EP3931381A1

EP3931381A1 - Method of ionizing irradiation of textile polyacrylonitrile fibres and use thereof as carbon fibre precursor

Info

Publication number: EP3931381A1
Application number: EP20709517.5A
Authority: EP
Inventors: Simon König; Elisabeth Giebel; Michael R. Buchmeiser; Andreas Jürgen WEGO; Christian Herbert
Original assignee: Deutsche Institute fuer Textil und Faserforschung Stuttgart; Deutsche Institute fuer Textil und Faserforschung Denkendorf DITF
Current assignee: Deutsche Institute fuer Textil und Faserforschung Stuttgart; Deutsche Institute fuer Textil und Faserforschung Denkendorf DITF
Priority date: 2019-03-01
Filing date: 2020-02-27
Publication date: 2022-01-05
Anticipated expiration: 2040-02-27
Also published as: EP3931381C0; EP3931381B1; DE102019105292A1; WO2020178149A1

Abstract

What is described is a method of irradiating and oxidatively thermally stabilizing PAN fibres for production of a precursor fibre of carbon fibres. This method is characterized in that PAN fibres that are especially intended for textiles are subjected to ionizing irradiation and then specifically to an oxidative thermal stabilization. The thermal stabilization should preferably be effected as quickly as possible after the irradiation. The lowered T_onset-Z temperature (T_{onset-Z E-PAN}) of the E-PAN fibres obtained by irradiation is determined and then the oxidative thermal stabilization is initiated at a starting temperature corresponding to T_{onset-Z E-PAN} ± 30°C. The oxidative thermal stabilization is conducted with rising temperature up to a minimum density of the oxidatively thermally stabilized PAN fibres of 1.30 g/cm³. The method described is inexpensive and leads to advantageous precursor fibres of carbon fibres. The resultant carbon fibres show particularly favourable tensile strength values. Thus, inexpensive starting fibres, especially of PAN for textiles, are used to produce carbon fibres having good mechanical properties comparable to commercial carbon fibres.

Description

Process for ionizing radiation of textile polyacrylonitrile fibers and their use as a carbon fiber precursor

description

The invention relates to a method for electron irradiation of textile poly acrylonitrile fibers and their use for the production of carbon moldings, in particular carbon fibers.

Flexible, elongated molded bodies which contain at least 92% by weight of carbon and are produced from organic polymeric precursors are referred to as carbon fibers.

According to the current state of the art, the predominantly used precursor in carbon fiber production is polyacrylonitrile, the polymer of acrylonitrile. For the manufacture of carbon fibers, polyacrylonitrile fibers are first oxidatively stabilized and then carbonized. If necessary, the carbon fiber is then graphitized. During oxidative stabilization, the polyacrylonitrile is cyclized and dehydrated, i.e. converted into a polyaromatic structure at temperatures of 200 to 300 ° C under air. This temperature range is referred to below as the cycling temperature. The resulting polyaromatic structure is called Ox-PAN in the following. The polyaromatic structure of Ox-PAN enables the high carbon yield in the subsequent carbonization. At the Ox-PAN is converted into a turbostratic modification of the carbon by splitting off CO2 and HCN by pyrolysis.

Not only the homopolymer of acrylonitrile is usually referred to as polyacrylonitrile, but also copolymers and terpolymers consisting of acrylonitrile and comonomers such as vinyl acetate, methyl acrylate, methyl methacrylate, itaconic acid, acrylic acid, acrylamide and others. For carbon fibers, according to the current state of the art, high molecular weight terpolymers, consisting mostly of over 95% by weight of acrylonitrile and up to 5% by weight of other comonomers, primarily methyl acrylate and itaconic acid, with a number average molecular weight of about 120,000 to 1,500 000 g / mol identified as particularly suitable precursor polymers, which are referred to below as CF-PAN. The particular suitability for carbon fibers results primarily from the thermal properties of such a terpolymer. In particular, comonomers with one or more carboxyl groups lead to a lowering of the cyclization temperature and a wider temperature window for the cyclization reactions that take place. Itaconic acid with its two carboxyl groups is therefore an often used comonomer for CF-PAN. The thermal properties can be verified using dynamic differential calorimetry (DSC) in accordance with DIN EN ISO 11357-5: 2014-07. Important parameter here is the onset temperature of the cy clic sierungsreaktion measured under air, hereinafter referred to as _n To se _t z, analogous to Tei, r in DIN EN ISO 11357-5: 2014-7. Typical values for _t- z for a CF-PAN are 200 to 240 ° C, depending on the composition of the CF-PAN. Another parameter is the temperature of the highest exothermicity, measured in air, hereinafter referred to as 7pea _k -z, analogous to T _p, in DIN EN ISO 11357-5: 2014-7. 7 ^" _Pe a _k -z is typically 280-300 ° C for CF-PANs. The distance between 7 ^" _on set-z and 7 ^" _Pe a _k -z should be as large as possible to prevent overheating or even burning of the Avoid fibers during oxidative stabilization, for CF-PAN this is typically> 60 ° C.

Polyacrylonitrile is mostly converted into fibers by wet or dry spinning. The productivity of the spinning plant correlates with the molecular weight and comonomer content in such a way that a higher molecular weight or a lower comonomer content lower productivity. Polyacrylonitrile fibers are currently not only used for carbon fiber production, but to a significant extent primarily for textiles, especially for home and outdoor textiles as well as work and sportswear. For these textile applications, polyacrylonitrile with a lower number average molecular weight of about 30,000 to 250,000 g / mol and a comonomer content of up to 15% by weight is usually used in favor of productivity, referred to below as the textile PAN. Most comonomers used in textile PAN are vinyl acetate, methyl acrylate and others. Rarely comonomers be used with carboxyl groups as those as mentioned above, lead to a low ren To _n s _t z. A low _n To se _t z is usually not desired for textile PAN, as the cyclization accompanied by a color change. Comonomers containing carboxyl groups would therefore lead to undesired discoloration in textile PAN at elevated temperatures, for example when ironing. The low molecular weight and the high comonomer content of the textile PAN enables higher spinning solution concentrations and thus higher productivity. Textile PAN fibers are therefore around 50% cheaper per kilogram than CF-PAN fibers. Since the precursor in carbon fiber production according to the current state of the art, i.e. the CF-PAN fibers, makes up about half the costs of the resulting carbon fiber, the use of textile PAN fibers would potentially reduce the costs of carbon fiber production by around 25 % to reduce.

