US2555300A - Wet-spinning process - Google Patents

Description

Patented June 5, 1951 WET-SPINNING PROCESS Joseph. Gordon: Galtom. Bu'fialo, andQaentin John OBrien Kenmore, N. Y., assignors. to E. I.. du Pont de Nemours; & Company, Wilmington, Del.,.acorporationof Delaware No Drawing. Application February 13; 1947.

Serial No. 728,372,

8 Claims. (01. 18- 54') This invention relates to, an improvedv process for the formation of shaped. polymeric materials. In particular, this invention is concerned with an improved method for wet-spinning acrylonitrile; polymer and copolymers, thereof contain,- ing at least; 85% acrylonitrile.

The processof this invention is generally applicable to the production of any shaped article, as, for example, yarns, films,.b.r.istles. tubing and the. like. For convenience, the discussion herein is directed chiefly to. the production of yarns of polymers of acrylonitrile by the wet. spinning method.

It has been disclosed, for example, in U. Patent 2,40%,722 and in copending application W. W. Watkins, Serial No. 496,376, issued as. U. S. Patent. No. 2,426,119, that solutions: of acrylonitrile polymers or copolymers can beextruded into coagulating baths, thereby forming yarns, films, etc., The apparatus described. therein or similar apparatus may be used in this. invention. If solvents; of. fairly low boiling points, e. g.,.1-50 (3., are used,v hot. glycerol,.e.

120 15.0150. may be employed as, a coagulating bathto produce yarn having a dry tenacity of 2 to 4 grams per denier. However, it; is frequently desirable: to use polymer solvents. having high boiling points. In this casev the. use of hot ycerol as a spinning. bathdoes not lead. to maximum yarn ten'acities because the yarn sets up very slowly. Under these conditions extreme care and a long. bath, travel are required to complete coagulation. Furthermore, special spinning rollers must. be used in the bath to prevent. the development of high tensions prior ta the wind-up because the yarn sets up so slowly. These disadvantages slow the rate of production materially and the process is not of commercial value. A spinning procedure which would permit the use of friction snubbing devices normally used in wet-spinning would considerably simplify the process and. allow the production of. higher tenacity yarns. under optimum conditions.

This invention has as. an object. the improvement of yarn properties of polyacrylonitrile and.

its copolymers obtained by wet spinning fromhigh boiling solvents. A further object is the provision of coagulating baths which permit faster coagulation of wet-spun. yarn. A still further object. is the provision of spinninsmetm;

ads which permit the use of higher yarntake-up speeds. and increased spinning: tensionsi yQther objects will appear hereinafter.

These obiects are accomplished by dissolving polyacrylonitrile. in a, suitable high boiling water-r soluble solvent extruding the solution, through a spinneret. into. a hot. glycerinecoagulating bath,.

and after a short. travel. passing the yarn from the glycerine bath through a water dip. After the water treatment the yarn may be either taken up. immediately or passed through a second hot glycerine bath before collecting on a, spinning bobbin. After washing; and. drying. the yarn. is stretched andheat-treated in air. The inter mediate water bath in this case accelerates the setting up of the warm. Due. to the faster rate of yarn coagulation, higher spinning tensions can be used and consequentlyhigher tenacity yarn is formed.

The following examples in which parts... Dercentages, and proportions are by weight are: given to illustratethe principles-of this invention and. are not to be. considered as limitative.

v Etcamples Eleven parts of acrylonitrile. polymer, prepared by the polymerization of monomeric. acrylonitrile in accordance with the teachingsof U. S. Patent. No. 1160;0541 to Bauer et al'.,.and possessing an average molecular weight of 89,000: as determined by the Staudinger equation from viscosity data, are ground to an average particle size. of v mesh and mixed with 89.. parts of tetramethylene sulfone to form a thin slurry. Air entrapped in the polymer slurry is removed using vacuum techniques: The'slurryis then heated to C. over a' period of 30 minutes to form a clear soluti'on possessinga viscosity of 1'80 p'oises at C. This solution is" extruded through a (SO-hole spinneret'into a glycerol precipitating bath (a) heated to a temperature of 140 C; The delivery of the spinneret is-6 gramsper minute. The yarn formed thereby travels through this bath as described in the table below. During the coagulating period theyarn is given a room temperature water dip- ('b). This treatment is omitted in the control experiment below. A second glycerol bath (0) may be used. The spinning tension is as descr-ibed inthe followingtable. The yarn is 'collectedon a bobbin wind-up and pressure washed with water. on the bobbin. The

