US3296348A - Method for treating acrylonitrile polymer fibers to improve heat stability - Google Patents

Description

United States Patent 3,296,348 METHOD FOR TREATING ACRYLONITRILE POLYMER FIBERS TO IMPROVE HEAT STA- BILITY John Moore, Williamsburg, Va., assignor to The Dow Chemical Company, Midland, Mich., a corporation of I Delaware No Drawing. Filed Aug. 23, 1963, Ser. No. 304,206 Claims. (Cl. 264182) spinning techniques and are in a highly swollen, or gel condition.

Acrylonitrile polymer fibers containing at least about 80 weight percent of polymerized acrylonitrile are particularly adapted for the preparation of synthetic fibers and filaments. While the properties of these acrylonitrile polymers are well suited for textile fiber purposes, it has been observed that such polymers have a tendency to be somewhat heat sensitive and to discolor and become stiff or brittle when subjected to elevated temperatures.

It can well be appreciated that these degrading factors should be avoided, if at all possible, in that textile products are quite apt to be subjected to high temperatures in processing and subsequent use, including dyeing, drying, laundering, and pressing, or ironing. While the heat sensitivity of some of the polymers may only lead to discoloration, and not to the point of causing embrittlement of the fibers, discoloration itself is an especially undesirable feature when white or faintly colored fabrics of the fibers of filaments is desired.

The tendency of fibers from acrylonitrile polymers to discolor when exposed to heat is often more pronounced and more frequently encountered when homopolymeric acrylonitrile is used as the sole fiber forming polymer. When copolymers of acrylonitrile and another ethylenically unsaturated monomer are extruded into fibers, it is frequently noted that these fibers may be more heat resistant. The reasons for this are not fully known, but it is a likely theory-that the other monomers in the polymer chain aid in proving heat stability to the fibers formed from these polymers. It has been observed also that discoloration of acrylonitrile polymer fibers occurs more frequently in polymers that are spun from aqueous saline solutions that are solvents for the polymers than from organic solvents.

It is the chief concern and primary object of this invention to provide a means for improving the stability of wet spun acrylonitrile polymer filaments. It is a further object of the invention to improve the heat stability of acrylonitrile polymer filaments that have been wet spun from aqueous saline solutions of the polymer. In a more particular aspect, it is the object of this invention to provide a means for preparing acrylonitrile polymer fibers having improved heat stability that have been spun from aqueous solutions of zinc chloride into an aqueous coagulation bath. It is a still further object of the invention to treat wet spun homopolymeric acrylonitrile polymer fibers to improve their heat stability.

The foregoing and additional objects and advantages of the invention are achieved in and by the practice of the present invention, which involves the method for preparing acrylonitrile polymer filaments having improved heat stability comprising impregnating a wet spun gel filament of an ethylenically unsaturated monomeric ma, terial containing :at least about weight percent of acrylonitrile with a water soluble zirconium salt such that between about 0.1 and about 2 weight percent of zirconium, based on dry fiber weight, is incorporated in said filament. In a preferred embodiment of the invention the wet spun lgel filaments are impregnated with a water soluble zirconium salt after the gel filament has been washed essentially completely free of any residual polymer solvent.

The acrylonitrile polymer fibers or filaments treated in accordance with the present invention have excellent and much improved heat stability over the untreated fibers, and the fibers so treated remain unchanged in color even after extended exposure times to elevated temperatures. Additionally, the presence of the zirconium salt in the fiber has no apparent deleterious elfects on the properties or utilities of the impregnated fibers. The zirconium salts with which the fibers are impregnated are unusually compatible with an adherescent to the fibers, either being chemically or physically entrapped in the fiber, such that lasting and essentially permanent heat stability properties are observed in the impregnated fibers.

The zirconium salts found useful for enhancing the heat stability of the acrylonitrile polymer fibers are those having some water solubility. These need not be infinitely water soluble, but only to a small extent since the impregnation of the fibers is ordinarily accomplished with a relatively dilute solution of the zirconium salt. Thus, exemplary of some of the zirconium salts that can be employed in the present invention are zirconium tetrachloride, zirconyl chloride, zirconyl tetrabromide, zirconyl nitrate, carbonated hydrous zirconia, zirconium sulfate, zirconium acetate, including their partially hydrolyzed and partially neutrallized forms. Advantageously, zirconium oxychloride or zirconyl chloride is employed.