Compared to CF-PAN, however, the thermal properties of textile PANs are disadvantageous for carbon fiber production. 7 ^" _on set-z is typically between 240 and 300 ° C. As a result, the use of textile PAN leads to higher energy costs for temperature control of the oxidative stabilization. In addition, the difference between 7 ^" onset-z and Tpea _k -z is smaller . The difference is usually between 10 ° C and 50 ° C. This narrower temperature window of the cyclization reaction leads to problems when handling the stabilization step, since even small temperature fluctuations in the stabilization furnace lead to a significantly higher exothermicity of the cyclization reaction. Overheating of a multifilament with a large overall diameter, such as, for example, a "heavy tow" (50,000 filaments) customary in the industry, is also conceivable due to this exotherm.

In the worst case, this leads to the ignition and burning of the fibers in the stabilization oven. In addition, the mechanical properties of the carbon fibers made from textile PAN are usually significantly worse than those made from carbon fibers CF-PAN. Because of this, despite the low price, the use of a textile PAN for carbon fiber production was refrained from for a long time.

One way of changing the thermal properties of PAN is to irradiate the PAN with high-energy radiation such as gamma rays or electron beams. This radiation generates radicals in the backbone of the polymer. The amount of radicals generated correlates with the dose of radiation. This enables shorter stabilization times. This was already described in 1996 in JPH0827619A. In this document, fibers irradiated with electrons are stabilized and carbonized in air, the stabilization time being shortened in comparison to stabilization without prior irradiation. A CF-PAN with 0.1-10% by weight of carboxylic acid-containing comonomer was used. The resulting carbon fibers achieve the usual tensile strengths of 3.0-3.5 GPa and 220 to 250 GPa E-modulus for CF-PAN. According to the technical teaching disclosed in this document, costs are saved in the stabilization step, but the significantly more decisive precursor costs are unchanged because of the use of CF-PAN instead of textile PAN.

Recently, KR 20160140268A also showed how textile PAN can be changed in its thermal properties by electron irradiation in such a way that it is suitable for carbon fiber production. The electron irradiation resulted in a lower _{S ound} se _t z and a wider temperature window of the cyclization, so a larger From stand 7 ^"onset-z and TPeA _k z> 50 ° C. During irradiation Accelerati were supply voltages of> 1 MV selected. In the examples of the known teaching, the radiation dose was between 200 and 1500 kGy, the exposure was 50-3000 kGy. The atmosphere during the irradiation was air. The stabilization and the carbonization were carried out discontinuously. In this document, the great savings potential was shown described when using a textile precursor, the achieved mechanical properties of a maximum of 1.9 GPa tensile strength and 150 GPa modulus of elasticity were, however, significantly below the typical mechanical properties of carbon fibers made from CF-PAN fibers -Precursor is outweighed by it. Based on the above prior art, the invention is therefore based on the task of proposing a method which is characterized in that it is practicable and economically applicable, in particular for the production of carbon fibers from textile PAN. The mechanical properties of the carbon fibers produced from textile PAN should clearly exceed those of the state of the art and should be comparable to carbon fibers made from CF-PAN, so that the savings potential of around 25% of carbon fiber production costs can be exploited.

The object on which the invention is based is achieved by a method for irradiation and oxidative stabilization of PAN fibers for the production of a precursor fiber of carbon fibers, characterized in that (1) the PAN fibers are based on a homopolymer or copolymer of PAN based, with the Ho mopolymer or copolymer of PAN to a _n se _tz -Temperature of at least 245 ° C measured in air (DIN EN ISO 11357-5: 2014-07), a number mitt Leres molecular weight from 20,000 to 250,000 g / mol polymethyl methacrylate molar mass equivalents (determined in accordance with DIN 55672-2: 2016-03) and a comonomers content of not more than 15.0% by weight, (2) the PAN fibers of ionizing radiation with a irradiation dose be subjected to from 10 to 5000 kGy, (3) from the obtained by irradiation e-PAN-fibers, the reduced 7 _on se _tz -Temperature is determined by air (7 _on se _tz e-PAN) (according to DIN EN ISO 11357-5: 2014-07), on it the oxidative thermostat _on bilisierung at ei ner starting temperature of 7 se _tz E-PAN ± is initiated 30 ° C and the oxidative thermal stability with increasing temperature up to a minimum density of the oxidation stabilized PAN fiber (Ox-PAN) of 1.30 g / cm ³ performed becomes.

The invention shows various advantageous embodiments, which are characterized below be:

It is preferred that the PAN has a number average molecular weight of 30,000 to 150,000 g / mol, in particular from 50,000 to 120,000 g / mol. A further advantage is that the comonomer content of PAN is 0.0 to 15.0% by weight, in particular 0.0 to 12.0% by weight and particularly preferably 0.0 to 7.5% by weight. -% is. In addition, it is useful that the comonomer of the PAN Vinyl compound, in particular vinyl acetate, vinyl propionate, methyl acrylate, methyl methacrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, tert-butyl acrylate, sodium methallylsulfonate, sodium vinyl sulfonate, acrylamide, methacrylamide and / or vinyl acetamide. It is particularly preferred if the PAN fibers are textile PAN fibers.

In principle, the ionizing irradiation with electron beams, gamma rays, in particular low-energy gamma rays, and / or x-rays, in particular with high-energy x-rays, could be carried out. However, it is preferred that the ionizing irradiation takes place with electron beams, preferably in an inert gas atmosphere, in particular in a nitrogen atmosphere. In various experiments it was surprisingly found that an inert gas atmosphere compared to air leads to better mechanical properties of the resulting carbon fibers under otherwise identical process conditions. It is preferred here that the radiation dose for ionizing radiation is 70 to 2500 kGy, in particular 300 to 1000 kGy. The acceleration voltage in the ionizing irradiation with electron beams is preferably 100 to 900 kV, in particular 160 to 600 kV, the range from 180 to 400 kV being particularly preferred. Furthermore, it is preferred that the current intensity in the ionizing irradiation with electron beams is 0.1 to 100 mA, in particular 1 to 50 mA and particularly preferably 2 to 10 mA.

