Long fibers based on cellulose and / or cellulose derivatives, their production method and uses

Abstract

The present invention relates to filaments based on cellulose and / or cellulose derivatives, in particular for producing flame-retardant fabrics or carbon fibers, in which the cellulose and / or cellulose derivatives are present in dehydrated form. The oxygen content is 29-39% by weight, the limiting oxygen index LOI is 25-40 (according to DIN EN ISO 6941; 2004-05), and the density is 1.3-1.45 g / cm. 3 (according to DIN 65569-1; 1992-10). These filaments can be advantageously produced by impregnating the starting fibers with aqueous solutions of special salts which, in particular under thermal conditions, release dehydrating acids, thereby causing dehydration of the cellulose and / or cellulose derivatives during a subsequent thermal step. Particularly advantageous carbon fibers can be produced using the filaments according to the invention.

Description

[Technical Field]

[0001] explanation The present invention relates to long fibers based on cellulose and / or cellulose derivatives, to a process for their production and to their advantageous uses, in particular for producing flame-retardant fabrics or carbon fibers. [Background technology]

[0002] There are many polymer-based continuous fibers, including modified polyacrylonitrile in the form of acrylonitrile / acrylamidine copolymers, which are precursor fibers to carbon fibers, sometimes used in the production of flame-retardant fabrics. In most known methods to date, the extruded carbon fiber precursor fibers must be converted to an infusible state. This requires oxidative heat stabilization, a costly and complex process step. This step is carried out under oxygen or a protective gas atmosphere; the atmosphere involved can contain gas mixtures with various oxygen contents. The gas pressure used for oxidative heat stabilization is, for example, 0.5 to 1 bar. Heat stabilization is based on a final temperature between 180 and 300 °C. This final temperature is set by slowly increasing the temperature linearly or stepwise.

[0003] This is generally the procedure for the aforementioned well-known precursor fibers. However, when fibers based on cellulose and / or cellulose derivatives are used to produce carbon fibers, there are important issues to consider: one of the events in the conventional oxidative thermal stabilization of cellulose materials is the elimination of water, which begins at 250 °C, triggering undesirable secondary reactions that result in poor quality and a decrease in carbon yield due to liquid carbon-containing pyrolysis products during carbonization. The countermeasures used are particularly slow methods or additional chemical reactions, making the process uneconomical and harmful to the environment. Furthermore, additional problems arise in the aforementioned stabilization of cellulose, which also affects cellulose derivatives. These include excessive tar content in these stabilized fibers. The products in question can only be competitive if thermal stabilization can be carried out industrially with optimal management. Furthermore, conventional stabilized cellulose fibers are known to have too low a limiting oxygen index (LOI) (a parameter used to describe combustion behavior and indicating the minimum oxygen concentration of an oxygen-nitrogen mixture at which combustion sustains under the respective test conditions), insufficient strength, and therefore insufficient carbonization yields, for their use as flame-retardant fabrics. Furthermore, the resulting stabilized cellulose fibers do not have an optimal elemental composition and exhibit defects due to early thermal decomposition, making it impossible, in particular, to produce flame-retardant fabrics or carbon fibers with good use properties. Summary of the Invention [Problem to be solved by the invention]

[0004] The object addressed by the present invention was therefore to propose a filamentary fiber based on cellulose and / or cellulose derivatives that can be used in particular for the production of advantageous flame-retardant fabrics and carbon fibers of improved quality. The aim here is to optimize the oxygen content, the LOI, and the density. The aim is thereby to develop advantageous carbon fibers that are notable for, among other things, desirable density, fiber strength, and elongation at break without harmful oxidative heat stabilization.

[0005] The present invention also proposes an advantageous method for producing long fibers. The goal is to produce competitive cellulose-based carbon fibers with qualities comparable to those of conventional carbon fibers based on oil-based polyacrylonitrile. Furthermore, the method of the present invention should improve / reduce the CO balance and energy costs, increasing sustainability. Furthermore, no toxic exhaust gases, such as hydrocyanic acid and nitrogen oxides, should be produced during production. A further goal is to achieve improved flame retardancy. Other possible operations carried out under air or atmospheric conditions proceed too slowly, require additives, and do not achieve the required qualities, for example, for cellulose fibers. One particular problem addressed by the present invention is that if the oxygen content in the long fibers is too high, the resulting long fibers become brittle and porous after oxidation, making them unusable for standard processing, for example, into flame-retardant fabrics, and thus preventing the production of high-quality carbon fibers from these long fibers. [Means for solving the problem]

[0006] The above-mentioned object on which the present invention is based is achieved by means of long fibers based on cellulose and / or cellulose derivatives, in particular for producing flame-retardant fabrics or carbon fibers, in which the cellulose and / or cellulose derivatives are present in dehydrated form, have an oxygen content of 29 to 39% by weight, a limiting oxygen index LOI of 25 to 40 (according to DIN EN ISO 6941; 2004-05) and a density of 1.3 to 1.45 g / cm 3 (Complies with DIN 65569-1;1992-10). DETAILED DESCRIPTION OF THE INVENTION

[0007] The degree of dehydration of the dehydrated cellulose or dehydrated cellulose derivative present in the filaments of the present invention is clearly of major importance. In this context, the degree of dehydration is preferably at least 1.0, more preferably at least 1.5, and particularly preferably at least 2.0. The filaments of the present invention are particularly advantageous when the degree of dehydration is at least 2.5, especially 3.0. A particular advantage associated with this degree of dehydration is the thermal stabilization of the fibers while maintaining their useful properties.

