Classifications

• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
  • D01D4/00—Spinnerette packs; Cleaning thereof
  • D01D4/02—Spinnerettes

Definitions

• This invention relates to a process for forming fibers, and fibers formed by the process. More particularly, this invention relates to such a process in which said fiber is formed by spinning a melt or solution of a polymer through a capillary spinneret having a length/diameter (L/D) ratio equal to or greater than about 60:1, and fibers formed by such method.
• L/D length/diameter
• Prior Art Melt and solution methods of spinning fibers are known.
• PAN has been spun conventionally using either wet spinning (e.g., 9.5% PAN in sodium thiocyanate-water (50:50) spun into 10% sodium thiocyanate in water at -2°C for coagulation) or dry spinning (e.g., 30% PAN in diethylformamide spun at 103oC).
• Typical properties of the resultant fibers are 2.4-3.7 g/denier tenacity and 42-53 g/denier tensile molecules. See Table 1 on page 155 of S.S. Chari et al., Fibre Science and Technology, Vol. 15, pp. 153-60
• Patent 4,344,908 to Smith et al. (1982) concerned primarily with polyethylene fibers. Also concerned primarily with polyethylene fibers is U.S. Patent
• the reference indicates that the earlier systems employ 10-20%, 25-40% and 45-55% polymer concentrations, respectively, and that they differ in the manner in which low molecular weight materials (solvents such as water) are removed.
• the reference also indicates some earlier systems to be restricted in spinneret hole size, attenuation permitted or required, maximum production speed and attainable fiber properties.
• Phase Separation process described in Zwick et al. employs a polymer content of 10-25% (broadly 5-25% in the Patent which covers other polymers as well) dissolved at high temperatures in a one or two-component solvent (low molecular weight component) system that phase separates on cooling.
• This phase separation took the form of polymer gellation and solidification of the solvent (or one of its components), although the latter is indicated in the patent to be optional.
• the solution was extruded through apertures at the high temperature through unheated air and wound up at high speeds hundreds or thousands of times greater than the linear velocity of the polymer solution through the aperture. Thereafter the fibers were extracted to remove the occluded or exterior solvent phase, dried and stretched.
• An earlier, more general description of Phase Separation Spinning is contained in Zwick, Applied Polymer Symposia, no. 6, pp. 109-49 (1967).
• U.S. Patent Nos. 4,599,267 and 4,440,711 describe a process for preparing fibers composed of a linear ultrahigh molecular weight polyvinyl alcohol.
• Polyester and polyamide fibers and processes for forming such fibers are known.
• the preparation and properties of nylon 6 and nylon 66 fibers are described in "Man Made Fibers, Science and Technology," Vol. 2. H. F. Mark et al., Eds., Interscience, New York, 1968.
• Polyester Fibers and Spinning Processes are described in Vol. 3 of the same work.
• spinneretes it is said, "The capillary diameters ususally range from 0.2 to 0.3 mm and their height ranges from 1 to 3 times the diameter.” From a rheological point of view, the spinneretes must be properly considered as holes in a plate" p. 258, lines 1-4, "Man Made Fibers Science and Technology," Vol. 2, H. F.
• the length of the spinning aperature in the flow direction should normally be at least about 10 times the diameter of the aperature, or other similar major axis, preferably at least 15 times and more preferably at least 20 times the diameter, or other similar major axis.
• L/D (length/diameter) ratios of about 20/1 for the spinneret were within the bounds of prior art. See for example, "Man Made Fibers, Science and Technology Vol 1, p. 39, Interscience Publishers, New York, 1967.
• This invention relates to an improved process for forming fibers of the type in which a melt or solution of a polymeric material is spun through a spinneret, the improvement comprising a capillary spinneret having an
• L/D ratio greater than about 25:1.
• L/D ratio is the ratio of the length of the spinneret to the diameter of the orifice of the spinneret. It will be understood that the constant or substantially constant diameter section of the orifice may be preceeded by a tapered inlet or included angle between about 3o and 150o. The L/D ratio applies to that section of the spinneret having a substantially constant diameter.
• L/D ratios greater than about 25:1 are employed, high tenacity, high modulus fibers of improved uniformity and cylindricity may be prepared. Furthermore, the tenacity and modulus of such yarns are improved and are less sensitive to spinning throughout than if the yarns are prepared with dies of lesser L/D.
• the present invention includes one essential step of spinning a "fiber spinning composition" through at least one capillary spinneret having a position extending from the orfice of substantially constant cross-section and which has an L/D ratio greater than about 25:1.