The oxidative thermal stabilization to be used in the invention is accessible to various advantageous configurations: It is preferred that the start temperature for the oxidative thermal stabilization 7 ^" _on set-z E-PAN is ± 20 ° C, in particular ± 10 ° C. The final temperature of the oxidative thermal stabilization 7 ^″ _Pe a _k -z E-PAN is preferably ± 30 ° C, in particular ± 20 ° C. Furthermore, it is preferred that the oxidative heat stabilization up to a density of the oxidatively thermostabilized PAN (Ox-PAN) of 1.30 to 1.5 g / cm ³ , in particular from 1.35 to 1.39 g / cm ³ , is carried out. It has been shown that the end temperature of the oxidative thermal stabilization is preferably between 250 and 300 ° C, in particular between 260 and 290 ° C. In addition, it is preferred that as little time as possible pass between the oxidative thermal stabilization and the ionizing radiation, in particular electron radiation, and the oxidative thermal stabilization particularly preferably takes place immediately after the ionizing radiation. It is preferred that the storage time between ionizing radiation and carbonization is less than a day, preferably less than an hour. It is particularly preferred that the ionizing radiation is connected directly upstream of the oxidative thermal stabilization when the thread runs continuously.

The product obtained according to the invention can be put to advantageous uses. However, preference is given to using the oxidatively thermally stabilized PAN fibers (Ox-PAN) obtained according to the invention for the production of carbon fibers by carbonization, optionally with subsequent graphitization.

The object on which the invention is based is accordingly achieved by an advantageous method for stabilizing molded articles, in particular fibers, consisting in particular of textile PAN. The shaped bodies, in particular the fibers, are irradiated with ionizing radiation, preferably with electron beams, preferably in an inert gas atmosphere, particularly preferably in a nitrogen atmosphere, followed by oxidative thermal stabilization, which is preferably carried out immediately after the irradiation, and whatever Has temperature profile that is matched to the thermal properties of the particular irradiated textile PAN. The shaped bodies or fibers thus stabilized according to the invention can be carbonized and, if appropriate, graphitized by conventional methods. The carbon fibers produced according to the invention correspond in their properties to typical carbon fibers made from CF-PAN.

The invention is to be presented below for further explanation in detail: 1. Output fiber

According to the invention, the starting fiber used is in particular a fiber made of "textile PAN". The properties of this PAN are explained below in connection with the term "textile PAN". Even if a fiber is not expressly used for the production of textiles, it is referred to in the context of the invention as "textile-PAN fiber". The textile PAN preferably has a number average molecular weight of 20,000 to 250,000 g / mol, in particular from 30,000 to 150,000 g / mol of polymethyl methacrylate molar mass equivalents according to DIN 55672-2: 2016-03. Textile PAN with a number average molecular weight of 50,000 to 120,000 g / mol of polymethyl methacrylate molar mass equivalents is particularly advantageous .

The textile-PAN used in the invention is also characterized net gekennzeich that there is a 7 _on se _t z, measured in air, has in excess of 245 ° C, in particular above 250 ° C, and most preferably from 250 to 300 ° C . The 7 _on se _t z- temperature in the invention is preferably up to 320 ° C, especially up to 300 ° C. The 7 _on se _t z-temperature corresponds to 7 _{egg, r} in DIN EN ISO 11357-5. 2014- 07 and represents the extrapolated initial temperature of the cyclization of PANs of air towards the Ox-PAN represents Moreover, the fabric used in the invention -PAN a 7p _eak- z, measured under air, accordingly in DIN EN ISO 11357-5: 2014-7, from 260 to 360 ° C, in particular from 290 to 320 ° C. T _on- se _t z and z _k 7pea will be on DSC under air in Temperaturabtastverfahren True, the heating rate used for the purpose of comparability is 10 K / min. A TA-Instruments Q2000 differential scanning calorimeter with an autosampler unit was used for the measurements, and the “TZero” aluminum pans from TA-Instruments were used as the measuring crucible.

Various comonomers with a vinyl group, such as are typically used in textile PAN, can be used as comonomers. The use of a carboxylic acid-containing comonomer is not necessary because of the thermal properties that can be controlled by irradiation. Particularly suitable as comonomers are vinyl acetate, vinyl propionate, methyl acrylate, methyl methacrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, tert-butyl acrylate, sodium methallyl sulfonate, sodium vinyl sulfonate, acrylamide, methacrylamide and vinyl acetamide. The comonomers vinyl acetate and methyl acrylate are particularly preferred.

The comonomer content in the polymer, with a view to productivity when spinning the polymer, is between 0 and 15% by weight, in particular between 0 and 7.5% by weight.

Typically, but not explicitly limited to this, the textile PAN according to the invention is converted into fiber form via solution spinning processes, in particular via wet, dry or airgap spinning. According to the invention, industrial-scale spinning processes for polyacrylonitrile are generally used which have been optimized over several decades in terms of productivity and economy.

According to the invention, the fibers used, preferably made of textile PAN, expediently have a single filament diameter of 5 to 30 μm, in particular 8 to 18 μm and very particularly preferably 8 to 13 μm. It is also advantageous that the tensile strengths of the fibers are between 25 and 80 cN / tex, in particular between 35 and 60 cN / tex. The modulus of elasticity of the fibers is preferably 500 to 2500 cN / tex, particularly preferred are moduli of elasticity from 900 to 1500 cN / tex and in particular from 950 to 1250 cN / tex. The elongation of the textile PAN fibers is preferably from 5 to 25%, in particular from 8 to 16%.

For the successful implementation of the invention it is also advantageous if the textile fibers are arranged in a multifilament, that is to say the fibers are arranged in a potentially endless fiber bundle consisting of several filaments. The multifilament consists preferably of 1,000 to 10,000,000 filaments, in particular of 3,000 to 300,000 filaments.

2. Irradiation

An essential feature of the invention is the ionizing irradiation of the fibers, preferably using an electron beam. The resulting irradiated textile PAN fibers are referred to here as E-PAN fibers. Electron irradiation can be carried out under various atmospheric conditions. In the prior art, air is mostly used. It has been shown, however, that, surprisingly, an inert gas atmosphere according to the invention, such as nitrogen, leads to better mechanical properties of the carbon fibers. In a preferred embodiment of the invention, the use of an inert gas atmosphere in the irradiation of the textile PAN fibers resulted in carbon fibers with 31% better tensile strength compared to the use of air. Various gases such as helium, neon, argon, krypton, xenon, nitrogen and carbon dioxide can be used as the inert gas. According to the invention, nitrogen is particularly suitable. The use of an inert gas for irradiation also prevents the formation of ozone, which means that it does not have to be removed from the exhaust air.

