CA1052064A - Extrusion of polyacrylonitrile into pressurized zone with water into filaments - Google Patents

Abstract

A B S T R A C T
A single phase fusion melt of acrylonitrile polymer and water is melt-spun into a pressurized solidification zone wherein certain temperature, pressure, and composition conditions obtain. After spin-drawing the nascent extrudate in the solidification zone, it may be relaxed in a free-to-shrink condition. In a preferred embodiment, the nascent fiber is dried at elevated temperature before it is cooled or before it loses water upon cooling.

Description

O~i~
i 1 This invention relates to a process for melt-spinning shaped articles of acrylonitrile polymer whereby articles of exceptional properties are obtained. Mbre particularly, this invention relates to an economical process for melt-spinning ; 5 a single phase fusion melt of acrylonitrile polymer and water ! into a solidification zone wherein certain conditions are main-tained in order to achieve high jet stretch.
In general, shaped articles, such as synthetic fila-ments, fibers, films, etc., can be produced from polymer materials by melt-spinning, dry-spinning, or wet-spinning pro-cesses. In the "melt-spinning process~ for forming synthetic filaments, polymer liquefied by melting is extruded through spinnerette orifices or slots to form an extrudate which is ` coagulated by cooling. Typically, polyamide, polyester, and polyolefin, fibers or films are produced by melt-spinning. In , ....
i the "dry-spinning process" for forming synthetic filaments, polymer liquefied by dissolving in a volatile solvent is ex-truded through spinnerette orifices to form an extrudate which is coagulated by evaporation of the volatile solvent.
Typically, cellulose acetate solutions in acetone, acryloni-trile polymer solutions in dimethylformamide, etc., are spun into fibers by dry-spinning. In the "wet-spinning process" for forming synthetic filaments, polymer liquefied by dissolving in a solvent is extruded through spinnerette orifices or ; 25 slots to form an extrudate which is coagulated by removal of : solvent in a liquid coagulating medium. In wet-spinning fibers of some polymers, such as from solutions of acryloni-trile polymers in aqueous nitric acid, aqueous salt, or organic ~olvents, the solvent is removed by leaching it out of the extrudate in an aqueous coagulant. In wet-spinning fibers .
., ~

lOS'~064 or films of other polymers, such as from viscose (aqueous sodium hydroxide solution of cellulose xanthate), the solvent is removed by chemical reaction with an aqueous sulfuric acid coagulant.
For various reasons, it has been recognized that melt-spinning processes are preferable to dry-spinning or wet-spinning processes whenever a choice is possible~ Among the reasons for such preference are (a) the increased speed of operation when cooling rather than solvent diffusion (evaporation or leaching) is involved as the solidification mechanism, and tb) the extremely high spin draw-down ratios or jet stretches achievable - 10 permitting spinning fine denier fibers from the rela~ively large spinnerette orifices required to avoid excessive extrusion pressure when spinning the very viscous polymer melt. Further reasons for preferring melt-spinning processes include avoidance of the need for washing the product free of residual solvent, and avoidance of solvent recovery from coagulation liquids or gases. However, since acrylonitrile polymers do not readily melt without degradation, melt-spinning processes have not been available for spinning ~;; acrylonitrile polymers, and major attention has been directed to wet-spinning and dry-spinning processes for spinning such polymers.
Recognizing the desirability of melt_spinning processes, attempts have been made to find ways of liquefying acrylonitrile polymers so they could be extruded and then solidified by cooling alone, Such pseudo-melt-spinning processes have utilized latent or partial solvents which could be used, in combination with acrylonitrile polymers, to form liquids at eleva ted temperatures which liquids could solidify, after extrusion, merely on -cooling However, such products still had to be washed free of latent or partial solvent and still required solvent recovery systems, :~o5'~0~i4 1 whereby such pseudo-melt-spinning processes still do not possess all the advantages and desirable characteri~tics of true melt-spinng processes.
Many polymers are known which have properties making them useful or potentially useful as shaped articles, such as fibers, films, filaments, ribbons, etc. Refractory polymers l are polymers which are difficult or impossible to soften under r heat without degradation or use of excessively high temperatures.
The refractory polymer of principal commercial importance at present for forming shaped articles by spinning processes is acrylonitrile polymer. While the principles and conditions of this invention can be used for melt-spinning other single phase fusion melts of melt assistant and refractory polymer, ~` such as the various cellulose acetates, polyvinyl halides ; 15 (e.g. polyvinyl chloride, polytetrafluoroethylene, polytrifluoro-' chloroethylene, polyvinylidene chloride, etc.), polyvinyl alcohol, very high molecular weight polyamides, polyimides, and polyesters, refractory polyamides, polyimides, and poly-esters derived from aromatic mono e rs, the further description herein will be principally directed toward the commercially important acrylonitrile polymers. It will be understood that the invention is not so limited in its application, but can be useful for melt-spinning a wide variety of refractory polymers wherein the m~lt assistant makes melting possible or reduces the melting point of such polymer.
~ melt assistant is a material or substance which is - capable, when used under pressure sufficient to prevent boiling at temperatures above its atmospheric boiling point, of reducing the melting point of the acrylonitrile polymer when used in the proper concentration, to a temperature pre-1~5'~0~4 1 ferably below the degradation range for the acrylonitrile polymer to form a single phase fusion melt. This does not in-clude materials or substances normally considered good solvents for acrylonitrile polymers, such as dimethylformamide, S dimethylacet d de, ethylene or propylene carbonate, dimethyl sulfoxide, dimethylsulfone, tetramethylenesulfone, concen-trated nitric acid, very concentrated aqueous solutions of salts of strongly hydrated ions such as thiocyanate salts, zinc chloride, calcium or lithium bromide, iodide salts, alkali metal perchlorates, etc., or other solvents, such as those mentioned in such prior art as United States Patents