• L/D ratio of the spinneret it has been discovered that a relationship between L/D ratio of the spinneret and the properties of the fibers exists. More particularly, it has been discovered that when capillary spinnerets with L/D ratios greater than about 25:1 are employed, the uniformity of the physical parameters, such as modulus, tenacity, of the fiber are improved.
• the L/D ratio of the spinnerets used in the practice of this invention is greater than about 25:1.
• the upper limit of the L/D ratio is not critical and can vary widely depending only on such factors as the desired denier of the fiber and the practical limitation, space, and the like on the length of the fiber.
• the L/D ratio of the spinneret is equal to or greater than about 60:1, and in the particularly preferred embodiments of the invention the L/D ratio of the capillary spinneret is equal to or greater than about 70:1.
• most preferred are those in which the L/D ratio of the spinneret is equal to or greater than about 80:11, with a ratio equal to or greater than about 100:1 being the ratio of choice.
• the soinneret is of "substantially constant cross- section", As psed herein, "substantially constant means over the length of the spinneret.
• the cross- section of the spinneret along its entire length does not vary more than about 10%, and in the most preferred embodiments of the invention, the cross-section does not vary more than about 5%.
• Preferred spinnerets for use in the practice of this invention are “capillary spinnerets".
• capillary spinnerets are spinnerets in which the geometric shape of the spinneret is substantially constant along the length of the spinneret. Thus, if the cross-section of the spinneret is circular at its entry end, it is circular at its exit end. Similarly, if the cross-section is rectangular or other shape at the entry end, the exit cross-section is a rectangle or other shape of the same relative proportions.
• a “fiber spinning composition” is used.
• a “fiber spinning composition” is a melt or solution of a polymer of fiber forming molecular weight.
• the nature of the spinning composition may vary widely.
• the spinning composition may be a melt, of a polymer or other material used in the formation of the fiber, and may be spun using conventional techniques as for example those melt spinning techniques described in "Man Made Fibers Science and Technology” Vol. 1-3, H. F. Mark et al., Interscience New York, 1968 and "Encyclopedia of Polymer Science and Technology," Vol. 8.
• the fiber spinning composition may be a solution of the polymer and other material used in the formation of the fiber, which may be spun by using conventional solution spinning techniques, as for example those described in U.S. Patent Nos. 2,967,085; 2,716,586; 2,558,730; 3,147,322; 3,047,356; 3,536,219; 3,048,465; British Patent Nos. 985,729 and 1,100,497; and in the article by M. E. Epstein and A.J. Rosenthal, Textile res. J. 36,813 (1966).
• fiber spinning compositions are solutions of natural or synthetic polymers, and solution spinning techniques are employed, especially those described in U.S. Patent No. 4,413,110; 4,440,711, 4,551,299 and 4,599,267.
• the fibers are spun from melts or solutions of polymers of fiber forming molecular weight.
• the nature of the polymer can vary widely, and any polymer known for use in forming fibers may be used.
• the polymer may be any of a variety of conventional thermoplastics used in fiber production which are of fiber forming molecular weight. The meaning of this term is well known in the art.
• a fiber forming molecular weight generally means a number average molecular weight of at least about 10,000.
• ⁇ ⁇ - unsaturated monomers such as polyethylene, polyacrylonitrile and polyvinyl alcohol as fiber forming molecular weight is usually a number average molecular weight of at least about 2,000, and in the case of polyesters such as polyethylene terephthalate a fiber forming molecular weight is usually a number of at least about 10,000.
• Any polymer that can be spun into a fiber can be used in the process of this invention.
• Illustrative of polymers which may be utilized in the process of this invention are synthetic linear polycarbonamides characterized by the presence of recurring carbonamide groups as an integral part of the polymer chain which are separated from one another by at least two carbon atoms.
• Polyamides of this type include polymers, generally known in the art as nylons, obtained from diamines and dibasic acids having the recurring unit represented by the general formula:
• R is an alkylene group of at least two carbon atoms, preferably from about 2 to about 10; and R 1 is selected from R and phenyl groups.
• copolyamides and terpolyamides obtained by known methods, as for example, by condensation of hexamethy- lene diamine and a mixture of dibasic acids consisting of terephthalic acids and derivatives thereof, as for example, lactams.