The key parameter of electron irradiation for controlling the thermal properties of the E-PAN is the irradiation dose. As a function of this, 7 ^" _on set-z and 7 ^" _Pe ak-z are shifted to lower temperatures in such a way that a higher radiation dose results in lower temperatures T _on- set-z and 7peak-z. This reduced compared to the non-irradiated textile PAN in e-PAN 7 ^_"on set-z and ^7" _Pe ak-z ^"set-z _on E _P AN and ^7" in the following seven named _Pea kz E _P AN. According to the invention, the distance of 7 ^" _on set-z E- _P AN and 7peak-z E- _P AN is preferably set to about 40 to 110 ° C., in particular to 60 to 90 ° C. In the case of non-irradiated textile PAN, the distance is between to _n se _t and z 7 ^_"Pea kz usually 10 to 60 ° C. The distance between 7 ^" _on set-E-PAN and 7p _e ak-zE- _P AN is thus greater than that between 7 ^" _on set-z and 7 ^" _Pea kz. The risk of a textile PAN multifilament in the Exothermic oxidative thermal stabilization, overheating in an uncontrolled manner, or even burning off, is thereby minimized.

In terms of the successful implementation of the invention, the radiation dose can preferably be 10 to 10,000 kGy, in particular 10 to 5000 kGy. Radiation doses of 70 to 1500 kGy, in particular 300 to 1000 kGy, are particularly preferred. Another important parameter of electron irradiation is the acceleration voltage. The higher this is, the deeper a fiber bundle is penetrated by the electron beam. However, radiation protection and the necessary financial outlay for plant construction are all the more complex. The inventors therefore endeavored to use the lowest possible acceleration voltage. High acceleration voltages of> 1 MV, as used in the prior art, unnecessarily increase the radiation protection measures required. At 900 kV, electron beam penetration depths of> 3 mm are already achieved in the multifilament, which corresponds to> 250 individual filaments lying one above the other. In view of the fact that the multifilaments are typically expanded to more than 10 centimeters for better gas diffusion, a multifilament made of> 2,000,000 individual filaments could be irradiated with an acceleration voltage of 900 kV, which is already a factor of 40 above the current state of the art typically used 50 K multifilaments. According to the invention, acceleration voltages of 100 to 900 kV, in particular 160 to 600 kV and particularly preferably 180 to 400 kV have therefore proven particularly advantageous.

In addition, the current intensity is another important quantity of the radiation. The irradiation dose results from the current intensity, acceleration voltage and time. The current intensity during irradiation with electron beams is preferably 0.1 to 100 mA, the preferred range being 1 to 15 mA, in particular 2 to 10 mA.

The irradiation can be carried out discontinuously or continuously. With regard to a technical, cost-efficient process in which the shortest possible time should pass between irradiation and oxidative thermal stabilization, continuous irradiation appears to be more advantageous. The process speed at which the fibers are continuously irradiated is preferably 0.5 to 100 m / min, in particular 5 to 50 m / min.

During the continuous irradiation, it is also advantageous if the fiber to be irradiated is exposed to a tensile force which prevents the fiber from shrinking. This tensile force is preferably between 0.001 and 1 cN / filament, in particular between 0.03 and 0.3 cN / filament. 3. Oxidative thermostability

According to the invention, the irradiation of the fiber made of textile PAN is followed by oxidative thermal stabilization. The E-PAN fibers can be stored for several weeks. It would therefore be conceivable to carry out a continuous irradiation "online" immediately before the oxidative thermostabilization or to carry out the irradiation continuously, but then to lay down or roll up the fibers and store them for any time. Therefore, experiments were carried out in which E-PAN Fibers were stabilized one hour, one day, one week and 6 weeks after the irradiation to form Ox-PAN fibers. The Ox-PAN fibers were then carbonized. It was found that the mechanical properties of the resulting carbon fibers with the storage time between Be Radiation and stabilization correlated to the effect that a longer storage time worsened the mechanical properties - especially the tensile strength. A storage time of the E-PAN fibers of 6 weeks reduced the tensile strength of the resulting carbon fibers by an average of 18% compared to carbon fibers, in which the storage time was about an hour.

It is therefore advantageous that the fibers are oxidatively thermostabilized immediately after the irradiation. "Immediately" can also mean that stabilization and irradiation are connected by a continuous thread guide and that their process speeds are coordinated with one another.

The atmosphere during stabilization should have an oxidizing character, so the use of air is particularly expedient.

It has been shown that it is advantageous if the temperature is not constant during the oxidative Thermostabiiisierung. A continuously increasing temperature during the oxidative thermostability with a defined start and end temperature and a defined stabilization time is advantageous. Preferably, but not limited to, this is accomplished through the use of a stabilizing oven with multiple fleizzones. The temperature profile over the entirety of the meat zones is basically characterized by the fact that from the second meat zone onwards, each of the meat zones has a higher temperature than the previous one. In order to match the temperature profile to the E-PAN according to the invention, 7 ^" onset-z E-PAN and 7 ^" _Pe ak-z E-PAN must first be determined by DSC under air in accordance with DIN EN ISO 11357-5: 2014-07 to find out in which temperature range the cyclization reactions of the E-PAN occur, which are necessary for the oxidative thermal stabilization. Heating rates of 10 K / min should be used. The starting temperature of the oxidative thermal stability should not exceed 30 ° C, particularly preferably at most 20 ° C, of Tonset-z E-PAN deviate ^¬ chen, preferably at most 10 ° C. The final temperature of the oxidative thermal stabilization should not exceed 30 ° C from 7p _eak -z E-PAN, preferably a maximum of 20 ° C.