Optimum Dry Spinning Bath Spinning mer'stretch Drawn Yarn C(Trave nd) Tension, Denier omposi 1011 grams T m W E1ng O ity ation Control. go; 78: glyoerine-.. 6X 162 74.4 4. 62 6.0 1 fg f 30 "x 174 56.7 5.10 1.2

(a 27' gIyceIineIZ 2 4' water; 73 1. 75X 183 99. 6 6. 23 7.4

c) 3' glycerine- 1 Too low to measure accurately.

when only a glycerine bath is used, 78" of bath travel are required, the spinning tensions being too low to measure accurately and special spinning rollers are required. However, when a water bath is used in conjunction with the glycerine coagulating bath, only 31 to 34" of bath travel are needed and the normally used snubbing devices can be employed. The fact that the optimum after-stretch ratios in Examples 1 and 2 above are considerably lower than that in the control example indicate that in the processes of this invention some of the stretching occurs in the spinning baths whereas little or no stretching does or can occur in the control. Further, the use of the two component bath system leads to yarns having substantially improved tenacities and elongations. The faster rate of coagulation under tension leads to partial orientation and a yarn with a 10 to 35% higher tenacity plus an increased elongation.

A suitable solvent within the scope of this invention is one with a rather high boiling point i. e., above 200 C. In the case of a solvent of fairly low boiling point (e. g., dimethylformamide), the glycerol bath at the temperatures employed acts to set up the yarn at a conveniently fast rate and no water dip is required for attainment of high yarn porperties. However, when solvents having a high boilin point, say above 200 C., are employed, the glycerol temperatures used do not remove solvents from the coagulating filament at a desirable rate. This occurs probably, because the low vapor pressure of the solvent at the spinning temperatures causes relatively little solvent to be removed by evaporative processes and only solution processes arising from the solubility of the solvent in the bath are operative. In the process of this invention the use of a water dip results in a considerable increase in rate of coagulation with consequent improvement in the physical properties of the yarn.

While tetramethylene sulfone is described herein as a suitable solvent for the wet spinning of polyacrylonitrile by this invention, it is to be understood that the method may be applied to spinnin from other solvents as well. As examples of suitable polyacrylonitrile solvents which are useful in the process of this invention are the water-soluble solvents disclosed in U. S. Patents Nos. 2,404,714-2,404,727, inclusive, which possess high boiling points, for example, in excess of 200 C. Thus, in general, this invention is applicable broadly to the use of any high boiling water-soluble organic solvents for the acrylonitrile polymers. Specific solvents which may be mentioned here for; illustrative purposes include malononitrile, methyl ethyl sulfoxide and methyl ethyl sulfone.

The temperature of the water dip may be varied from 0 to 100 C. Room temperature, however, is most convenient and. gives excellent results.

The glycerine bath temperatures may be from 100 C. to 160 C., but a temperature of about 140 C. gives optimum yarn properties. The length of travel of the yarn through the glycerine and water baths depends upon the rate of coagulation of the yarn. The bath length will also vary directly with the spinning speed. Since the water dip accelerates the rate of yarn coagulation, the length of travel through the glycerine bath can be much less than when used without a water dip. The use of the water dip as described herein accelerates the rate of coagulation of a spinning solution from 10 to 75% or more.