• Polyamides of the above description are well known in the art and include, for example, the copolyamide of
• nylon 66 poly(4-aminobutyric acid) (nylon 4), poly(7- aminoheptanoic acid) (nylon 7), poly(8-aminooctanoic acid) (nylon 8), poly(6-aminohexanoic acid) (nylon 6), poly(hexamethylene sebacamide) (nylon 6,10), poly(hepta- methylene pimelamide) (nylon 7,7), poly(octamethylene suberamide) (nylon 8,8), poly(hexamethylene sebacamide)
• nylon 6,10 poly(nonamethylene azelamide) (nylon 9,9), poly(decamethylene azelamide) (nylon 10,9), poly(deca- methylene sebacamide (nylon 10,10), poly [bis ( 4-amino- cyclohexyl)methane-1,10-decanedicarboxamide] ( (Oiana)
• polyhexamethylene isophthalamide polyhexamethylene terephthalamide
• poly(9-aminononanoic acid) nylon 9
• polycaproamide polycaproamide
• the polyamide for use in the most preferred embodiments of this invention is polycapralactam which is commercially available from Allied Corporation under the tradename
• polymers which may be employed in the process of this invention are linear polyesters.
• the type of polyester is not critical and the particular polyester chosen for use in any particular situation will depend essentially on the physical properties and features, i.e., tensile strength, modulus and the like, desired in the final fiber.
• a multiplicity of linear thermoplastic polyesters having wide variations in physical properties are suitable for use in the process of this invention.
• polyester chosen for use can be a homo-polyester or a co-polyester, or mixtures thereof as desired.
• Polyesters are normally prepared by the condensation of an organic dicarboxylic acid and an organic diol, and, therefore, illustrative examples of useful polyesters will. be described hereinbelow in terms of these diol and dicarboxylic acid precursors.
• Polyesters which are suitable for use in this invention are those which are derived from the condensation. of aromatic, cycloaliphatic, and aliphatic diols with aliphatic, aromatic and cycloaliphatic dicarboxylic acids and may be cycloaliphatic, aliphatic or aromatic polyesters.
• Exemplary of useful cycloaliphatic, aliphatic and aromatic polyesters which can be utilized in the practice of their invention are poly(ethylene terephtha- late), poly(cyclohexylenedimethylene, terephthalate, poly(ethylene dodecate), poly(butylene terephthalate, poly[ethylene(2,7-naphthalate)], poly(metaphenylene isophthalate), poly(glycolic acid), poly(ethylene succinate), poly(ethylene adipate), poly(ethylene sebacate), poly(decamethylene azelate), poly(ethylene sebacate), poly(decamethylene adipate), poly(deca- methylene sebacate), poly ( ⁇ , ⁇
• Polyester compounds prepared from the condensation of a diol and an aromatic dicarboxylic acid are preferred for use in this invention.
• aromatic carboxylic acids are terephthalic acid, isophthalic acid and an o-phthalic acid, 1,3-, 1,4-, 2,6- or 2,7-napthalenedicarboxylic acid, 4,4'-diphenyl- dicarboxylic acid, 4,4'-diphenysulphone-dicarboxylic acid, 1,1,3-trimethyl-5-carboxy-3-(p-carboxyphenyl)- indane, diphenyl ether 4,4'-dicarboxylic acid, bis- p(carboxyphenyl)methane and the like.
• aromatic dicarboxylic acids based on a benzene ring such as terephthalic acid, isophthalic acid, orthophthalic acid are preferred for use and amongst these preferred acid precursors, terephthalic acid is particularly preferred.
• poly(ethylene terephthalate), poly(butylene terephthalate), and poly(1,4-cyclohexane dimethylene terephthalate) are the polyesters of choice. Among these polyesters of choice, poly(ethylene terephthalate) is most preferred.
• Still other polymers which may be used in the practice of this invention are polymers derived from unsaturated monomers of the formula:
• R 1 and R 2 are the same or different and are hydrogen, alkyl, phenyl, alkaxyphenyl, alkylphenyl, halophenyl, alkylphenyl, perhalophenyl, haloalkyl, perhaloalkyl, nephthyl, cyano, phenoxy, hydroxy, carboxy, alkanoyl, amino, halogen, amide, alkoxycarbonyl, phenol, alkylamino, alkoxy, alkoxyalkyl, dialkylamino, pyridimo, carbazole, haloalkanoyl, perhaloalkanoyl, phenylcarbonyl, phenoxy carbonyl and pyrrolidino.
