CA1214909A - High strength and modulus polyvinyl alcohol fibers and method of their preparation - Google Patents
High strength and modulus polyvinyl alcohol fibers and method of their preparationInfo
- Publication number
- CA1214909A CA1214909A CA000436574A CA436574A CA1214909A CA 1214909 A CA1214909 A CA 1214909A CA 000436574 A CA000436574 A CA 000436574A CA 436574 A CA436574 A CA 436574A CA 1214909 A CA1214909 A CA 1214909A
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- Canada
- Prior art keywords
- solvent
- denier
- polyvinyl alcohol
- temperature
- stretching
- Prior art date
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Classifications
-
- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
- D01F6/00—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof
- D01F6/02—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds
- D01F6/14—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds from polymers of unsaturated alcohols, e.g. polyvinyl alcohol, or of their acetals or ketals
Abstract
ABSTRACT
HIGH STRENGTH AND MODULUS POLYVINYL ALCOHOL
FIBERS AND METHOD OF THEIR PREPARATION
Polyvinyl alcohol of molecular weight over 500,000 (i.e. 1,500,000 to 2,500,000) is spun as a dilute solution (2-15%) in a relatively non-volatile solvent such as glycerin. The resultant gel fiber is extracted with a volatile solvent such as methanol and dried. Upon stretching at one or more stages during the process, fibers of tenacity above 10 g/denier and modulus above 200 g/denier (e.g. 18 and 450, respect-ively) are produced.
HIGH STRENGTH AND MODULUS POLYVINYL ALCOHOL
FIBERS AND METHOD OF THEIR PREPARATION
Polyvinyl alcohol of molecular weight over 500,000 (i.e. 1,500,000 to 2,500,000) is spun as a dilute solution (2-15%) in a relatively non-volatile solvent such as glycerin. The resultant gel fiber is extracted with a volatile solvent such as methanol and dried. Upon stretching at one or more stages during the process, fibers of tenacity above 10 g/denier and modulus above 200 g/denier (e.g. 18 and 450, respect-ively) are produced.
Description
9L2~
DESCRIPTION
HIGH ST~ENGTH AND MODULUS POLYVINYL ALCOHOL
FIBERS AND METHOD OF THEIR PREPARATION
The present invention relates to polyvinyl alcohol fibers of high molecular weight, strength (ten-acity) and tensile modulus, and methods of preparing same via the extrusion of dilute solutions to prepare gel fibers which are subsequently stretched.
Zwick et al. in Soc Chem Ind, London, Mono-graph No. 30, ppO 188-207 (1968) describe the spinning of polyvinyl alcohol by a Phase Separation technique said to differ from earlier Wet Spinning, Dry Spinning and Gel Spinning techniques. 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 si~e, attenuation permitted or required, maximum production speed and attainable fiber properties.
The Phase Separation process described in Zwick et al. (see also UK Patent Specification 1,100,497) 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 ~:, .i solvent (or one of its components), although the latter is indicat~d 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 hun-dreds or thousands o~ times greater than the linear velocity of the polymer solution through the apertureO
Thereafter the fibers were extractecl to remove the occluded or exterior solvent phase, dried and stretched. An earlier, more yeneral description of Phase Separation Spinning is contained in Zwick Applied Polymer Symposia, no. 6, pps 109-49 (1967).
Modifications in the spinning of hot solutions ultrahigh molecular weight polyethylene (see Examples 21-23 of UK 1,100,497) have been reported by Smith and Lemstra and by Pennings and coworkers in various arti-cles and patents including German Offen 3004699 (August 21, 1980); UK Application 2,051,667 (January 21, 1981);
Polymer Bulletin, vol. 1, pp. 879-880 (1979) and vol. 2, pp. 775-83 (1980); and Polymer 2584-90 91980). Kavesh et al.~ U.SO Patent 4,413,110 and EPA 64,167 describe processes including the ex-trusion of dilute, hot solu-tions of ultrahigh molecular weight polyethylene or polypropylene in a nonvolatile solvent followed by cool-ing, extraction, drying and stretching. While certain other polymers are indicated in EPA 64,167 as being use-ful in addition to polyethylene or polypropylene, such polymers do not include polyvinyl alcohol or similar materials.
While U.~. Patent 1,100,497 indicates molecular weight to be a factor in selecting best polymer concen-tration (page 3, lines 16-26), no indication is given that higher moleculaL weights give improvecl fibers for polyvinyl a]cohol. The Zwick article in Applied Polymer Symposia suggests 20-25% polymer concentra-tion as opti-mum or fiber~grade polyvinyl alcohol, but 3% polymer concentration to be optional for polyethylene. The Zwick et al article states the polyvinyl alcohol content of 10-25% in the polymer solution to be optimal, at g~
least in the system explored in most detail where the solvent or a component of the solvent solidified on cooling to concentrate the polyvinyl alcohol in the liquid phase on cooling before the polyvinyl alcohol gels.
Unlike the systems used in EPA 64,167 and Smith and Lemstra, all three versions of Zwick's Phase Separation process take up the fiber directly from the air gap, without a quench bath, such that the draw-down occurred over a relatively large length of cooling fiber~
~RIEF DESCRIPTION OF THE DRAWING
Figure l is a schematic vlew of a first form of the process of the present invention~
Figure 2 is a schematic view of a second form of the process of the presen-t invention.
Figure 3 is a schematic view of a third form of the process of the present invention.
