US3895908A - Autoclaving procedure for textile fibers - Google Patents

Abstract

Disclosed is an improvement in the method of steam treating batches of oriented acrylic fibers to upgrade their physical properties, i.e., to relax strains, increase the extension, reduce the fibrillation tendency, and enhance the dyeability of the fibers. The present improvement, which affords a uniformly treated fiber mass, comprehends 1. PRETREATING THE FIBERS TO BE STEAMED BY EVENLY DISTRIBUTING THEREON A SMALL AMOUNT OF WATER; AND 2. ENSURING COMPLETE PENETRATION OF THE TREATING STEAM INTO ALL PORTIONS OF THE FIBER MASS, INCLUDING THE CENTERMOST.

Description

Harder et a1.

[ AUTOCLAVING PROCEDURE FOR TEXTILE FIBERS [75] Inventors: Richard E. Harder; Leland B.

Ticknor, both of Williamsburg. Va.

[73] Assignee: Dow Badische Company,

Williamsburg, Va.

[22] Filed: Jan. 28, 1971 [21] Appl. No.: 110,644

[52] US. Cl 8/130.1; 8/DIG. 15 [51] Int. Cl D06m 3/26 [58] Field of Search 8/130.l, DIG. 15

[56] References Cited UNITED STATES PATENTS 2,920,934 1/1960 Schaefer et al. 8/130.1 3,085,848 4/1963 Hinton 8/21 A July 22, 1975 3,098,371 Fleissner..... 68/5 Primary Examiner-Thomas J. Herbert, Jr. Attorney, Agent, or Firm-George F. Helfrich ABSTRACT Disclosed is an improvement in the method of steam treating batches of oriented acrylic fibers to upgrade their physical properties, i.e.. to relax strains, increase 6 Claims, No Drawings AUTOCLAVING PROCEDURE FOR TEXTILE FIBERS SUBJECT MATTER PRIOR ART Acrylic fibers, i.e., fibers wherein the fiber-forming substance is a long-chain synthetic polymer composed of at least about 85% by weight of acrylonitrile units, are very well known in the art. Various methods are known for their production, the most common of which utilize the wet spinning technique viz. a solution of the chosen homopolymer or copolymer is extruded through a spinnerette into a coagulating liquid which precipitates the polymer, the filaments so produced being carried through the liquid for a period of time sufficient to solidify the polymer to a predetermined extent. whence the filaments are washed to remove solvent and coagulent, and then elongated to improve their physical properties by orienting the molecules of which they are composed.

Acrylic fibers prepared in this manner are advantageously steam treated after production to relax strains therein, increase their extension, reduce their fibrillation tendency, and enhance their dyeability. Such steam treatment is conveniently effected by batch autoclaving, as, for example, by employing the procedure disclosed in Schaefer, U.S. Pat. No. 2,920,934.

Unfortunately, however, uniformity of treatment of the fibers has not been achieved by application of these prior art procedures to large masses of hot, dry fiber, which emanate from production units; such lack of uniformity being most noticeably evidenced by undesirable wide variations in the color of samples of the treated fibers from the same autoclave cart, which have been subsequently subjected to identical dyeing operations. Painstaking control of the steam variables, as, for example, autoclave steam pressure, in an effort to ensure uniformity, has not resulted in any improvement. Furthermore, these variations become more pronounced as the amount of fiber treated in a given batch is increased.

SUMMARY OF THE PRESENT INVENTION Accordingly, it is an object of this invention to provide an improved batch process for upgrading the physical properties of oriented acrylic fibers by steam treating, the sought after characteristic thereof being uniformity of treatment of the mass of fibers in the batch.

In accordance with the present invention, this object has been achieved, and the disadvantages presented by the prior art processes have been obviated, by the practice of a procedure which comprehends:

l. pretreating the fibers to be steamed by evenly applying thereto at least about 5 weight per cent, and preferably between about 5-15 weight per cent of water, whereby subsequent contact of the fibers with the treating steam results in a substantially equal condensation of moisture on all fiber surfaces, no matter what their location in the fiber mass; and

2. ensuring complete penetration of the treating steam into all portions of the fiber mass, including the centermost. These individual measures cooperate to bring about a uniformity of treatment heretofore unobtainable, yet long sought after in the steam treating of large masses of hot, dry acrylic fibers by batch autoclaving. Such uniformity of treatment results in acrylic fibers having upgraded physical properties without, for example, accompanying wide variations in the color of individual portions of the steam treated fibers which have been subsequently subjected to identical dyeing operations, thereby widening the scope of the commercial application of these fibers, and consequently increasing the extent of their utilization.