• polymers polyethylene, polyvinyl alcohol, polypropylene, polystyrene, polyvinyl chloride, polyvinylene fluoride, polyacrylamide, poly- acrylonitrile, polyvinyl pyridine, polyvinyl acetate, polyacrylic acid, polyvinyl pyrrolidine, polyvinyl methyl ether, polyvinyl formal, poly (P-vinyl phenol) and the like.
• the polymer is a polymer formed from an ⁇ , ⁇ -unsaturated olefins, especially those of the above formula in which R 1 is hydrogen and R 2 is hydrogen, alkyl, phenyl, cyano, and amide; polyesters and aromatic or aliphatic polyamides.
• the polymer is polyethylene terephthalate nylon 6, nylon 66, aramid, polyacrylonitrile, polyvinyl alcohol and polyethylene.
• most preferred are those embodiments in which the polymer is polyethylene, polyacrylonitrile, and polyvinyl alcohol.
• Preferred polyvinyl alcohol for use in this invention is linear and of weight average molecular weight of at least about 100,000.
• the weight average molecular weight is from about 200,000 to about 2,000,000, and in the particularly preferred embodiments is from about 250,000 to about 1,000,000.
• the molecular weight of the polyvinyl alcohol is from about 300,000 to about 750,000.
• the term linear is intended to mean no more than minimal branches of either the alpha or beta type.
• PV-Ac polyvinyl acetate
• Preferred polyacrylonitrile for use in this invention is linear and of weight average molecular weight of at least about 200,000.
• Preferred polyacrylonitrile has a weight average molecular weight of from about 300,000 to about 4,000,000, and in the particularly preferred embodiments of the invention the polyacrylonitrile has a weight average molecular weight of from about 400,000 to about 2,500,000.
• the weight average molecular weight of the polyacrylonitrile is from about 1,000,000 to about 2,500,000.
• Preferred polyethylene for use in this invention is linear and has a weight average molecular weight of at least about 200,000.
• Preferred polyethylene has a weight average molecular weight of from about 500,000 to about 4,000,000, and in the particularly preferred embodiments of the invention the polyethylene has a weight average molecular weight of from about 600,000 to about 3,000,000. Amongst these particularly preferred embodiments most preferred are those embodiments, the polyethylene has a weight average molecular weight of from about 700,000 to about 2,000,000.
• Spinning apparatus used in the practice of this invention may vary widely and the extrusion step of our process may be conventional extrusion apparatus for spinning ordinary fibers of the same polymer.
• extruders and spinnerets may be used as described in "Encyclopedia of Polymer Science and Technology", Vol. 8, pps. 326-381.
• solution spinning of polyethylene polyacrylonitrile and polyvinyl alcohol conventional solution spinning systems as described in British Patent 1,100,497; and U. S. Patent Nos. 3,536,219; 3,048,465; and 4,421,708.
• th e spinneret may have any number of apertures preferably of substantially constant cross-section.
• Each aperature will have the required L/D (length to diameter) ratios of equal to or greater than about 60:1 and may have various cross-sectional shapes, e.g., circular, rectangular Y-shaped, dog-boned, hexalobal, trilobal and the like.
• the effective diameter in the case of a circle, an equivalent dimension giving the same cross-sectional area for the other shapes
• An effective diameter from about 0.1 mm to about 1.5 mm is preferred, and an effective diameter between about 0.1 mm and about 1.0 mm is more preferred.
• the first solvent should be substantially nonvolatile under the processing conditions. This is necessary in order to maintain essentially constant the concentration of solvent upstream and through the aperture (die) and to prevent non-uniformity in liquid content of the gel fiber or film containing first solvent.
• the vapor pressure of the first solvent should be no more than 80 kPa (four-fifths of an atmosphere) at 130°C, or at the first temperature.
• the polymer may be present in the first solvent at a first concentration which is selected from a relatively narrow range, e.g., about 2 to about 30 weight precent, preferably about 5 to about 20 weight percent more preferably about 6 to about 15 weight percent; however, once chosen, the concentration should not vary significantly adjacent the die or otherwise prior to cooling to the second temperature.
• the concentration at any one point should not vary adjacent the die or otherwise prior to cooling to the second temperature.
• the concentration should also remain reasonably constant over time (i.e., length of the fiber or film).
• the first temperature is chosen to achieve complete dissolution of the polymer in the first solvent.
• the first temperature is the minimum temperature at any point between where the solution is formed and the die face, and must be greater than the gelation temperature for the polymer in the solvent at the first concentration. While temperatures may vary above the first temperature at various points upstream of the die face, excessive temperatures causative of polymer degradation should be avoided.
