US2622003A - Method of making shaped articles of an acrylonitrile polymer - Google Patents

Description

Patented Dec. 16, 1952 METHOD OF MAKING SHAPED ARTICLES OF AN ACRYLONITRILE POLYMER Howard M. Hoxie, Chester, Pa., assignor to American Viscose Corporation, Wilmington, Del., a

corporation of Delaware No Drawing. Application October 27, 1949, Serial No. 123,994

Claims. 1

This invention relates to the production of shaped articles, such as fibers, yarns, and films, from acrylonitrile polymers by the wet-spinning or wet-casting process.

The acrylonitrile polymers which can be formed into shaped articles in accordance with this invention include polyacrylonitrile and fiberforming copolymers or interpolymers of acrylonitrile containing at least 70%, preferably from 70 to 98%, of acrylonitrile in the polymer molecule and obtained by copolymerizing acrylonitrile with one or more other polymerizable substances which contain the group C=C such as oopolymers of acrylonitrile with one or more of the following: vinyl acetate, styrene, vinyl chloride, the vinylpyridines and particularly 2-vinylpyridine, isobutene, dimethylfumarate, methyl methacrylate, methacrylonitrile, acrylic acid and its esters, etc.

The prior art processes for producing fibers from the acrylonitrile polymers by the wet-spinning process involves extruding a solution of the polymer into a precipitant for the polymer, for example extruding a solution of the polymer in dimethylformamide into water. When the fiberforming solution is extruded into water at a practical working temperature C. or below), the spinning must be performed at very low speed and, moreover, regardless of the bath temperature, the fibers withdrawn from the bath are so brittle and inextensible that they cannot be stretched at ordinary temperatures, but must be stretched at elevated temperatures. When it is attempted to stretch these brittle, inextensible fibers by passing them through a heat-stretching tube,

considerable difiiculty is encountered in lacing the tube, and usually a tube of special design is required. The brittle character and relative inextensibility of the fibers formed in the water bath results from the fact that when the spinning solution is extruded into water it is impossible to control the rate of diffusion of the water into the interior of the freshly formed fibers in relation to the rate of diffusion of the spinning solvent out of the freshly formed fibers. As a consequence, the fibers are set while the molecules are arranged in the heterogeneous, non-oriented condition in which they occur in the freshly formed fibers in the setting medium. The fibers which are set in this condition are very weak and cannot be subjected to mechanical stress or pressure under ordinary-conditions. As pointed out above, the fibers cannot be given a godet stretch at ordinary temperature for improving their handling properties and conditioning them 2 for subsequent strong stretching at elevated temperatures.

I have found that when a homogeneous mixture of the polymer and dimethylacetamide is extruded into a, setting medium comprising a mixture of water and dimethylacetamide containing dimethylacetamide in a controlled selected proportion between 20 and by volume, the fibers withdrawn from the bath are tough and extensible and can be subjected to strong stretching, either at ordinary temperature or at elevated temperature, without rupture.

The fibers advancing from the setting bath may be stretched between godets, as they are advanced over a thread-advancing, threadstretching reel, or by passage through a steam tube, the extent of stretching depending on the temperature. For example, the fibers may be given a, stretch between godets of from to 300%, preferably 100 to 200%, at ordinary temperature or at elevated temperatures up to 100 C.

