US3900285A

US3900285A - Process for producing fireproof fibers

Info

Publication number: US3900285A
Application number: US299401A
Authority: US
Inventors: Michakaze Ono; Hajime Sahara; Masonori Akasaka
Original assignee: Mitsubishi Rayon Co Ltd
Current assignee: Mitsubishi Rayon Co Ltd
Priority date: 1971-10-21
Filing date: 1972-10-20
Publication date: 1975-08-19
Anticipated expiration: 1992-08-19
Also published as: IT969753B; DE2251320A1; FR2156805B1; JPS4845697A; FR2156805A1; DE2251320C3; GB1401649A; DE2251320B2; JPS5410677B2

Abstract

An acrylic fiber is contacted with hydroxylamine at a pH of not higher than 7 to such an extent that the contacted fiber has a solubility of not more than 50% in DMF at 90*C and the fiber so contacted is heated in a gaseous atmosphere. The products have an improved fire resistance while retaining a desirable combination of mechanical properties.

Description

United States Patent Ono et al. Aug. 19, 1975 1 PROCESS FOR PRODUCING FIREPROOF [56] References Cited FIBERS UNITED STATES PATENTS [75] Inventors: Michakaze Ono; Hajime Sahara; -159L595 7/l97l Masonori Akasaka, all of Nagoya. 1 6 2 Japan 3.729.549 4/1973 Assignee: vitlsubishi Rayon Tokyo Primary liramirier-$tephen J. Lechert, Jr.

Japan Armrney, Agenl. or Firm-Armstrong, Nikaido 84 22] Filed: Oct. 20. I972 wfigner 7 [-l l Appl. No 299,401 ABSTRACT An acrylic fiber ls contacted with hydroxylamine at a Form! Appl'cat'on Pnomy Data pH of not higher than 7 to such an extent that the con- Oct. 2|. Japan tacted fiber has a solubility of not more than 50% in DMF at 90C and the fiber so contacted is heated in a 2/ gaseous atmosphere. The products have an improved [5! Int. Cl. D 6: 1/ fire resistance while retaining a desirable combination (58] Field of Search 8/] |5.5; l 17/136; 252/81, f h i al roperties,

13 Claims, 2 Drawing Figures PATENTEB AUG 1 9 I975 HYDROXYLAMINE SULFATE (g/E) Fig. 2

32 0ZF mI mom mi;

5'0 350 SOLUBlLlTY IN DMF we) PROCESS FOR PRODUCING FIREPROOF FIBERS The invention relates to a process for the production of fireproof fibers from acrylic fibers. More particularly, it relates to a process for the production of fireproof fibers wherein an acrylic fiber is chemically modified by treating the fiber with hydroxylamine and the fiber so modified is then heated in an gaseous atmosphere.

Various methods have been reported for the production of fireproof fibers. Among others, Textile Research Journal 20, 786 (1950) discloses a process wherein acrylic fibers are heated at 200C for 16 hours. It is taught in Textile Research Journal 30, 882 I960) to heat acrylic fibers at a temperature of from 150 to 300C for a period of time reciprocally proportional to the temperature. In Japanese Patent Publication No. 2316/1964 multi-stage heat-treatment is proposed in which acrylic fibers are heated in sequential three stages at respectively selected temperatures. However, these processes require complicated and prolonged operation for the heat-treatment and often result in products which are unsatisfactory with respect to fire resistance and/or mechanical properties.

It is also disclosed in Textile Research Journal 30, 882 1960) to treat the acrylic fiber with a certain chemical prior to the heat treatment thereof. Phosphorus pentasulfide and a mixture of zince chloride and diethyl malonate are mentioned therein as a suitable catalyst for promoting effects of the heat-treatment.

Japanese Patent Publication Nos. 15254/66 and 15726/66 teach to impregnate acrylic fibers with an aqueous solution containing ammonium sulfamate and a nitrogen-containing phosphate followed by heating the impregnated fibers in air. In all of these processes, the acrylic fibers, essentially as such, are heated in air in the presence of a certain chemical which is intended to act as a catalyst. However, none of the proposed chemicals give fully satisfactory catalytic effects.

It has now been found that if acrylic fibers are chemically modified in a manner and to an extent as herein described, such chemically modified fibers can readily be oxidized by beating them for a short period of time to provide products having an improved fire resistance with a minimum loss of desirable mechanical properties.

