DE1939390A1 - Process for the thermal stabilization of acrylic fiber material - Google Patents

Description

1939-39Q

PATENT LAWYERS OR.-ING. BY KREISLER DR.-JNG. SCHONWALD DR.-ING. TH. MEYER DR. FUES DIPL.-CHEM. ALEK VON KREISLER DIPL-CHEM. CAROLA KELLER DR.-ING. KLDPSCH COLOGNE 1, DEICHMANNHAUS

Cologne, August 1st, 1969 Ke / Ax

Celanese Corporation,

522 Fifth Avenue, New York, N. Y. 10036 (, V.St.A.) .

Process for the thermal stabilization of acrylic fiber material

There have already been "methods of transferring! Fibers." proposed from acrylic polymers in a modified form with increased thermal stability. This modification has generally been achieved by leaving the fiber material in an oxygen-containing atmosphere for a long time heated to moderate temperatures. The product obtained can be used as an intermediate for the manufacture of charred (carbonize) fiber materials or for the direct use as refractory fiber.

U.S. Patent Nos. 2,913,802 and 3,285,696 describe Process for converting fibers from acrylonitrile homopolymers or copolymers into a heat-resistant one Shape. These known stabilization processes are usually carried out in batches using Acrylonitrile copolymers worked. The Belgian patent specification 700 655 describes a process in which endless lengths of acrylonitrile copolymer continuously a pre-oxidation treatment up to practically complete Oxygen saturation while being subjected to

Air at a temperature of not more than 25O ⁰ C, e.g.

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3 or more hours at 220 ⁰ C are kept.

The stabilization of fibers from acrylonitrile comopolymers and copolymers in an oxygen-containing atmosphere includes 1) an oxidative crosslinking reaction of adjacent ones Molecules and 2) a cyclization reaction of pendant nitrile groups to form a fused dihydropyridine structure. The mechanism of the reaction is complex and difficult to explain, but it is believed that this both reactions take place at the same time or are to some extent competing reactions.

The cyclization reaction is exothermic and must be controlled or directed if the fiber shape of the stabilization Subject to acrylic polymers should be retained · As already mentioned, was in the known processes this difficulty usually eliminated by keeping the fiber generally for a period of many hours heated to moderate temperatures. However, these methods are due to their excessive time requirements technically uninteresting. After the charring (carbonization) or after the charring and graphitization of the previously stabilized fiber also cared for the final product due to its poor strength properties to be of limited use.

The invention relates to an improved method for stabilizing and flame-proofing fiber materials from acrylic polymers to form products that are suitable for charring (carbonization) or for charring and graphitization, after which char or char and graphitization have superior tensile strength and in the stabilized form have substantially the same fiber shape as the starting material.

The invention is also directed to a method for effective Transfer of fiber materials made of acrylic polymers in a non-burning form, whereby the difficult- » which is normally characterized by the critical heat

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development results when the starting materials are subjected to the action of heat, completely switched off .-- is ».: ...- ■■ · ■ -. -

The invention also encompasses an acrylic polymer derived, derived, or charred, or charred and graphitized

... fiber materials with superior strength, stabilized,., ^ Light fiber materials used in the aerospace industry can be used, and stabilized fiber materials, the. derived from acrylic polymers consisting essentially of recurring acrylonitrile units

·. ', And after graphitization result in fiber products, .: which have a strength of at least about 14 g / den.

The method according to the invention for stabilizing Acrylic polymer fiber materials can be used in at least some of its embodiments extremely effective continuously " be performed.