or they may be stretched more than 300%, if the stretching is performed at temperatures above 100 C. This stretch may be the only stretch to which the fibers are subjected or, if the fibers are stretched between godets, they may be given an after-stretch at elevated temperature, either while they are subjected to hot air, in an atmosphere of steam, wet or dry, or while they are passed through a heated liquid which is inert to the acrylonitrile polymer. The stretching may be performed on the freshly spun fibers advancing from the setting bath, or it may be preceded by removal of or substantial reduction in the amount of residual spinning solvent, for example by washing the fibers or by subjecting them to heat to volatilize the solvent; or the stretching may be preceded by washing and drying of the fibers. In one preferred embodiment, the fibers are stretched between godets or the like as they are withdrawn from the bath, washed to reduce the residual spinning solvent carried thereby to not more than 1.5% by weight, dried in air, and afterstretched 300% at a temperature of to C. by passing them through a steam tube. However, the non-brittle, extensible fiber withdrawn from the water-dimethylacetamide setting bath may be sent directly to a steam tube and heatstretched, which method may be preferred when the fibers are destined to be reduced to discontinuous lengths. After such heat-stretching, the fibers may be forwarded to a cutter, or collected in the form of a filamentary bundle of large total denier such as a tow, and converted directly from tow to top, the discontinuous fibers being treated with a non-solvent relaxing liquid, for instance hot water, which shrinks and curls the fibers. One of the advantages to be derived from the method of the invention, in accordance with which the dimethylacetamide solution of the acrylonitrile polymer is spun into a setting medium comprising water and from 20 to 70% by volume of dimethylacetamide, is that it affords a choice in the manner in which the fibers are handled, since the fibers can be stretched at high temperatures immediately or, as is generally preferred, they can be stretched between godets at lower temperatures, including roomv temperature, and subsequently after-stretched at higher temperature, or they can be stretched at the lower temperatures only, with no after-stretch- The proportion of dimethylacetamide to water in the setting medium is critical and is between 20 and 70% by volume. Moreover, the relative proportions of dimethylacetamide and water in the setting medium must be maintained constant or substantially constant throughout the spinning. If the bath consists of 20% dimethylacetamide and 80% water at the start of spinning, the concentrations of dimethylacetamide and water are maintained at 20 and 80% respectively, throughout the entire spinning operation. If the concentration of dimethylacetamide in the setting medium is 70% by volume, or any value between 20 and 70%, at the start of operations, the dimethylacetamide is maintained constant or substantially constant at that concentration. The concentration of the dimethylacetamide should not vary by more than 2% and in any event must be at least 20% by volume. The composition of the setting medium can be controlled by periodic observation of the refractive index of the medium, and the simple expedientof adding water to the bath, in calculated amount based on the amount of dimethylacetamide introduced as spinning solvent, either continuously or at intervals. The exact amount of water to be added will vary and cannot be stated in advance for all conditions of spinning. As an example, the composition of a, setting medium consisting initially of 33% water and 67% dimethylacetamide was maintained constant by adding 0.5 liter of water to the bath for each liter of dimethylacetamide pumped in as spinning solution.

Another remarkable and distinguishing advantage in the present method is that the concentration of dimethylacetamide in the setting medium, within the range 20 to 70% by volume, has a direct influence on the character of the fibers obtained, which can be predetermined. When the setting medium consists of water and an amount of dimethylacetamide between 20 and about 45% by volume, the fibers are opaque, dull fibers of low density which, on examination under the microscope, are found to contain numerous bubbles or voids which reduce the transparency and luster of the fibers and materially affect the dye acceptance of the fibers. The opaque fibers containing voids which are capable of accepting dyes are dyed to pale, pastel shades under usual dyeing conditions. Those fibers are useful for any purpose for which fibers of low density and'luster, and dyed to pale shades are desired. on the other hand, a concentration of dimethylacetamide in the setting bath of from about 45% up to the upper limit of the range, 70%, by volume, 'is essential to the production of fibers which, after washing, drying,

and after-stretching under heating are dense, transparent, and free of voids or bubbles as determined by microscopic examination. The dense, transparent fibers which are dye acceptors can be dyed to more intense, more brilliant shades under ordinary dyeing conditions than the opaque fibers obtained when the solution is extruded into a bath containing water and a lower proportion of dimethylacetamide in the range stated.