[0008] The invention described above is developed in a particularly advantageous manner when the oxygen content is between 29 and 32% by weight, the limiting oxygen index LOI is between 28 and 37, and / or the density is between 1.35 and 1.45.

[0009] The present invention is characterized by the following further advantageous properties: a fiber tenacity of 8 to 30 cN / tex, in particular 10 to 16 cN / tex (according to DIN EN ISO 5079;1996-02), an elongation at break of 12 to 25%, in particular 10 to 16% (according to DIN EN ISO 5079;1996-02), and / or a linear density of 0.5 to 18 dtex, in particular 1 to 8 dtex (according to DIN EN ISO 1973;1995-12).

[0010] The starting materials in the realization of the present invention are cellulose and / or cellulose derivatives, which according to the invention are present in dehydrated form in the claimed filaments. First, non-dehydrated fibers of cellulose, in particular regenerated cellulose, and / or cellulose derivatives are processed into the advantageous filaments by the method of the present invention described below.

[0011] Regarding the cellulose fibers and / or regenerated cellulose fibers used as starting materials, the following should be noted: cellulose fibers include fibers consisting predominantly of cellulose, in particular more than 80% by weight, preferably 90% by weight, and particularly more than 98% by weight of cellulose; it is particularly preferred that they are entirely composed of cellulose. The fibers in question may in particular be fibers produced by modern technology from cellulosic starting materials, which are also sometimes called modified or synthetic cellulose fibers. A notable potential example is viscose fibers produced by the viscose process, which uses a spinning solution containing NMMO (N-methylmorpholine N-oxide) as a solvent. Particularly advantageous cellulose fibers are those obtained in a spinning solution using an ionic liquid as a solvent (see WO 2007 / 076979). Particularly advantageous regenerated cellulose fibers are those produced by the air-gap spinning process. Particularly useful in particular are tire cord yarns.

[0012] A further particularly advantageous embodiment of the present invention is the use of cellulose derivatives to produce the filaments of the present invention, which also contain the cellulose derivatives in dehydrated form. Particular candidates here are cellulose acetate, cellulose propionate, cellulose butyrate, and their mixed esters. This means that in each case, fibers of cellulose acetate, cellulose propionate, cellulose butyrate, and their esters can be used in individual fibers, but can also be present in a mixed form in the yarn. Further advantageous cellulose derivatives include cellulose formate, cellulose carbamate, and / or cellulose allophanate.

[0013] The aforementioned long fibers of the present invention can be advantageously used to produce flame-retardant fabrics. In this context, the term "fabric" should be interpreted broadly. It therefore includes woven fabrics, knitted fabrics, nonwoven fabrics, etc. The specific properties of the long fibers of the present invention in the form of fabrics provide advantageous use opportunities, such as for use in fire-resistant professional clothing, fire-resistant leisure clothing, especially in the automotive field, and as fire-resistant fabric materials for technical applications in filtration or insulation, and in the construction field.

[0014] The inventive long fibers can be used equally advantageously to produce carbon fibers by carbonization, optionally followed by graphitization. In this context, it is noted that the inventive carbon fibers produced from the inventive long fibers described above have the following advantageous physical values: 1.55 to 1.75 g / cm 3 , especially 1.6 to 1.7 [g / cm 3 ] density (according to DIN 65569-1;1992-10), a fiber strength of 2.0 to 5 GPa, in particular 2.5 to 4 (according to DIN EN ISO 5079;1996-02), and an elongation at break of 2 to 5%, in particular 2.5 to 3.5% (according to DIN EN ISO 5079;1996-02).

[0015] The long fibers of the present invention can therefore be advantageously carbonized. This is preferably carried out by heating the long fibers under protective gas within a temperature range of 600°C to 2400°C, in particular 1000°C to 2400°C, with the range of 1200°C to 1600°C being preferred. Heating is particularly preferably carried out up to 1600°C. The resulting carbon fibers are optionally graphitized and usefully have a carbon content of more than 98% by weight. The optional subsequent graphitization is preferably carried out by heat treatment under protective gas, in particular nitrogen, at 1700°C to 3000°C, in particular 2000°C to 2500°C. Graphitized carbon fibers have a higher modulus of elasticity than simply conventional carbonized fibers.