Successful stabilization within the meaning of the invention is also characterized in that the density of the Ox-PAN fiber is at least 1.30 g / cm ³ . The density of the Ox-PAN fiber is preferably in the range from 1.35 to 1.5 g / cm ³ , particularly preferably between 1.35 and 1.39 g / cm ³ . If the density of the resulting Ox-PAN fibers is outside this density range, either the temperature in the heating zones of the stabilization oven or the process speed must be changed. An increase in the temperature in the heating zones or a slowdown in the process speed lead to a higher density of the Ox-PAN fibers. A decrease in the temperature or an increase in the process speed lead to a lower density of the Ox-PAN fiber. This iterative parameter change is carried out until the Ox-PAN fiber reaches the corresponding density range.

The oxidative thermal stabilization lasts preferably 10 minutes to 4 hours, in particular 1 hour to 3 hours, particularly preferably 1 hour to 2 hours. However, it has also been shown that the range from 1.5 to 2.5 hours is advantageous.

The oxygen content of the Ox-PAN fiber is preferably from 5 to 25% by weight, in particular from 10 to 15% by weight and very particularly preferably from 11 to 13% by weight.

Furthermore, it is important for the success of the invention that the fibers are preferably subjected to a tensile force during stabilization. A high traction stabilization usually leads to better mechanical properties of the resulting carbon fibers. The amount of tensile force also results in stretching or shrinking of the fibers during stabilization. It has been shown that, especially at the beginning of the oxidative thermal stabilization, it is advantageous to choose the tensile force so that the result is a stretching of 0 to 50%, preferably from 0 to 10%. The tensile forces that occur are preferably 0.03 to 1 cN per filament, in particular 0.05 to 0.5 cN per filament, the range from 0.1 to 0.3 cN per filament being very particularly preferred. Surprisingly, it was also found that an increase in the radiation dose is accompanied by an increase in the tensile forces with the same stretching.

4. Carbonization

In order to obtain a carbon fiber, the Ox-PAN fibers are preferably carbonized under an inert gas atmosphere after stabilization. Inert gases that can be used are helium, neon, argon, krypton, xenon and nitrogen; the use of nitrogen is preferred.

For the degree of carbonization and for the mechanical properties of the resulting carbon fibers, the final temperature during carbonization is decisive. The final temperature of carbonization can be up to 1800 ° C.

The carbonization can be carried out continuously or discontinuously. In discontinuous carbonization, the Ox-PAN fiber is heated under an inert gas atmosphere from any temperature, usually room temperature, to the final temperature of the carbonization. The heating rate during the carbonization is preferably between 1 and 100 K / min, in particular between 5 and 20 K / min. The Ox-PAN fiber should experience a tensile force in the fiber axis during the discontinuous carbonization.

In addition, and preferably, continuous carbonization is possible. With the continuous carbonization the Ox-PAN fibers are over Galettes passed through a carbonization furnace, which has several heating zones in an advantageous configuration. The use of several carbonizing furnaces is particularly preferred. When using two consecutive carbonizing ovens, these are called LT (low temperature) and HT (high temperature) ovens. The temperature in the LT oven can be between 200 and 1000 ° C, preferably between 300 and 750 ° C. This temperature range should be completely covered over several heating zones in the oven. In the HT furnace, the temperature can be between 800 and 1800 ° C, preferably between 1000 and 1400 ° C.

Even during continuous carbonization, it is advantageous if the fibers experience a tensile force. This should lead to a total stretching of the fibers of -10 to + 10%. In particular, it is advantageous if a positive stretching of 0.1 to 15% is achieved in the LT oven and a negative stretching or shrinkage of -0.1 to -15% in the HT oven. The winding speed for continuous carbonization should be between 0.5 and 50 m / min and is essentially dependent on the size of the carbonization plant.

The density of the resulting carbon fibers is preferably between 1.65 and 1.9 g / cm ³ , in particular between 1.7 and 1.8 g / cm ³ . A higher density is often associated with an improvement in the mechanical properties. Surprisingly, the irradiation of the multifilaments made of textile PAN leads to higher densities of the carbon fibers with a comparable density of the Ox-PAN fibers.

5. Graphitization

Graphitization can optionally be carried out after the carbonization. As with carbonization, this uses an inert gas atmosphere. The inert gases are helium, neon, argon, krypton and xenon. The use of argon is preferred.

The graphitization is preferably carried out between 1800 and 3000 ° C. This is achieved using one or more graphitization ovens, each of which are preferably equipped with several heating zones. The start temperature of the graphing can be between 1800 and 2200 ° C. The final temperature can be between 2200 and 3000 ° C.

The graphitization is advantageously carried out continuously. During the graphitization, the multifilament should experience a tensile force. This is preferably between 0.01 and 0.5 cN per filament. The resulting stretching is preferably between -5 and + 5%, in particular between -2 and + 2%.

In summary, it can be stated that the invention, as shown above, has many advantages:

The invention relates to a simple, inexpensive method for electron beam irradiation of multifilaments, consisting of textile PAN, and their use as a precursor for the production of carbon fibers.

The textile-PAN multifilaments are preferably irradiated under nitrogen. This inert gas atmosphere surprisingly leads to better mechanical properties of the resulting carbon fibers. It also proves to be advantageous to carry out the oxidative thermal stabilization immediately after the irradiation. The irradiated multifilament can be converted into an Ox-PAN multifilament by means of a defined oxidative thermal stabilization, which is advantageously designed with regard to the thermal properties of the precursor. This can be converted into carbon fibers under an inert gas atmosphere. The resulting carbon fibers show the best values for maximum tensile strengths (according to DIN EN ISO 5079: 1995) of up to 3.1 ± 0.6 GPa on average. The modulus of elasticity averages up to 212 ± 9 GPa.

Accordingly, the essence of the present invention relates to the process guidance in electron irradiation and oxidative thermal stabilization.

The present invention is to be explained in more detail below by means of various examples: Examples

Example 1 (irradiation, stabilization and carbonization of textile PAN 1)

500 m of a wet-spun 3k multifilament of textile PAN 1 (93.5% by weight acrylonitrile, 6% by weight methyl acrylate, 0.5% by weight methallyl sulfonate, M _n = 72,000 g / mol, PDI = 3, 0.7 _on se _t- z = 249 ° C, Tpea _k- z = 299 ° C) was continuous (winding speed = 6.6 m / min) with 1000 kGy electron beams at 200 kV acceleration voltage and 3.5 mA current under nitrogen irradiated. The mechanical properties of the multifilament before and after irradiation are given in Table 1.