In accordance with the invention there is provided a process for the production of fireproof fibers which comprises treating an acrylic fiber with hydroxylamine at a pH of not higher than 7 to such an extent that the treated fiber has a solubility of not more than 50 percent in dimethylformamide at 90C and heating the treated fiber in a gaseous atmosphere.

Acrylic fiber referred to herein can be in the form of tows, filamentary yarns, slivers spun yarns, woven fabrics, knitted fabrics, non-woven fabrics, or a paper. When acrylic fibers in the form of tows, yarns or slivers are chemically modified in accordance with the invention, the treated fibers may be fabricated into fabrics before being heated.

The acrylic fiber is composed of a fiber-forming polymer containing at least 85 percent by weight of units from acrylonitrile and up to percent by weight of units from at least one unsaturated vinyl or allyl compound which is copolymerizable with acrylonitrile. Examples of such comonomers are vinyl esters such as vinyl acetate; acrylates such as methyl acrylate and ethyl acrylate; methacrylates such as methyl methacrylate, ethyl methacrylate and Z-diethylaminoethyl methacrylate; vinyl ethers such as methyl vinyl ether; acrylic acid and metal salts thereof; methacrylic acid and metal salts thereof; acryloyl or methacryloyl chloride; acrylamide and methacrylamide, itaconic acid and metal salts thereof; itaconamide; N-substituted derivatives of vinyl acid amides such as N-methyl acrylamide, N-methoxy acrylamide, N-methyl methacrylamide and N-methoxy methacrylamide; vinyl chloride; vinylidene chloride; vinyl pyridines; vinyl glycidyl compounds such as glycidyl acrylate and glycidyl methacrylate; vinylsulfonic acid, vinylbenzene sulfonic acid, allylsulfonic acid, methallylsulfonic acid, allyloxybenzene sulfonic acid, methallyloxybenzene sulfonic acid and metal salts thereof.

A typical reaction of acrylic fiber with hydroxylamine will be the formation of amidoxime as illustrated by the following equation:

CN CN Practically, however, oxidation of the amidoxime to hydroxamic acid and other side reactions will also occur depending on particular reaction conditions employed.

Such reactions should be carried out to produce an evenly modified fiber with minimum loss of desirable mechanical properties. If the reaction is localized and- /or too severe, beneficial advantages of the invention will not be enjoyed and the final product will have unsatisfactory mechanical properties. It has now been found that if the acrylic fiber is treated with hydroxylamine at a pH of not higher than 7 the reaction proceeds evenly and mildly to produce an evenly chemically modified fiber which can readily be oxidized, when heated, to the product having an improved fire resistance and a desirable combination of mechanical properties. In other words, when the pH is higher than 7, hydroxylamine exists in free state and it reacts with acrylic fiber so rapidly that the even modification of the acrylic fiber is difficult. Further, at the pH of higher than 7, many side reactions occur and the modified acrylic fiber to be obtained is considerably coloured. Still further, free hydroxylamine is a poison and there is a danger that it may explode at a temperature higher than C.

The hydroxylamine should preferably be in the form of acid addition salts such as sulfate, hydrochloride, nitrate, phosphate, acetate, formate, oxalate, succinate, fumarate, maleate, lactate, tartrate, benzoate and the like. A pH of the reaction medium can be adjusted to a level of not higher than 7, preferably from 3.0 to 7.0, by addition of appropriate amounts of suitable known buffering agents ifdesired. Examples of suitable buffering agents include, for example, sodium, potassium, ammonium-, zincor other soluble metal phthalate, secondary phosphate, tertiary phosphate, pyrophosphate, triphosphate, secondary citrate, tartrate, oxalate or acetate. A preferred reaction medium is an aqueous solution of hydroxylamine sulfate or hydrochloride maintained at a pH of 3 to 7 by addition of at least one of the above-mentioned buffering agents.

It is essential to maintain a pH of the reaction mcdium not higher than 7, otherwisc the final products will not possess an optimum combination of mechanical properties and fire resistance. On the other hand an excessively low pH level is not so advantageous because it has been found that the reaction requires higher temperatures and/or a prolonged period when carried out at a pH substantially lower than 3.

Practically, the reaction can be carried out at a temperature of below 200C, preferably from about 80C to about 130C. Higher temperatures often lead to an unacceptable loss of desirable mechanical properties.

ticular reaction conditions involving a temperature and a concentration of the hydroxylamine reactant, it usu ally varies from 30 to 90 minutes for immersion, or from 5 to 30 minutes for padding.