BRIEF DESCRIPTION OF THE INVENTION
The present inven-tion includes a process comprising the steps:
(a) forming a solution of a linear polyvinyl alco-hol having a weight average molecular weight at least 500,000 in a first solvent at a first concentration between about 2 and about 15 weight percent polyvinyl alcohol, (b) extruding said solution through an aperture, said solution being at a temperature no less than a first temperature upstream of the aperture and being substantially at the first concentration both upstream and downstream of said aperture, (c) cooling the solution adjacent to and down-stream of the aperture to a second teMperature below the temperature at which a rubbery gel is formed, forming a gel containing first solvent oE substantially indefinite length, (d) extracting the gel containing first solvent with a second, volatile solvent Eor a sufficient contact time to form a fibrous structure containing second -3a-solvent, which struc-ture is substantially free of first solvent and i.s of substantially indefinite length;
(e) drying the fibrous structure containing second solvent to form a xerogel of substantially ~., indefinite length ree of first and second solvent; and tf) stretching at least one o:
(i) the gel containing th~ first solvent, ~ii) the fibrous structure containing the second solvent and, (iii) the xerogel, at a total stretch ratio sufficient to ~chieve a tena-city of at least about 10 g/denier and a modulus oE at least 200 g/denier.
The present invention also inc~udes novel stretched polyvinyl alcohol fibers of we~ght average molecular weight at least about 500,000, tenacity at least about 10 g/denier, tensile modulus at least abo~t 200 g/denier and melting point at least about 238C.
The present invention also includes novel stretched polyvinyl alcohol fibers of weight average molecular weight at least about 750rOOO~ tenacity at least about 14 g/denier and tensile modulus at least about 3G0 g/denier.
DETAILED D~SCRIPTION OF THE INVENTION
The process and fibers of the present inven-tion employ a linear ultrahigh molecular weight poly-vinyl alcohol (PV-OH) described more fully below that enabl~s the preparation of PV-O~l fibers ~and films~ of heretofore unobtained properties by extrusion of dilute solutions of concentration lower than used in Wet Spinning, Dry Spinning, Gel Spinning or Phase Separa-tion Spinning, all as described by Zwick, Zwick et al.
and UK Patent Speci~ication 1,100,497. Furthermore, the preferred solvents of the present invention do not phase-separate from PV-OH on cooling to orm a ~on-PV-OH
coating or occluded phase, but rather form a dispersed fairly homogeneous gel unlike that achieved in Phase Separation Processes. The ability to process such gels formed by extruding and cooling dilute solutions is different from conventional gel spinnin~ of PV-OH, which, according to Zwick et al, requires an even higher solid content of the spinning dope (45~55%) to allow the polymer to be extruded and fibers to be collected in the form of a concentrated, tough gel wlthout prior removal of solvent.
The PV-OH polymer used is linear and of weight average molecular weight at least about 500,000, pre-ferably at least about 750,000, more preferably between about 1,000,000 and about 4,000,000 and most preferably between about 1,500,000 and about 2,500,000. The term linear is intended to mean no more than minimal branches 1 of either the alpha or beta type. Since the most common branching in polyvinyl acetate (PV-Ac) manufacture is on the acetate side-groups, such branching will result in side-groups being split off during hydrolysis or metha-nolysis to PV-OH and will result in the PV-OH size being lowered rather than its branching increased~ The amount of total branching can be determined most rigorously by nuclear magnetic resonance. ~hile totally hydrolyzed material ~pure PV-OH) is preferred, copolymers with some vinyl acetate reinaining may be used.
Such linear ultrahigh molecular weight PV-OH can be prepared by low temperature photoinitiated vinyl acetate polymerization, followed by methanolysis, using process details described in J. West and T.C. Wu, U.S. Patent 4,463,138, exemplified in the description preceding Table I, below The first solvent should be non-volatile under the processing conditions. This is necessaLy 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. Preferably, the vapor pressure of the first solvent should be no more than 80 kPa (four-fifths of an atmosphere) a~ 180C, or at the first temperature. Suitable first solvents for 3 PV-OH include aliphatic and aromatic alcohols of the desired non-volatility and solubility for the polymer.
Preferred are the hydrocarbon polyols and alkylene ether ..
~æ~ 9 polyols having a boiliny point (at 101 kpa) between about 150C and about 300C, such as ethylene glycol, propylene glycol, glycerol, die~hylene glycol ana triethylene glycol. Also suitable are water and solutions in wa~er or in alcohols of various salt such as lithium chloride, calcium chloride or other materials capable of disrupting hydrogen bonds and thus increasing the solubility of the PV-O~. The polymer may be present in the first solvent at a first concentration which is selec~ed from a relatively narrow range/ e.g~
DESCRIPTION
HIGH ST~ENGTH AND MODULUS POLYVINYL ALCOHOL
FIBERS AND METHOD OF THEIR PREPARATION
The present invention relates to polyvinyl alcohol fibers of high molecular weight, strength (ten-acity) and tensile modulus, and methods of preparing same via the extrusion of dilute solutions to prepare gel fibers which are subsequently stretched.
Zwick et al. in Soc Chem Ind, London, Mono-graph No. 30, ppO 188-207 (1968) describe the spinning of polyvinyl alcohol by a Phase Separation technique said to differ from earlier Wet Spinning, Dry Spinning and Gel Spinning techniques. 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 si~e, attenuation permitted or required, maximum production speed and attainable fiber properties.
The Phase Separation process described in Zwick et al. (see also UK Patent Specification 1,100,497) 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 ~:, .i solvent (or one of its components), although the latter is indicat~d 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 hun-dreds or thousands o~ times greater than the linear velocity of the polymer solution through the apertureO
Thereafter the fibers were extractecl to remove the occluded or exterior solvent phase, dried and stretched. An earlier, more yeneral description of Phase Separation Spinning is contained in Zwick Applied Polymer Symposia, no. 6, pps 109-49 (1967).