[0016] A further subject of the present invention is an advantageous process for producing long fibers based on cellulose and / or cellulose derivatives, in particular for use in the production of flame-retardant fabrics and carbon fibers, in particular a process for producing the long fibers of the invention, characterized in that (1) the long fibers based on cellulose and / or cellulose derivatives are brought into contact with a solution, in particular an aqueous solution, of a salt, in particular an ammonium salt of a sulfonic acid, which releases a dehydrating acid for dehydrating the cellulose and / or cellulose derivative under subsequent thermal conditions, and (2) the long fibers thus provided are heated to a temperature of 160°C to 300°C, in particular 180°C to 240°C, and this temperature is maintained for at least 5 minutes, in particular at least 10 minutes, particularly preferably at least 20 minutes, and during each heating step and between heating steps, the long fibers provided are placed in an inert gas atmosphere, in particular a nitrogen atmosphere, under a reduced pressure of 5 mbar to 500 mbar, in particular 50 mbar to 200 mbar, whereby the cellulose and / or cellulose derivatives are dehydrated by the dehydrating acid formed.

[0017] In step (1) according to the invention, before the subsequent thermal step (2), the filaments are, so to speak, impregnated with a suitable salt, and a dehydrating acid is formed by elimination of ammonia, which acid then dehydrates the cellulose and / or cellulose derivatives involved in the present invention.

[0018] This method advantageously develops in that in step (2), the long fibers provided in step (1) are heated to a first temperature, in particular 180 to 240°C, and this first temperature is maintained for at least 5 minutes, and subsequently the long fibers are heated to at least one second temperature higher than the first temperature, in particular 240 to 300°C, and this second temperature is also maintained for at least 5 minutes, and during each heating and between heating steps, the long fibers are placed in an inert gas atmosphere, in particular a nitrogen atmosphere, under a reduced pressure of 5 mbar to 500 mbar, in particular 50 mbar to 200 mbar, whereby the cellulose and / or cellulose derivatives are dehydrated by the dehydrating acid formed.

[0019] The thermal step (2) described above can advantageously be developed as follows: the supplied long fibers are heated in step (2) from a first temperature to at least one further temperature and then to a second temperature, with the temperature difference between successive heating steps being at least 5°C, in particular at least 10°C, and the supplied long fibers being maintained at at least one temperature for at least 3 minutes. It is furthermore useful if the second temperature is set in step (2) to be at least 30°C, in particular at least 40°C, higher than the first temperature. It is also considered advantageous if the supplied long fibers are maintained in step (2) at the first temperature, the second temperature, and at least one optional intermediate temperature for at least 10 minutes, in particular at least 20 minutes.

[0020] Between steps (1) and (2) of the method scheme of the present invention, it is useful to carry out intermediate drying, in particular by contact heat on a heated godet, preferably between 60°C and 140°C, in particular between 80°C and 139°C, or in a hot air tunnel, preferably between 60°C and 140°C, particularly preferably between 80°C and 120°C. This intermediate drying is preferably carried out continuously. The filament yarn is then wound up after step (2). The resulting spool can be stored and transported and is sent to step (2) at a specific time, which is preferably carried out continuously.

[0021] As is evident, the method of the present invention is preferably a two-stage process comprising the aforementioned steps (1) and (2). In the first stage, the cellulose and / or cellulose derivative-based filaments are treated under the thermal conditions described in the following step (2) with a solution of a salt, in particular an aqueous solution, which releases a dehydrating acid for dehydrating the cellulose and / or cellulose derivative under the described thermal conditions. The target substance is in particular an ammonium salt of a sulfonic acid. In principle, however, other salts which release a dehydrating acid under the conditions of the present invention can also be used. Specific possibilities here include ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphonate, ammonium chloride, ammonium hydrogen sulfate, and / or ammonium hydrogen carbonate.

[0022] The relevant salts which release dehydrating acids to dehydrate cellulose and / or cellulose derivatives under the thermal conditions described below preferably take the form of ammonium salts of sulfonic acids.

[0023] Thus, the sulfonium salts used according to the invention are of formula (I) [ka] where R 1 is a hydrocarbon group, and K + is represented by formula (II) [ka] is a cation of R 2 ~R 5 are each independently an H atom or an organic group having 1 to 20 C atoms, and therefore the cation is an unsubstituted ammonium ion (NH 4 ) + or substituted ammonium.

[0024] As shown, R 1is preferably a hydrocarbon group having 1 to 20 carbon atoms, and particularly preferably said hydrocarbon group contains 2 to 15 carbon atoms, in particular 2 to 10, and very particularly preferably 2 to 5 carbon atoms. 1 is or contains an aromatic group. Thus, R 1 may be an optionally substituted aryl group, particularly an optionally substituted phenyl, biphenyl, or naphthyl group, or an alkaryl group, particularly an optionally substituted phenyl, biphenyl, or naphthyl group bonded to the sulfur atom via an alkylene group.