2,140,921: 2,356,767; 2,404,713-728; 2,648,648-9; etc.
We have arrived at certain theoretical considerations useful in selecting substances which are useful as melt assist-~` 15 ants. According to my theory, melt assistahts can be selected on the basis of certain thermodynamic properties, viz., the solubility parameter, the hydrogen bond strength, and the dipole moment. The solubility parameter of a substance, which is defined as the square root of the cohesive energy density, is preferably greater than about 8.7 for a melt assistant for acrylonitrile polymer. The cohesive energy density is the latent heat of vaporization in calories per mole divided by the molar volume or alternatively, is the latent heat of vaporization in calories per gram times the specific gravity of the liquid. The hydrogen bond strength for a melt assi-:
tant for acrylonitrile polymer is greater than zero, and p~eferably greater than about 4. If the solubility parameter is toward the lower values, such as between about 8.7 to about 11, then the hydrogen bond strength is preferably higher, i.e., above about 12. The dipole moment for a melt assistant for 5'~ i4 1 acrylonitrile polymer i8 greater than zero.
Substances which meet the foregoing criteria and which are relatively volatile, i.e., which have boiling points at atmospheric pressure which are below the temperature to which they can depress the acrylonitrile polymer melting point, and therefore have boiling points below the extrusion temperature of the single phase fusion melt, can ~e selected from low molecular weight members of various classes of L materials, such as alcohols, halogen-substituted alcohols, ; 10 amino-substituted alcohols, nitroalkanes, heterocyclic nitrogen compounds, cyanoalkanes, fatty acids, acylacetones, aldehydes, alkenyl sulfones, alkynyl sulfones,S~ngly-etherified glycols, mercaptans, thiocyanoalkanes, cyclic ethers, amines, etc. Compounds of relatively low atmospheric boiling point i~- 15 which contain a hydroxyl group form an especially useful sub-~ grouping of these materials because the hydroxyl group imparts :
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to the lecule a ~ipole moment, hydrogen bonding properties, and good solubility parameters. In general compounds of these types may, if desired, also contain other substituents ` ~ thereon to lower their boiling points. Also, mixtures of these compounds with each other, with water, or with other compounds may be used to lower their boiling points or to lower the melting temperature of single phase fusion melts made utilizing them. Also, the melt assistant may have in-corporated therein minor amounts (e.g., less than 50%) of materials which are solvents for the acrylonitrile polymer to further depress the melting point of the polymer.
Melt assistants ~elected in accordance with the foregoing principles which are useable in the practice of this invention include water, methyl alcohol, ethyl alcohol, ~ , l~ O~i~
n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, sec.-butyl alcohol, t-butyl alcohol, nitromethane, nitroethane, pyridine, piperi-dine, morpholine, n-butylamine, isobutylamine, sec -butylamine, t-butyl-amine, acetronitrile, propionitrile, acetic acid, formic acid, acetylacetone, ethylene glycol monoethyl ether, 1,3-dioxane, dimethylfuran, sylvan, 1-chloro-2-hydroxyethane, propyl mercaptan, butyl mercaptan, methyl thiocyanate, diallyl sulfone, and mixtures of these compounds with each other or with known solvents or swelling agents for acrylonitr~e polymers, such as dimethyl-formamide-water, acetonitrile-water, dimethylacetamide-water, methyl alcohol-water, methyl alcohol dimethylformamide, phenol-water, phenol-methanol, glycol-water, glycerol-water,dilute aqueous solutions of sodium thiocynate, zinc chloride, lithium bromide, guanidine thiocyanate, nitric acid, etc.
While all these melt assistants are useful in the practice of the present invention to produce the melt-spinning advantages of high speed of operation and extremely high spin draw-down ratios or jet stretches, water is the one ; melt assistant greatly preferred since it also produces the added melt-spinning advantages of avoiding the need for washing the product free of melt-assistant and, therefore, also avoiding the need or recovery systems for recovering melt assistant.
In accordance with the present invention there is provided a process for preparing an acrylonitrile polymer fiber which comprises spinning a homogeneous single phase fusion melt of 90~65% acrylonitrile polymer and 10-35% water at a temperature ranging from minimum melt temperature M to below the temperature of significant polymer degradation to produce an ex-trudate, cooling the extrudate in a steam-pressurized zone maintained at a steam pressure such as to enable the extrudate to cool to a temperature below said minimum melt temperature M but not re than 20C, below said minimum melt temperature M, and stretching said extrudate at a stretch ratio of 25-250 while said extrudate is in said steam-pressurized zone.
In accordance with a preferred aspect of the present invention, these is psovided a process for melt-spinning shaped articles of acrylo-nitrile polymer wherein the polymer is prepared as a single phase fusion melt ~t5;~ i4 consisting essentially of acrylonitrile and water at a temperature Tf which is above the single phase fusion melt melting temperature M and also above the boiling point at atmospheric pressure of water and the fusion melt is extruded through a spinnerette to form shaped articles characterized by extruding the shaped article directly into a pressurized solidification zone wherein the following conditions are maintained: (a) the partial pressure of water vapor is between 56% and 100% of the vapor pressure of water at tem-perature Tf; ~) the temperature T is at least equal to the saturation tem-; perature of water at a vapor pressure equal to said partial pressure p; and (c) the total pressure P is at least equal to said partial pressure p; and drawing the nascent extrudate at a stretch ratio of 25 to 250 in the pressure solidification zone.
In accordance with a preferred embodiment of the present inven-tion, it is further characterized by drying said fibers at a temperature above 90C. while substantially preventing loss of water from the freshly melt-spun fibers at any temperature below about 90C. until said drying stops, thereby minimizing the tendency of such fibers to form voids and micro-voids therein.
In melt-spinning organic polymers, such as polyamides, polyesters, and polyolefins, and in wet~spinning or dry-spinning acrylonitrile polymers, the filaments after extrusion and spin draw~down or jet stretch must be later subjected to a secondary stretching or after drawing to orient the polymer molecules therein followed by a relaxation step to ease internal strains whereby the characteristic good fiber properties are developed. Surprisingly and unexpectedly, as one aspect of the present invention, the filaments spun by the process of the present invention did not need any secondary stretching or after drawing process steps. Thus the characteristic good fiber properties of acrylonitrile polymer fibers can be obtained with the process . .