Modifications in the spinning of hot solutions ultrahigh molecular weight polyethylene (see Examples 21-23 of UK 1,100,497) have been reported by Smith and Lemstra and by Pennings and coworkers in various arti-cles and patents including German Offen 3004699 (August 21, 1980); UK Application 2,051,667 (January 21, 1981);
Polymer Bulletin, vol. 1, pp. 879-880 (1979) and vol. 2, pp. 775-83 (1980); and Polymer 2584-90 91980). Kavesh et al.~ U.SO Patent 4,413,110 and EPA 64,167 describe processes including the ex-trusion of dilute, hot solu-tions of ultrahigh molecular weight polyethylene or polypropylene in a nonvolatile solvent followed by cool-ing, extraction, drying and stretching. While certain other polymers are indicated in EPA 64,167 as being use-ful in addition to polyethylene or polypropylene, such polymers do not include polyvinyl alcohol or similar materials.
While U.~. Patent 1,100,497 indicates molecular weight to be a factor in selecting best polymer concen-tration (page 3, lines 16-26), no indication is given that higher moleculaL weights give improvecl fibers for polyvinyl a]cohol. The Zwick article in Applied Polymer Symposia suggests 20-25% polymer concentra-tion as opti-mum or fiber~grade polyvinyl alcohol, but 3% polymer concentration to be optional for polyethylene. The Zwick et al article states the polyvinyl alcohol content of 10-25% in the polymer solution to be optimal, at g~
least in the system explored in most detail where the solvent or a component of the solvent solidified on cooling to concentrate the polyvinyl alcohol in the liquid phase on cooling before the polyvinyl alcohol gels.
Unlike the systems used in EPA 64,167 and Smith and Lemstra, all three versions of Zwick's Phase Separation process take up the fiber directly from the air gap, without a quench bath, such that the draw-down occurred over a relatively large length of cooling fiber~
~RIEF DESCRIPTION OF THE DRAWING
Figure l is a schematic vlew of a first form of the process of the present invention~
Figure 2 is a schematic view of a second form of the process of the presen-t invention.
Figure 3 is a schematic view of a third form of the process of the present invention.
BRIEF DESCRIPTION OF THE INVENTION
The present inven-tion includes a process comprising the steps:
(a) forming a solution of a linear polyvinyl alco-hol having a weight average molecular weight at least 500,000 in a first solvent at a first concentration between about 2 and about 15 weight percent polyvinyl alcohol, (b) extruding said solution through an aperture, said solution being at a temperature no less than a first temperature upstream of the aperture and being substantially at the first concentration both upstream and downstream of said aperture, (c) cooling the solution adjacent to and down-stream of the aperture to a second teMperature below the temperature at which a rubbery gel is formed, forming a gel containing first solvent oE substantially indefinite length, (d) extracting the gel containing first solvent with a second, volatile solvent Eor a sufficient contact time to form a fibrous structure containing second -3a-solvent, which struc-ture is substantially free of first solvent and i.s of substantially indefinite length;
(e) drying the fibrous structure containing second solvent to form a xerogel of substantially ~., indefinite length ree of first and second solvent; and tf) stretching at least one o:
(i) the gel containing th~ first solvent, ~ii) the fibrous structure containing the second solvent and, (iii) the xerogel, at a total stretch ratio sufficient to ~chieve a tena-city of at least about 10 g/denier and a modulus oE at least 200 g/denier.
The present invention also inc~udes novel stretched polyvinyl alcohol fibers of we~ght average molecular weight at least about 500,000, tenacity at least about 10 g/denier, tensile modulus at least abo~t 200 g/denier and melting point at least about 238C.
The present invention also includes novel stretched polyvinyl alcohol fibers of weight average molecular weight at least about 750rOOO~ tenacity at least about 14 g/denier and tensile modulus at least about 3G0 g/denier.
DETAILED D~SCRIPTION OF THE INVENTION
The process and fibers of the present inven-tion employ a linear ultrahigh molecular weight poly-vinyl alcohol (PV-OH) described more fully below that enabl~s the preparation of PV-O~l fibers ~and films~ of heretofore unobtained properties by extrusion of dilute solutions of concentration lower than used in Wet Spinning, Dry Spinning, Gel Spinning or Phase Separa-tion Spinning, all as described by Zwick, Zwick et al.
and UK Patent Speci~ication 1,100,497. Furthermore, the preferred solvents of the present invention do not phase-separate from PV-OH on cooling to orm a ~on-PV-OH
coating or occluded phase, but rather form a dispersed fairly homogeneous gel unlike that achieved in Phase Separation Processes. The ability to process such gels formed by extruding and cooling dilute solutions is different from conventional gel spinnin~ of PV-OH, which, according to Zwick et al, requires an even higher solid content of the spinning dope (45~55%) to allow the polymer to be extruded and fibers to be collected in the form of a concentrated, tough gel wlthout prior removal of solvent.
The PV-OH polymer used is linear and of weight average molecular weight at least about 500,000, pre-ferably at least about 750,000, more preferably between about 1,000,000 and about 4,000,000 and most preferably between about 1,500,000 and about 2,500,000. The term linear is intended to mean no more than minimal branches 1 of either the alpha or beta type. Since the most common branching in polyvinyl acetate (PV-Ac) manufacture is on the acetate side-groups, such branching will result in side-groups being split off during hydrolysis or metha-nolysis to PV-OH and will result in the PV-OH size being lowered rather than its branching increased~ The amount of total branching can be determined most rigorously by nuclear magnetic resonance. ~hile totally hydrolyzed material ~pure PV-OH) is preferred, copolymers with some vinyl acetate reinaining may be used.