DETAILED DESCRIPTION The present invention is applicable to acrylic fibers, i.e., fibers formed from various acrylonitrile polymers and blends thereof, including poly (acrylonitrile), and copolymers and terpolymers containing at least about 85 weight per cent of acrylonitrile and up to about 15 per cent of other polymerizable mono-olefinic mono mers, such as: vinyl acetate; methyl methacrylate and other alkyl esters of methacrylic acid; methyl acrylate, ethyl acrylate, and other alkyl esters of acrylic acid; vinyl bromide; monomers having an affinity for acid dyestuffs, particularly those containing a tertiary or quarternary nitrogen in the molecule, such as vinyl pyridine or methyl vinyl pyridine: monomers having an affinity for basic dyestuffs, particularly those containing a sulfonic or carboxylic acid group, such as alkyl sulfonic acid, itaconic acid, among many others.

Various known methods may be employed to produce the acrylonitrile polymers for use in the preparation of the acrylic fibers, upon which the present invention operates. Although the monomer or comonomer mixture may be polymerized employing suspension, emulsion or solution polymerization techniques. suspension procedures are the most widely used commercially. Herein the monomer(s), in the form of small globules dispersed by agitation throughout an aqueous solution of a catalyst, are polymerized at suitable temperatures. Commonly employed catalysts are watersoluble compounds such as hydrogen peroxide, per salts such as ammonium or alkali metal persulfates, and redox catalysts such as persulfate and a bisulfite, at a concentration rangingfrom about 0.1 to 5% of the total monomer(s) present. The monomer suspension containing the polymerization catalyst is held at a temperature between about 30 and C to form the polymer, which is insoluble inthe aqueous medium in which the polymerization proceeds. The solid polymer is filtered from the aqueous reaction medium and washed to remove any impurities present. A practical procedure for such a polymerization is found in U.S. Pat. No. 2,847,405.

Preparation of the acrylic fibers from the solid acrylonitrile polymers is accomplished by various methods known in the art, the most common of which employ the wet spinning technique. Herein a solution of the polymer (in a suitable organic or inorganic solvent) is first de-gassed and filtered, after which it is spun or extruded through multiple-holed jets into a coagulating bath, where the polymer is precipitated. The filaments so produced are washed (generally countercurrently with water) to remove the spinning solvent, and are then elongated and finally dried. Examples of the wet spinning of acrylic fibers from solutions of acrylonitrile polymers in inorganic solvents are found in U.S. Pat.

Nos. 2,916,348 and 2,558,730; the employment of organic solvents is shown in Knudsen. Textile Research Journal 33, 13-20 (1963). g

The elongation referred to above, which serves to improve-the physical properties of the fibers (esp their bers. A six to -fold increase in length is' not at all uncommon. This elongation may be accomplished in a single stage or distributed between multiple stages.

The process of elongation is followed by that of drying, which is carried out while the fibers are under tension or in a relaxed or partially relaxed condition. For non-shrinkable products, drying always includes a heatsetting operation, which stabilizes the structures at temperatures above any to which the fibers may be subsequently subjected during processing and ultimate use. Such an operation is described in US. Pat. No. 2,614,289. After being dried, the acrylic fibers are almost always steam treated to relax strains therein, increase their extension, reduce their fibrillation tendency, and enhance their dyeability. This steam treat ment is conveniently effected by a batch autoclaving procedure, which is improved upon by the practice of the present invention.