, '' ' ` ' ' . `
, 1~5'~0~4 1 of the present invention merely by relaxing such filament~ at elevated temperature after the jet stretch has been applied without use of any secondary stretching or after drawing steps.
The acrylonitrile polymers which can be used in the practice of this invention are those polymers or blends of polymers containing greater than about 50% combined acryloni-trile. In addition to homopolyacrylonitrile, copolymers of acrylonitrile with one or more copolymerizable mono-olef~ic nomers can be used. Such nomers include acrylic, alpha-1~ chloroacrylic and methacrylic acids, the methacrylates, such . as methyl methacrylate, ethyl methacrylate, butyl methacry-late, methoxy-methyl methacrylate, beta-chloroethyl metha-crylate, and the corresponding estersof acrylic and alpha-chloroacrylic acids, vinyl bromide, vinyl chloride, vinyl flouride, vinylidene bromide, vinylidene chloride, allyl ~: chloride, l-chloro-l-bromoethylene; methacrylonitrile, allyl alcohol; acrylamide and methacrylamide; alpha-chloroacrylamide, . ~ or mono-alkyl substitution products thereof; methyl vinyl : ketone; vinyl carboxylates, such as vinyl formate, vinyl acetate, vinyl chloroacetate vinyl propionate, vinyl stearate, ~ and vinyl benzoate; ~-vinylimides, such as N-vinylphthalimide ;. and N-vinylsuccinimide; methylene malonic esters; itaconic acid and itaconic esters; N-vinylcarbazole; vinylfuran;
.~ alkyl vinyl ethers; vinyl sulfonic acids, such as vinyl as sulfonic acid, styrene sulfonic acid, methallyl sulfonic acid, p-methallyloxy benzene sulfonic acid and their salts;
ethylene alpha, beta-dicarboxylic acids or their anhydrides or derivatives, such as diethyl citraconate, diethyl mesa-conate; styrene; dibromostyrene; vinylnaphthalene; vinyl-~ubstituted tertiary heterocyclic amines such as the - - r ~ S'~0~4 1 vinylpr~dines and alkyl-substituted vinylpyridines for example, 2-vinylpyridine, 4-vinylpyridine, 2-methyl-S-vinylpyridine,and the like; l-vinylimidazole and alkyl-substituted l-vinyl-imidazoles, such as 2-, 4-, or 5-methyl--l-vinylimidazole, vinylpyrrolidone,~ vinylpiperidone, and other mono-olefinic copolymerizable monomeric materials. The acrylonitrile polymers or blends of polymers may contain vary-ing quantities of one or more commonomers, as, for examp~e, a total of about 5, 10, 15,20, 25, 30, or 40% comonomer content based on the total acrylonitrile polymer composition and may have molecular weights ranging from 10,000 to 200,000, as for example, about 20,000; 40,000; 50,000; 60,000: 70,000; 85,000;
100,000; 130,000; etc. The quantity of comonomer and the - molecular weights may vary outside these indicated ranges - 15 since the present invention does not depend upon the~e features for operativeness although the consideration of the properties of the products for their end uses may indicate such variations.
~he degradation range for acrylonitrile polymer as used herein refers to the range of temperatures wherein acry-lonitrile polymers suffer degradation, usually evidenced by discoloration, on exposure to such temperatures for the time normally required for fluidizing and extruding the polymer.
Usually, this degradation range starts at about 180C. to about 220C., depending on polymer composition, etc., and extends upwardly therefrom. Where the quality of the polymer in the product is not critical and some polymer degradation can be tolerated, the single phase fusion melt may be heated to m~re ; elevated temperatures into the degradation range in the practice of this invention, however, in general, it is pre-ferred to operate at lower temperatures to avoid degradation.

_g_ 105'~0~;4 1 In the years that acrylonitrile polymer fibers have been commercially available from wet-spinning and dry-spinning processes, and even before, it has become recognized that it is desirable that the fibers be as free of w ids and micro-voids as possible for many reasons, among which are the better tensile and abrasion properties, the preferred aesthetics, and the higher apparent dyeability of the denser fibers free of voids. Accordingly, it is an object of the present invention to melt-spin acrylonitrile polymer fibers while substantially preventing the development of voids and micro-voids therein.
As previously mentioned, a single phase fusion melt of acrylonitrile polymer and water suitable for melt-spinning contains somewhere between`about 10~ and about 35~ water, depending on acrylonitrile polymer composition and other variables. In the melt-spinning process, the material being formed into fibers during passage through the spinnerette orifices, therefore, contains somewhére between about 10%
and about 35% water. Somewhere during the subsequent processing, whether immediately or rem~tely, this water must be evaporated to pro~uce the dry acrylonitrile polymer fibers one finds in the ~inish products, such as clothing, blankets, carpets, etc.
As used herein, "dry" fibers are those which contain about the equilibrium moisture regain they assume on exposure to ambient conditions or less moisture. Por acrylonitrile ~olymer fibers, ! 25 this means the dry fibers contain less than about 5% moisture re-gain. An important part of the present invention is the find-ing that the formation of nicro-voids in the fibers resulted from improper drying of the nascent fibers. When the nascent fibers are permitted to cool and partially or completely dry at m~derate or low temperatures, this improper drying led to .

105;~0~;4 1 to the formation of the voids and micro-void~. Proper drying to minimize or prevent this requires that the nascent fiber~
be prevented from losing water until they are dried at ele-vated temperature, i.e., above about 90C.
S One type of process sequence incorporating proper drying according to the present invention involves drying the nascent fibers, after leaving a hot, pressuri7ed, steam-containing pressurized solidification zone, may pa~s directly into and through a heated chamber wherein they are dried in an environment maintained at above about 100C., which heated chamber may contain air at about the same temperature and ; pressure at the steam in the solidification zone.
Another type of process sequence incorporating proper drying according to the present invention involves ! ~ 15 keepiaZg the nascent fibers wet even though they may be cooled to below about 90C. until such time as they are dried at .Z
elevated temperature, i.e., above about 90C. Illustrative of this process sequence, the nascent fibers, after leaving a hot pressurized solidification zone, are cooled in a water bath, and thereafter, are reheated while still wet in a drier operating to dry the fibers at above about 90C. In this process sequence, if the nascent fibers are crimped while still wet prior to the initial drying step, the crimp obtained can be very stable, resisting loss of crimpiness during tex-tile processing on cards, etc. and even during exposure to hot water, as in a dye-bath.
During tests related to this second type of process 8equence, a surprising phenomenon was observed. When the nas-cent fibers, after leaving the spinnerette, were cooled to room temperature, the fiber became white and opaque due to ' . .

105'~0~;4 1 formation of voids and micro-voids therein. When these white opaque fibers were heated on a hot plate at about 120C., they became transparent due to the redissolving of the water into the polymer with disappearance of the voids and micro-voids.
When these transparent fibers were cooled to room temperature immediately after becoming transparent, the white opaque appearance reappeared due to the water "precipitating~ out of the polymer to recreate voids and micro-voids. This pheno-menon can be repeated for several hot-cold cycles. However, once the fiber has lost enough water at elevated temperature to become dry, cooling the fiber still results in a transparent fiber free of voids and micro-voids.
To locate the proper conditions for preparing a single phase fusion melt consisting essentially of acrylo-~, - 15 nitrile and water for any specific acrylonitrile p~lymer, i a mixture of the acrylonitrile polymer and water is prepared and heated, under pressure, to a temperature sufficient to cause fusion of the polymer. If a single phase fusion melt

3 ~ is produced, the minimum temperature to cause fusion (tempera-~` ) 20 ture M) is noted. A more detailed discussion of how to pro-vide a single phase fusion melt is next given in the description of determination of phase diagram which follows and refers to Figure 2 of the accompanying drawings.
Determination of Phase Diagram ,, In the practice of this invention, it is necessary to first determine the phase diagram for the specific acryloni-trile polymer to be spun in order to obtain the required conditions for extrusion of a "single phase fusion melt" of the polymer. Referring to Figure 2, point A is first located, then lines ABF and ACG are located, after which the preferred ',.~,~
' -12-.. .. .
,~ .
r .~ .