Such linear ultrahigh molecular weight PV-OH can be prepared by low temperature photoinitiated vinyl acetate polymerization, followed by methanolysis, using process details described in J. West and T.C. Wu, U.S. Patent 4,463,138, exemplified in the description preceding Table I, below The first solvent should be non-volatile under the processing conditions. This is necessaLy 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. Preferably, the vapor pressure of the first solvent should be no more than 80 kPa (four-fifths of an atmosphere) a~ 180C, or at the first temperature. Suitable first solvents for 3 PV-OH include aliphatic and aromatic alcohols of the desired non-volatility and solubility for the polymer.
Preferred are the hydrocarbon polyols and alkylene ether ..
~æ~ 9 polyols having a boiliny point (at 101 kpa) between about 150C and about 300C, such as ethylene glycol, propylene glycol, glycerol, die~hylene glycol ana triethylene glycol. Also suitable are water and solutions in wa~er or in alcohols of various salt such as lithium chloride, calcium chloride or other materials capable of disrupting hydrogen bonds and thus increasing the solubility of the PV-O~. The polymer may be present in the first solvent at a first concentration which is selec~ed from a relatively narrow range/ e.g~
2 to 15 weight percent, preferably 4 to 10 weight percent; however, once chosen/ the concentration 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)O
The first temperature is chosen to achieve complete dissolution of the polymer in the first solvent. The first temperature is the minimum tempera-ture at any point between where the solution is formedand the die face, and must be grea~er than the gelation temperature for the polymer in the solvent at ~he first concentration. For PV-OH in glycerine at 5-15~ concen-tration, the gelation temperature is approximately 25-100C; therefore, a preferred first temperature can bebetween 130C and 250C, more preferably 17~-230C.
While temperatures may vary above the first temperature at various points upstream of ~he die face, excessive temperatures causitive of polymer degradation should be avoided. To assure complete solubility, a first temper-ature is chosen whereat the solubility of the polymer exceeds the first concentration and is typically at least 20~ greaterO 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 subse~uent handling. Cooling of the extruded polymer solution from the first temperature to the second temperature should be accomplished at a rate ..
--7~
sufficiently rapid to form a gel fiber which is of substantially the same polymer concentration as existed in the polymer solution. Preferably the rate at which the extruded polymer solution is cooled from the first temperature to the second temperature should be at least 50C per mirute.
A preferred means of rapid cooling to the second temperature involves the use of a quench bath cont~ining a liquid such as a hydrocarbon (e.g., paraf-fin ~il) into which the extruded polymer solution fallsafter passage through an air gap (which may be an inert gas). It is contemplated to combine the quench step with the subsequent extraction by having a second sol vent (e.g~, methanol) as the quench liquid. Normally, however, the quench liquid (e.g.~ parrafin oil) and the first solvent (e.g., glycerol) have only limited miscibility~
Some stretching during cooling to the second temperature is not excluded from the present invention, but ~he total stretching during this stage should not normally exceed 10:1. As a result of those factors the gel fiber formed upon cooling to the second temperature consists of a continuous polymeric network highly swollen with solvent.
If an aperture of circular cross sec~ion (or other cross section without a major axis in the plane perpendicular to the flow direction more than 8 times the s~allest axis in the same plane, such as oval, Y- or X-shaped aperture) is used, then both gels will be gel fibers, the xerogel will be an xerogel fiber and the ther~oplastic 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 10 times the diameter of the aperture ~or other similar major axis), perferably at least 15 times and more preferably .. .
at least 20 times the diameter (or other similar major axis).
I an aperture of rectangular cross section is used~ then both gels will be gel films, the xerogel will be a xerogel film and the thermoplastic article will be a film. The width and heiyht of the aperture are not critical, with representative apertures being between 2.5 mm and 2 m in width ~corresponding to film width), ¦ between 0~25 mm and 5 mm in height (corresponding to film thickness). The depth of the aperture (in the flow direction~ should normally be at least 10 times the height of the aperture, preferably at least 15 times the height and more preferably at least 20 times the height.
The extraction with second solvent is con-ducted in a manner that replaces the first solvent inthe gel with second more volatile solvent. When the first solvent is glycerine or ethylene glycol, suitable second solvents include methanol~ ethanol, ethers, ace-tone, ketones and dioxane. Water is also a suitable second solvent, either for extraction of glycerol (and similar polyol first solvents) or for leaching of aqueous salt solutions as first solvent. The most preferred second solvent is methanol ~B.P. 64.7C).
Preferred second solvents are the volatile solvents having an atmospheric boiling point below 80C, more preferably below 70C. Conditions of extraction should remove the first solvent to less than 1% of the total solvent in the gel.
With some first solvents such as water or ethylene glycol, it is contemplated to evaporate the solvent from the gel fiber near the boiling point o~
the first solvent instead of or prior to extraction.
A preferred combination of conditions is a first temperature between 130C and 250C, a second tem-perature between 0C and 50C and a cooling ratebetween the first temperature and the second temperature of at least 50C/minute. It is preferred that the first solvent be an alcohol. 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), and more preferably less than 10 kPa. In choosing the first and 5 second solvents, the primary desired difference relates to volatility as discussed above.
Once the fibrous structure containing second solvent is formed, it is t.~en Ar ed under conditions where the second solvent is removed leaving the solid network of polymer substantially intact. By analogy to silica gels, the resultant material is called herein a "xerogel" meaning a solid matrix corresponding to the solid matrix o a wet gel, with the liquid replaced by gas (e.g. by an inert gas such as nitrogen or by air).
The term "xerogel" is not intended to delineate any particular type of surface area, porosity or pore size.
A comparison of the xerogels of the present invention with corresponding dried gel fibers prepared according to Phase Separation Spinning is expected to yield some morphological differences.