According to an embodiment of the present invention, large, hot masses of elongated, dried acrylic fibers from the production processes described above are pretreated prior to their contact with steam, by dispersing throughout the mass of the fibers at least about 5 weight per cent of water. The fibers are then contacted with steam in a pressure chamber at a temperature of about 105 to 140C and a steam pressure of at least about 20 pounds per square inch (absolute pressure), while the fibers are in a relaxed condition. Thereupon the pressure chamber is exhausted, followed by a re-pressurization and re-exhaustion, such alternating steam-exhaust cycles being continued until the treating steam has penetrated all portions of the fiber mass. The steam-treated fiber mass, upon removal from the pressure chamber, may be subsequently treated, if desired, before employment in the construction of a wide variety of fabrics of current interest in the industry. The fibers may be crimped, and finish may be applied thereto, either before or after autoclaving.

The present invention, in all of its embodiments,

. comprehends the immediate treatment of the large, hot

masses of elongated, dried acrylic fibers emanating from production units. In a preferred embodiment of the invention, the fibers, which are conveniently present in the form of a tow, are first plaited into perforated aluminum push carts, in amounts up to about 1000 pounds per cart, during which water, in an amount between about 5 and per cent by weight, based upon the weight of the fibers, is dispersed throughout the fiber mass in each cart. The water may be applied to the fibers by pouring, spraying, fogging, or other suitable means. When a simple pouring is'employed, it has been found advantageous to allow the moistened fibers to stand for a short period of time, eg. 30 minutesto 1 hour, before commencement of the actual steam treatment, thereby effecting an even distribution of moisture on the fiber surfaces. To be sure, more than about 10 ing, and desired ultimate physical properties of the fi- 5-15 weight per cent of water may be employed to achieve the same beneficial results; however, no advantage is seen in so doing. Moreover, as one of ordinary skill in the art will immediately discern, utilization of very large amounts of water could well interfere with the subsequent penetration of the treating steam into all portions of the fiber mass. Accordingly, it is preferred to employ from about 5 to about 15 per cent of water.

After dispersion of the water throughout the mass of the fibers, the fiber-containing carts are inserted into a pressure chamber or autoclave, into which steam is then introduced, advantageously at temperatures between about C and C, until a practical working pressure for the particular autoclave is attained,

such pressure being generally between about 20 and about 40 pounds per square inch (absolute pressure). Complete penetration of the steam into all portions of the mass of fibers isthen advantageously achieved by effecting a number of pressure-exhaust cycles within the autoclave. For example, after the initial steam pressurization of the autoclave to about 20-40 pounds per square inch, the autoclave is exhausted, followed by a re-pressurization to the initial pressure, which in turn is followed by a re-exhaustion, such alternating steamexhaust cycles being continued until the steam has penetrated all portions of the fiber mass. That such penetration has in fact occurred can be determined in numerous ways, eg. by the employment of thermocouples embedded in the fiber mass at different positions therein, the thermocouples having been positioned by means of lead-in wires installed in the autoclave wall. The extent of exhaustion of the autoclave during each exhausting thereof is not critical, being rather a choice influenced by the nature of the autoclave and the efficiency of the exhaust means. It is, of course, desirable that the difference between the upper and lower values of the absolute pressure in the chamber during each cycle be as great as can be practically achieved. Since the purpose of the alternating steam-exhaust cycles is to afford penetration of the steam into all portions of the fiber mass, the duration of each pressurizing phase need be only long enough to achieve the desired level of pressure, after which the exhausting phase may begin. Moreover, it has been found advantageous to stop the exhausting phase at an autoclave pressure of slightly above 15 pounds per square inch (absolute pressure), below which pressure exhausting is an extremely slow process. Furthermore, exhaustion to below atmospheric pressure by means of a pump is not advisable, inasmuch as most autoclave vessels are not sufficiently air tight.

Once the treating steam has been caused to penetrate all portions of the mass of fibers to be treated, the steam should be allowed to remain in contact with the fibers for a period of time sufficient to ensure that any time-related shrinkage, relaxation, and other changes have taken place. This period, which varies with the nature of the fiber being treated, has been empirically determined to be at least about 5 minutes, and more advantageously, about 15-30 minutes for most of the common acrylic fibers utilized in the industry today.