"The improved method according to the invention for the stabilization of acrylic aserma.terialien, which consist primarily of recurring Acryliiiiitril units, is characterized in that the material is heated in an oxygen-containing atmosphere to a temperature which is about is 10 ° to 100 ⁰ C below its critical temperature, to the fiber material at least about 5 parts by weight 70 contains oxygen, while its original fiber form in

25, essentially preserved, and then the fiber material obtained subjected to the action of an acidic atmosphere at a temperature for at least about 1 minute, which is roughly between the critical temperature of the Starting material and a temperature of about 50 C above

5C is half the critical temperature of the starting material, whereby a stabilized fiber product is obtained which can be charred, its original fiber shape in the. ■ essential- preserved and does not burn when exposed to the action subjected to an ordinary match flame

"^ v.ird. The stabilized product can optionally be

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heat in an inert atmosphere, or be charred and graphitized.

The acrylic fiber materials stabilized according to the invention can be in various forms, e.g. in the form of individual continuous threads, staple fibers, Bundles, yarns, ropes, ribbons, knitted fabrics, braids, woven fabrics or other fiber constructions. With a preferred Embodiment of the invention is the fiber material in endless form, e.g. in the form of individual continuous threads, continuous yarns or endless ribbons. With one especially The preferred embodiment of the invention is the acrylic fiber material treated in the form of a continuous filament yarn. This yarn can according to the usual known Processes, for example by dry spinning or wet spinning, are produced. That as the starting material for The process-serving yarn can optionally have a twist which improves its handling properties. For example, about 4 to 40, preferably about 4 to 28 turns per meter can be incorporated.

Yarns or other fiber structures can generally 1) before the stabilization treatment, 2) between the pre-oxidation stages of the process or 3) immediately after the otabilization treatment can be formed.

The acrylic polymer used as the starting material consists mainly of repeating iicrylonitrile units. For example, the acrylic polymer should generally be at least about 85% hol- # acrylonitrile and no more than about 15 MoI- ^ S of a copolymer is baren with acrylonitrile Honovinyl compound, e.g. / styrene, methyl acrylate, methyl methacrylate, Vinyl acetate, vinyl chloride, vinylidene chloride and vinyl pyridine or more of these monomers.

V / hen the process according to the invention is continuous for Stabilization of endless fiber materials carried out

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is to be, it is recommended that the starting material according to the

Teachings of the German patent .. »(patent application

of the same day according to the TJ.S.A. patent application 7 ^ 9 951) of the applicant. That Copolymers should not be more than about 5 moles or $ 5 contain several monovinyl monomers copolymerized with acrylonitrile. In a "particularly preferred embodiment According to the invention, the acrylic polymer is either 1) an acrylonitrile homopolymer or 2) an acrylonitrile copolymer, that no more than about 1 mol- ^ one or contains several monovinyl comonomers which are copolymerized with acrylonitrile.

The acrylic fiber material used as the starting material is preferably highly oriented. Through this orientation the tensile properties of the stabilized fiber material obtained and of the carbon products obtained therefrom can be increased. For example, the starting material can be strongly oriented prior to stabilization by it is hot drawn to a relatively high single filament tensile strength of at least about 5 g / den will. Particularly preferred starting materials for the process according to the invention are fiber materials, whose individual threads have a strength of about 7 »5" to 8 g / den to have.

If a highly oriented endless acrylic fiber material, the individual threads of which have a tensile strength of at least about 5 g / den, is continuously stabilized according to the invention, this fiber material is according to the teachings of the German patent ....... _β .. (patent application of the same Days according to the applicant's USA patent application 750 018) preferably held during the entire heat treatment under conditions in which substantial shrinkage can take place.

The one that occurs when the acrylic fiber material is heated

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Oyclization reaction involving pendant nitrile groups are involved is generally strongly exothermic and, if not controlled, leads to the destruction of the Fiber shape of the starting material. In certain cases this exothermic reaction takes place with explosive violence instead and leads to the incineration of the fiber material Flame formation. More often, however, only a break, a disintegration and / or a fusion of the fiber material takes place instead of when the critical temperature is reached. As the amount of comonomer in an acrylonitrile copolymer increases is present, a fiber material made of it tends to soften at increasingly low temperatures, and the possible destruction of the original fiber shape by fusing adjacent threads becomes a factor of increasing importance. "This softening is generally of marked deterioration accompanied by strength, which in severe cases leads to the destruction of the original fiber shape by breaking which is a consequence of the inability of the fiber material to support its own weight. Also maintain Fiber materials that are strongly oriented have a higher critical temperature than the corresponding Materials that lack this orientation. The one mentioned here "Critical temperature" is defined as the temperature where the fiber shape of a given sample of a starting acrylic fiber material is lost if no stabilization has been carried out beforehand.