iO5'~0~;4 1 portion ABC is determined to locate the conditions from which the improved shaped articles may be extruded.
To determine point A, a series of polymer samples i9 exposed to saturated steam in an autoclave for five minute~
each. Each sample is exposed to increasing temperatures. The melting point of the polymer in saturated steam i8 the mini-mum temperature where flow has occurred. The surface of melted polymer appears glassy and particles of polymer are strongly bonded together. This minimum temperature establishes the line DAE shown in Figure 2.
On~e the melting line DAE is known, the minimum water content necessary for fusion at that temperature is determined.
,~ This minimum water content and temperature is point A. At , this point all water is hydrogen-bonded to the acrylonitrile ~, 15 polymer and no free water as a second phase exists. A sample ; of polymer mixed with a known guantity of water is placed into .~.,:, , a steel cell equipped with a glass window. The cell is `' sealed to retain the pressure gene~rated by the test. The cell is heated in an oil bath so that the sample can be observed at all times. In separate tests, samples containing various watex-to-polymer ratios are placed in the cell and heated ~-~ to the temperature indicated by line DAE. When excess water i8 present, two phases are visible when the polymer melts.
Samples of progressively lower water contents are tested un-til a sample exhibiting only one phase is visible, establishing point A at that concentration. With further reduction in water-to-polymer ratio, melting will not occur at the tempera-ture established by line DAE.
To determine the phase fusion region, it is necessary to establish the lines ABF and ACG as shown in Figure 2. This ~,', ' :' .

~l~5~0~i4 .~
iB done by placing in the steel cell samples of polymer whose water content in one case contains approximately 5-10% more water than the concentration at point A. Line ABF is determined ` by locating the point which represents the temperature and ` S concentration at which the mixture of polymer and water having the lower amount of water melts into a single phase. Line " ACG is established by locating the point at which the two-phase mixture of polymer and water having the greater a unt of water become a single phase after passing through a two-phase liquid state. Since physical mixing i-s difficult to obtain in the sealed cell, this latter point may be time con-suming to obtain.
After locating point A and lines ABF and ACG, line BC
.; .
is drawn at a temperature about 30C. above the te~perature of ~-point A. Thus, the preferred portion ABC of the single phase fusion melt region is defined.
Generally, the single phase fusion melt compositions will be located somewhere in the region of about 10% to about 35~ water, with correspondingly, about 90% to about 65% acry-~;
lonitrile polymer. If the single phase fusion melt composition range for any specific acrylonitrile polymer water extends over a wide range of compositions having usefully low melting points (viz., below the polymer degradation temperature range), ~ it is preferred, in accordance with the present invention, to ', 25 - select a composition toward the side of such composition range having the lower amounts of water.
y Sometimes, the quantity of water can vary outside this range and still form a single phase fusion melt. For in-stance, more water may be used if there is added a third ; 30 material (such as a polymer soluble in the water; a hydrophilic ,.' : ,_; ~

105'~0~i4 polymer which, with the water, forms a melt, a finely dividet hydrophilic 1 solid; or a hydrophilic liquid) which binds up excess water leaving the acrylonitrile polymer as a single phase fusion melt.
Thi5 third material must not significantly interfere with the formation of a single phase fusion melt with the water. This third material may be compatible with the acrylonitrile polymer a~dthe products produced may be a uniform blend or may have ~3 the third material as a permanent inclusion therein. Thisthird material may be incompatible making the products readily ;, fibrillatable. This third material may be readily re vable, as by washing with water or organic liquid, to leave a porous structure. Such third materials include hygroscopic or water-`~ soluble polymers, such as polyvinyl alcohol, polyethylene glycol, polyacrylamide and derivatives thereof, polyacrylic acid, poly-vinyl pyrrolidone, polyelectrolytes, proteins, such as gelatin, ; 15 casein, and finely divided hygroscopic solids, such as silica gel, starch, aluminum chlorohydrate, alumina gel, diatomaceous earths, kaolin clays, and lecular sieves, and other water ~i binders, such as anhydrides, such as acetic anhydride, and in-organic salts, such as anhydrous sodium sulfate, calcium , 20 chloride, sodium phosphate, etc.
, In accordance with the present invention, a single `~ phase fusion melt of the acrylonitrile polymer and water is ex-truded, at a temperate (Tf) above the minimu~ fusion temperature (M) thereof but preferably not more than 30C. above such `i 25 temperature through a spinnérette directly into a pressurized solidification zone having certain pressure, temperature, and composition conditions maintained therein. The conditions in ::
the solidification zone which permit very high jet stretches are such that the composition profile across the cross-section of the nascent extrudate remains relatively flat as it moves 'i ' ~j' :
:` r l~S;~0~;4 ~ 1 away from the spinnerette face, that a relatively high con-`~ centration of melt assistant is retained in the nascent extrudate, and the temperature of the nascent extrudate is lowered to below the extrusion temperature Tf but not more than about 20C.
~s 5 below minimum fusion temperature M. By "the composition pro~
'.t file .... remains relatively flat~ is meant that the concentra-; t~on of acrylonitrile polymer near the surface of the nascent extrudate and the concentration of acrylonitrile polymer deep within the nascent extrudate are approximately the s~mP (e.g.
; 10 not more than about 10%, and preferably not more than about 5%, difference in polymer concentration) for any single cross-` section of the nascent extrudate. Of course, as the cross-section of the nascent extrudate moves away from the spinner-ette during spin draw-down in the solidification zone, the concentration of water therein may change, but at least 70%
~` of the concentration of water in the single phase fusion melt will be present. To obtain these extrudate conditions in the pressurized solidification zone, the ambient conditions therein are preferably controlled and maintained as follows. The absolute partial pressure p of water vapor therein is prefer-ably 56~ to 110%, and more preferably between 80% and 100%, of the absolute vapor pressure of water at the extrusion ` temperature Tf. The temperature T in the pressurized solidi-~`~` fication zone is at least equal to the saturation temperature '`` 25 of water at a vapor pressure equal to the partial pressure p in the solidification zone and may range upwardly to a temperature at which substantial decomposition of the nascent extrudate occurs, although it is preferred to maintain the temperature T near the lower end of the indicated range. The - 30 total pressure p in the solidification zone must be at least ';
~ -16-. , li, `~ lOS;~0~;4 1 e~jual to the partial pressure p but preferably should not exceed25 times said partial pressure p. Even higher total pressures may be used but such are not usually desired. The excess of the total pressure P over the partial pressure p, if any, com-S prises other fluids, such as air, nitrogen, sulfur dioxide, etc.
Preferably, the total pressure P i9 egual to or does not appre-ciably exceed the partial pressure p and very little, if any, other fluids are present. Use of the foregoing conditions within the solidification zone results in boundary control of the rate of evaporation of water from the nascent extrudate.
The term "boundary control" of evaporation means that the rate ;~ of evaporation of water from the surface of the nascent extrudate is equal to or less than the rate of diffusion of water from within the nascent extrudate to its surface, as a consequence s~ 15 of which, the composition across the cross-section of the ~ . .i nascent extrudate is relatively uniform while within the soli-;; dification zone.
While in said solidification zone, the nascent extru-date is given a spin draw-down or jet stretch at a stretch ratio .
; 20 of ~5 to 250, preferably 35 to 150. The linear speed through the spinnerette is computed by dividing the volume per unit time of melt being extruded by the total cross-sectional area ~; of all orifices in the spinnerette. The jet stretch or spin draw-down ratio is the linear speed of the shaped articles as x they pass a pulling device (such as driven godet or thread-advancing rolls wherein the peripheral speed of such pulling rolls is taken as the linear speed of the shaped articles) divided by the linear speed through the spinnerette. Outside of the temperature, pressure, and composition conditions pre-viously specified for the solidification zone environment, ' .
., ,~,i .