Samples of chemically modified acrylic fibers having different values of solubility in DMF were heated in a hot air circulating oven at a temperature of 270C until the products having a fire resistance of grade B, as hereinafter defined, were obtained. The values of solubility (in and the times (in minutes) required for the heat-treatment were plotted in a curve, which is shown In practice the acrylic fiber may be immersed and heated in a bath containing a hydroxyamine reactant and maintained at a prescribed pH level. Alternatively, the fiber may be padded with a liquid containing a hydroxylamine reactant and kept at a prescribed pH level, and then heated e.g. by steaming and then dry heating.

The reaction should be carried out to such an extent that the treated fiber has a solubility in dimethylformamide of not more than 50 percent, and preferably not more than 30 percent, as measured at 90C. When the solubility is more than 50 percent, it is impossible to obtain fireproof fibers having excellent fire resistance in a short period of time. The factors which influence the reaction are concentration of the hydroxylamine reactant, pH, temperature, reaction time, a ratio of goods to liquid and a mode of operation. Preferred reaction conditions will be further described with reference to the attached drawing, in which:

FIG. 1 is a graph showing a relation between a concentration (in g/l) of hydroxylamine sulfate in the liquid reaction medium and a solubility (in of the treated fiber in DMF:

FIG. 2 is a graph showing a relation between a solubility (in of the treated fiber in DMF and a time (in min) of the heat-treatment required for attaining a fire resistance of grade B as defined hereinafter. Samples of Vonnel 17" (an acrylic fiber produced by Misubishi Rayon Co., Ltd. and composed of a copolymer containing 93 percent by weight of units from acrylonitrile and 7 percent by weight of units of vinyl acetate) were heated in an aqueous solution containing varied concentrations (in g/l) of hydroxylamine sulfate and maintained at pH 5.5 by addition of sodium secondary phosphate at 100C for 60 minutes with a ratio of goods to liquid of l 7. The concentrations of hydroxylamine sulfate and the values of a solubility of the treated fiber in DMF as measured at 90C were plotted in a curve, which is shown in FIG. 1.

As seen from FIG. 1, the higher the concentration of hydroxylamine sulfate, the lower the solubility of the treated fiber achieved. In the case wherein the acrylic fiber is reacted with hydroxylamine by immersing the fiber in a bath containing the hydroxylamine reactant, it has been found practical to use a concentration of the hydroxylamine reactant of l to 30 g/l, especially 2 to 20 g/l, with a ratio of goods to liquid of l 5 to l 80, especially 1 10 to l 50. Whereas in the case wherein the acrylic fiber is reacted with hydroxylamine by padding the fiber with a liquid containing the hydroxylamine reactant and heating, a pick-up of the hydroxylamine reactant on the fiber may be I to 10% by weight.

Although the reaction time required for achievement of the intended degree of modification (i.e. solubility in DMF of not more than 50 percent, preferably not more than 30 percent, as measured at 90C) depends on parin FIG. 2.

FIG. 2 shows that the modified acrylic fibers having values of solubility in DMF of 50 and I0 percent require a heating period of about 120 and about 5 minutes, respectively, to achieve the identical fireproof grade of B. It is also noted from FIG. 2 that the solubility values of not more than 50 percent are essential in order to achieve the desired grade of fire resistance within a relatively short time of heating.

The acrylic fiber which has chemically been modified with hydroxylamine in a manner as described above and has a solubility in DMF of not more than 50 percent, preferably not more than 30 percent, as measured at C is then heated in a gaseous atmosphere to provide a fireproof product.

Although the gaseous atmosphere in which the modified fiber is heated may advantageously be air, other oxidizing atmospheres such as an oxygen-enriched air, nitrogen monoxide, nitrogen dioxide and a halogencontaining gas may also be used. The gaseous atmosphere may contain nitrogen or argon as diluent.

Preferred temperatures at which the modified fiber may be heated are from about 245 to about 305C. When the modified fiber is heated at these temperatures, a fireproof product can readily obtained within a short period of usually I to I20 minutes, with a minimum loss of desirable mechanical properties. Excessively high temperatures should be avoided because they lead to deterioration of mechanical properties of the products. Whereas temperatures substantially lower than 245C are undesirable since the intended fire resistance cannot be attained within a reasonable period of time.