Homogeneous mixtures of dimethylacetamide and from 5 up to 30% or more, preferably from 8 to 30%, of the a'crylonitrile polymer can be used in practicing the invention. The immersion length is not critical and may be from 1 to 100 inches. Immersion distances of from to inches are preferred. Spinning may be performed. at temperatures between 25 and 60 C. These are practicable working temperatures. Higher bath temperatures may be used if desired.

The acrylonitrile polymers which are formed into fibers in accordance with this invention may be either homogeneous or heterogeneous, and may be produced by any suitable polymerization process. The polymer may be polyacrylonitrile or a copolymer or interpolymer containing from 70 to 98% acrylonitrile in the molecule.

The term fibers as used herein includes fibers, filaments, threads, yarns, and filamentary bundles generally.

Although the invention has been discussed in detail in connection with the production of synthetic fibers, it is not limited thereto. Films, sheets, tubes, rods and other shaped articles which can be obtained by extruding a solution of the polymer into a liquid setting medium can be produced by the present method.

The following examples are illustrative of preferred specific embodiments of the invention.

Example I A spinning solution comprising a homogeneous mixture of dimethylacetamide and 18% by weight of a copolymer containing, in the polymer molecule, 92% acrylonitrile and 8% 2-vinyl pyridine, by weight, was extruded through a spinneret having 44 holes each 0.00; inches in diameter into a setting medium consisting of 65% dimethylacetamide and water by volume at a temperature of 30 C. The filaments were withdrawn from the bath after an immersion of 8 inches, stretched 290% as they were passed to godets immersed in water at 83 C., and washed on the godets. The yarn was then dried on a revolving drum heated internally by steamat a pressure of 20 lbs/sq. in. and stretched 225% in a tube containing steam at a pressure of lbs/sq. in. The yarn was twisted and permitted to shrink freely in boiling water. This yarn was dense and transparent, and did not contain voids or small bubbles as determined by microscopic examination of the cross-section. It was dyed to a scarlet of high intensity in a dyebath containing 2%, onthe weight of the fiber, of Wool Fast Scarlet G. Supra (C. I. 252), under usual Wool-dyeing conditions.

Example II A spinning solution comprising a homogeneous mixture of dimethylacetamide and 18% by weight of a copolymer containing, in the polymer molecule, 92% acrylonitrile and 3% of 2-vinyl pyridine, by weight, was extruded through a spinneret containing 44 holes each 0.004 inches in diameter, into a'setting medium consisting of 35% water and 65% dimethylacetamide, by volume, at a temperature of 40 C. The filaments were withdrawn from the bath, stretched 150% at ordinary temperature, washed by immersion in water at 95 C., dried in air, and stretched 500% in steam at a pressure of 65 lbs/sq. in. The yarn was twisted and collected. After relaxation by free shrinkage in boiling water, it exhibited a tenacity of 3.1 gms/denier and an extensibility of 19%. The yarn did not contain voids or bubbles and was dyed to a deep scarlet in a dyebath containing 2%, on the weight of the fiber, of Wool Fast Scarlet G Supra. (0.1. 252).

Example III A spinning solution comprising 18% by weight of a copolymer containing, in the molecule, 92% acrylonitrile and 8% 2-vinyl pyridine, by weight, in dimethylacetamide, was extruded through a spinneret containing 40 holes each .003 inch in diameter, into a setting medium consisting of 37% water and 63% dimethylacetamide, by volume, at a temperature of 68 C. The filaments were withdrawn from the bath, stretched 800% in a tube containing steam at a pressure of 45 p. s. i. and the heat-stretched oriented fibers were forwarded directly to a staple fiber cutter. The staple fibers were allowed to drop into water at 97 C. in which they were relaxed, with accompanying shrinkage and curling. The residual dimethylacetamide was extracted from the staple fibers by the hot water. The shrunk, curled fibers were removed from the relaxing bath and dried.

The fibers contained voids or bubbles and were dyed to a pale pink shade in a dyebath containing 2%, on the weight of the fibers, of Wool Fast Scarlet G Supra.