In another preferred embodiment of the present invention, complete penetration of the treating steam into all portions of the fiber mass is rapidly achieved, and a desirable rapid operation of the autoclave is thereby afforded, if, after the moistened fibercontaining carts have been inserted into the autoclave, an initial vacuum phase is effected before the initial pressurization with steam, whereby. much of the air inside the chamber and therefore within the fiber mass is very quickly removed. In this embodiment, it has been found desirable to evacuate the autoclave to a pressure of about 1 to pounds per square inch, whereupon EXAMPLE 1 This example is illustrative of the present invention. Approximately 800 pounds of acrylic tow, which had just exited from a drying operation, was plaited into a perforated aluminum cart. The tow was composed of 3-denier fibers of 91% acrylonitrile, 8% methyl acrylate, and 1% of a monomer containing sulfonate groups, the fibers having been wet spun from an aqueous zinc chloride solution, employing well known, standard techniques. Before being dried at 285F the fibers had been washed and elongated to approximately 10 times their original length. As it wasplaited into the cart, the tow was sprayed with water, and the so moistened fibers were allowed to stand for approximately one hour, whereupon the cart was inserted into an au- The steam-treated fiber tow was subsequently removed from the autoclave cart, and a standard finish was applied. Thefibers were then crimped and dried,

toclave. The amount of water used was approximately 5 per cent, based on the total weight of the dried tow. After being sealed, the autoclave was evacuated to a pressure of about 3 pounds per square inch. The autoclave was then immediately pressurized to about 35 pounds per square inch with saturated steam at a temperature of about 126C, whence it was exhusted to about l9 pounds per square inch. This pressureexhaust cycle was repeated until the steam had penetrated all portions of the moistened fiber mass in the cart. That complete penetration had actually occurred was ascertained by the utilization of thermocouples embedded in the fiber mass at various positions therein, the thermocouples having been attached to lead wires installed through the autoclave wall, and the temperatures having been recorded with a Westronics potentiometric recorder. The time of rapid change in temperature at a given thermocouple was considered to be a valid indication of the time at which steam reached this thermocouple and, therefore, the fibers in close proximity thereto. Complete penetration of the steam was found to occur in this instance after pressureexhaust cycles, the duration of each having been only long enough for attainment of the desired pressures. After complete penetration of the steam into all portions of the fiber mass, the steam pressure in the autoclave was allowed to remain at pounds per square inch for 30 minutes, after which the fiber was dried to approximately its original condition by placing the autoclave under full vacuum for 10 minutes.

and 15 samples thereof were afterwards taken from equally spaced positions'along the length of the tow. These samples were dyed competitively in a Gaston County package dyeing machine with 0.5% Maxilon Blue 56 dye, based upon the weight of the fiber. After the dyeing and subsequent drying of each sample had been accomplished, the reflectivity of each sample was measured on' a Color Eye abridged spectrophotometer with the Y (green) filter. From each value of reflectivity, the K/S'value was' calculated using the Kubelka- Munk Equation. See D. B. Judd and G. Wyszecki, Color in Business, Science, and Industry, 2 Ed., John Wiley & Sons, lnc., New York, 1963, p. 417. The per cent dye strength of each sample was then computed from the ratio of the 'K/S value of that sample to the av erage of the K/S values of 3 standards included in the dye batch. Thereupon the standard deviation was computed. The value thereof was 1.7% as compared with the standard deviation of the dye test itself (within a single dye batch) of 1% indicating a uniformity of dyeability throughout the steam-treated fiber mass.

EXAMPLE 2 EXAMPLE 3 This example, which is not illustrative of the present invention, is set forth for comparative purposes only. A

procedure identical in all aspects to that employed in Example 1 above was followed, except that approximately 400 pounds of the hot, dry fiber was treated, no water whatever was added, 18 steam-exhaust cycles were required for complete penetration of the fibers by the steam, and a final steaming of about 10 minutes at a pressure of 35 pounds per square inch was effected. The standard deviation of the dye test samples was computed to be 6.1% dye strength, indicating a pronounced non-uniformity of dyeability throughout the steam-treated fiber mass.

EXAMPLE 4 This example, which is not illustrative of the present invention, is set forth for comparative purposes only. Herein a procedure otherwise identical to that employed in Example 3 above was followed, except that after the final steaming and drying under vacuum, the tow was removed from the autoclave cart and replaited into a second autoclave cart, whereupon it was reautoclaved according to the same autoclave schedule. The standard deviation of the dye test samples was computed to be 4.0% dye strength, indicating a pronounced non-uniformity of dyeability throughout the steamtreated fiber mass.