Stretching may be performed upon the gel fiber after coo1in~ to the second temperature or during or after extraction. Alternatively, stretching of the xerogel fiber may be conducted, or a combination of gel stretch and xerogel stretch may be performed. The stretching may be conducted in a single stage or it may be conducted in two or more stages. The first stage stretching may be conducted at room temperatures or at an elevated temperature. Preferably the stretching is conducted in two or more stages with the last of the stages performed at a temperature between 120C and 250C. Most preferably the stretching is conducted in at least two stages with the last of the stages per-formed at a tempera~ure between 150C and 250C.
Such temperatures may be achieved with heated tubes as in the Figures, or with other heating means such as heating blocks or steam jets.
The product PV-OH fibers produced by the pre-senl: process represent novel articles in that they include ibers with a unique rombination of properties:
a molecular weight of at lea~t about 500,000, a modulus at lPast about 200 g/t3enier" a tenacity at least about 10 g/denier, melting temperature of at least about 238~C. For this fiber~ the ~lecular weigh'c is pre-ferably at leas~ about 7~0,000, more preferably between about 1, 00Q, ono and about ~ ,000, 000 and lllO5t preferably between aboutc 1,500,000 and about 2,500,000. The lû tenacity is preferably at le;~st abc)ut 14 g/denier and more preferably at least about 17 g/denier. ~he tensile modulus is preferably at leas~ about 300 g/denier, mor~
preiEerably 400 g/denier and IlDost preferably at least about 550 g/denier. ~he n~elting point is preferabl~ at least about 245~C.
It is also conte~plated that the preferred other physical properties ~n be achieved without the 238C melting point, especially if the PV-OH contairl~
comonomers ~;uch as unhydrolyzed vinyl acetate. There-fc>re, the invention includes PV-O~ f ibers with molecular weight at least about 750,000" tenacity of at 1east about 14 g/denier and tensile modulus a'c le~st about 300 g/ denier, regardless of melting pointO Again, the more pre~erred value~ are molecular weight between about 1,000,0D0 and about 4,00û,000 tesPecially abou~
1,500,000 - 2,500~000~, tena~ity at least about 17 g/
denier and modulus at least about 400 g/denier (espe-cially at least about 550 g~denier). The product PV OH
fibers also exhibit shrinka~e at 160C less than 2% in most casesO Preferably the fiber has ~n elongation to break at most 7~
DESCRIPTION OF THE PREFERRED LMBOD~MENTS
Figure 1, illustrates in schematic form a first embodiment of the present invention, ~herein the 35 ~tretching ~ep F is condu~ted in two ~tages on ~he xerogel fiber ~ubsequeng to drying 6tep ~. In Figure 1, a first mixing vessel 10 is shown, which i~ fed with an ultra high molecular weight polymer 11 such as PV-O~ Of --ll--weight average molecular weiyht at least 500,000 and frequently at least 750,000, and to which is also fed a first, relatively non~volatile solvent 12 such as glycerine~ First mixing vessel 10 is equipped with an agitator 13. The residence time of polymer and first solvent in first mixing vessel 10 is sufficient ~o form a slurry containing some dissolved polymer and some relatively finely divided polymer particles, whi~h slurry is removed in line 14 to an intensive mixing vessel 15. Intensive mixing vessel 15 is equipped with helical agitator blades 16. The residence time and agitator speed in intensive mixing vessel 15 is sufficient to convert the slurry into a solution. It will be appreciated that the temperature in intensive mixing vessel 15, either because of external heatiny, heating of the slurry 14, heat generated by the intensive mixing, or a combination of the above is sufficiently high ~e.g. 200C3 to perrnit the polymer to be completely dissolved in the solvent at the desired concentration (generally between 5 and 10 percent polymer, by weight of solution). From the intensive mixing vessel 15, the solution i5 fed to an extrusion device 18, containing a barrel 19 within which is a screw 20 operated by motor 22 to deliver polymer ~5 solution at reasonably high pressure to a gear pump and housing 23 at a controlled flow rate. A motor 24 is provided to drive gear pump 23 and extrude ~he polymer solution, still hot/ through a spinnerette 25 comprising a plurality of aperatures, which may be circular, X-shaped, or, oval-shaped, or in ~ny of a variety of shapes having a relatively small major axis in the plane of the spinnerette when it i5 desired to form fibers, and having a rectangular or other shape with an extended major axis in the plane of the spinnerette when it is desired to form films. The temperature of the solution in the mixing vessel 15, in the extrusion device 18 and at the spinnerette 25 should all equal or exceed a first temperature (e.g. 190C) chosen to exceed the gellation -temperature (approximately 25-1~0C for PV-OH in glycerine). ~he temperature m~y vary (e.g. 190C, 180C) or may be constant (e.g. 190C~ from the mixing vessel 15 to extrusion device 18 to the spinnerette 25~
At all points, however, the concentration of polymer in the solu~ion should be substantially the same. The number of aperatures, and ~hus the number of fibers formed, is not critical, with c~llvenient numbers of apertures being 16, 120, or 240.
From the spinnerette 25, the polymer solution passes through an air gap 27, ~ptionally enclosed and filled with an inert gas such a~ nitroyen, and option-ally provided with a flow of qas to facilitate cooling.