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~' lOS'~O~i~
such extremely high jet stretches are not obtained. While ~' the spin draw-down occurring in the solidification zone be accomplished in a single stage, it is also possible to achieve the total spin draw-down in two stages, namely a first stage at a stretch ratio of 5 to 150 followed by a second stage at a stretch ratio of about 1.1 to 30, or even more, to produce the total spin draw-down within the solidi-'~ fication zone.
Since filaments made by the process of this inven-tion do not require any secondary stretching or after drawing, in contradistinction to other melt-spinning processes for '- organic filaments and to dry-spinning or wet-spinning processes ~- for making acrylonitrile polymer filaments, the filaments issuing from the solidification zone may be collected directly ~
or they may be relaxed in a free-to-shrink condition by any ~-of the known procedures for so doing, such as by passing f'" them over a heated feed roll to a slower moving thread-advanc-ing roll or by passing them on a conveyor belt through an atmosphere of saturated steam under pressure.
For a further and more detailed explanation of this invention and additional advantages thereof, reference should ,~.' , . . .
be made to the sub~o m ed descrlptlon and examples of pre-~- ferred embodiments taken in conjunction with the accompany drawings wherein:
Figure 1 is a schematic drawing illustrating the process of this invention as applied to making continuous ~7t~,., filaments, and Figure 2 is a phase diagram of the acrylonitrile polymer-water system utilized in Example 1.
In Figure 1, there is shown generally an extruder 11 provided with a spinnerette 12 at its outlet and a pressurized :,. :

~' .. . . .
i.. .

~ ~.os~0~4 1 solidification chaS~ber 13 positioned to receive extrudate issuing from spinnerette 12. As ~llustrated, extruder 11 is hown as a piston extuder wherein cylinder 15 is provided with a closely fitted piston 16 moveable by means, not shown, S to force the contents of cylinder 15 through spinnerette 12 directly into pressurized solidification chamber 13. With ~ cylinder 15, single phase fusion melt 17 i5 heated to the ; proper temperature by heating means, not shown, such as ~team jackets or electrical heaters in the walls of cylinder 15.
Cylinder 15 is also provided with a thermDmeter 18 and a ''t,': pressure gauge 19 for monitoring the temperature and pressurewithin extruder 11 during melt-spinning. While extruder 11 is shown as a piston extruder, other types of extruders, such as screw extruders, gear pumps, etc., as are known for melt-spinning other organic polymers, may be used.
At the outlet of the extruder 11, a spinnerette 12 is mounted. Spinnerette 12 may be provided with circular or : . -non-circular orifices for spinning filaments or fibers or with slots for spinning ribbons or films. The extrudate ~- 2~ -:; issuing from spinnerette 12, here shown as filaments 21, goes directly into pressurized solidification chaSmber 13 from ~` which it is drawn, under tension, by rapidly rotating godet :;. -: .
or thread-advancing rolls 22 which produce the extremely high jet stretches of this process. Pressurized solidification chamber 13 is provided with an inlet 24 through which fluid under pressure and at elevated temperature can be admitted, an outlet 25 from which liquid can be withdrawn as necessary, and a thermometer 26 and a pressure gauge 27 for m~nitoring the temperature and pressure within chamber 13. Chamber 13 is also provided at its outlet with a pressure seal 28, illus-.
~ :`

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., .

1~)5'~ 4 ; 1 trated herein as a long thin slot only slightly lar~er than the diameter of the bundle of filaments 21 passing there-through. Other pressure sealing devices may be used, illustrative of which are those described in United States Patents 2,708,843; 2,920,934; 2,932,183; 3,012,427; 3,027,740;
3,037,369; 3,046,773' 3,066,006; 3,083,073; 3118,154;
3,126,724; 3,137,151; and 3,152,379, all of which relate generally to continuous relaxation of filaments of acryloni-~i trile polymers under superatmospheric steam pressure at ele-14 vated temperatures.
,; From godet or thread-advancing rolls 22, which may ;~ optionally be located within pressurized chamber 13 or out-i side thereof as illustrated, filaments 21 may be wound up on yarn package 30 by a suitable winder, not shown, or pre-ferably, filaments 21 may be relaxed in steam chamber 33 wherein steam under superatmospheric pressure and at elevated ; temperature is permitted to contact filaments 21 in a relaæ d free-to-shrink condition as described in the United States Patents listed in the preceding paragraph. In steam chamber 33, filaments 21 are fed through inlet pressure seal, not shown, by inlet rolls 35 onto a conveyor belt 36 where they ~` are conveyed through steam chamber 33 to exit rolls 37 which feed the relaxed filaments through exit pressure seal, not shown, out of steam chamber 33 to be wound onto yarn package 1 ` 25 40 by a suitable winder, not shown.
It is well known to incorporate various additives ~' i ; in shaped articles by including such additives in the ~ liquefied polymer prior to extrusion. These additives are i normally utilized to modify the properties of the shaped articles so produced or to improve spinnability. Such addi-~' ; -20-~' ,. , ` 105'~0~4 1 tives may be stabilizers, such as light stabilizers, heat stabilizers, antioxidants, gas-phase stabilizers, ultra-violet stabilizers, etc., pigments, dyes, brighteners, whiteners, flame-retardants, anti-bacterial agents, delusterants, luster enhancers, antistatic agents, dye-site-containing materials, porosity promoters, fibrillation enhancers, soil retardants, ~' fillers, reinforcing agents, microencapsulated materials, latexes, etc. In the practice of the present invention, minor amounts (e.g. up to about 25%) of such materials may be incorporated in the single phase fusion melt-prior to melt-spinning providing (a) they have particle sizes small enough to permit them to pass freely through the extrusion orifices or (bj they have melting points near or below the minimum ~- fusion temperature (M) of the polymer in the presence of melt . 15 assistant or are soluble in the fusion melt`. Among such additives are such polymers as polyvinyl alcohol, polyvinyl chloride, polyacrylamide, polyacrylic acid, polyalkylene glycol ether, etc. These polymers may have molecular weights ~ from about 1,000 to above 100,000. Other additives which t may be utilized include haloalkyl phosphate flame retardants, titanium dioxide pigments, cationic dyes, anionic dyes, dis-perse dyes, silica, aliphatic or aromatic halogen compounds, organic phosphorous compounds, antimony oxides, etc. as will be readily apparent. These additives normally do not affect the location of the single phase fusion melt region of the phase diagram: however, if any such are utilized, the phase diagram should be redetermined with them present to be certain of the boundaries of this region to be used for the melt-spinning process.
~; 30 Optionally, the process sequencé described above ~,' .