Preferably the modified acrylic fiber is heated under conditions such that the fiber undergoes little or no shrinkage although it is not essential to do so. It has been found that the products obtained by heating the modified fiber under no tension still have acceptable mechanical properties and are superior to those comparable products obtained from an unmodified acrylic fiber. For tows, yarns and slivers 0 20 percent stretch is preferable; for woven fabrics, non-woven fabrics, and papers 0 l5 percent stretch in both longitudinal and transverse directions, and; for knitted fabrics 0 30 percent stretch in both longitudinal and transverse directions.

If desired, the products obtained by a process of the invention may be carbonized, for example, by heating them in an inert gaseous atmosphere at temperatures of about 300 to l,000C to produce carbon fibers which may further be graphitized, for example, by heating them in an inert gaseous atmosphere at temperatures of about l,000 to about 2,500C.

The invention will be further illustrated by the following examples.

Solubility of a given acrylic fiber was determined as follows:

About one gram of a sample of the fiber was weighed (W It was then immersed in 100 ml of dimethylformamide at a temperature of 90C for 20 minutes. The undissolved portion of the sample was filtered out by means of a glass filter, washed with water, dried and weighed (W The solubility of the sample was calculated by the following equation.

% solubility (W, W lOO/W,

The rating of fire resistance of a given sample was conducted as follows:

A sample of the fiber to be tested was dried at a temperature of 105C for 1 hour. At an angle of 45 the dried specimen was contacted with a flame of butane burning on a micro-burner for 60 seconds, a length of the flame being 45 mm. At the end of the period, the specimen was removed from the flame, and its behavior was observed and rated as follows:

Grade A: No flame and no smoke Grade B: A slight smoke without flame Grade C: Some flame, but self extinguishing Grade D: Burned.

EXAMPLE 1 A tow of acrylic filaments, Vonn-el 17 (produced by Mitsubishi Rayon Co., Ltd. and composed of a copolymer containing 93 percent by weight of units from acrylonitrile and 7 percent by weight of units from vinyl acetate) having a filamentary denier of 1.5 and a total denier of 480,000 was treated in an Obermayer dyeing machine with an aqueous bath containing 8 g/l of hydroxylamine sulfate and 12.5 g/l of sodium secondary phosphate at a temperature of 100C for 60 minutes. A ratio of goods to liquid was 1 10. A pH of the bath was 5.6. At the end of the period the tow was removed from the bath, washed with water and dried. The tow so treated, which will be designated as treated tow A, had a solubility of 12% in dimethylformamide (DMF). The starting untreated tow was completely soluble in DMF.

For a comparative purpose, the procedures as described above were repeated except that the bath was replaced by one containing 0.5 g/l of hydroxylamine sulfate and 0.7 g/l of sodium secondary phosphate and maintained at a pH of 5.5. The tow so treated which will be designated as treated tow 8, had a solubility of 81% in DMF.

Each of the treated tows and an untreated tow was heated in a hot air circulating oven at a temperature of 270C for 20 minutes under conditions such that the filament underwent percent stretch. In further runs, tows identical with the treated tow A were also heated in the oven at 230C for 120 minutes and at 330C for minutes, respectively, while being stretched 10 percent. Results are shown in Table 1 below.

Table l-Continued Heattrcatment Properties of the products Fire res- Elon Run Heated Temp. time ist- Tenacity gation No. fiber (C) (min) ance Denier (g/den.)

ed towB un- 3 treat- 270 20 D 1.77 0.16 1.3

ed tow treat- 4 ed 230 120 C 1.67 1.31 10.4

towA

treat- 5 ed 330 20 A 1.66 0.58 6.4

towA

As seen from Table l, the product obtained from the treated tow A in accordance with the invention (Run No. l) is far superior in fire resistance and mechanical properties to those obtained from the treated tow B and the untreated tow (Run Nos. 2 and 3). The table further shows that the products obtained from Run Nos. 4 and 5, wherein the treated tows A were heated at lower and higher temperatures outside the preferred range, are unstaisfactory with respect to fire resistance and mechanical properties, respectively.

EXAMPLE 2 Textile yarns of meter count No. l/56 spun from acrylic staple fibers, 2 deniers in thickness and 51 mm in length, were woven into a tropical fabric.