A plurali~y of gel fibers 28 c~ntaining first solvent 15 pass through the air gap 27 and into a quench bath 30 containing any of a variety of liquids, so as to cool ~he fibers, both in ~he air gap 27 and in the quench bath 30, to a second temperature at which the solubility of the polymer in the first sol~ent is relatively low, such that the polymer-solvent ~ystem solidifies to form a gel. It is preferred that ~he quench liquid in quench batch 30 be a hydrocarbon such as paraffin oil. While some stretching in the air gap 27 is permissible, it is preferably less than about lOolo Rollers 31 and 32 in the quench bath 30 oper-rate to feed the fiber through the quench bath, and preferably operate wi~h little or no ~tretch. In the event that some stretching does occur across rollers 31 and 3~, some first solvent exudes out of the fibers and can be collected as a top layer in quench bath 30.
From the quench bath 30, the cool first gel fibers 33 pass to a solvent ex~raction device 37 where a second solvent, being of relati~ely low boiling such as methanol, is fed in through line 38. The solvent out flow in line 40 contains second solvent and essentially all of the ~irst solvent brought in with the cool gel fibers 33/ either dissolved or dispersed in the second solvent. ~hus the fibrous structure 41 conducted out of .
~13-the solvent extraction device 3~ contains substantially only second solvent, and relatively little first sol-vent. The fibrous structure 41 may have shrunken some-what compared to the first gel ibers 33.
In a drying device 45; the second solvent is evaporated from the fibrous structure 41, forming essentially unstretched xerogel fibers 47 which are taken up on spool 52.
From spool 52, or fro~ a plurality of such spools if it is desired to oper~te the stretching line at a slower feed rate than the take up of spool 52 permits, the fibers are fed over driven f~ed roll 54 and idler roll 55 into a first heated tube 56, which may be rectangular, cylindrical or other convenient shape.
Sufficient heat is applied to the tube ~6 to cause the fiber temperature to be between 150-250C. The fibers are stretched at a relatively high draw ratio (e.g. 5:1) so as to form partially s~retched fibers 58 taken up by driven roll 61 and idler roll 62~ From rolls 61 and 62, the fibers are taken through a second heated tube 63, heated so as to be at somewhat higher temperature, e.g. 170-250C and are then taken up by driven take-up roll 65 and idler roll 66, operating at a speed suficient to impart a stretch ratio in heated tube 63 as desired, e.g. 1.8:1. The twice stretched fibers 68 produced ln this first embodiment are taken up on take-up spool 72.
With reference to the six process steps of the present invention, it can be seen that the solution forming step A is conducted in mixers 13 and 15. The extruding step B is conducted with device 18 and 23, and especially through spinnerette ~5. The cooling step C
is conducted in airgap 27 and guench bath 30O Extrac tion step D is conducted in solvent extraction device 37t The drying step E is conducted in drying device 45O The stretching step F is conducted in elements 52- -72, and especially in heated tubes 56 and 63. It will be appreciated, however, that various other parts of the system may also perform some stretching, even at temperatures substan~ially below those of heated tubes 56 and 63. Thus, for example, SO~R stretching (e.g.
2:1) may occur within quench bath 30, within solvent ex raction device 37, within drying device 45 or between solvent extraction device 37 and drying device 45.
~ second embodiment of the present invention is illus~rated in schematic form by ~igure 2. The solution forming and extruding steps A and B of the second embodiment are substantially the same as those in the first embodiment illus~rated in Figure l. Thus, polymer and first solvent are mixed in first mixing vessel 10 and conducted as a slurry in line 14 to intensive mixing device 15 operative to form a hot solution of polymer in first solvent. Extrusion device 18 impells the solution under pressure through the gear pump and housirlg 23 and then through a plurality of apperatures in spinnerette 27. T~e hot first gel fibers 28 pass through air gap 27 and quench ba'ch 30 so as to 20 form cool first gel fibers 33.
The cool first gel fibers 33 are conducted over driven roll 54 and idler roll 55 ~hrough a heated tube 57 which, in general, is lonqer than the first heated tube 56 illustrated in Figure l. The fibers 33 are drawn through heated tube 57 by driven take up roll 59 and idler roll ~n, so as to cause a relatively high stretch ratio (e.g. lOol)~ The ~nce stretched first gel fibers 35 are conducted into extraction device 37.
In the extraction device 37, the first solvent is extracted out of the gel fibers by second solvent and the fibrous structures 42 containing second solvent are conducted to a drying device 45. There the second solvent is evaporated from the ~i~rous structures; and xerogel ibers 48, being once-stretched, are taken up on spool 52.
Fibers on spool 52 are then taken up by driven feed roll 61 and idler 62 and pas~ed through a heated tube 63, operating at the relatively high ~emperature of between 170 and 270C. The fibers are taken up by driven take up roll 65 and idler roll 66 operating at a speed sufficient to impart a stretch in heated tube 63 as desired, e.g. 1.8:1. The twice-stretched fibers 69 produced in the second embodiment are then taken up on spool 72.
It will be appreciated that, by comparing the embodiment of Figure 2 with the embodiment of Figure 1, the stretching step F has been divided into two parts, with the irst part conducted in heated tube 57 per-formed on the first gel fibers 33 prior to extraction (D) and drying tE), and the second part conducted in heated tube 63, being conducted on xerogel fibers 48 subsequent to drying (E).
The third embodiment of the present invention is illustrated in Figure 3, with the solution forming step A, extru6ion step B, and cooling step C being sub-stantially identical to the first embodiment of Figure 1 and the second embodiment of Figure 2. Thus, polymer and first solvent are mixed in first ~ixing vessel 10 and conducted as a slurry in line 14 to in~ensive mixing device 15 operative to form a hot solution of polymer in firs solven~ ExtrusiOn device 18 i~pells the solution under pressure through the gear pump an~ housing 23 and then through a plurality of ~pertures in spinnerette 27. The hot first gel fibers 28 pass ~hrough air gap 27 and quench bath 30 ~o as to form cool first gel fibers 33.