• a first temperature is chosen whereat the solubility of the polymer exceeds the first concentration and is typically at least 20% greater.
• the second temperature is chosen whereat the first solvent-polymer system behaves as a gel, i.e., has a yield point and reasonable dimensional stability for subsequent handling.
• Cooling of the extruded polymer solution from the first temperature to the second temperature should be accomplished at a rate sufficiently rapid to form a gel fiber which is of substantially the same polymer concentration as existed in the polymer solution.
• the rate at which the extruded polymer solution is cooled from the first temperature to the second temperature should be at least 50oC per minute.
• a preferred means of cooling to the second temperature involves the use of a quench bath.
• the quench bath will preferably comprise a liquid which is relatively immiscible with the first solvent.
• the particularly preferred quench bath for use in the practice of this invention will comprise water or a mixture of the first solvent with water. Quenching temperatures that may be employed range from about 0°C to about 50°C with a temperature near room temperature being preferred.
• the gel fiber formed upon cooling to the second temperature consists of a continuous polymeric network highly swollen with solvent.
• both gels will be gel fibers
• the xerogel will be a xerogel fiber
• the thermoplastic article will be a fiber.
• the diameter of the aperture is not critical, with representative apertures being between 0.25 mm and 5 mm in diameter (or other major axis).
• the length of the aperture in the flow direction should normally be at least 60 times the diameter of the aperture (or other similar major axis), preferably at least 70 times and more preferably at least 80 times the diameter (or other similar major axis).
• both gels will be gel films
• the xerogel will be a xerogel film
• the thermoplastic article will be a film.
• the width and height of the aperture are not critical, with representative apertures being between
• the depth of the aperture should normally be at least 60 times the height and more preferably at least 80 times the height.
• the extraction with second solvent is conducted in a manner that replaces the first solvent in the gel with a second more volatile solvent.
• a suitable second solvent is water.
• Preferred second solvents are the volatile solvents having an atmospheric boiling point of 100oC or lower. Conditions of extraction should remove the first solvent to less than 1% solvent by weight of polymer in the gel after extraction.
• first solvents such as DMSO or DMF
• a preferred combination of conditions is a first temperature between 130°C and 250°C, a second temperature between 0°C and 50oC and a cooling rate of at least 50°C/minute.
• the first solvent should be substantially non-volatile, one measure of which is that its vapor pressure at the first temperature should be less than four-fifths atmosphere (80 kPa).
• the primary desired difference relates to volatility as discussed above.
• the fibrous structure containing second solvent is formed, it is then dried under conditions where the second solvent is removed leaving the solid network of polymer substantially intact.
• the resultant material is called herein a "xerogel” meaning a solid matrix corresponding to the solid matrix of a wet gel, with the liquid replaced by gas
• xerogel is not intended to delineate any particular type of surface area, porosity or pore size.
• Stretching may be performed upon the gel fiber after cooling to the second temperature or during or after extraction.
• stretching of the xerogel fiber may be conducted, or a combination of gel stretch and xerogel stretch may be performed.
• the first stage stretching may be conducted in a single stage or it may be conducted in two or more steps.
• the first stage stretching may be conducted at room temperature or at an elevated temperature.
• the stretching is conducted in two or more stages with the last of the stages performed at a temperature between 100°C and 260°C.
• Most preferably the stretching is conducted in more than two stages with the last of the stages performed at a temperature between 130oC and 250oC.
• Such temperatures may be achieved with heated tubes as in the Figures, or with other conventional heating means such as heated pins, heating blocks, steam or gas jets, pressurized steam, heated liquids or heated rolls.
• the stretching temperatures may also be obtained by use of laser or dielectric (microwave) heating.
• the fiber product may be circular, polygonal, polylobal, or irregular in cross-sectional shape, and ordinarily has an "effective diameter" of between about
• the effective diameter of the fiber is the diameter of a circle whose diameter corresponds to the cross sectional area of the fiber. Effective diameter corresponds generally to a denier which can range from about 0.8 to about 8000, and which preferably ranges between about 0.8 and about 80.
• the fibers of this invention have unique properties.
• the fibers have improved uniformity and cylindricity, and exhibit high tenacity and high modulus.
• the product polyacrylonitrile fibers produced by the present process represent novel articles in that they include fibers with a unique combination of properties: a molecular weight of at least about 200,000, a (secant) modulus at least about 100 g/denier and a tenacity at least about 7 g/denier.