Table 1

Fiber tensile strength modulus of elasticity elongation diameter density [MPa] [GPa] [%] [pm] [g / cm ³ ]

0 kGy 540 ± 35 11.3 ± 0.9 12.3 ± 0.8 12.1 ± 0.8 1.18

E-PAN 1000 1.18

520 ± 35 12.1 ± 0.8 11.1 ± 0.6 12.8 ± 0.5 kGy

Ox-PAN 330 ± 40 7.9 ± 1.0 19.3 ± 4.0 11.4 ± 0.9 1.36

Carbon fiber 2650 ± 600 206 ± 9 1.24 ± 0.25 7.0 ± 0.6 1.77

Note: Mechanical properties of a wet-spun 3K multifilament consisting of textile PAN 1, unirradiated and electron-irradiated under nitrogen with a dose of 1000 kGy, the resulting Ox-PAN fiber and the resulting carbon fiber. The values are based on 20 individual fiber measurements, with carbon fiber on 30 individual fiber measurements.

Subsequently, a DSC measurement of the irradiated fiber was used to determine its tone set-z E-PAN at 204 ° C and a 7p _eak- z E-PAN at 282 ° C. The multifilament was then stabilized in a stabilization oven with 4 meat chambers. Using the specific clay set E-PAN, a temperature of 210 ° C was selected in meat chamber 1. In the following meat chambers 2 to 4, 225 ° C, 245 ° C and 265 ° C were set. In meat chambers 1 and 2, the fiber was drawn 5% each. The The tensile force occurring was 426 cN in heating chamber 1, 527 cN in heating chamber 2, 428 cN in heating chamber 3 and 460 cN in heating chamber 4. The density of the resulting Ox-PAN multifilament was 1.36 g / cm ³ . The mechanical properties and the density of the Ox-PAN fibers can be seen in Table 1.

The subsequent carbonization was carried out continuously with the aid of an LT and an HT carbonization furnace in a nitrogen atmosphere. The temperature profile and the stretching in the LT oven can be seen in Table 2, the temperature profile and the stretching in the HT oven in Table 3. The resulting mechanical properties and the density of the carbon fiber can be seen in Table 1.

Table 2

Heating zone 1 2 3 4 5 6

Temperature [° C] 300 390 480 570 660 750 Drawing [%] +5

Note: Temperature profile and stretching in the LT oven during carbonization in Example 1.

Table 3

Heating zone 1 2 3

Temperature [° C] 1000 1175 1350

Stretching [%] -3.5

Note: temperature profile and stretching in the HT oven during carbonization in example 1. Table 4

Tensile strength modulus of elasticity elongation diameter [MPa] [GPa] [%] [Mm]

3250 211.23 1.47 6 ^ 84

2800 188.85 1.39 7.88

3470 225.68 1.47 6.18

2330 204.28 1.11 7.53

2390 207.99 1.11 7.33

2930 213.84 1.31 6.57

2870 204.10 1.35 7.59

3340 207.88 1.54 6.34

2680 212.53 1.22 8.11

3960 218.22 1.73 6.35

2360 207.74 1.11 6.73

2640 209.00 1.22 7.98

1670 203.82 0.82 7.40

1790 200.58 0.88 6.74

2120 213.07 0.99 6.49

2540 200.40 1.23 6.58

2710 196.56 1.32 5.65

2640 197.62 1.30 6.69

1660 218.81 0.76 6.55

2,140 204.31 1.02 7.26

3370 193.09 1.60 7.41 3420 201.74 1.62 7.77

2560 215.99 1.14 6.14

2920 214.81 1.32 7.44

3,080 186.63 1.56 7.14

2290 205.56 1.09 6.94

2190 205.65 1.04 7.36

1940 208.91 0.92 6.95

3,040 211.56 1.39 6.61

2310 202.89 1.11 7.38

Note: Individual fiber values for the mechanical properties of the carbon fibers from example 1. Comparative example 1: (stabilization and carbonization of textile PAN 1, without irradiation)

The multifilament from Example 1 was continuously stabilized and carbonized without irradiation. By means of DSC measurement, 7 ^" _on set-z was determined to be 249 ° C and 7 ^" _Pe ak-z to 299 ° C. The temperature in heating chamber 1 of the stabilization oven was 240 ° C, in heating chambers 2 to 4 250, 265 and 275 ° C were set. Analogously to Example 1, 5% each was stretched in heating chambers 1 and 2. The resulting tensile force was 171 cN in heating chamber 1, 203 cN in heating chamber 2, 255 cN in heating chamber 3, and 370 cN in heating chamber 4. The density of the Ox-PAN multifilament was 1.39 g / cm ³ , the mechanical properties can be seen in Table 5. The carbonization was also carried out analogously to Example 1. The mechanical properties and the density of the resulting carbon fibers can be seen in Table 5. Table 5

Tensile strength E-modulus elongation diameter density

fiber

speed [MPa] [GPa] [%] [gm] [g / ml]

Ox-PAN 280 ± 40 8.2 ± 1.0 16.8 ± 3.4 10.7 ± 1.2 1.39

Carbon fiber 2250 ± 400 196 ± 6 1.12 ± 0.2 6.8 ± 0.4 1.73

Note: Mechanical properties of Ox-PAN fibers and carbon fibers, resulting from a wet-spun 3K multifilament of textile PAN 1, without electron irradiation.

Comparison example 2: (irradiation under air, stabilization and carbonization analogous to KR 20160140268A)

The multifilament from Example 1 was irradiated analogously to Example 1, but under air instead of nitrogen, so that the irradiation dose and atmosphere are the same as those in KR 101755267. Then a piece of each of the fibers irradiated under air, about 15 cm long, was fixed in graphite boats. The fibers were then oxidatively stabilized in a muffle furnace under air. It was heated from 200 to 240 ° C within 150 minutes and from 240 to 260 ° C within 90 minutes. The fibers were then carbonized at a rate of 5 K / min up to 1200 ° C. under nitrogen. The resulting mechanical properties can be seen in Table 6. The tensile strength of these fibers roughly corresponds to the tensile strength of the carbon fibers according to KR 20160140268A, the E modulus is around 50 GPa above that of the carbon fibers according to KR 20160140268A.