While for purposes of convenience this :process is described with relation to a glycerine coagulating bath, it is to be understood that the other non-aqueous coagulating mediums may be used as well. It is only necessary that the bath be capable of precipitating the polymers from its solutions. As examples of other baths that are operative in any of the processes of this invention may be mentioned triethanolamine and hexaethylene glycol. Thus, when a plurality of nonaqueous baths is used, the baths may be alike or different. The main determining factor is that the baths used must be capable of coagulating or further coagulating the spinnin solutions in a short period of time to facilitate rapid spinning of yarn.

The spinning tensions are applied by means of the usual friction snubbing devices described elsewhere in the wet-spinning art. Yarns spun from high boiling solvents without an intermediate water dip cannot be subjected to the desired spinning tension, because of the slow rate of coagulation. Since yarns spun under low tension do not develop optimum properties, it is especially advantageous to be able to subject the yarn to tension as it coagulates.

The after-stretch ratio for wet-spun acrylonitrile polymer usually is somewhat lower than that experienced with dry spun yarn. Generally, this ratio may be from 1.5X to 9X with the range of 1.'75X to 5X preferred.

The temperature of the after-stretching largely depends on the physical and chemical properties of the polymer. For yarns prepared from the preferred range of polymers of acrylonitrile within the scope of this invention, after-stretch ing temperatures of C. to 210 C. are possible with the range C. to 0. preferred. The yarn after-stretching may be carried out on any suitable apparatus which allows the yarn to be heated prior to drawing. A preferred process and apparatus is described in the copending application of Daniel T. 'Meloon, Serial Number guesses 496,397, filed July 28; 1943, nowabandonded. Another process might bethe drawing ofthe yarn as it passes through a heated medium, such;

as a hot vapor or liquid. When they stretching operation is carried out in the presence of steam or other vapor, the preferred temperature range: is considerably lower, 1. e., 110 C. to 140 C.

A greater degree of elongation in. the finished yarn may be obtained by allowing the yarn to relax (5-15%) immediately after drawingmay be accomplished by passing the yarn over a hot plate or through a heated atmosphere at a temperature slightly above the draw temperature and allowing the yarn to relax (contract) the desired amount by running the take-up roll the desired relaxed ratio percentage slower than the feed roll.

The heat-treating of polyacrylonitrile yarn to improve elongation without loss in tenacity may be carried out by heating the yarn cones in a thermostatically controlled oven or other suitable means. The time of heat treatment will normally vary inversely with the temperature. Depending upon the heat-treating temperature, the time may be varied from 1 to 10 hours at temperatures of 100 C. to 200 C. When heattreating the yarn, care must be taken to avoid subjecting it to such a severe treatment that discoloration of the yarn results. The preferred range of temperature is 100 C. to 150 C, for a treatment time of /2 to 2 hours.

The polymers for use in this invention preferably have molecular weights within the range of 15,000 to 250,000 or even higher as calculated from viscosity measurements by the Staudinger equation:

Molecular weight= viscosity of solution N31): specific viscosity:

and

C=concentration of the solution expressed as the number of moles of the monomer (calculated) per liter of solution.

Polyacrylonitrile itself may be used and copolymers of acrylonitrile with such monomers as vinyl esters, vinyl halides, vinylidene halides or other ethylenic compounds such as ethylene or butadienes may be employed in the process of this invention.

The use of a water dip in the wet-spinning process of this invention allows the production of higher tenacity yarn. When the yarn has passed around friction snubbing devices in.the water dip or immediately thereafter, it tends to become partially oriented while in the gel or partially swollen state. This allows the formation of a stronger, better yarn. If a water dip is not used, it is very difficult to apply high spinning tension to the yarn. In addition, the slow rate of coagulation necessitates a very long bath travel and slow wind-up speed.

Furthermore, the vrocess of this invention allows the use of high boiling solvents that would otherwise have little commercial value due to the excessive length of time necessary to set up the yarn as it is spun. In the process of this invention, high boiling solvents can be used at temperatures considerably below their boiling point, thus making commercially available a large num- 6. her of suitable solvents for the spinning of polyacrylonitrile yarns.

Any departure from the above description Which conforms to the present invention is intended to be included within the scope of the claims.