..
, ~' .

0~
1 may include additional steps, such as secondary stretching or after drawing, ~rimping, restretching, washing, treating with antistatic agents, anti-soiling agents, fire-retardants, adhesion promoters, lubricants, etc., dyeing, post-treating S chemically, as for cross-linking, stample cutting, and the like to produce such product modifications as these conventional steps are known to produce. Some of such additional steps may be performed within the same physical structure as the solidification zone, if desired, although under ambient con-,i~
ditions outside those required for the solidification zone.
Illustrative of such additional steps performable within the same physical structure as contains the solidification ~-~ zone may be mentioned secondary stretching or after drawing, -~f~ relaxing, restretching, pressure dyeing, drying, etc. Usually but not necessarily, such additional steps would be performed ~:.
under elevated pressure.
Also, a plurality of single phase fusion melts may be extruded concurrently through the spinnerette to make composite or multi-component shaped articles, such as side-2~ -by-side, sheathcore, or random, bi-, tri-, or multi-component fibers using known apparatus for such purpose. The single phase fusion melts used for this purpose may be of the same or similar polymer, e.g. all acrylonitrile polymers, or may be of different polymers. The single phase fusion melts , 25 may be incompatible to form fibers which easily split apart or they may be compati~ble to remain permanently adhered to-gether in the Shaped articles. Additionally, hollow fibers can be prepared by extruding a sheath of single phase fusion melt about a gaseous core. In all these alternative embodi-ments, the extrusion takes place directly into a solidification :
~' , lOS;~0~4 1 zone having the defined temperature, pressure, and compo-- sition conditions.
This invention and additional advantages thereof will be further understood by reference to the following illustrative examples which illustrate preferred embodiments thereof. All parts and percentages are by weight unless other-wise indicated.
Example 1 ; This example first illustrates a method for determin-ing a phase diagram to locate the single phase fusion melt region thereof. The example then illustrates melt-spinning - - an acrylonitrile polymer in accordance with the present invention and, for comparison, in accordance with a melt-spinning process outside the scope of the present invention.
~5 The phase diagram, illustrated in Figure 2, for an acrylonitrile polymer-water system wherein the acrylonitrile .. . .
polymer was a polymer of 89.3% acrylonitrile and 10.7% methyl methacrylate having a molecular weight of approximately 58,000 was determined by the following series of tests.
A 1 gram bone dry sample of the acrylonitrile ` polymer was placed in an aluminum dish and autoclaved in saturated steam at 135C. for 5 minutes. $he sample was removed and cooled. The polymer was readily crumbled into a powder, had a dull appearance and microscopically no fused pa~ticles were observed. The procedure was repeated at 140C.
and 145C. with substantially the same result. The procedure was again repeated at 150C. This time the polymer would not crumble, appeared completely fused, and had a shiny surface.
Under the microscope this sample had a continuous surface and no individual particles were observed. The p~rocedure was ~' ~ -23-.~.
$ ~ t :;~
5'~0~4 :`

1 repeated again at 155C., 160C., and 165C. with no apparent change from the 150C~ sample except for a sonewhat increased yellowness in the polymer. ~ine DAE of Figure 2 was there-fore established at 150C.
A polymer/water mixture was prepared consisting of 40% polymer and 60% water. m e mixture was placed into a sealed cell, as previously described, and heated in an oil bath to 150C. for 10 minutes. The sample was observed through the window as two phases. The sample was cooled and removed from the cell. The two phases were found to be fused polymer and free water. This procedure was repeated with ' mixtures of polymer and water consisting of 60%, 70%,75%,and 80% polymer, the balance being water. Two phases were ob-served in each case. When the procedure was again repeated using a mixture of 85% polymer and 15% water only one phase could be observed at 150C., andA after cooling and re val of the sample, only partial fusion of the polymer was ob-served in spite of the fact that only one phase was observed.
This test was repeated again using a polymer sample con-`` ` 20 taining 82~ polymer and 18% water. When heated to 150C. only i one phase was observed. After cooling and examination, it was found that the polymer had undergone complete fusion or ~ melting. Point A of Figure 2 was now established to be at 9 about 18% water and 82% polymer at 150C. There may, of course, be a small range of perhaps 17% to 19% water at 150C.
designating point A. In no case, however, is it as low as 15%
or as high as 20% water for this particular polymer at 150C.
Point A, the minimum single phase fusion melt melting point, having been established, it was next necessary ~ 30 to establish phase boundary lines ABF and ACG of Figure 2.
', :
.

;,~, ,., l~S;~ i4 1 Sufficient water was added to bone dry polymer to " form a mixture of 88% polymer and 12~ water. When placed inthe sealed cell and heated to 150C. no fusion or phase separation waJ observed. In separate tests, the sample was heated to 155C., 160C , 165C., and 170C. There was an increasing tendency of the sample to partially fuse with increasing tempera-ture. Complete fusion or melting was not observed, however, ~; until the sample was heated to 170C. In all cases only one phase was observed. This series of tests locate a point on the line ABF at 12% water and 88% polymer at 170C. Additional points on the line ABF of Figure 2 can be determined in the same manner using other compositions, such as 85% polymer, Pi~ ' ' 15S water The procedure was repeated using a polymer mixture of 75% polymer and 25% water. At 150C. two phases are ob-served. In spearate tests the sample was heated to 155C., 160C., 165C., 170C., 175C., and 180C. In all cases, two ~ ~ phases were observed. In eaah case the polymer was fused or ;~ melted and in each case a layer of excess free water was noted. The procedure was repeated by heating a sample to 185C. As the polymer fused, only one phase was observed and no excess or free water could be detected. Upon cooling and examination, the sample was found to be completely fused or melted and no water was detected in the sample cell. A point on the line ACG was therefore located at 25% water and 75%
polymer at 185C. Additional points on the line ACG of Figure 2 can be determined in the same manner using other com-positions, such as 22% water and 78% polymer.
Having determined the phase diagram for mixtures of this polymer with water, as shown in Figure 2, the following J

i:
S;~
1 experimental melt-spinnings were made, using apparatu~ sub-~ stantially as schematically illustrated in Figure 1.
j~ To 15 grams of dry polymer wa~ added 3.3 grams of water thus providing an acrylonitrile polymer-water mixture ' S containing 18% water. The mixture was sealed in a jar and I mixed on a roll mill fox 30 minutes to ensure complete blending. The blended mixture was then placed into a picton extruder 11 equipped with a spinnerette 12 having a single orifice of 16 mils diameter and 128 mils orifice length.
The orifice opening was temporarily sealed to prevent any premature loss of moisture during start-up. The extruder 11 and spinnerette 12 were heated to 154C. under sufficient ., .
pressure to prevent water vaporization. The spinnerette ~;~ orifice was unsealed and 800 psi of force was applied by ~` 15 piston 16 in order to extrude a fi-lament. In a first run, ; for comparison purposes, pressurized solidification chamber 13 was left open to the atmosphere so the filaments 21 .
extruded into a region of ambient temperature and pressure.
Pressure on the piston 16 was adjusted so that the flow rate of single phase fusion melt through the spinnerette orifice as 0.446 meters per minute. The resulting filaments were taken up directly on yarn package 30 (without use of godet ~: rolls 22) on a rotating winder. After starting up, the . speed of the rotating winder was gradually increased until a maximum, determined by continuing filament breakage, was reached. The maximum take-up speed achieved was 1.16 meters per minute for spin draw-down ratio or jet stretch ratio of 1.16/0.446 or 2.6 (260% jet stretch).
In a second run, in accordance with the pxesent ~ 30 inventi~n,pressurized solidification chamber 13 was sealed j~ !