The amount of the zirconium salt that is impregnated or otherwise incorporated in the fiber is beneficially enough to incorporate in the fiber between about 0.01 and about 2 Weight percent zirconium, based on the Weight of the dry fiber. Preferably, between about 0.3 and 0.75 weight percent zirconium is impregnated in the fiber. It

is generally desirable to employ as little as possible of the zirconium salt that is called for to obtain the desirable or necessary heat stability. In order to impregnate the acrylonitrile polymer gel filament with the zirconium salt, only a relatively dilute solution of the salt is necessary, as indicated. Thus, generally a solution containing between :about 0.1 up to about 1.5 or so percent of the zir conium salt is adequate to deposit the required amount of zirconium in the fiber. Solutions containing concentrations of the zirconium salt up to the saturation concentration of the salt can be employed, but, beneficially, solutions containing between 0.5 and 1.5 weight percent of the zirconium salt are used to avoid undue accumulation of the salt in and on the fiber which may deleteriouly elfect the properties or end uses to which the filaments or fibers can be put. The amount of the salt that is incorporated in the fiber can be controlled by the concentration of the impregnation bath that is employed, as well :as the speed with which the fibers pass through the impregnation bath.

The impregnation of the gel filament is preferably accomplished from an aqueous solution of the zirconium 'parts by weight of water for salt. The impregnation, can, if desired, be carried out by spraying, padding or wiping the gel filaments'with an aqueous solution of the zirconium salt, however, best results are obtained when the impregnation is performed by immersing the gel filaments in an aqueous solution of the zirconium salt. This is conveniently done under conventional wet spinning conditions and at conventional spinning rates. Thus, in ordinary wet spinning techniques, the wet spun fiber is withdrawn from the coagulation bath, washed essentially completely free of any residual polymer solvent, and then stretched to orient the molecules of the fiber to impart suitable physical properties to the fiber. to the conventional wet spinning techniques in that excellent impregnation of the zirconium salt results when the gel filaments are continuously passed through an aqueous bath containing the zirconium salt, which impregnation can be completed in a matter of seconds. In practice, the impregnation of the fiber with the zirconium salt can be accomplished before-,during, or after the orientation of the fiber molecules. Most generally, however, the impregnation always succeeds the washing of the gel filament free of residual polymer solvent.

The temperature of impregnation is not critical and may be at ambient temperature, or lower, up to the boil of the impregnating solution.

The invention is applicable to treating acrylonitrile polymer fibers which are fabricated from fiber forming acrylonitrile polymers that contain in the polymer molecule at least about 80 weight percent of polymerized acrylonitrile, and is especially applicable to treating fibers of homo- The present method is therefore well suited 7 polymeric acrylonitrile, which are wet-spun in and with I systems that are adapted to utilize aqueous coagulating liquids in the spinning operation, such as systems wherein ethylene glycol, dimethylformamide, dimethylacetamide, dirnethylsulfoxide, butyrolactone and the like or the various saline polyacrylonitrile-dissolving solvents are em ployed as spinning solution solvents for the polymer and are also present in non-polymer dissolving quantities in the aqueous coagulating liquid used in the spin bath;

The utile, known aqueous saline solvents for the various fiber forming acrylonitrile polymers and polyacrylonitrile include zinc chloride, the various thiocyanates such as' calcium and sodium thiocyanate, lithium bromide, salt mixtures of the so-called lyotropic series, and others recognized by the art as has been disclosed, among other places, in United States Letters Patents Nos. 2,425,192;

and 2,949,435. Advantageously, aqueous'zinc chloride solutions are used for the purpose.