In a preferred embodiment of the invention, the starting material has a critical temperature of at least about 300 ⁰ O, for example from about 300 to 33O ⁰ O. In addition to visual observation, the determination of the critical temperature of a given acrylic resin material by using thermal analysis methods, e.g. methods under V. _e r-turn of differential scanning calorimeters (differential

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ft

scanning calorimeter), which makes flie location and strength of the exothermic reaction can be measured quantitatively. These methods are particularly beneficial when the acrylic resin material is an acrylonitrile homopolymer or a closely related acrylonitrile copolymer.

If the cyclization reaction is started without precautions being taken for heat dissipation reached the critical temperature quickly or below simultaneous Destruction of the product must be exceeded.

It follows from this that if, according to the invention, a bobbin of yarn is to be stabilized in which the heat dissipation is possible on the inside is impaired and in which parts of the fiber material touch each other, which are used on the thread spool The initial heat that has been brought into effect must be relatively moderate, so that the exothermic heat of reaction that occurs with As the cyanolation reaction proceeds within the package, not the threshold temperature for any one Part of the yarn body exceeds.

Achieving the best results will be constant Heat treatment in all 'files of the acrylic fiber material favored during the stabilization treatment, especially during its initial phase. This even Reaction conditions can best be achieved by adding the mass of the fiber material at each point is limited so that the heat dissipation from the interior of the material is not unduly impaired. For example aas the treated fiber material in a heated oxygen-containing atmosphere, e.g. in ordinary air, so arranged that generally a free access to a substantial part of its surface is guaranteed. In a preferred embodiment of the invention, a serving as a starting material is used endless acrylic fiber material, e.g. a yarn, continuously passed through suitable heating zones while it is in these hangs down. The fiber material can during the stabilization

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treatment treatment can also be present as windings on a carrier, provided that provisions are made for effective Dissipation of the heat within the windings, e.g. in the form of circulating fairy fans.

During the initial phase of the stabilization treatment according to the invention, the acrylic fiber material is heated to a temperature which is about 10 ° to 10O ⁰ O below its critical temperature until the pre-oxidation reaction has progressed to a point where bound oxygen is in a concentration of at least about 5 wt. - ^c fo is present in the material. The proportion of bound oxygen in the material can be determined using customary methods, for example the Unterzauher analysis. At this point in the process, the fibrous material is generally shiny in appearance and the fibrous shape of the starting material remains essentially intact. It. It has surprisingly been found that at the beginning of the subsequent phase of the stabilization process long before the point at which an oxygen content of at least about 5% by weight is reached, the process leads to an end product after carbonization or after carbonization and graphitization , which has less good strength properties, even if the product is given such strength during the initial stabilization phase that it subsequently withstands the usual critical temperature. A bound oxygen level of about 5 to 12 percent by weight is usually achieved during the initial phase of the process. Higher oxygen levels tend to require longer residence times and generally do not provide any adequate benefit. After completion of the initial stage of the stabilization process according to the invention, the fibrous material may or may not burn, depending mainly on its content of bound oxygen, when exposed to the action of an ordinary match flame. With increasing

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When an ordinary match flame is held on it, the material has less tendency to "burn" when a bound oxygen content of at least about 7 weight percent is reached during the first stage of the process, the material is normally incombustible.