[0025] The cation of formula (I) is not any organic or inorganic cation. Instead, it preferably has the advantageous structure described above. In this structure, as already identified, R 2 ~R 5 are, independently of one another, H atoms and / or organic radicals having 1 to 20 C atoms, preferably 2 to 15 C atoms, very preferably 5 to 10 carbon atoms. This may in particular be an alkyl radical having 1 to 4 C atoms. Advantageous substituents with these preferred details are methyl and ethyl substituents.

[0026] The amount of sulfonium salt initially present in the long fibers can be advantageously determined in that the long fibers contained 0.1 to 5% by weight, in particular 0.3 to 2% by weight, of sulfur, based on their dry weight, when fed to the heat treatment step (2) outlined below. It is particularly advantageous if the sulfonium salt of formula (I) described is soluble in at least 10 to 100 parts by weight of water (under standard conditions of 20°C and 1 bar). Particularly advantageously, the sulfonium salt is ammonium tosylate.

[0027] When sulfonates are used, hydrophilic solvents, particularly water or hydrophilic organic solvents such as alcohols, are preferred. The hydrophilic solvent is more preferably water or a mixture of water and another hydrophilic organic solvent that is fully miscible with water; in the case of a solvent mixture, the mixture preferably contains at least 50% by weight of water. Particularly preferred are solutions based entirely on water and containing the sulfonate of formula (I) in dissolved form.

[0028] The concentration of sulfonate in the solution, particularly in the aqueous solution, and the contact time of the filaments with the solution are usefully selected so that the dried filaments contain the advantageous sulfonate content described above, and to this end, the filaments can be passed through the solution for a sufficient time and / or, in a continuous operation, through a sufficiently long bath of the solution.

[0029] In a preferred embodiment, the fibers are continuously passed through a solution of sulfonate, preferably with a sulfonate content of 0.05 to 5 mol / l, particularly 0.1 to 2 mol / l. The contact time between the fibers and the sulfonate solution is preferably at least 0.5 seconds, particularly at least 2 seconds, and very particularly at least 10 seconds. This is generally not more than 100 seconds, preferably not more than 30 seconds.

[0030] The filaments of the present invention based on cellulose and / or cellulose derivatives can be further provided with additional additives. For this purpose, the sulfonate salts described above can contain such additives. These can be, in particular, additives for stabilizing the transport of the threads, preferably fatty acids, such as long-chain aliphatic monocarboxylic acids. Saturated fatty acids, such as palmitic acid or oleic acid, are particularly suitable.

[0031] These additional additives should preferably have a solubility in water of at least 10 parts by weight, preferably at least 20 parts by weight, in particular at least 30 to 100 parts by weight, under standard conditions (20°C, 1 bar). The additives are preferably low molecular weight compounds having a molecular weight of 1000 g / mol or less, in particular 300 g / mol or less. Specific additives that come into consideration are soaps or acids, examples being inorganic salts, inorganic acids, organic salts, or organic acids, such as carboxylic or phosphonic acids. In the case of salts, the cations may be, for example, metal cations, preferably alkali metal cations, such as NH + and K. + , or in particular ammonia (NH 4 ) + Furthermore, in one preferred embodiment, the filaments according to the invention do not contain any suitable amount of further additives apart from the sulfonate salt of formula (I) as broadly described above.

[0032] The following general remarks regarding the method of the present invention can be made for further explanation: The advantageous properties associated with the inventive filaments are achieved in a targeted and reliable manner in the thermal stage (2) of the process by the generation of a dehydrating acid, which can also be called a "carbonization aid" in the context of carbon fiber production. Usable low-pressure stabilization ovens have recently become known. This is particularly important for the implementation of the present invention. The values specified in the context of thermal stage (2) are preferred. First, a number of inventive filaments based on cellulose and / or cellulose derivatives and extending parallel to one another are passed from a feed unit through an airlock unit to an operating unit. From the operating unit, the filaments are passed through an airlock unit and then to a winding unit, where they are wound up again. The operating unit is subjected to a reduced pressure of 5 mbar to 500 mbar, in particular 50 mbar to 300 mbar. A pressure range of 50 to 200 mbar has proven particularly advantageous in this case. By supplying gas, the operating unit is exposed to a process gas, preferably an inert gas, preferably nitrogen, which is again extracted by a pump. The extracted gas contains not only ammonia but also water released as a result of the dehydration of cellulose and / or cellulose derivatives. The extracted gas is purified in a corresponding post-treatment step.

[0033] Furthermore, the heating elements are directed to the operating units so that a desired, particularly constant, temperature is achieved in each of their zones. In the first zone, for example, in the case of a multi-stage embodiment, a temperature of 180°C to 240°C is established. In subsequent zones, for example, temperatures of 200°C, 220°C, 240°C, and 250°C are established. The filaments are then passed through the operating units at a predetermined speed, which is usefully set so that it takes about 20 to 40 minutes for the filaments to pass through the entire heated operating unit.

[0034] It has been shown that higher temperatures can be used in a controlled reduced pressure atmosphere than in air at atmospheric pressure without the continuous fibers becoming burned and thermally damaged. As a result, in the case of carbon fibers, high-density precursor fibers containing uniformly stabilized, dehydrated forms of cellulose and / or cellulose derivatives can be reproducibly produced.