Exemplary of some of the monomeric materials that may be employed with the acrylonitrile in the preparation of the acrylonitrile polymer and copolymer fiber forming systems and treated in accordance with the practice of .the present invention include allyl alcohol, vinyl acetate, acrylamide, methacrylamide, methyl acrylate,

vinyl pyridine, ethylene sulfonic acid and its alkali metal salts, vinyl benzene sulfonic acid and its salts, 2-sulfo-' ethylmethacrylate and its salts, vinyl lactams such as vinyl caprolactam and vinyl pyrrolidone, etc. and mixtures thereof. I

As indicated, after acrylonitrile polymer fibers have 'been wet spun they are most frequently water washed or washed with an aqueous inert solution to remove any residual polymer solvent from the freshly formed filaments, thus forming an intermediate fiber product often referred to as a gel or aquagel filament. Thoroughly washed acrylonitrile polymer aquagel fibers, incidentally, are usually found to contain up to about 6 parts by weight of water (including residual extrinzic or exterior water associated therewith) for each part by weight of dry polymer therein. More frequently, washed acrylonitrile aquagel polymer fibers are found to contain from about 3 to 4 each part by weight of polymer.

Example 1 Acrylonitrile polymer fibers consisting of about, in copolymerized form, 91.5 percent acrylonitrile, 7 percent methyl acrylate and 1.5 percent 2-sulfoethylmethacrylate were prepared by spinning a solution of the polymer dissolved in an aqueous about 60 weight percent zinc chloride solution into an aqueous zinc chloride coagulation bath. The coagulated gel filaments were withdrawn from the coagulation bath, washed essentially completely free of residual zinc chloride and hot stretched to orient the molecules thereof. The washed and stretched 'gel fila- 'rnents were then passed through an aqueous about 1 percent solution of various zirconium salts to impregnate the gel filaments therewith. The impregnation was carried out in a continuous manner by passing the gel filaments through a bath containing the zirconium salt solution which was at about 30 C. The residence time of the gel filaments in the bath was about 5 seconds. Following the impregnation the gel filaments were ultimately irreversibly dried 6-7 minutes at about 125 C. to characteristically hydrophobic textile fibers.

Control'fibers were prepared in'the same manner, the only difference being that no zirconium salt was present in the impregnation bath. I V a Samples of each of the fibers so-prepared were cut into short staple lengths and formed into an aqueous slurry in a Waring Blender. The slurry was poured through a filter to form a pad of the fibers which was dried leaving about a inch thick pad of the fibers. The pad was then pressed between two metal plates of an AATCC Scorch Tester at 205 C. for 5 minutes. The measuring head of a Photovolt Corporation reflectorneter fitted with a green tristimulus filter was first placed on-the unscorched portion of the pad and the instrumentadjustedto a reflectance reading of a reflectancereading was then taken on the scorched portion of the fiber pad. The difference in reflectance is a measure of the color formation.

due to heat. The recorded values are the number of units below the control value of 100. The smaller the recorded value the less change from the unscorched reading of 100 and hence the better the heat stability of the fiber. The results are set forth in Table I.

The procedure of Example I was repeated excepting to employ airqonyl chloride in the impregnating solution at various concentrations. These results are set forth in Table II.

TABLE 11 Percent Percent Zirconium in Sample ZIOClz-SH O Fiber (based Heat Stability in Solution on fiber dry Reading weight) A 63 B 0. 0. 722 35 0 0 65 0. 5 0. 525 35 C 0 0 65 0. 5 0. 449 21 D 0 0 77 l. 0 1. 28 E 0 0 59 l. 0 0. 79 26 F 0 0 38 1. 0 0. 47 25 G 0 0 53 1. 0 0. 989 24 H 0 0 62 1. 5 0. 396 17 I 0 O 63 1. 5 0. 629 22 J 0 O 53 1. 5 0. 625 17 Example 3 The procedure of Example I was repeated employing zirconyl chloride and zirconium sulfate solutions of varying concentrations. These results are set forth in Table III.

TABLE HI Salt Solution Wt. Percent Zirconium Salt Concentration Zr in Fiber Heat Stabillty (Wt. Percent) (Based on Fiber Reading Z Dry Wt.)