EXAMPLE This example, which is not illustrative of the present invention, is set forth for comparative purposes only. Herein a procedure otherwise identical to that of Example 2 above was followed, except that no water whatever was added to the fiber. 2O steam-exhaust cycles were requiredfor complete penetration of the fibers by the steam, and a final steaming of 40 minutes at a pressure of 35 pounds per square inch was effected. The standard deviation of the dye test samples was computed to be 4.3% dye strength indicating a pronounced non-uniformity of dyeability throughout the steam-treated fiber mass.

Although the present invention has been described in considerable detail with reference to certain preferred embodiments, it is apparent to those having skill in the art that variations and modifications in this detail may be effected without any departure from the spirit and scope of the invention, as defined in the hereto appended claims.

What is claimed is:

1. in the process for improving the physical properties of fibers comprising acrylonitrile polymers containing at least about 85 weight per cent of acrylonitrile and up to about weight per cent of another polymerizable mono-olefinic monomer copolymerizable therewith, which process comprises contacting a mass of the fibers. while in an oriented state, with steam at a temperature of about l05 to 140C, at a steam pressure of at least about pounds per square inch in a closed chamber, the improvement therein comprising:

a. pretreating the fibers before their contact with steam by evenly distributing on the surface of the fibers at least about 5 weight per cent of water; and

b. ensuring complete penetration of the steam into all portions of the mass of fibers in the chamber.

2. In the process for improving the physical properties of fibers comprising acrylonitrile polymers containing at least about 85 weight per cent of acrylonitrile and up to about 15 weight per cent of another polymerizable mono-olefinic monomer copolymerizable therewith. which process comprises contacting a mass of the fibers, while in an oriented state, with steam at a temperature of about 105 to 140C, at a steam pressure of at least about 20 pounds per square inch in a closed chamber, the improvement therein comprising:

a. dispersing at least about 5 weight per cent of water throughout the mass of the fibers prior to the contact of the fibers with steam; and

b. subjecting the moistened fiber mass in the closed chamber to alternating steam-exhaust cycles until the steam has penetrated all portions of the fiber mass.

3. in the process for improving the physical properties of fibers comprising acrylonitrile polymers containing at least about weight per cent of acrylonitrile and up to about 15 weight per cent of another polymerizable mono-olefinic monomer copolymerizable therewith, which process comprises contacting a mass of the fibers, while'in an oriented state, with steam at a temperature of about to C, at a steam pressure of at least about 20 pounds per square inch in a closed chamber, the improvement therein comprising:

a. dispersing at least about 5 weight per cent of water throughout the mass of the fibers prior to the contact of the fibers with steam;

b. subjecting the moistened fiber mass in the closed chamber to alternating steam exhaust cycles until the steam has penetrated all portions of the fiber mass; and

c. pressurizing the chamber with steam to a pressure of about 20 to40 pounds per square inch, and maintaining this pressure for at least about 5 minutes.

4. The process of claim 3, wherein about 5 to about 15 weight per cent of water is dispersed throughout the fiber mass prior to contact of the fiber mass with steam.

5. The Process of claim 3,,wherein the chamber is evacuated to a pressure of about l-lO pounds per square inch prior to the initial pressurization thereof with steam. i l

6. In the process for improving the physical properties of fibers comprising acrylonitrile polymers containing at least about 85 weight per cent of acrylonitrile and up to about 15 weight per cent of another polymerizable mono-olefinic monomer copolymerizable therewith, which process comprises contacting a mass of the fibers, while in an oriented state, with steam at a temperature of about 105 to 140C, at a steam pressure of at least about 20 pounds per square inch in a closed chamber, the improvement therein comprising:

a. pretreating the fibers prior to their contact with steam by dispersing from about 5-15 weight per cent of water throughout themass of fibers;

b. evacuating the chamber to about l-lO pounds per square inch;

c. introducing steam into the chamber until the pressure therein is at least about 20 pounds per square inch;

d. reducing the pressure within the chamber until the pressure is less than about 20 pounds per square inch;

e. repeating steps (c) and (d) until the steam has penetrated all portions of the fiber mass; and

f. pressurizing the chamber with steam to a pressure of at least about 20 pounds per square inch, and maintaining this pressure for a period of at least about 15 minutes.