The time it takes to complete the initial phase of the stabilization reaction is reversed However, the relationship to the temperature to which the I fiber material is subjected is not unconditional proportional to this temperature. The heating time during the initial stage of the process is usually about 30 minutes to about 3 hours. In a preferred embodiment of the method according to the invention

applied temperature about 10 ° to 40 ⁰ C below the critical temperature of the starting material. If the first stage of the pre-oxidation reaction is carried out under such relatively severe conditions just below the critical temperature, the process according to the invention offers time advantages and a high process efficiency in addition to obtaining a superior product. If the fiber material consists of an acrylonitrile homopolymer, the first stage of the process is preferably at a temperature of about 260 to 290 C and in a particularly preferred embodiment of the

Invention carried out at a temperature of about 2'70 to 285 ° C. These pre-oxidation conditions are generally used during the initial stage of the pre-oxidation treatment worked with a heating time of about 30 minutes to 2 hours. The initial treatment below the critical Temperature gives the acrylic fiber material such a stability that it is this threshold temperature that the Starting material normally resists without destroying its original paser shape.

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The subsequent heating stage of the pre-oxidation treatment is carried out for at least about 1 minute in an oxygen-containing atmosphere, for example, in ordinary air. The temperature is raised above the applied in the initial stage of temperature addition and is in the range between about the critical temperature of the starting material and a temperature "to about 5O ⁰ C above the critical temperature of the Ausgangamaterials. In a preferred embodiment of the invention, in worked a temperature which is between approximately the critical temperature of the starting material and a temperature up to about 30 ⁰ G above the critical temperature of the starting material. The heating time for the subsequent stage of the stabilization process is generally about 1 minute to about 15 minutes Embodiment of the invention, in which an acrylonitrile homopolymer is used as the starting material, the subsequent stage of the pre-oxidation treatment is carried out at a temperature of about 310 to 350 ° C. In a particularly preferred embodiment of the invention, in which an acrylonitrile homopolymer s serves as a starting material, the subsequent step of Voroxydationsbehandlung about 3 performed ⁰ C to 9 minutes at a temperature of about 320 to 34O. The stabilized product must not burn if an ordinary match flame is held on it, and at the end of the subsequent pre-oxidation stage should contain at least about 7% by weight of bound oxygen in order to be sufficiently stabilized for charring.

The preoxidation steps according to the invention result in a stabilized fibrous material which can be charred or charred and graphitized in an inert atmosphere to a product of unusually high tensile strength. Charring temperatures of about 900 to 3000 ⁰ C can be used for about 3 seconds to 5 minutes.

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The first stage can in general immediately follow the multi-stage pre-oxidation treatment described above without an intermediate heating program being necessary. During the Verkohlungsreaktlon be the other than the carbon in the stabilized "existing fiber material elements, for example nitrogen, hydrogen and oxygen driven off. As used herein the term" carbonized product "w e * defined si" a product which is at least about 90 wt .- $ ⁺ / of atomic carbon. Optionally, there may be graphitic carbon in the product. suitable inert atmospheres where the carbonization can be made suitable check, for example, nitrogen, argon, helium and carbon dioxide ^like.

Includes +), and preferably at least about 95 wt. # A charred product containing substantial quantities graphitisehen carbon, is obtained when · substantially complete graphitization of the carbonized product may be sharper TemperaturbeöLngungen, eg operating at 2000 to 3000 ⁰ O, in generally in about 5 seconds to 2 minutes. It can be determined by the characteristic X-ray image of graphite. In a particularly preferred embodiment of the invention, a graphitized product is formed, in which the carbonized fiber material is at least about 5 seconds, for example about 5 to 60 seconds, to a temperature of about

Is heated 25 "2900 ° $. By changing the temperature, the properties of the obtained product can be changed. For example, maintains the modulus of the carbonized product with increasing temperatures to rise, while the tensile strength remains constant at all temperatures above about 1400 ⁰ O, provided that the fiber is not damaged by handling or heat shock.