Table 6

Tensile strength E-modulus elongation diameter density

dose

speed [MPa] [GPa] [%] [pm] [g / ml]

1000 kGy 1740 ± 500 178 ± 15 0.98 ± 0.28 8.4 ± 0.5 1.75 Note: Mechanical properties of the carbon fibers, resulting from textile PAN 1, irradiated in air, stabilized and carbonized analogous to KR 101 755 267.

Example 2: (irradiation, stabilization and carbonization of textile -PAN 2) 500 m of a wet-spun 3k multifilament, consisting of textile-PAN 2 (6.5

Wt% vinyl acetate; M _n = 51,000 g / mol, PDI = 4.9, 7 ^" _on set-z = 256 ° C, 7 ^" _Pe ak-z = 314 ° C), were continuous (6.6 m / min) with 1000 kGy electron beams irradiated at 200 kV acceleration voltage and 3.5 mA current strength under nitrogen. On closing was by a DSC measurement of the irradiated fiber whose 7 ^_"on set-z E-PAN 210 ° C and 7p _eak -z E-PAN determined to 291 ° C. The multifilament was subsequently ^¬ ßend in a stabilizing furnace 4 Using the specific E-PAN clay set, a temperature of 210 ° C. was selected in heating chamber 1. In the following heating chambers 2 to 4, 225 ° C., 245 ° C. and 265 ° C. were set. In heating chamber 1 The fiber was each stretched 5% and 2. The density of the resulting Ox-PAN multifilament was 1.36 g / cm ^3. The subsequent carbonization was carried out continuously with the aid of an LT and an HT carbonization furnace in a nitrogen atmosphere. The temperature profiles in LT and HT correspond to those in Example 1, the stretching in LT was + 2% and in HT -3.5%. The mechanical properties of the carbon fibers can be seen in Table 7.

Table 7

Dose of EB

Tensile strength E-modulus elongation diameter density

Irradiation

speed [MPa] [GPa] [%] [pm] [g / ml]

[kGy]

1000 2600 ± 600 184 ± 6 1.38 ± 0.34 7.0 ± 0.5 1.71

Note: Properties of the carbon fibers, resulting from a wet-spun 3-component multifilament made from textile PAN 2, electron-irradiated under nitrogen with a dose of 1000 kGy. Example 3: (Irradiation, stabilization and carbonization of textile PAN 1 with different time intervals between irradiation and stabilization)

800 m of a dry-spun 3 K multifilament made of textile PAN 1 (93.5% by weight acrylonitrile, 6% by weight methyl acrylate, 0.5% by weight methallyl sulfonate, M _n = 72,000 g / mol, PDI = 3 , 0.7 ^" _on set_z = 249 ° C, 7 ^" _Pe a _k -z = 299 ° C) were continuously (winding speed = 6.6 m / min) with 1000 kGy electron beams at 200 kV acceleration voltage and 3.5 mA current intensity irradiated under nitrogen. The 7 ^" onset-z E-PAN and 7peak-z E-PAN corresponded to that from Example 1. The multifilament was then in four experiments after a break with a duration of one hour, one day, one week and 6 weeks in one Stabilizing oven with 4 heating chambers stabilized The stretching and temperatures in the stabilizing oven correspond to those of Example 1. The tensile forces occurring in the stabilizing oven can be seen in Table 8.

Table 8

Note: Temperature profile, tensile forces and stretching in the stabilization oven for the Dralon X fiber during the oxidative stabilization of the dry-spun and irradiated with 1000 kGy after various time intervals between irradiation and stabilization.

The density and the mechanical properties of the resulting Ox-PAN multifilament are shown in Table 9. Table 9

interval

Tensile strength E-modulus elongation diameter density

Irradiance [cN / tex] [cN / tex] [%] [dtex] [g / ml]

stabilization

1 h 20.8 ± 1.8 550 ± 30 23 ± 5 1.1 ± 0.3 1.36

1 d 18.4 ± 2.0 530 ± 20 23 ± 5 1.2 ± 0.3 1.36

1 W 19.9 ± 2.2 560 ± 30 20 ± 6 1.1 ± 0.3 1.36

6 W 16.2 ± 1.1 500 ± 30 23 ± 5 1.2 ± 0.3 1.37

Note: Properties of the stabilized fibers resulting from dry-spun Dralon X fibers irradiated with 1000 kGy. The time between exposure and stabilization was varied between about an hour and 6 weeks.

The carbonization was then carried out as in Example 1. Table 10 shows the mechanical properties and the densities of the resulting carbon fibers. The stretching was varied between 2 and 7% in the tests in the LT oven.

Table 10

Interval LT

Tensile strength modulus elongation diameter

Irradiation - stretching

[GPa] [GPa] [%] [dtex] Stabilization [%]

2 2.49 ± 0.89 188 ± 7 1.29 ± 0.4 0.55 ± 0.09

1 h 5 3.08 ± 0.64 193 ± 9 1.54 ± 0.29 0.58 ± 0.09

7 2.89 ± 0.89 193 ± 7 1.46 ± 0.43 0.61 ± 0.10

2 2.52 ± 0.66 192 ± 9 1.29 ± 0.31 0.61 ± 0.19

1 d 5 2.85 ± 0.60 196 ± 9 1.42 ± 0.29 0.66 ± 0.18

7 2.60 ± 0.62 195 ± 9 1.30 ± 0.29 0.53 ± 0.08

2 2.16 ± 0.63 185 ± 11 1.15 ± 0.32 0.67 ± 0.25

1 W 5 2.67 ± 0.52 192 ± 10 1.35 ± 0.23 0.58 ± 0.09

7 2.46 ± 0.53 197 ± 9 1.23 ± 0.25 0.61 ± 0.16

2 2.72 ± 0.64 184 ± 8 1.44 ± 0.33 0.59 ± 0.07

6 W 5 2.17 ± 0.59 191 ± 14 1.12 ± 0.27 0.63 ± 0.16

7 2.07 ± 0.38 192 ± 11 1.07 ± 0.21 0.58 ± 0.13

Note: Mechanical properties of the carbon fibers made from a dry-spun 3K textile PAN-1 multifilament irradiated with 1000 kGy. The time between irradiation and stabilization was varied between 1 h and 6 W. The density of all carbon fibers was 1.77 g / ml.