Example IV A spinning solution prepared by dissolving by weight of polyacrylonitrile in dimethylacetamide was extruded through a spinneret containing forty 0.0035-inch holes into a setting medium consisting of 32% water and 68% dimethylacetamide at a temperature of 30. The yarn was removed from the bath after an immersion of 10 inches, stretched 200% in air, washed in water at 80 C. and collected on a spool. The yarn was allowed to dry in air at room temperature on the spool for several days and was then stretched 350% in a tube containing hot air at 150 C. The yarn was lustrous, free from voids and exhibited a tenacity of 3.7 gms./den.

Example V A spinning solution comprising a homogeneous mixture of dimethylacetamide and 18% by weight of a copolymer containing, in the polymer molecule, 90% acrylonitrile and 1 2-vinyl pyridine, by weight, was extruded through a spinneret having 44 holes each 0.004 inches in diameter into a setting medium consisting of dimethylacetamide and 75% water by volume at a temperature of C. The filaments were withdrawn from the bath after an immersion of 6 inches, stretched 50% between godets at ordinary temperature, washed by immersion in water at 93 C., and stretched 400% in steam at a pressure of '70 lbs./sq.in. The yarn was twisted and collected. On microscopic examination the opaque yarn was found to contain numerous voids or bubbles. It was dyed to a pale pink shade in a bath containing 2%, on the weight of the yarn, of Wool Fast Scarlet G Conc., under usual wool-dyeing conditions.

6 Erample VI A spinning solution comprising a homogeneous mixture of dimethylacetamide and 16 by weight of a copolymer containing, in the polymer molecule, 92% acrylonitrile and 8% vinyl acetate, by weight, was extruded (pump speed 12 cc./min.) through a spinneret having 40 holes each 0.0035 inch in diameter into a setting medium consisting of 66% dimethylacetamide and 34% water, by volume, at a temperature of 35 C. The filaments were withdrawn from the bath after an immersion of 6", stretched 142% between godets at ordinary temperature, washed in water at 0., dried on a drum heated internally by steam at a pressure of 22 lbs/sq. in. The dried yarn was heat-stretched 420% in a tube containing steam at a pressure of 50 lbs/sq. in. The yarns were dense and transparent, and did not contain voids or small bubbles.

Example VII A homogeneous mixture of dimethylacetamide and 19% of a copolymer containing 89% acrylonitrile and 11% of vinyl-a-chloroacetate was extruded (pump speed: 15 R. P. M.) through a spinneret having 44 holes each 0.004 inch in diameter, into a setting medium comprising 65% dimethylacetamide and 35% water, by volume, at 25 C. After an immersion of 8 inches, the filaments were withdrawn, stretched 114% between godets at ordinary temperature, washed in water at 0., dried, and heat stretched 180% in hot air (240 0.). The yarn was relaxed in boiling water. It was dense and transparent, and did not contain voids or bubbles.

Although the invention may be practed with any one of the modifications described herein, it is obvious that other changes or modifications may be made without departing from the nature and spirit of the invention, and the invention is not to be limited, therefore, except as defined by the appended claims.

I claim:

1. A method of making shaped articles from an acrylonitrile polymer containing at least 70% by weight acrylonitrile in the polymer molecule which comprises continuously extruding a homogeneous mixture of the polymer and dimethylacetamide into a setting medium consisting essentially of a mixture of water and dimethylacetamide containing the dimethylacetamide in a selected concentration between 20% and 70% by volume, the water and dimethylacetamide in the setting medium being maintained within 2% of the selected volumetric proportions throughout the extrusion, and stretching the article at a temperature which is at least room temperature afte it is withdrawn from the bath and prior to further treatment thereof.