,~, t~

0~4 1 and saturated steam was introduced through inlet 24 until a pressure of 38 psi gauge, corresponding to a temperature of 140C., was reached. This temperature was about 14C., be-low the single phase fusion melt temperature in the extruder and about 10C., below the minimum melting temperature of 150C. for this melt. Under these conditions, which were otherwise a duplication of the first run, the maximum take-up speed achieved was 3a meters per minute for a spin draw-down ratio or jet stretch ratio of 85 t8,500~ jet stretch).
A quantity of fiber so produced, having a denier per filament , of 15, was collected and exposed to saturated steam under pressure at 127C., in a relaxed free-to-shrink condition in an autoclave. The denier increased to 19.5, indicating about 23% shrinkage was achieved. Physical properties of this re-laxed fiber were: -Straight Tenacity 3.5 grams/denier Straight Elongation 43.0%
Loop Tenacity 1.98 grams/denier Loop Elongation 19.0%
`~ 20 Initial Modulus 58.0 grams/denier Example 2 This example illustrates this invention applied to melt-spinning acrylonitrile polymer filaments of finer denier than Example 1.
The second run of Example 1 was repeated except that s the flow rate of single phase fusion melt through the spin-nerette orifice was 0.792 meters per minute and the pressure of the saturated steam in solidification chamber 13 was in-creased to 49 psi gauge, correspond~ng to a temperature of 147C. Th~s temperature was was about 7C. below temperature ~` -27-,~

r; ' r 10~;~0~4 1 in the extruder and about 3C. below the minimNm single phase fuqion melt melting temperature of 150C for this composition.
At these conditions, the maximum take-up speed achieved was 89 meters per minute for a spin draw-down ratio or jet stretch S of 112 (11,200% jet stretch). The denier of the filaments obtained was 6.4, thus illustrating that a larger range of ~ deniers is possible with a single size of spinnerette orifice.
',J In the practice of this invention, using different sizes of spinnerette orifices, acrylonitrile polymer fibers may be ,- 10 prepared having deniers between 0.5 and 80, or even higher if desired.
Comparative Example A
$he first run of Example 1 was repeated ex~ept that a strip heater was installed along the full length of solidi-- fication chamber 13. With chamber 13 vented to the atmosphere, and the strip heater set to provide an air temperature in the chamber 13 of about 150C., closely simulating the conditions utilized in conventional melt-spinning of other organic fibers to obtain high spin draw-down ratios or high jet stretch ratios, a filament-like material was obtained which appeared to be completely filled with bubbles, resembling an elongated foam.
r, The maximum jet stretch ratio achieved was no higher than the , first run of Example 1 (no heat, no steam under pressure) and frequently was less due to breakage of this highly non-uniform material. This demonstrated that elevated temperature without r~. the environment of melt assistant under pressure was not cap-able of providing the extremely high jet stretches of the pre-~ent invention, but, instead, produces a degraded product.
Comparative Example B
The second run of Example 1 was repeated except that .j ".

1~5;~0~4 1 nitrogen under ambient temperature was used, instead of steam, to pressurize chamber 13. As the pressure of nitrogen was in-creased to 56 psi gauge, with the linear velocity of single phase fu~ion melt through the spinnerette orifice being 0.634 meters per minute, the maximum take-up speed for the uniform filaments produced which could be achieved was 2.9 meters per minute for a spin draw-down or jet stretch ratio of 4.6 ~460 jet stretch), which ratio was slightly higher than the jet - stretch ratio achieved at ambient temperature and pressure (the first run of Example 1), but nowhere the extremely high stretch ratios achieved by the present invention (the second .~ .
run of Example 1 and Example 2). This demonstrated that ~:, elevated pressure without the environment of melt assistant at elevated temperature was not capable of providing the $ 15 extremely high jet stretch ratios of the present invention.
Example 3 Example B was repeated uslng the strip heater de-scribed in Example A to heat the pressurized nitrogen at 56 psi ;A :: gauge in chamber 13 to various temperatures. As the tempera-ture of the nitrogen environment was raised to 140C., the maximum spin draw-down ratio achieved was raised from about

4.6 to about 10.1 (1,010% jet stretch) without formation of the bubbles of Example A. Continued heating to 150C. did ~ ~.
not result in any increase in spin draw-down ratio achievable.
Heating to above 150C. caused filament melting resulting in fiber discontinuity and breakage. This demonstrated that elevated temperature and elevated temperature without the environment of melt assistant, while producing some improve-ment in spin draw-down ratio, still was not capable of providing the extremely high jet stretch ratios achievable lOS;~0~i4 } 1 by the present invention.
~ Comparati~e Example C
!~ To 15 grams of dry polymer of 89.3~ acrylonitrile and 10.7% methyl methacrylate having a nolecular weight of approximately 58,000 was added 3.3 grams of water, thus pro-viding an acrylonitrile polymer-water mixture containing 18 water. The mixture was sealed in a jar and mixea on a roll mill for 30 minutes to ensure complete blending. The blended mixture was then placed in a piston extruder provided .~. .
at the outlet thereof with a spinnerette having a single ~.i orifice of 16 mils diameter and 128 mils orifice length.
The orifice opening was temporarily closed to prevent pre-mature loss of moisture during start-up. The extruder and ,.
~ spinnerette were heated to 154C. under sufficient pressure ,~
to prevent water vaporization, thereby converting the acrylo-..:
nitrile polymer-water mixture to a single phase fusion melt.
The spinnerette orifice was unsealed and 800 psi of force was applied by the piston of the piston extruder to extrude .~ ~
a filament through the orifice. The pressure on the piston ~`~- 20 was then adjusted so the flow of single phase fusion melt - through the spinnerette orifice was 0.446 meters per minute.
The resulting filaments, after passage through and cooling in ambient air from the spinnerette to a yarn winder, were collected on a yarn package at a jet stretch of slightly below the maximum attainable jet stretch of slight~y below the maximum attainable jet stretch ratio of about 2.6 and allowed to dry at room temperature. These filaments were opaque, white, and had a high gloss. On microscopic ex-amination they were found to contain many voids and micro--voids.