• the molecular weight is preferably at least about 2,000,000, more preferably between about 300,000 and about 4,000,000 and most preferably between about 400,000 and about 2,500,000.
• the tenacity of the polyacrylonitrile fibers is at least about 11 g/denier, and in the particularly preferred embodiments is from about 11 to about 19 g/denier. Amongst these particularly preferred embodiments, most preferred are those polyacrylonitrile fibers in which the tenacity is greater than about 20 g/denier.
• the secant modulus is preferably at least about 100 g/denier, more preferably at least about 125 g/denier.
• the fiber has an elongation to break at most 7%.
• Polyvinylalcohol fibers produced by the present process represent novel articles in that they include fibers with a unique combination of properties: a molecular weight of at least about 100,000, a modulus at least about 200 g/denier, a tenacity at least about 10 g/denier, melting temperature of at least about 238°C.
• the molecular weight is preferably at least about 200,000, more preferably between about 200,000 and about 2,000,000 and most preferably between about 250,000 and about 1,000,000.
• the tenacity is preferably at least about 14 g/denier and more preferably at least about 17 g/denier.
• the tensile modulus is preferably at least about 300 g/denier, more preferably 400 g/denier and most preferably at least about 550 g/denier.
• the melting point is preferably at least about 238°C.
• the preferred other physical properties can be achieved without the 238°C melting point, especially if polyvinyl alcohol fibers contains comonomers such as unhydrolyzed vinyl acetate. Therefore, the invention includes polyvinyl alcohol fibers with molecular weight at least about 200,000, tenacity of at least about 14 g/denier and tensile modulus at least about 300 g/denier, regardless of melting point. Again, the more preferred values are molecular weight between about 200,000 and about 2,000,000 (especially about 250,000-1,000,000), tenacity at least about 17 g/denier and modulus at least about 400 g/denier (especially at least about 550 g/denier).
• the product polyvinyl alcohol fibers also exhibit shrinkage at 160°C less than 2% in most cases. Preferably the fiber has an elongation to break at most 7%.
• a 6 wt% slurry of 22.4 IV polyethylene in mineral oil containing 0.25% antioxidant (Irganox 1010) was fed by means of a piston pump to a preheater and then under pressure to a single screw extruder of 3 inch (7.62 cm) ID barrel diameter and 3700 cu. cm. net internal volume.
• the temperature of the screw extruder was maintained at 290°C along its length.
• the polyethylene was dissolved by passage through the preheater and the screw extruder.
• the discharge of the screw extruder was fitted with a Zenith gear pump which conveyed the 6 wt% polyethylene solution in mineral oil through a screen pack and into a spinneret consisting of 118 holes each of 0.040" (0.102 cm) diameter, and having varying length/diameter (L/D) ratios.
• the length/diameter ratio of the spinneret was 25:1 in examples 1 and 2, and 100:1 in examples 3 and 4.
• the spinning throughput rate was 236 cc/mn. in examples 1 and 3 and 472 cc/min. in examples 2 and 4.
• the polymer solution was extruded through the spinneret to form solution filaments, which were quenched in water without change in composition to form gel filaments.
• the gel filaments were stretched at room temperature, extracted with trichlorotrifluoroethane, then dried and stretched again at 60°C, 130oC and 150°C.
• the properties of the resulting yarns and of the individual filaments in these yarns were measured.
• the filament aspect ratio is the ratio of the largest cross- sectional dimension to the smallest cross-sectional dimension averaged for about fifty filaments in each case.
• a 6 wt% solution of 22.4 IV polyethylene was prepared as in examples 1 to 4 and extruded at the rate of 177 cc/mn. through a 121 hole spinneret of 0.015" (0.0381 cm) diameter and on an L/D ratio of 15:1 L/D.
• the solution filaments were quenched in water to form gel filaments.
• a 6 wt% solution of 22.4 IV polyethylene was prepared as in Example 5 and extruded through a 118 hole spinneret of 0.015" (0.0381 cm) diameter and 200:1 L/D.
• the solution filaments were quenched in water to form gel filaments.
• the gel filaments showed no apparent diameter variation along their lengths.
• the gel yarn was stretched, extracted, dried and stretched again. The properties of the resulting yarn were:
• Example 7 The yarn prepared in Example 6 was annealed and restretched using the procedures described in copending application Serial No. 745,164. The properties of the annealed and restretched yarn were: 85 denier (0.72 denier/fil), 42.1 g/d tenacity, 2047 g/d/ modulus.

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