ZrO ClrSHzO 0. 0 54 0. l. 0. 537 46 2. O 0. 81 30 3. 0 0. 86 29 5. 0 1. 04 29 10. 0 1. 19 30 20. 0 1. 48 27 HzZtO (504)2-3Hz0 0. 0 54 0. 1 0. 309 37 1. 0 0. 413 27 2. 0 0. 47 40 3. 0 0. 54 34 5. 0 0. 68 34 10. 0 0. 94 33 20. 0 1. 16 29 Example 4 Fibers were prepared and treated with zirconyl chloride following the procedure of Example I except the fibers were homopolymeric acrylonitrile. These results Similar excellent results are obtained when the foregoing is repeated in accordance with the present invention employing other of the indicated zirconium compounds and acrylonitrile polymer compositions.

What is claimed is:

1. The method for preparing an acrylonitrile polymer fiber having improved heat stability comprising impregnating a wet spun gel filament of an ethylenically unsaturated monomeric material containing at least about weight percent acrylonitrile with a Water soluble zirconium salt until between about 0.01 and about 2 weight percent of zirconium, based on dry fiber Weight, is incorporated in said filament.

2. The method of claim 1, wherein said acrylonitrile polymer is polyacrylonitrile.

3. The method of claim 1, wherein said gel filament is impregnated with said zirconium salt by immersing said gel filament in an aqueous solution of said zirconium salt.

4. The method of claim 1, wherein said zirconium salt is zirconyl chloride.

5. The method for preparing an acrylonitrile polymer fiber having improved heat stability comprising (a) spinning a solution of a polymer of an ethylenical- 1y unsaturated monomeric material containing at least about 80 weight percent acrylonitrile dissolved in a solvent therefor into an aqueous coagulation bath;

(b) withdrawing a coagulated gel filament from said coagulation bath and washing said gel filament essentially completely free of any residual polymer solvent;

(c) impregnating said washed gel filament with an aqueous solution of a water soluble zirconium salt until between about 0.01 and about 2 weight percent of zirconium, based on dry fiber weight, is incorporated in said filament; and,

(d) subsequently, irreversibly drying said gel filament to a characteristically hydrophobic textile fiber.

6. The method of claim 5, wherein said acrylonitrile polymer is polyacrylonitrile.

7. The method of claim 5, wherein said zirconium salt is zirconyl chloride.

8. The method for preparing an acrylonitrile polymer fiber having improved heat stability comprising (a) spinning a solution of a polymer of an ethylenical- 1y unsaturated monomeric material containing at least about 80 weight percent acrylonitrile dissolved in an aqueous about 55 to 65 weight percent zinc chloride solution into a coagulation bath of an aqueous non-polymer dissolving zinc chloride solution;

(b) withdrawing a coagulated gel filament from said coagulation bath and washing said gel filament essentially completely free of residual zinc chloride;

(c) immersing said gel filament in an aqueous solution of a Water soluble zirconium salt until between about 0.01 and about 2 weight percent of Zirconium is incorporated in said filament; and,

(d) subsequently, irreversibly drying said gel filament to a characteristically hydrophobic textile fiber.

9. The method of claim 8, wherein said acrylonitrile polymer is polyacrylonitrile.

10. The method of claim 8, wherein said zirconium salt is zirconyl chloride.

References Cited by the Examiner UNITED STATES PATENTS 2,482,816 9/ 1949 Van Mater 260414 2,661,346 12/1953 Wesp et al. 26045.75 2,668,780 2/1954 Panik et al l17--138 2,813,845 11/1957 Wesp et al. 26045.75 3,097,054 7/1963 Routson et al. a; 264-182 ALEXANDER H. BRODMERKEL, Primary Examiner.

B. SNYDER, Assistant Examiner.

Claims (1)

1. THE METHOD FOR PREPARING AN ACRYLONITRILE POLYMER FIBER HAVING IMPROVED HEAT STABILITY COMPRISING IMPREGNATING A WET SPUN GEL FILAMENT OF AN ETHYLENICALLY UNSATURATED MONOMERIC MATERIAL CONTAINING AT LEAST ABOUT 80 WEIGHT PERCENT ACRYLONITRILE WITH A WATER SOLUBLE ZIRCONIUM SALT UNTIL BETWEEN ABOUT 0.01 AND ABOUT 2 WEIGHT PERCENT OF ZIRCONIUM, BASED ON DRY FIBER WEIGHT, IS INCORPORATED IN SAID FILAMENT.