The apparatus required to produce the Temperatures used to carry out the method according to the invention can vary widely be. For example, the highly oriented fiber material

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rial during the stabilization reaction can be continuously passed through an oven with air circulation or through the tube ■ a muffle furnace while it is in contact with air is set mperature in which each stage of the Toroxydationsbehandlung by a corresponding change of T _e · A single furnace can be used, , or the material can be placed in a series of ovens one at a time, each of which is maintained at the correct temperature. If necessary, a single tube furnace can be provided with zones that are heated to the required temperatures and the fiber material can be fed continuously through the zones.In continuous operation, an endless 3? ; every stage of the process is reached.

The carbonization or the carbonization and graphitization treatment can be carried out in any apparatus that can generate the required temperatures ability, while an oxidizing atmosphere is excluded. Suitable apparatus are, for example, induction furnaces, Arc furnaces, solar furnaces and Torrichtujigen, which generate low temperature plasma flames. When using an induction furnace of the Lepel type this can stabilized fiber material through a graphite tube or a graphite maniel that is in the windings an induction coil is arranged. It is also possible, the Pasermateriäl through a hollow graphite resistance tube to lead, which is provided with suitable electrodes, or to heat the material directly with the help of resistors.

example 1

Test with multi-stage toroxidation treatment according to. Invention '

An 800-thread continuous yarn produced by dry spinning, which consists of continuous threads made of an Acrsrlnitrilhomopoly-

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mers "and also having a fiesamttiter of 1150 to, had been used as the starting material. The yarn was highly oriented" up to a strength of the monofilaments of 7.5 Ms 8.0 g / den verstreokt katte and a critical temperature of about 310 ⁰ O.

A Lindberg muffle furnace, which had a tube diameter of 31.8 mm and a length of 132 cm, was used to carry out the stabilization treatment in an air atmosphere. The yarn was continuously fed over rollers, arranged at each end of the furnace, and hung over a residence time of 48 minutes, "at 285 ⁰ C along the axial center of the tube furnace. During the first stage of the Voroxydations" was treatment, a content of bound oxygen of 7 »2 wt .- ^ reached. The yarn was "black and shiny" upon completion of the first stage of the pre-oxidation treatment.

The temperature of the muffle furnace was increased to 330 ⁰ O and the yarn was again passed continuously through the muffle furnace for a total dwell time of 2 minutes. At the end of this second stage of the pre-oxidation treatment, the bound oxygen content was 9.5% by weight. The stabilized yarn was black and shiny and was suitable for the production of non-burning textiles or as a starting product for the production of charred materials. Throughout the stabilization treatment, the bobbin winding tension applied to the yarn was adjusted so that there was a shrinkage of 16-17% of the original length of the yarn.

The stabilized yarn was then continuously fed into a Lepel 450 kHz induction furnace and withdrawn from the furnace, the total residence time being 40 seconds. The yarn was charred and graphitized by heating it to a maximum temperature of about 2900 ^{0 O.} The induction furnace contained a water

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cooled copper coil with / an inner diameter of 19.05 and a length of 5.08 cm. It was connected to a power source of 20 kW and with a hollow graphite tube provided that was suspended in the coil and had a length of 216 mm, an outer diameter of 12.7 mm and a Had an inner diameter of 3.2 mm. The previously stabilized yarn was fed continuously through this tube. the Copper coil surrounding part of the hollow graphite tube was arranged to be substantially the same Distance from the ends of the graphite tube. An inert nitrogen atmosphere was maintained in the induction furnace obtain. The graphitized product consisted essentially of pure carbon. His filaments had one Strength of 15.5 g / den.

Trial with one-stage pre-oxidation treatment

The experiment described in Example 1 was repeated with the difference that the 2 minutes at 33O ⁰ C performed the second stage Voroxydationsbehandlung omitted was. After graphitization, the product consisted of essentially pure carbon, but had a lower filament strength of 12.5 g / den.