The fabric was padded with an aqueous solution of pH 6.3 containing g/l of hydroxylamine sulfate and g/l of sodium tripolyphosphate, squeezed to a liquor content of 60 percent by weight, and steamed in a J-type normal pressure steamer at a temperature of 100C for 20 minutes. At the end of the period, the fabric ws removed from the steamer, washed with water and dried. These procedures were carried out continuously. The fabric so treated had a solubility of 6% in DMF, while the untreated fabric was completely soluble in DMF.

The treated and untreated fabrics were then continuously fed to a tender-type heater using high voltage at a rate of 1 m/min and heated in the heater at a temperature of 300C for 15 minutes under conditions such that the fabric underwent 2% weft (transverse) stretch based on the Corresponding property of the unheated fabric.

It will be seen from Table [1 that the product obtained by a process in accordance with the invention has an improved fire resistance and retains desirable mechanical properties, especially the softness of the original fabric.

EXAMPLE 3 A cheese of acrylic filamentary yarn 150 den/60 til-- aments) of a copolymer containing 85% by weight of units from acrylonitrile, 10% by weight of units from methyl acrylate and 5% by weight of units from acrylamide was treated with an aqueous bath containing 6 g/l of hydroxylamine sulfate and 6 g/l of sodium acetate trihydrate at 100C for 60 minutes. A ratio of goods to liquid was 1 20, and a pH of the bath was 5.4. At the end of the period, the yarn was removed from the bath, washed with water and dried. The yarn so treated had a solubility of 18% in DMF, whereas the untreated yarn was completely soluble in DMF.

Using a circular knitting machine, each of the treated and untreated yarns was knitted into plain knittings. Samples of the knittings were heated in a hot air circulating oven at a temperature of 250C for 115 minutes under no tension as well as under conditions such that the knitting underwent 10% stretch in both warp and weft directions. Results are shown in Table 11] below.

"based on the corresponding property of the unheated knitting. "heated with 10% stretch in both directions. "'heated under no tension.

As seen from Table 111, the products obtained by a process in accordance with the invention exhibit an improved fire resistance and retain desirable mechanical properties, when compared with those obtained from untreated yarns.

EXAMPLE 4 A tow of bright acrylic filaments of a copolymer containing 99 percent by weight of units from acrylonitrile and 1 percent by weight of units from sodium vinylbenzene sulfonate having a filament denier of 1.5 and a total denier of 480,000 was treated in an Obermayer dyeing machine under super-atmospheric pressures with an aqueous bath containing 30 g/l of hydroxylamine sulfate at a temperature of 120C for 90 minutes. A ratio of goods to liquid was 1 7 and a pH of the bath was 3.5. At the end of the period, the tow was removed from the bath, washed with water and dried. The tow so treated had a solubility of 14.5 in DMF, while untreated tow was completely soluble in DMF.

A half of the treated tow was drawn 1.39 and cut to staple fibers of 64 mm in length, which had a steam shrinkage at 100C of about 30 percent. Another half of the tow was cut to fibers of the same length without drawing. Both the drawn and undrawn fibers were blended, made into a web, needle-punched and steamed at 125C for 15 minutes to produce a nonwoven fabric of treated fibers.

Using the untreated tow, the above procedures were repeated to produce a non-woven fabric of untreated fibers as a control.

Each of the non-woven fabrics was heated in a hot air circulating oven to a temperature of 200C, and from 200C to 270C over a period of 40 minutes, and then maintained at 270C for further 40 minutes. Results are shown in Table IV below.

based on the corresponding property of the unheated fabric.

It is apparent from Table IV that the non-woven fabric obtained by a process in accordance with the invention is superior in fire resistance and retention of desirable mechanical properties to that obtained from untreated fibers.

EXAMPLE 5 A tow of acrylic filaments of a copolymer containing 93 percent by weight of units from acrylonitrile, 5.5 percent by weight of units from vinyl acetate and 1.5 percent by weight of methylvinylpyridine having a filamentary denier of 1.5 and a total denier of 480,000 was treated in an Obermayer dyeing machine with an aque ous bath containing 15 g/l of hydroxylamine sulfate and 9 g/l of sodium tertiary phosphate at a temperature of C for 60 minutes. A ratio of goods to liquid was 1 z 7 and a pH of the bath was 5.5. At the end of the period, the tow was removed from the bath, washed with water and dried. The tow so treated had'a solubility of l 1.5% in DMF, while the untreated tow was completely soluble in DMF.