2. A method of making shaped articles from an acrylonitrile polymer containing at least 70% by weight acrylonitrile in the polymer molecule which comprises continuously extruding a homo geneous mixture of the polymer and dimethylacetamide into a setting medium consisting essentially of mixture of water and dimethylacetamide containing the dimethylacetamide in a selected concentration between 20% and 70% by volume, the water and dimethylacetamide in the setting medium being maintained within 2% of the selected volumetric proportions throughout the extrusion, and stretching the article at a temperature between room temperature and C. after it is withdrawn from the bath and prior to further treatment thereof.

3. A method of making synthetic fibers from an acrylonitrile polymer containing at least 70% by Weight acrylonitrile in the polymer molecule which comprises continuously extruding a homogeneous mixture of the polymer and dimethylacetamide through a spinneret into a setting medium consisting essentially of a mixture of water and dimethylacetamide containing the dimethylacetamide in a selected concentration between 20% and 70% by volume, the water and dimethylaoetamide in the setting medium being maintained within 2% of the selected volumetric proportions throughout the extrusion, withdrawing the fibers from the setting medium, stretchingthe fibers from 100% to 300% at a temperature up to 100 C. after they are withdrawn from the bath and prior to any other treatment thereof, washing the fibers, and subsequently further orienting the fibers by simultaneous. heating and stretching.

4. The method of claim 3, wherein the setting medium consists essentially of a mixture of water and dimethylacetamide containing the dimethylacet'amide in a selected concentration between 20% and about 45% by volume.

5. The method or claim 3, wherein the setting mediumconsists essentially of a mixture of water and dimethylacetamide containing the dimethylacetamide in a selected concentration between about 45% and 70% by volume.

6. A method as in claim 1, wherein the acrylonitrile polymer is a copolymer containing, in

the molecule, from 90 to 92% of acrylonitrile and from 8 to 10% of Z-Vinylpyridine, by weight.

7. A method as in claim 1, wherein the acrylonitrile polymer is a fiber-forming polyacrylonitrile.

8. A method as in claim 1, wherein the acrylonitrile polymer is a copolymer containing 92% acrylonitrile and 8% vinyl acetate, by weight, in the polymer molecule.

9. A method as in claim 1, wherein the acrylonitrile polymer is a copolymer containing 89% acrylonitrile and 11% vinyl-a-ohloroacetate by weight, in the polymer molecule.

10. A setting bath for use in the production of shaped articles from a homogeneous mixture of dimethylacetamide and an acrylonitrile polymer, which bath consists essentially of a mixture of water and dimethylacetamide containing the dimethylacetamide in a selected concentration between 20 and by volume.

HQWARD M. HOXIE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,404,? 17 Houtz July 23, 1946 2,420,565 Rugeley et a1. May 13, 1947 2,531,407 DAlelio Nov. 28, 1950

Claims (1)

1. A METHOD OF MAKING SHAPED ARTICLES FROM AN ACRYLONITRILE POLYMER CONTAINING AT LEAT 70% BY WEIGHT ACRYLONITRILE IN THE POLYMER MOLECULE WHICH COMPRISES CONTINUOUSLY EXTRUDING A HOMOGENEOUS MIXTURE OF THE POLYMER AND DIMETHYLYACETAMIDE INTO A SETTING MEDIUM CONSISTING ESSENTIALLY OF A MIXTURE OF WATER AND DIMETHYLACETAMIDE CONTAINING THE DIMETHYLACETAMIDE IN A SELECTED CONCENTRATION BETWEEN 20% AND 70% BY VOLUME, THE WATER AND DIMETHYLACETAMIDE IN THE SETTING MEDIUM BEING MAINTAINED WITH 2% OF THE SELECTED VOLUMETRIC PROPORTIONS THROUGHOUT THE EXTRUSION, AND STRETCHING THE ARTICLE AT A TEMPERATURE WHICH IS AT LEAST ROOM TEMPERATURE AFTER IT IS WITHDRAWN FROM THE BATH AND PRIOR TO FURTHER TREATMENT THEREOF.