Claims (6)

1. IN THE PROCESS FOR IMPROVING THE PHYSICAL PROPERTIES OF FIBERS COMPRISING ACEYLONITRILE POLYMERS CONTAINING AT LEAST ABOUT 85 WEIGHT PER CENT OF ACRYLONITRILE AND UP TO ABOUT 15 WEIGHT PER CENT OF ANOTHER POLYMERIZABLE MONO-OLEFINIC MONOMER COPOLYMERIZABLE THEREWITH WHICH PROCESS COMPRISES CONTACTING A MASS OF THE FIBERS WHILE IN AN ORIENTED STATE WITH STEAM AT A TEMPERATURE OF ABOUT 105* TO 140*C AT A STEAM PRESSURE OF AT LEAST ABOUT 20 POUNDS PER SQUARE INCH IN A CLOSED CHAMBER THE IMPROVEMENT THEREIN COMPRISING: A. PRETREATING THE FIBERS BEFORE THEIR CONTACT WITH STEAM BY EVENLY DISTRIBUTING ON THE SURFACE OF THE FIBERS AT LEAST ABOUT 5 WEIGHT PER CENT OF WATER AND B. ENSURING COMPLETE PENETRATION OF THE STEAM INTO ALL PORTIONS OF THE MASS OF FIBERS IN THE CHAMBERS.

2. In the process for improving the physical properties of fibers comprising acrylonitrile polymers containing at least about 85 weight per cent of acrylonitrile and up to about 15 weight per cent of another polymerizable mono-olefinic monomer copolymerizable therewith, which process comprises contacting a maSs of the fibers, while in an oriented state, with steam at a temperature of about 105* to 140*C, at a steam pressure of at least about 20 pounds per square inch in a closed chamber, the improvement therein comprising: a. dispersing at least about 5 weight per cent of water throughout the mass of the fibers prior to the contact of the fibers with steam; and b. subjecting the moistened fiber mass in the closed chamber to alternating steam-exhaust cycles until the steam has penetrated all portions of the fiber mass.

3. In the process for improving the physical properties of fibers comprising acrylonitrile polymers containing at least about 85 weight per cent of acrylonitrile and up to about 15 weight per cent of another polymerizable mono-olefinic monomer copolymerizable therewith, which process comprises contacting a mass of the fibers, while in an oriented state, with steam at a temperature of about 105* to 140*C, at a steam pressure of at least about 20 pounds per square inch in a closed chamber, the improvement therein comprising: a. dispersing at least about 5 weight per cent of water throughout the mass of the fibers prior to the contact of the fibers with steam; b. subjecting the moistened fiber mass in the closed chamber to alternating steam - exhaust cycles until the steam has penetrated all portions of the fiber mass; and c. pressurizing the chamber with steam to a pressure of about 20 to 40 pounds per square inch, and maintaining this pressure for at least about 5 minutes.

4. The process of claim 3, wherein about 5 to about 15 weight per cent of water is dispersed throughout the fiber mass prior to contact of the fiber mass with steam.

5. The Process of claim 3, wherein the chamber is evacuated to a pressure of about 1-10 pounds per square inch prior to the initial pressurization thereof with steam.

6. In the process for improving the physical properties of fibers comprising acrylonitrile polymers containing at least about 85 weight per cent of acrylonitrile and up to about 15 weight per cent of another polymerizable mono-olefinic monomer copolymerizable therewith, which process comprises contacting a mass of the fibers, while in an oriented state, with steam at a temperature of about 105* to 140*C, at a steam pressure of at least about 20 pounds per square inch in a closed chamber, the improvement therein comprising: a. pretreating the fibers prior to their contact with steam by dispersing from about 5-15 weight per cent of water throughout the mass of fibers; b. evacuating the chamber to about 1-10 pounds per square inch; c. introducing steam into the chamber until the pressure therein is at least about 20 pounds per square inch; d. reducing the pressure within the chamber until the pressure is less than about 20 pounds per square inch; e. repeating steps (c) and (d) until the steam has penetrated all portions of the fiber mass; and f. pressurizing the chamber with steam to a pressure of at least about 20 pounds per square inch, and maintaining this pressure for a period of at least about 15 minutes.