In a control run the procedures as described above were repeated except that the bath was replaced by one containing 15 g/l of hydroxylamine sulfate and 60 g/l of sodium tertiary phosphate. A pH of the bath was 8.0 which is outside the range specified by the invention. The tow thus treated had a solubility of 13.1% in DMF.

Each of the treated and untreated tows was heated in a hot air circulating oven at a temperature of 270C for 20 minutes under conditions such that the filament underwent 10% stretch. Results are shown in Table V belowv It is apparent from Table V that the products obtained from the treated tows are superior in fire resistance and mechanical properties to that from the untreated tow. lt is also noted from Table V that the treatment at an acid ph is essential for an optimum combination of mechanical properties and fire resistance.

EXAMPLE 6 Acrylic fibers of a copolymer cohtaining 93 percent by weight of units from acrylonitrile, percent by weight of units from methyl acrylate and 2 percent by weight of units from vinyl chloride having a denier of 1.5 and a length of 44 mm were spun into a two-folded yarn of a cotton count of No. 48 and reeled to a hank having a peripheral frame length of 1.8 in.

Using a reflux type hank dyeing machine the bank of the yarn was treated with an aqueous bath containing g/l of hydroxylamine hydrochloride and 8 g/l of ammonium secondary phosphate at a temperature of 85C for 60 minutes. A ratio of goods to liquid was 1 50 and a pH of the bath was 5.0. The yarn so treated had a solubility of 20.5 percent in DMF, while the untreated yarn was completely soluble in DMF.

In a control run the procedures as described above were repeated except that the bath was replaced by one containing 10 g/l of hydroxylamine hydrochloride and 12 g/l of anhydrous sodium carbonate. A pH of the bath was 9.5 which is outside the range specified by the invention. The yarn so treated had a solubility of 21.8% in DMF.

Each of the treated and untreated hank was placed in a hot air circulating oven at 100C and a temperature of the oven was raise to 280C at a rate of 3C/rnin during which the hanks were prevented from shrinking by circular frames around which they had been reeled. The hanks were then formed into cones and tested for fire resistance and mechanical properties. Results are shown in Table VI below.

Table Vl Properties of products Table VI shows the same tendency as revealed in Table Example 7 A tow of Vonnel 17 as employed in Example I was cut to staple fibers 56 mm in length, spun into a twofolded yarn of a meter count of No. 56, which was then knitted into a flat fabric by means of a 14 G V bed knitting machine. A. A sample of the knitted fabric was treated in a beaker with an aqueous bath containing 10 g/l hydroxylamine phosphate at 100C for 60 minutes. A ratio of goodsto liquid was 1 40 and a pH of the bath was 5.3. The fabric was then removed from the bath, washed with water and dried. The treated fabric had a solubility of 9% in DMF. The fabric was then heated in a hot air circulating oven at 280C for 60 minutes under conditions such that the fabric underwent no shrinkage in both warp and weft directions. B. The procedures as in (A) above were repeated except that the bath was replaced by one containing 10 g/l of ammonium hydroxide. A pH of the bath was 9.2. The treated fabric was still completely soluble in DMF. C. A sample of the untreated fabric was heated in a manner as described in (A) above. D. Another sample of untreated fabric was impregnated with an aqueous solution containing 10 g/l of hydroxylamine phosphate at a room temperature, squeezed to a wet pick up of 60 percent based on the weight of the dry fabric, and then heated in the oven at 280C for minutes under tensions preventing it from shrinkage. F. The procedures as in (D) above were repeated with the exception that a sample was impregnated with an aqueous solution containing 10 g/l of ammonium hydroxide. F. A further sample of the untreated fabric was heated as in (D) above without impregnation.

The heated samples were tested for fire resistance and mechanical properties. Results are shown in Table Vll below.

What is claimed is:

l. A process for producing fireproof fibers which comprises contacting an acrylic fiber with hydroxylamine to effect chemical reaction at a pH of not higher than 7 at a temperature of below 200C for a time sufficient that the contacted fiber has a solubility of not more than 50% in dimethylformamide at 90C and heating the contacted fiber to oxidize the fiber at a temperature of 245C to 305C in a gaseous atmosphere.

2. A process in accordance with claim 1 wherein the acrylic fiber is contacted with hydroxylamine for a time sufficient that the contacted fiber has a solubility of not more than 30% in dimethylformamide at 90C.