The cool first gel fibers 33 are conducted over driven roll 54 and idler roll 55 through a heated tube 57 whichD in general, is longer than the first heated tube 56 illustrated in Figure 1. The length of heated tube 57 compensates D in general, for the higher velocity of fibers 33 in the third embodiment of Figure
The first temperature is chosen to achieve complete dissolution of the polymer in the first solvent. The first temperature is the minimum tempera-ture at any point between where the solution is formedand the die face, and must be grea~er than the gelation temperature for the polymer in the solvent at ~he first concentration. For PV-OH in glycerine at 5-15~ concen-tration, the gelation temperature is approximately 25-100C; therefore, a preferred first temperature can bebetween 130C and 250C, more preferably 17~-230C.
While temperatures may vary above the first temperature at various points upstream of ~he die face, excessive temperatures causitive of polymer degradation should be avoided. To assure complete solubility, a first temper-ature is chosen whereat the solubility of the polymer exceeds the first concentration and is typically at least 20~ greaterO 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 subse~uent handling. Cooling of the extruded polymer solution from the first temperature to the second temperature should be accomplished at a rate ..
--7~
sufficiently rapid to form a gel fiber which is of substantially the same polymer concentration as existed in the polymer solution. Preferably the rate at which the extruded polymer solution is cooled from the first temperature to the second temperature should be at least 50C per mirute.
A preferred means of rapid cooling to the second temperature involves the use of a quench bath cont~ining a liquid such as a hydrocarbon (e.g., paraf-fin ~il) into which the extruded polymer solution fallsafter passage through an air gap (which may be an inert gas). It is contemplated to combine the quench step with the subsequent extraction by having a second sol vent (e.g~, methanol) as the quench liquid. Normally, however, the quench liquid (e.g.~ parrafin oil) and the first solvent (e.g., glycerol) have only limited miscibility~
Some stretching during cooling to the second temperature is not excluded from the present invention, but ~he total stretching during this stage should not normally exceed 10:1. As a result of those factors the gel fiber formed upon cooling to the second temperature consists of a continuous polymeric network highly swollen with solvent.
If an aperture of circular cross sec~ion (or other cross section without a major axis in the plane perpendicular to the flow direction more than 8 times the s~allest axis in the same plane, such as oval, Y- or X-shaped aperture) is used, then both gels will be gel fibers, the xerogel will be an xerogel fiber and the ther~oplastic 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 10 times the diameter of the aperture ~or other similar major axis), perferably at least 15 times and more preferably .. .
at least 20 times the diameter (or other similar major axis).
I an aperture of rectangular cross section is used~ then both gels will be gel films, the xerogel will be a xerogel film and the thermoplastic article will be a film. The width and heiyht of the aperture are not critical, with representative apertures being between 2.5 mm and 2 m in width ~corresponding to film width), ¦ between 0~25 mm and 5 mm in height (corresponding to film thickness). The depth of the aperture (in the flow direction~ should normally be at least 10 times the height of the aperture, preferably at least 15 times the height and more preferably at least 20 times the height.
The extraction with second solvent is con-ducted in a manner that replaces the first solvent inthe gel with second more volatile solvent. When the first solvent is glycerine or ethylene glycol, suitable second solvents include methanol~ ethanol, ethers, ace-tone, ketones and dioxane. Water is also a suitable second solvent, either for extraction of glycerol (and similar polyol first solvents) or for leaching of aqueous salt solutions as first solvent. The most preferred second solvent is methanol ~B.P. 64.7C).
Preferred second solvents are the volatile solvents having an atmospheric boiling point below 80C, more preferably below 70C. Conditions of extraction should remove the first solvent to less than 1% of the total solvent in the gel.
With some first solvents such as water or ethylene glycol, it is contemplated to evaporate the solvent from the gel fiber near the boiling point o~
the first solvent instead of or prior to extraction.
A preferred combination of conditions is a first temperature between 130C and 250C, a second tem-perature between 0C and 50C and a cooling ratebetween the first temperature and the second temperature of at least 50C/minute. It is preferred that the first solvent be an alcohol. 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), and more preferably less than 10 kPa. In choosing the first and 5 second solvents, the primary desired difference relates to volatility as discussed above.
Once the fibrous structure containing second solvent is formed, it is t.~en Ar ed under conditions where the second solvent is removed leaving the solid network of polymer substantially intact. By analogy to silica gels, the resultant material is called herein a "xerogel" meaning a solid matrix corresponding to the solid matrix o a wet gel, with the liquid replaced by gas (e.g. by an inert gas such as nitrogen or by air).
The term "xerogel" is not intended to delineate any particular type of surface area, porosity or pore size.
A comparison of the xerogels of the present invention with corresponding dried gel fibers prepared according to Phase Separation Spinning is expected to yield some morphological differences.
Stretching may be performed upon the gel fiber after coo1in~ to the second temperature or during or after extraction. Alternatively, stretching of the xerogel fiber may be conducted, or a combination of gel stretch and xerogel stretch may be performed. The stretching may be conducted in a single stage or it may be conducted in two or more stages. The first stage stretching may be conducted at room temperatures or at an elevated temperature. Preferably the stretching is conducted in two or more stages with the last of the stages performed at a temperature between 120C and 250C. Most preferably the stretching is conducted in at least two stages with the last of the stages per-formed at a tempera~ure between 150C and 250C.
Such temperatures may be achieved with heated tubes as in the Figures, or with other heating means such as heating blocks or steam jets.