Example 2

Experiment multistage Voroxydationsbehandlung according to the invention _m

* A sample of the same yarn as in Example 1 was stabilized in the manner described in Example 1, charred and graphitized, but with the following exceptions *

The first stage of the pre-oxide treatment was 73 minutes. performed at 285 ° C. A content of bound oxygen of 10.3 wt .- ^ was achieved here. The second stage of Voroxydationsbehandlung was conducted for 5 Hinuten at 335 ⁰ C. A bound oxygen content of 10.8% by weight was found in the stabilized product.

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After "graphing" the product consisted of essentially isinem carbon and had a! strength of ! Single threads of 16.2 g / den »-

Experiment with single-substance oroxidationst> ehandluuig

The experiment described in Example 2 was repeated with the difference that the 5 minutes at 335 ⁰ G conducted two th stage of Vorojcydations was omitted * treatment! Times the G-raphitierung was the product '. Made of essentially pure carbon, but had a lower thread strength of 13.1 g / den.

■ "· ■. ■ ■. Example 3 ■ - -

HersUCh with multi-stage toroxidation treatment according to

invention .

A sample of the same yarn as used in Example 1 was stabilized in the manner described in Example 1, charred and graphitized, but below the. The following changed conditions for the multi-stage pre-oxidation treatment solution s

The first stage of Yoroxydationsbehandlung was carried out for 50 minutes at 27O ⁰ C, a content of bound oxygen from 5.2 wt .- * was achieved j6 · The anschlieSende stage of ¥ ^ oro3 dizer treatment was 10.5 minutes at 315 ⁰ Q carried out · Sa stabilized product, a total content of bound oxygen of 8.0 wt · - ^ was found. '

After graphitization, the product consisted essentially of pure carbon and had a! strength of the Single thread of 14.3 g / den.

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Example 4

Experiment with multi-stage pre-oxidation treatment according to the ". " Invention

A sample of the same yarn used in Example 1 was stabilized, charred and graphitized in the manner described in Example 1, but below the the following changed conditions in the multi-stage pre-oxidation treatment:

The first stage of Voroxydationsbehandlung was carried out at 285 ⁰ C Minzten 35, wherein a content of bound oxygen has been reached of 5.3 wt .- $. The subsequent stage of VorOxydationsbehandlung was conducted for 2 minutes at 33O ⁰ C. A total of 7 * 1% by weight of bound oxygen was found in the stabilized product.

In view of the graphitization, the product consisted of essentially pure carbon and had a strength of the individual threads of 15 _f 1 g / denier.

Test with imperfect multistage Voroxydationsbe action _Λ ......

The experiment described in Example 4 was repeated with the difference that an insufficient content of bound Oxygen is reached during the first stage of the pre-oxidation treatment and the duration of the subsequent one The stage of the pre-oxidation treatment was extended so that when the stabilization treatment ended, yes and no comparable Bound oxygen content was obtained.

In detail, the first stage of the Voroxydationsbehandlung was performed 21 minutes at 285 ⁰ C, with a content of bound oxygen from only 3 »5 wt .- ^ has been reached. The subsequent stage of the pre-oxidation treatment was carried out at 315 ° C for 10.5 minutes. A total bound oxygen content of

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7.1 wt .- $ found.

After graphitization, "the product consisted of essentially pure carbon, it had a filament strength of only 10.8 g / den «although the same content of bound oxygen as in Example 4 "upon completion of the imperfect multi-stage pre-oxidation treatment was reached, the strength of the carbonized and graphitized product obtained was much lower.

Example 5

Trial with multi-stage pre-oxidation treatment according to the invention

A sample of the same yarn as in Example 1 was made on stabilized, charred and graphitized in the manner described in Example 1, but changed from the following Conditions for the multi-stage oxidation treatment!

The first stage of Voroxydationsbehandlung was carried out for 45 minutes at 285 ⁰ O, wherein a content of bound oxygen from 7> 2 wt .- ^ has been reached. The subsequent stage of the pre-oxidation treatment was carried out ^{at 325 0 O for 5 minutes.} In the stabilized product has a content of bound oxygen from a total of 9 »2 percent was -. $ Found.