[0035] In summary, in view of the advantages associated with the present invention, the present invention can be described as follows: The long fibers of the present invention, comprising cellulose and / or cellulose derivatives in dehydrated form, exhibit significant advantages in relation to their excellent properties as flame-retardant fibers, with advantageous applications as precursors to carbon fibers, preferably as carbon fibers, as a result of their flame-retardant properties (LOI), strength, purity, carbon yield (high carbon yield in the production of carbon fibers), density, elongation, good environmental balance, and low cost. The method of the present invention avoids the undesirable step of oxidative thermal stabilization. It uses a low-pressure process, preferably using an inert gas, especially nitrogen. Further features of the method are that it can be carried out continuously and scalably, requires short residence times, uses only a low temperature range, allows controlled and rapid dehydration and the formation of low levels of by-products, produces no toxic exhaust gases, and exhibits a very good CO balance. Finally, this allows for the advantageous use of cellulose and derivatives, as well as tire cord.

[0036] The purpose of the following examples is to further illustrate the invention. They are proceeded by the following explanations: Standard cellulose fibers have a limiting oxygen index (LOI) of 20. LOI is a parameter used to indicate combustion behavior. This numerical index indicates the minimum oxygen concentration of an oxygen-nitrogen mixture at which combustion is sustained under test conditions. The method of the present invention produces flame-retardant cellulose fibers with a high LOI between 25 and 40. The flame-retardant cellulose fibers have a flame-retardant viscosity of 1.3 to 1.45 g / cm. 3It is distinguished by a high density between 0.90 and 1.45 dtex, a pore-free structure, and a smooth surface. The individual fibers are not stuck together and have a linear density between 0.90 and 1.45 dtex. The carbon content of the flame-retardant cellulose fibers is between 55 and 60% by weight, and the oxygen content is between 29 and 39% by weight.

[0037] Cellulose fibers used: The examples used are two types of cellulose fibers. Both are man-made fibers formed from regenerated cellulose or coagulated cellulose, respectively. The cellulose fibers used in automobile tires are tire cord fibers. The coagulated cellulose fibers were produced from cellulose dissolved in an ionic liquid (1-ethyl-2-methylimidazolium octanoate [EMIM] [Oct]). These are referred to below as IL fibers. Both types of fibers are notable for their particularly high tensile strength.

[0038] Obtained carbon fiber: According to the present invention, the flame-retardant cellulose fibers can be further processed into carbon fibers (CF). In this case, the flame-retardant cellulose fibers are converted into CF by pyrolysis. This pyrolysis is generally carried out at temperatures between 500 and 1400°C. This can be carried out under a protective gas, such as nitrogen or helium. The resulting carbon fibers have very good mechanical properties, in particular good strength and elasticity. The method of the present invention allows for a high carbon yield. The carbon yield is 70 to 90%, which means that the carbon fibers contain between 70 and 90% by weight of the carbon present in the cellulose fibers. [Example]

[0039] Example 1 The manufacture of the flame retardant cellulose fiber of the present invention is described. To deliver the additive, industrial regenerated cellulose fiber yarn used as tire cord fiber is provided, which has a single filament density of 2.2 dtex and contains 1000 filaments.

[0040] The fiber is fed and dried in continuous operation on godets. All godets have a speed of 10 m / min. The first godet serves as the fiber unwinding unit. Before feeding, the fiber is washed in a washing bath with water (95°C) and by means of a godet sprayed with water. The fiber is then passed through an aqueous ammonium tosylate solution (ammonium tosylate concentration: 0.35 mol / kg). This is followed by drying on a heated godet (80°C). The dried fiber is wound up using a tension-controlled winder under an initial tension of 0.3 cN / tex (stage 1).

[0041] The regenerated cellulose, now supplied with dehydration additives, is then further processed under protective gas (nitrogen) and reduced pressure (200 mbar). This processing is carried out using a low-pressure oven with 24 heating zones. The fiber is unwound onto a triple godet and introduced into the oven's process tunnel via three pressure locks. The pressure locks are sealed off from each other by their respective roll pairs. The pressure in the locks and in the process tunnel is regulated by a vacuum pump and nitrogen supply. The supplied cellulose fiber is passed through the oven at a speed of 0.2 m / min, which corresponds to a residence time of 60 minutes. The temperature is set between 195 and 240 °C. The fiber is then removed from the oven again via three pressure locks and wound up with an initial tension of 4 cN / tex (stage 2).

[0042] The residual mass of the fiber was 86% by weight, and the fiber density was 1.42 g / cm 3 The strength is 16 cN / tex, the elongation at break is 25%, the LOI is 30.5, and the oxygen content is 30 wt%.

[0043] Example 2 The fibers are produced as in Example 1. The residence time in the low pressure oven is reduced to 30 minutes.