We claim:

1. A process for wet spinning'of yarn of an acrylonitrile polymer containing at least of acrylonitrile which comprises extruding a solution of said polymer in a high-boiling, watersoluble organic solvent through a shaped orifice into a first coagulant spinning bath selected from the group consisting of glycerol, triethanolamine and hexaethylene glycol, thereby precipitating said polymer from its said solution in the form of yarn; passing said yarn into a second coagulant bath consisting of water; and subsequently into a third coagulant bath selected from the group consisting of glycerol, triethanolamine and hexaethylene glycol, and stretching said yarn during the spinning.

2. A process according to claim 1 in which the said first and third coagulant baths consist of glycerol.

3. A process according to claim 1 in which the said first and third coagulant baths consist of triethanolamine.

4. A process according to claim 1 in which the said first and third coagulant baths consist of hexaethylene glycol.

5. A process in accordance with claim 1 in which the said water bath is heated to a temperature of from 20 to C. and the said first and third baths are heated to a temperature of about 100 C.

6. A process for wet spinning of yarn of an acrylonitrile polymer containing at least 85% of acrylonitrile which comprises extruding a solution of said polymer, in a high-boiling, watersoluble organic solvent, through a shaped orifice into a spinning, coagulant bath consisting of glycerol heated to a temperature of at least 100 C.; passing the yarn formed thereby into a second coagulant bath consisting of water heated to a temperature from about 20 C. to about 100 0.; and passing said yarn into a third coagulant bath consisting of glycerol heated to a temperature of at least 100 C.; and stretching said yarns during the spinning.

'7. A process for Wet spinning of yarn of an acrylonitrile polymer containing at least 85% of acrylonitrile which comprises extruding a solution of said polymer in tetramethylene cyclic sulfone through a shaped orifice into a first coagulant spinning bath selected from the group consisting of glycerol, triethanolamine and hexaethylene glycol, thereby precipitating said polymer in the form of yarn from a solution comprising about 89% tetramethylene cyclic sulfone and about 11% said polymer; passing the yarn formed thereby into a second coagulant bath consisting of water; passing said yarn from said second bath into a third coagulant bath consisting of glycerol; and stretching said yarn during the spinning.

8. A process for wet spinning of yarn of an acrylonitrile polymer containing at least 85% of acrylonitrile which comprises extruding a solution of said polymer in a high boiling water soluble organic solvent through a shaped orifice into a glycerol coagulant spinnin bath heated to a temperature of about 100 (3., thereby precipitating said polymer from its said solution in the form of yarn; passing the said yarn through the said glycerol coagulant spinning bath for a distance'of about 2'7 inches; passing 'said-- yarn through a second coagulating bath'consisting of 7 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PA'I'ENTS Number Name Date Rochet Mar. 20, 1934 Houtz Nov. 6, 1945 Latham July 23, 1946 Houtz July 23, 1946 Watkins Sept. 2, 1947

Claims (1)

1. A PROCESS FOR WET SPINNING OF YARN OF AN ACRYLONITRILE POLYMER CONTAINING AT LEAST 85% OF ACRYLONITRILE WHICH COMPRISES EXTRUDING A SOLUTION OF SAID POLYMER IN A HIGH-BOILING WATERSOLUBLE ORGANIC SOLVENT THROUGH A SHAPED ORIFICE INTO A FIRST COAGULANT SPINNING BATH SELECTED FROM THE GROUP CONSISTING OF GLYCEROL, TRIETHANOLAMINE AND HEXAETHYLENE GLYCOL, THEREBY PRECIPITATING SAID POLYMER FROM ITS SAID SOLUTION IN THE FORM OF YARN; PASSING SAID YARN INTO A SECOND COAGULANT BATH CONSISTING OF WATER; AND SUBSEQUENTLY INTO A THIRD COAGULANT BATH SELECTED FROM THE GROUP CONSISTING OF GLYCEROL, TRIETHANOLAMINE AND HEXAETHYLENE GLYCOL, AND STRETCHING SAID YARN DURING THE SPINNING.