After graphitization, the product consisted of essentially pure carbon. It had a single thread strength of 14.7 g / den.

The stabilized fiber material obtained by the pre-oxidation treatment obtained according to the invention is suitable for purposes where a refractory fiber material is required. For example, non-burning substances can be made from it. As already mentioned, The Yoroxidized fiber materials are particularly suitable good as starting materials for the production of fiber

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shaped graphite products of high strength and high Module. These fibrous graphite products can be incorporated into a binder or an investment and serve as a reinforcing agent. The graphite component can accordingly be strong as a light weight bearing component Components and structural parts subject to stress are used, which are particularly used in the aerospace industry Find",

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Claims (1)

193939a * ■ - 19 -. "pat.entanspücäe X ») A method for the thermal stabilization of acrylic fiber material, characterized in that the fiber material, which consists primarily of recurring acrylonitrile elements, is heated in an oxygen-containing atmosphere to temperatures about 10 ° to 10O ⁰ G below its critical temperature until the fiber material Contains at least about 5% by weight of oxygen while it essentially retains its original fiber shape, and then subjecting the fiber material obtained to the action of an oxygen-containing atmosphere at a temperature which is about 50 ^° C. above the critical temperature of the starting material for at least about 1 minute Formation of a stabilized fiber product, which can be charred, its original fiber frame essentially preserved and which cannot be brought to a fire by means of a whisker flame. 2 ·) VerfÄhs? ®S SB & h fesjsnagfo I ₅ as & mreti in that "at least about 85 mol $ Äcryliii'ferileiiiieifeSia uad up to about 15 MoIJf of one or more monovinyl units so eopolynterisierter used as Acrylfaseffsastaiiitl? 1m Äerylsa.ts'ilcä © pslymep . 3.) The method according to claim 1, characterized in that »that there is an acrylonitrile copolymer as the acrylic fiber material at least -95 mole # acrylonitrile units and up to about 5 MoIJi of one or more mono copolymerized therewith vinyl units used. 4.) The method according to claim 1, characterized in that an acrylonitrile homopolyra is used as the acrylic fiber material. 009808/1661 8AD ORIGINAL 193939Q 5 ·) Method according to claim 1 to 4, characterized in that an acrylic fiber material is used, the single thread of which a tear strength of at least about 5 g / den before stabilizing. 6.) Process according to claim 1 to 5, characterized in that air is used as the oxygen-containing atmosphere. 7.) Process according to claim 1 to 6, characterized in that a yarn is used as the acrylic fiber material. 8.) Process according to claim 1 to "J, characterized in that in the first stage up to a temperature of 4o ° C below the critical temperature of the fiber material and in the second stage up to a temperature of about 30 ⁰ C above the critical temperature of the fiber material heated. 9.) Process according to claim 1 to 8, characterized in that an acrylonitrile copolyraer is used as the acrylic fiber material having at least about 99 mole # acrylonitrile units and up to about 1 mole # of one or more copolymerized therewith Monovinyl units used. 10.) The method according to claim 1 to 9, characterized in that in the case of an acrylonitrile ^{homopolymer, the material is heated to temperatures in the range of about 260 ° to 290 0} C until the material contains at least about 5 % oxygen and then the material to temperatures Heats in the range from about 310 ° to 350 ° C. 11.) The method according to claim 1 to 10, characterized in that the stabilized fiber ^{product is heated in an inert atmosphere to temperatures of about 900 ° to 3000 0} C with the formation of a charred product. 009808/166 1 BADORfGINAl. 193939Q 12.) The method according to claim 1 to 11, characterized in that the stabilized fiber material is ^{heated to temperatures in the range of about 2000 ° to 5000 0} C in an inert atmosphere until complete graphitization. 808