[0044] The residual mass of the fiber was 86% by weight, and the fiber density was 1.40 g / cm 3The strength is 16 cN / tex, the elongation at break is 21%, the LOI is 29, and the oxygen content is 32 wt%.

[0045] Example 3 Fibers are produced as in Example 1. The residence time in the low pressure oven is reduced to 15 minutes.

[0046] The residual mass of the fiber was 86% by weight, and the fiber density was 1.39 g / cm 3 The strength is 13 cN / tex, the elongation at break is 21%, the LOI is 26, and the oxygen content is 38 wt%.

[0047] Example 4 The production of carbon fibers from flame-retardant cellulose fibers of the present invention is described. Flame-retardant cellulose fibers are produced as described in Example 1 by using additive-containing regenerated cellulose fibers, so-called tire cord fibers, processed using a low-pressure process. The flame-retardant cellulose fibers thus produced are then subjected to a two-stage treatment under protective gas to obtain carbon fibers. In the first stage, the fibers are treated at a maximum temperature of 750°C. The fibers are then further treated in a second stage at 1400°C.

[0048] The carbon yield was 72 wt %, the strength of the carbon fiber was 2.5 GPa, the modulus of elasticity was 96 GPa, the elongation at break was 2.5%, and the density was 1.42 g / cm 3 is.

[0049] Example 5 The production of carbon fibers from flame-retardant cellulose fibers of the present invention is described. Flame-retardant cellulose fibers are produced by so-called additive-containing tire cord fibers processed using a low-pressure process as described in Example 2. These flame-retardant fibers are then subjected to a two-stage treatment under protective gas as described in Example 4 to obtain carbon fibers.

[0050] The carbon yield was 72 wt %, the strength of the carbon fiber was 23.2 GPa, the modulus of elasticity was 110 GPa, the elongation at break was 2.8%, and the density was 1.7 g / cm 3 is.

[0051] Example 6 The production of carbon fibers from flame-retardant cellulose fibers of the present invention is described. Flame-retardant cellulose fibers are produced by so-called additive-containing tire cord fibers treated using a low-pressure process as described in Example 3. These flame-retardant fibers are then subjected to a two-stage treatment under protective gas as described in Example 4 to obtain carbon fibers.

[0052] The carbon yield was 82 wt %, the strength of the carbon fiber was 2.6 GPa, the modulus of elasticity was 82 GPa, the elongation at break was 2.5%, and the density was 1.68 g / cm 3 is.

[0053] Example 7 The production of flame-retardant cellulose fibers of the present invention is described. The starting material used is regenerated cellulose fibers (IL fibers) obtained by air-gap spinning directly from ethyl- and methyl-imidazolium octanoate, with a single filament density of 2.2 dtex and containing 1,000 filaments. The flame-retardant cellulose fibers are produced as in Example 1 after adding an additive (ammonium tosylate) by a low-pressure process.

[0054] The residual mass of the fiber is 78% by weight, and the fiber density is 1.38-1.42 g / cm 3 The strength is 12 cN / tex, the elongation at break is 13%, and the LOI is 31.

[0055] Example 8 The production of carbon fibers from the flame-retardant IL fibers of the present invention is described. Flame-retardant cellulose fibers are produced as in Example 7. These flame-retardant fibers are then subjected to a two-stage treatment under protective gas as described in Example 4 to obtain carbon fibers.