Example 4: (irradiation, stabilization and carbonization of textile PAN 3)

500 m of a wet-spun 3k multifilament, consisting of textile -PAN 3 (100% acrylonitrile, M _n = 84,000 g / mol, PDI = 5.6, 7 ^" _on set-z = 298 ° C, 7 ^" _Pe ak-z =

313 ° C), were irradiated continuously (6.6 m / min) with 1000 kGy electron beams at 200 kV acceleration voltage and 3.5 mA current strength under nitrogen. A DSC measurement of the irradiated fiber was then used to determine its 7 ^" onset-z E-PAN at 217 ° C and 7 ^" _Pe ak-z E-PAN at 279 ° C. The multifilament was then stabilized in a stabilization oven with 4 heating chambers. Based For the specific clay set E-PAN, a temperature of 210 ° C was selected in heating chamber 1. In the following heating chambers 2 to 4, 225 ° C., 245 ° C. and 265 ° C. were set. In heating chambers 1 and 2 the fiber was drawn 2% each, in heating chambers 3 & 4 the drawing was -0.5%. The density of the resulting Ox-PAN multifilament was 1.37 g / cm ³ . The subsequent carbonization was carried out continuously with the aid of an LT and an HT carbonization furnace in a nitrogen atmosphere. The temperature profiles in LT and HT correspond to those in Example 1, the stretching in LT was + 5%, in HT -3.5%. The mechanical properties of the carbon fibers can be seen in Table 11.

Table 11

Dose of EB

Tensile strength E-modulus elongation diameter density

Irradiation

speed [MPa] [GPa] [%] [pm] [g / ml]

[kGy]

1000 2980 ± 660 212 ± 9 1.38 ± 0.30 7.0 ± 0.5 1.78

Note: Properties of the carbon fibers, resulting from a wet-spun 3K multifilament made of textile PAN 3, electron-irradiated under nitrogen with a dose of 1000 kGy.

* * *

Claims

1. A method for the irradiation and oxidative stabilization of PAN fibers for the production of a precursor fiber of carbon fibers, characterized in that

(1) the PAN fibers is based on a homopolymer or copolymer of PAN, wherein the homopolymer or copolymer from a PAN 7 _on se _tz -Temperature of at least 245 ° C measured in air (according to DIN EN ISO 11357- 5: 2014- 07), has a number average molecular weight of 20,000 to 250,000 g / mol polymethyl methacrylate molar mass equivalents (determined according to DIN 55672-2: 2016-03) and a comonomers content of not more than 15.0% by weight,

(2) the PAN fibers are subjected to ionizing radiation with a radiation dose of 10 to 5000 kGy,

(3) from the results obtained by irradiation E PAN fiber the reduced To _n s _t _z -temperature of air is determined (7 _on se _t z E-PAN) (according to DIN EN ISO 11357-5: 2014-07 ), afterwards the oxidative thermal stabilization PAN e ± 30 ° C is introduced at an initial temperature of 7 _0n se _tz and oxidative Ther mostabilisierung with increasing temperature up to a minimum density of the oxidation stabilized PAN fiber (Ox-PAN) from 1, 30 g / cm ^{3 is} carried out.

2. The method according to claim 1, characterized in that the PAN has a number average molecular weight of 30,000 to 150,000 g / mol, in particular from 50,000 to 120,000 g / mol.

3. The method according to claim 1 or 2, characterized in that the comonomer content of PAN 0.0 to 12.0 wt .-%, in particular 0.0 to 9.0 wt .-% and particularly preferably 0. Is 0 to 7.5 wt%.

4. The method according to at least one of the preceding claims, characterized in that the comonomer of PAN is a vinyl compound, in particular vinyl acetate, vinyl propionate, methyl acrylate, methyl methacrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, tert-butyl acrylate, sodium methallylsulfonate, Represents sodium vinyl sulfonate, acrylamide, methacrylamide and / or vinylacetamide.

5. The method according to at least one of the preceding claims, characterized in that the PAN fibers are textile PAN fibers.

6. The method according to at least one of the preceding claims, characterized in that the radiation dose of the ionizing radiation is 70 to 2500 kGy, in particular 300 to 1000 kGy.

7. The method according to at least one of the preceding claims, characterized in that the ionizing irradiation with electron beams, gamma rays, in particular low-energy gamma rays, and / or X-rays, in particular high-energy X-rays, is carried out.

8. The method according to claim 7, characterized in that the ionizing radiation with electron beams, preferably in an inert gas atmosphere, in particular in a nitrogen atmosphere, is carried out.

9. The method according to claim 7 or 8, characterized in that the acceleration voltage in the ionizing irradiation with electron beams is 100 to 900 kV, in particular 160 to 600 kV and particularly preferably 180 to 400 kV.

10. The method according to at least one of claims 7 to 9, characterized in that the current intensity in the ionizing irradiation with electron beams is 0.1 to 100 mA, in particular 1 to 50 mA and particularly preferably 2 to 10 mA.

11. The method according to at least one of claims 7 to 10, characterized in that the storage time between irradiation and oxidative thermal stabilization is less than a day, preferably less than an hour.

12. The method according to at least one of claims 7 to 11, characterized in that the ionizing radiation is connected directly upstream of the oxidative thermal stabilization with a continuous thread run.

13. The method according to at least one of the preceding claims, characterized in that the start temperature in the oxidative thermal stabilization is 7 ^" ₀ nset-z E-PAN ± 20 ° C, in particular ± 10 ° C.

14. The method according to at least one of the preceding claims, characterized in that the final temperature of the oxidative thermal stabilization 7peak-z E-PAN is ± 30 ° C, in particular ± 20 ° C.

15. The method according to at least one of the preceding claims, characterized in that the oxidative thermostabilization up to a density of the oxidatively thermostabilized PAN (Ox-PAN) of 1.30 to 1.5 g / cm ³ , in particular from 1.35 to 1 , 39 g / cm ³ .

16. Use of the Ox-PAN fibers obtained by a process according to at least one of the preceding claims for the production of carbon fibers by carbonization, optionally with subsequent graphitization.

17. The method according to at least one of the preceding claims, characterized in that the 7 _on se _tz -temperature up to 320 ° C, especially up to 300 ° C, is.

* * *