:

:, , 0~4 . .
1 ~bmparati~e EXample D
The procedure of Comparative Example C was repeated except that the nascent filaments extruding through the spinnerette orifice entered directly into a pressurized S chamber containing steam at a pressure of 38 psi gauge and a temperature of 140C. The resulting filaments, after passage through the steam pressure zone, were collected on a yarn package on a yarn winder at a jet stretch of slightly below ;~ the maximum attainable jet stretch ratio of about 8S. These - 10 filaments were then relaxed in a free-to-shrink condition in ; an autoclave in steam under pressure at 127C. These fila-ments were also opaque, white, and had a high gloss. On microscopic examination they were found to contain many voids ~micro-voids. However, they did have physical properties which were acceptable for use as textile fibers.
Comparati~e Example E
The filaments of Comparative Example C, after drying .j~ .
at ambient conditions, were heated in an oven in an attempt to make the voids and micro-voids disappear. There was no change in appearance noted. Relaxation in steam under pressure at 127C. after the heating in the oven also did not change the , appearance of these filaments.
~; Example 4 Repeating the procedure of Comparative Example D
except that the filaments, directly as they leave the steam-pressurized chamber, pass through a second pressurized chamber containing air or nitrogen at 38 psi gauge and 140C. where they are dried produces, in accordance with this invention, filaments which are free of voids and micro-voids, are trans-parent, and have a luster similar to commercially available q~ ' .

., ~s~
E
.;.

lOS;~0~4 ^~ 1 acrylic fibers. This illustrates drying the freshly spun acrylonitrile polymer while still hot from spinning before permitting cooling to below about 90C.
Example 5 In accordance with this example, the procedure of Comparative Example B is modified to produce fibers possessing - a crimp which is stable to textile processing. Within the pressurized chamber containing steam at a pressure of 38 psi gauge and a temperature of 140C., there are disposed a first set of thread-advancing rolls which serve to stretch the nascent filaments emerging from the spinnerette orifices to impart a jet stretch ratio of about 75 and a second set of thread-advancing rolls rotating at a lower speed which serve to relax the filaments. From the second set of thread--advancing rolls, ~he filaments are fed to a stuffing-box crimper ~hich serves as a pressure seal in a wall of the pressurized chamber. Within the stuffing box of the crimper, the crimped fibers are quenched with cold water. After exiting from the crimper, the filaments are kept wet until ^ ~ 20 they are dried in an oven at 110C. Filaments so produced, in accordance with this invention, are transparent, free of voids and micro-voids, and have good luster.
Example 6 This example illustrates melt-spinning acrylonitrile polymer filaments according to the process of this invention using other melt assistants.
Using the same apparatus as in Examples 1 and 2, the acrylonitrile polymer of Example 1 can be spun into fila-` ments under the following conditions:
A. A single phase fusion melt of acrylonitrile : .:

. . .

0~4 1 polymer a~d methanol (about 75~ acrylonitrile polymer and about ~s 25% methanol) at 155C. can be extruded through the spinnerette'~ orifice at a flow rate of 0.792 meters per minute directly intoa solidification zone containing an atmosphere of methanol vapor at a temperature of 148C. and a pressure of 164 psi gauge to ~ yield filaments to which a spin draw-down ratio or jet stretch 'r~ of 100 times can be imparted.
B. A single phase fusion melt of acrylonitrile polymer and acetonitrile (about 80% acrylonitrile polymer and about 20%
acetonitrile) at 155C. can be extruded at 0.792 meters per minute directly into a solidification zone containing an atmos-phere of acetonitrile vapor at a temperature of 141C. and a pressure of 66 psi gauge to yield filaments spin drawable to at least 100 times.
C. A single phase fusion melt of acrylonitrile polymer ~, and dilute aqueous sodium thiocyanate solution (about 75% acryloni-trile polymer, about 19% water, and about 6% sodium thiocyanate ~ - such aqueous sodium thiocyanate solution being denominated "di-# lute" because it is of a concentration which will not normally dissolve the acrylonitrile polymer and is, in fact, sufficiently dilute to be used as a coagulant in wet-spinning acrylonitrile polymers) at 141C. can be extruded at 0.792 meters per minute ~- . directly into a solidification zone containing steam at 140C.and 38 psi gauge to yield filaments jet stretchable at least 100 times.
D. A single phase fusion melt of acrylonitrile polymer ~ and acetic acid (about 77% acrylonitrile polymer and about 23%
'~ acetic acid) at 155C can be extruded at 0.792 meters per minute directly into an atmosphere of acetic acid vapor at a temperature of 145C. and a pressure of 17 psi gauge to yield filaments spin drawable at least 100 times.
~., "

Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for preparing an acrylonitrile polymer fiber which comprises spinning a homogeneous single phase fusion melt of 90-65% acryloni-trile polymer and 10-35% water at a temperature ranging from minimum melt temperature M to below the temperature of significant polymer degradation to produce an extrudate, cooling the extrudate in a steam-pressurized zone maintained at a steam pressure such as to enable the extrudate to cool to a temperature below said minimum melt temperature M but not more than 20°C,below said minimum melt temperature M, and stretching said extrudate at a stretch ratio of 25-250 while said extrudate is in said steam-pressurized zone.

2. A process as defined in claim 1 additionally comprising the step of relaxing the thus-drawn extrudate in a free-to-shrink condition.

3. A process as defined in claim 1 for melt-spinning of shaped articles of acrylo-nitrile polymer wherein the polymer is prepared as a single phase fusion melt consisting essentially of acrylonitrile and water at a temperature Tf which is above the single phase fusion melt melting tempera-ture M and also above the boiling point at atmospheric pressure of water and the fusion melt is extruded through a spinnerette to form shaped articles characterized by extruding the shaped article directly into a pressurized solidification zone wherein the following conditions are maintained: (a) the partial pressure of water vapor is between 56% and 100% of the vapor pressure of water at temperature Tf; (b) the temperature T is at least equal to the saturation temperature of water at a vapor pressure equal to said partial pressure p; and (c) the total pressure P is at least equal to said partial pressure p; and drawing the nascent extrudate at a stretch ratio of 25 to 250 in the pressure solidification zone.

4. A process as claimed in claim 1, 2 or 3 wherein the fiber is dried at a temperature above 90°C and loss of water from the freshly melt-spun fiber at any temperature below 90°C is substantially prevented until drying is completed.

5. A process as claimed in claim 1, 2 or 3 wherein the acrylonitrile polymer is an acrylonitrile-methyl methacrylate copolymer.

6. A process as claimed in claim 1, 2 or 3 wherein the acrylo-nitrile polymer is a copolymer of about 89.3% acrylonitrile and about 10.7%
methyl methacrylate.