utilized. Alternatively, a two- stage regeneration system comprising a first regeneration solution and a second regeneration solution may be utilized. When only one regeneration solution is used, the regeneration solution is an acidic aqueous solution. In a two-stage regeneration system the first regeneration solution may be for example neutral or alkaline aqueous solution, the second regeneration solution in that case being an acidic aqueous solution.

[0042] The regenerated cellulosic material can be extracted from the regeneration solution for its desired application (e.g., for use as textile fibers). Prior to its use, the regenerated cellulosic material may be washed and dried.

[0043] Examples

[0044] Effect of the ammonium ions on the stability of the spinning solution was demonstrated by the following experiments.

[0045] A reference spinning solution consisting of 7 wt.% of cellulose material, 1.3 wt.% of ZnO, 7.8 wt.% of NaOH and 83.9 wt.% of water was prepared.

[0046] The spinning solution according to example 1 consisted of 7 wt.% of cellulose material, 1 .3 wt.% of ZnO, 7.37 wt.% of NaOH, 0.43 wt.% of NH4OH and 83.9 wt.% of water.

[0047] The spinning solution according to example 2 consisted of 7 wt.% of cellulose material, 1 .3 wt.% of ZnO, 7.37 wt.% of NaOH, 0.43 wt.% of NH4CI and 83.9 wt.% of water.

[0048] Hydrolyzed pulp was used in all examples.

[0049] The prepared spinning solutions were stored at temperature of about 6-8 degrees C. Spinning solution stability was investigated by measuring the Brookfield viscosity values of the spinning solutions at about 5-6 degrees C daily. Brookfield viscosity values were measured using a Brookfield digital viscometer DV1 MRVMBO. Amount of the sample measured was from 60 g to 200 g and the spindle was separated by at least 2 cm from wall of the container holding the sample. Spindle having a capacity up to 10 000 mPa s (theoretical error ± 100, measured error ± 147.87) was used. Speed of rotation was 100 rpm and duration of the measurements was 30 seconds. Graphs showing the spinning solution stability are presented in Figure 1 . The reference spinning solution was shown to be stable for two days. On the third day, the Brookfield viscosity value was shown to be over 7000 mPa s and thereby too high for extrusion process. The spinning solution according to example 1 with ammonium ions originating from ammonium hydroxide showed good stability even until the 23rd day. The Brookfield viscosity values of the spinning solution according to example 2 with ammonium ions originating from ammonium chloride showed stability until the tenth day. The results show that the spinning solution stability is markedly improved by the addition of ammonium ions to the spinning solution. Further, the addition of ammonium ions does not affect the solubility of the cellulose material or the spinnability of the spinning solution by extrusion.

Claims

Claims:1 . A spinning solution for producing regenerated cellulosic material, wherein- the spinning solution comprises cellulose material, aqueous alkaline solution and ammonium ions, and- the aqueous alkaline solution comprises as an alkaline component at least one of the following: sodium hydroxide, potassium hydroxide, or lithium hydroxide.

2. The spinning solution according to claim 1 , wherein amount of the cellulose material is from 5 to 15 wt.% of the weight of the spinning solution.

3. The spinning solution according to claim 1 or 2, wherein amount of the alkaline component is from 5 to 10 wt.% of the weight of the spinning solution.

4. The spinning solution according to any of the preceding claims, wherein the ammonium ions originate from water-soluble ammonium salt.

5. The spinning solution according to claim 4, wherein the water-soluble ammonium salt is at least one of the following: ammonium hydroxide, ammonium chloride, ammonium bromide, ammonium iodide or ammonium nitrate.

6. The spinning solution according to claim 4 or 5, wherein the amount of the water-soluble ammonium salt is from 0.1 to 20 wt.% of the weight of the spinning solution.

7. The spinning solution according to any of the preceding claims, further comprising zinc oxide, thiourea and / or urea as additive(s).

8. A method for producing a spinning solution according to any of the claims 1-7, the method comprising- providing an aqueous alkaline solution comprising ammonium ions,- cooling the aqueous alkaline solution comprising ammonium ions to a lowered temperature, and- dissolving cellulose material into the aqueous alkaline solution comprising ammonium ions at temperature ranging from -30 degrees C to 50 degrees C so as to form the spinning solution, wherein- the aqueous alkaline solution comprises as an alkaline component at least one of the following: sodium hydroxide, potassium hydroxide, or lithium hydroxide.

9. The method according to claim 8, wherein the method further comprises- dissolving additive(s) in the aqueous alkaline solution comprising ammonium ions.

10. A method for producing regenerated cellulosic material, the method comprising- providing the spinning solution according to any of the claims 1-7 and- extruding the spinning solution into a regeneration solution so as to form regenerated cellulosic material.

11. The method according to claim 10, wherein temperature of the spinning solution at time of extrusion is from 0 to 10 degrees C.

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