3. A process in accordance with claim 1 wherein the acrylic fiber is contacted with hydroxylamine in a liquid maintained at a pH of 3 to 7.

4. A process in accordance with claim 2 wherein the acrylic fiber is contacted with hydroxylamine in a liquid maintained at a pH of 3 to 7.

5. A process in accordance with claim 3 wherein the acrylic fiber is contacted with hydroxylamine at a temperature of 80C to 130C.

6. A process in accordance with claim 4 wherein the acrylic fiber is contacted with hydroxylamine at a temperature of 80C to 130C.

7. A process in accordance with claim 1 wherein the starting acrylic fiber is in the form of a tow, a filamentary yarn, a sliver, a spun yarn, a woven fabric, a knitted fabric, a non-woven fabric, or a paper.

8. A process in accordance with claim 1 wherein the heating of the contacted fiber is performed for a period of not more than 2 hours.

9. A process in accordance with claim 8 wherein the contacted fiber is heated to oxidize the fiber under conditions such that the fiber undergoes little or no shrinkage.

10. A process in accordance with claim 4 wherein the acrylic fiber is contacted with hydroxylamine in one of the forms of sulfate and hydrochloride in an aqueous solution and wherein the heating of the contacted fiber is performed in air for a period of not more than 2 hours under conditions such that the fiber undergoes little or no shrinkage.

11. A process in accordance with claim 10 wherein the contacted fiber is in the form of a tow, a filamentary yarn, a sliver or a spun yarn and wherein the contacted fiber is heated in air under conditions such that it undergoes 0 20 percent stretch.

12. A process in accordance with claim 10 wherein the contacted fiber is in the form of woven fabric, a non-woven fabric, or a paper and wherein the contacted fiber is heated in air under such conditions that it undergoes 0 15 percent stretch in both longitudinal and transverse directions.

13. A process in accordance with claim 10 wherein the contacted fiber is in the form of a knitted fabric and wherein the fiber is heated in air under conditions such that it undergoes 0 30 percent stretch in both longitudinal and transverse directions.

l 1 i I UNETED STATES PATENT OFFICE CERTIFICATE OF COBRECTEON Patent No. 3,900,285 Dated August 19, 1975 Inventor(s) Michikaze Ono et a1 It is certified that error appears in the above-1'.dentified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet, item [75] change the inventor '5 name "Michakaze" to --Michikaze-- Signcd and Scaled this Third Day of August 1976 [SEAL] A nest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner ufPalents and Trademarks

Claims

1. A PROCESS FOR PRODUCING FIRBERS WHICH COMPRISES CONTACTNG AN ACRYLIC FIBER WITH HYDROXYLAMINE TO EFFECT CHEMICAL REACTION AT A PH OF NOT HIGHER THAN 7 AT A TEMPERATURE OF BELOW 200*C FOR A TIME SUFFLICIENT THAT THE CONTACTED FIBER HAS A SOLUBILITY OF NOT MORE THAN 50% IN DIMETHYLFOMAMIDE AT 90%C AND HEATING CONTACTED FIBER TO OXIDIZE THE FIBER AT A TEMPERATURE OF 245*C TO 305*C IN A GASEOUS ATMOSPHERE.

2. A process in accordance with claim 1 wherein the acrylic fiber is contacted with hydroxylamine for a time sufficient that the contacted fiber has a solubility of not more than 30% in dimethylformamide at 90*C.

5. A process in accordance with claim 3 wherein the acrylic fiber is contacted with hydroxylamine at a temperature of 80*C to 130*C..

6. A process in accordance with claim 4 wherein the acrylic fiber is contacted with hydroxylamine at a temperature of 80*C to 130*C.

11. A process in accordance with claim 10 wherein the contacted fiber is in the form of a tow, a filamentary yarn, a sliver or a spun yarn and wherein the contacted fiber is heated in air under conditions such that it undergoes 0 - 20 percent stretch.

12. A process in accordance with claim 10 wherein the contacted fiber is in the form of woven fabric, a non-woven fabric, or a paper and wherein the contacted fiber is heated in air under such conditions that it undergoes 0 - 15 percent stretch in both longitudinal and transverse directions.

13. A process in accordance with claim 10 wherein the contacted fiber is in the form of a knitted fabric and wherein the fiber is heated in air under conditions such that it undergoes 0 - 30 percent stretch in both longitudinal and transverse directions.