[0056] The carbon yield was 80 wt %, the strength of the carbon fiber was 2.5 GPa, the modulus of elasticity was 90 GPa, the elongation at break was 2.5%, and the density was 1.69 g / cm 3 is. Embodiments of the present invention: [1] Long fibers based on cellulose and / or cellulose derivatives, in particular for producing flame-retardant fabrics or carbon fibers, wherein the cellulose and / or the cellulose derivatives are present in dehydrated form; The oxygen content is 29 to 39% by weight, Limiting oxygen index LOI is 25-40 (according to DIN EN ISO 6941;2004-05), Density 1.3 to 1.45 g / cm 3 (in accordance with DIN 65569-1;1992-10) A long fiber characterized by: [2] The long fiber according to [1], characterized in that the dehydration degree of the cellulose and / or the cellulose derivative is at least 1.0, preferably at least 1.5, and particularly preferably at least 2.0. [3] The long fiber according to [2], characterized in that the degree of dehydration is at least 2.5, particularly 3. [4] The long fiber according to [1] or [2], characterized in that the oxygen content is 29 to 32% by weight, the limiting oxygen index LOI is 28 to 37, and / or the density is 1.35 to 1.45. [5] Filament according to [1], characterized in that it has a fiber tenacity of 5 to 30 cN / tex, in particular 8 to 16 cN / tex (according to DIN EN ISO 5079;1996-02), an elongation at break of 12 to 25%, in particular 10 to 16% (according to DIN EN ISO 5079;1996-02), and / or a linear density of 0.5 to 18 dtex, in particular 1 to 8 dtex (according to DIN EN ISO 1973;1995-12). [6] The filament according to any one of [1] to [5], characterized in that the filament containing dehydrated cellulose is obtained from regenerated cellulose fiber, particularly viscose fiber or regenerated cellulose fiber produced by air-gap spinning, and also from tire cord yarn, and the filament containing dehydrated cellulose derivative is obtained from filament of a cellulose ester or ether, particularly cellulose acetate, cellulose propionate, cellulose butyrate, and / or mixed esters thereof. [7] A method for producing a long fiber based on cellulose and / or a cellulose derivative, particularly for use in the production of flame-retardant fabrics and carbon fibers, in particular a method for producing a long fiber according to any one of [1] to [6], (1) contacting long fibers based on cellulose and / or cellulose derivatives with a solution, particularly an aqueous solution, of a salt, particularly in the form of an ammonium salt of a sulfonic acid, which releases a dehydrating acid for dehydrating the cellulose and / or cellulose derivatives under subsequent thermal conditions, (2) A method characterized in that the thus-supplied long fibers are heated to a temperature of 180°C to 300°C, particularly 180°C to 240°C, and this temperature is maintained for at least 5 minutes, particularly at least 10 minutes, and particularly preferably at least 20 minutes, and during each of the heating steps and between the heating steps, the supplied long fibers are placed in an inert gas atmosphere, particularly a nitrogen atmosphere, under a reduced pressure of 5 mbar to 500 mbar, particularly 50 mbar to 200 mbar, thereby dehydrating the cellulose and / or cellulose derivatives with the dehydrating acid formed. [8] The method for producing long fibers based on cellulose and / or cellulose derivatives according to [7], characterized in that in step (2), the long fibers provided in step (1) are heated to a first temperature, particularly 180 to 240°C, and maintained at this temperature for at least 5 minutes, and subsequently the provided long fibers are heated to at least one second temperature higher than the first temperature, particularly 240 to 300°C, and the first temperature and the second temperature are maintained for at least 5 minutes, and the provided long fibers are placed under a reduced pressure of 5 mbar to 500 mbar, particularly 50 mbar to 200 mbar, in an inert gas atmosphere, particularly a nitrogen atmosphere, during each of the heating steps and between the heating steps, thereby dehydrating the cellulose and / or cellulose derivatives with the dehydrating acid formed. [9] The method according to [7] or [8], characterized in that between steps (1) and (2), heating is carried out by contact heat on a heated godet, in particular at a temperature of 60°C to 140°C, or in a hot air tunnel, in particular at a temperature of 60°C to 140°C, to adjust the moisture content of the long fibers fed to step (2) to about 1 to 4% by weight.

[10] The sulfonate salt is represented by formula (I) [ka] where R 1 is a hydrocarbon group, and K + is represented by formula (II) [ka] is a cation of R 2 ~R 5 are each independently a H atom or an organic group having 1 to 20 C atoms, and the cation represents a substituted or unsubstituted ammonium ion.

[11] The method according to

[10] , characterized in that the supplied long fibers contain 0.1 to 5 wt. %, in particular 0.3 to 2 wt. % sulfur, based on the dry weight of the supplied long fibers.

[12] The method according to

[10] or

[11] , characterized in that the sulfonate salt of formula (I) in water has a water solubility (under standard conditions of 20°C and 1 bar) of at least 10 parts by weight to 100 parts by weight, in particular ammonium tosylate.

[13] The method according to any one of [7] to

[12] , characterized in that in step (2) the supplied long fibers are heated stepwise from the first temperature to at least one further temperature and then to the second temperature, the temperature difference between successive heating steps in time being at least 5°C, in particular at least 10°C, and the supplied long fibers are maintained at the at least one temperature for at least 3 minutes.

[14] The method according to any one of [7] to

[13] , characterized in that the second temperature in step (2) is set to be at least 30°C, particularly at least 40°C higher than the first temperature.

[15] The method according to any one of [7] to

[14] , characterized in that the supplied long fibers in step (2) are maintained at the first temperature, the second temperature, and at least one optional intermediate temperature for at least 10 minutes, particularly at least 20 minutes.

[16] Use of the long fiber according to any one of [1] to [6] for producing a flame-retardant fabric for use in fire-resistant professional clothing, fire-resistant leisure clothing, in particular as a fire-resistant fabric material for technical applications in the automotive field, filtration or thermal insulation, and as a fire-resistant fabric material in the construction field.

[17] Use of the long fiber according to any one of [1] to [6] for producing carbon fiber by carbonization, optionally followed by graphitization.

[18] A carbon fiber, particularly a carbon fiber produced from the long fiber according to any one of [1] to [6], 1.55~1.75g / cm 3 , especially 1.6 to 1.7 [g / cm 3 ] density (according to DIN 65569-1;1992-10), Fiber strength of 2.0 to 5 GPa, in particular 2.5 to 4 (according to DIN EN ISO 5079;1996-02), and elongation at break of 2 to 5%, in particular 2.5 to 3.5% (according to DIN EN ISO 5079;1996-02) Carbon fiber characterized by:

Claims

1. Long fibers based on cellulose and / or cellulose derivatives, said cellulose and / or said cellulose derivatives being present in dehydrated form, The oxygen content is 29 to 39% by weight, a limiting oxygen index LOI of 25 to 40 (in accordance with DIN EN ISO 6941; 2004-05); Density is 1.3 to 1.45 g / cm ３ (in accordance with DIN 65569-1; 1992-10) A long fiber characterized by:

2. 2. The filament according to claim 1, wherein the oxygen content is 29 to 32% by weight, the limiting oxygen index LOI is 28 to 37, and / or the density is 1.35 to 1.

45.

3. 2. The filament according to claim 1, characterized in that it has a fiber tenacity of 5 to 30 cN / tex (according to DIN EN ISO 5079; 1996-02), an elongation at break of 10 to 25% (according to DIN EN ISO 5079; 1996-02), and / or a linear density of 0.5 to 18 dtex (according to DIN EN ISO 1973; 1995-12).

4. The long fiber according to any one of claims 1 to 3, characterized in that the long fiber containing dehydrated cellulose is also obtained from regenerated cellulose fiber, and the long fiber containing dehydrated cellulose derivative is obtained from long fiber of cellulose ester or ether.

5. 1. A method for producing long fibers based on cellulose and / or cellulose derivatives, comprising: (1) contacting cellulose and / or cellulose derivative-based filaments with a salt solution that releases a dehydrating acid to dehydrate the cellulose and / or cellulose derivatives under subsequent thermal conditions; (2) A method characterized in that the thus-supplied long fibers are heated to a temperature of 180°C to 300°C, maintained at this temperature for at least 5 minutes, and during each of the heating steps and between the heating steps, the supplied long fibers are placed under a reduced pressure of 5 mbar to 500 mbar in an inert gas atmosphere, whereby the dehydrating acid formed causes the dehydration of the cellulose and / or cellulose derivatives.

6. 6. The method for producing long fibers based on cellulose and / or cellulose derivatives according to claim 5, characterized in that in step (2), the long fibers provided in step (1) are heated to a first temperature and maintained at this temperature for at least 5 minutes, and subsequently the provided long fibers are heated to at least one second temperature higher than the first temperature and maintained at the first temperature and the second temperature for at least 5 minutes, and the provided long fibers are placed under a reduced pressure of 5 mbar to 500 mbar in an inert gas atmosphere during each heating and between the heating steps, whereby the cellulose and / or cellulose derivatives are dehydrated by the dehydrating acid formed.

7. 7. The method according to claim 5 or 6, wherein heating is carried out between steps (1) and (2) to adjust the moisture content of the long fibers fed to step (2) to 1 to 4% by weight.

8. the salt capable of releasing a dehydrating acid for dehydrating cellulose and / or a cellulose derivative under subsequent thermal conditions is a sulfonate salt of formula (I), 【Chemical 1】 Here, R １ is a hydrocarbon group, and K ＋ is represented by formula (II) 【Chemistry 2】 is a cation of R ２ ~R ５ are, independently of one another, an H atom or an organic group having 1 to 20 C atoms, and the cation represents a substituted or unsubstituted ammonium ion.

9. 9. The method of claim 8, wherein the provided long fibers contain 0.1 to 5 weight percent sulfur based on the dry weight of the provided long fibers.

10. 10. The method according to claim 8 or 9, characterized in that the sulfonic acid salt of formula (I) in water has a water solubility (under standard conditions of 20°C and 1 bar) of at least 10 parts by weight to 100 parts by weight.

11. 11. The method of claim 10, wherein the sulfonate salt of formula (I) is ammonium tosylate.

12. 7. The method of claim 6, wherein the supplied long fibers in step (2) are heated stepwise from the first temperature to at least one further temperature and then to the second temperature, the temperature difference between successive heating steps in time being at least 5°C, and the supplied long fibers are maintained at the at least one temperature for at least 3 minutes.

13. 7. The method of claim 6, wherein the second temperature in step (2) is set to be at least 30° C. higher than the first temperature.

14. 7. The method of claim 6, wherein the provided filaments in step (2) are maintained at the first temperature, the second temperature, and at least one optional intermediate temperature for at least 10 minutes.

15. Use of the filaments according to any one of claims 1 to 4 for the production of flame-retardant fabrics for use in fire-resistant professional clothing, fire-resistant leisure clothing, for technical applications in filtration or thermal insulation or as fire-resistant textile materials in the automotive sector, and as fire-resistant textile materials in the construction sector.

16. Use of the long fibers according to any one of claims 1 to 4 for producing carbon fibers by carbonization.

17. The carbon fiber, 1.55-1.75g / cm ３ density (according to DIN 65569-1; 1992-10), a fiber strength of 2.0 to 5 GPa (according to DIN EN ISO 5079; 1996-02), and Elongation at break of 2-5% (according to DIN EN ISO 5079; 1996-02) 17. The use according to claim 16, wherein

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