The product PV-OH fibers produced by the pre-senl: process represent novel articles in that they include ibers with a unique rombination of properties:
a molecular weight of at lea~t about 500,000, a modulus at lPast about 200 g/t3enier" a tenacity at least about 10 g/denier, melting temperature of at least about 238~C. For this fiber~ the ~lecular weigh'c is pre-ferably at leas~ about 7~0,000, more preferably between about 1, 00Q, ono and about ~ ,000, 000 and lllO5t preferably between aboutc 1,500,000 and about 2,500,000. The lû tenacity is preferably at le;~st abc)ut 14 g/denier and more preferably at least about 17 g/denier. ~he tensile modulus is preferably at leas~ about 300 g/denier, mor~
preiEerably 400 g/denier and IlDost preferably at least about 550 g/denier. ~he n~elting point is preferabl~ at least about 245~C.
It is also conte~plated that the preferred other physical properties ~n be achieved without the 238C melting point, especially if the PV-OH contairl~
comonomers ~;uch as unhydrolyzed vinyl acetate. There-fc>re, the invention includes PV-O~ f ibers with molecular weight at least about 750,000" tenacity of at 1east about 14 g/denier and tensile modulus a'c le~st about 300 g/ denier, regardless of melting pointO Again, the more pre~erred value~ are molecular weight between about 1,000,0D0 and about 4,00û,000 tesPecially abou~
1,500,000 - 2,500~000~, tena~ity at least about 17 g/
denier and modulus at least about 400 g/denier (espe-cially at least about 550 g~denier). The product PV OH
fibers also exhibit shrinka~e at 160C less than 2% in most casesO Preferably the fiber has ~n elongation to break at most 7~
DESCRIPTION OF THE PREFERRED LMBOD~MENTS
Figure 1, illustrates in schematic form a first embodiment of the present invention, ~herein the 35 ~tretching ~ep F is condu~ted in two ~tages on ~he xerogel fiber ~ubsequeng to drying 6tep ~. In Figure 1, a first mixing vessel 10 is shown, which i~ fed with an ultra high molecular weight polymer 11 such as PV-O~ Of --ll--weight average molecular weiyht at least 500,000 and frequently at least 750,000, and to which is also fed a first, relatively non~volatile solvent 12 such as glycerine~ First mixing vessel 10 is equipped with an agitator 13. The residence time of polymer and first solvent in first mixing vessel 10 is sufficient ~o form a slurry containing some dissolved polymer and some relatively finely divided polymer particles, whi~h slurry is removed in line 14 to an intensive mixing vessel 15. Intensive mixing vessel 15 is equipped with helical agitator blades 16. The residence time and agitator speed in intensive mixing vessel 15 is sufficient to convert the slurry into a solution. It will be appreciated that the temperature in intensive mixing vessel 15, either because of external heatiny, heating of the slurry 14, heat generated by the intensive mixing, or a combination of the above is sufficiently high ~e.g. 200C3 to perrnit the polymer to be completely dissolved in the solvent at the desired concentration (generally between 5 and 10 percent polymer, by weight of solution). From the intensive mixing vessel 15, the solution i5 fed to an extrusion device 18, containing a barrel 19 within which is a screw 20 operated by motor 22 to deliver polymer ~5 solution at reasonably high pressure to a gear pump and housing 23 at a controlled flow rate. A motor 24 is provided to drive gear pump 23 and extrude ~he polymer solution, still hot/ through a spinnerette 25 comprising a plurality of aperatures, which may be circular, X-shaped, or, oval-shaped, or in ~ny of a variety of shapes having a relatively small major axis in the plane of the spinnerette when it i5 desired to form fibers, and having a rectangular or other shape with an extended major axis in the plane of the spinnerette when it is desired to form films. The temperature of the solution in the mixing vessel 15, in the extrusion device 18 and at the spinnerette 25 should all equal or exceed a first temperature (e.g. 190C) chosen to exceed the gellation -temperature (approximately 25-1~0C for PV-OH in glycerine). ~he temperature m~y vary (e.g. 190C, 180C) or may be constant (e.g. 190C~ from the mixing vessel 15 to extrusion device 18 to the spinnerette 25~
At all points, however, the concentration of polymer in the solu~ion should be substantially the same. The number of aperatures, and ~hus the number of fibers formed, is not critical, with c~llvenient numbers of apertures being 16, 120, or 240.
From the spinnerette 25, the polymer solution passes through an air gap 27, ~ptionally enclosed and filled with an inert gas such a~ nitroyen, and option-ally provided with a flow of qas to facilitate cooling.
A plurali~y of gel fibers 28 c~ntaining first solvent 15 pass through the air gap 27 and into a quench bath 30 containing any of a variety of liquids, so as to cool ~he fibers, both in ~he air gap 27 and in the quench bath 30, to a second temperature at which the solubility of the polymer in the first sol~ent is relatively low, such that the polymer-solvent ~ystem solidifies to form a gel. It is preferred that ~he quench liquid in quench batch 30 be a hydrocarbon such as paraffin oil. While some stretching in the air gap 27 is permissible, it is preferably less than about lOolo Rollers 31 and 32 in the quench bath 30 oper-rate to feed the fiber through the quench bath, and preferably operate wi~h little or no ~tretch. In the event that some stretching does occur across rollers 31 and 3~, some first solvent exudes out of the fibers and can be collected as a top layer in quench bath 30.
From the quench bath 30, the cool first gel fibers 33 pass to a solvent ex~raction device 37 where a second solvent, being of relati~ely low boiling such as methanol, is fed in through line 38. The solvent out flow in line 40 contains second solvent and essentially all of the ~irst solvent brought in with the cool gel fibers 33/ either dissolved or dispersed in the second solvent. ~hus the fibrous structure 41 conducted out of .
~13-the solvent extraction device 3~ contains substantially only second solvent, and relatively little first sol-vent. The fibrous structure 41 may have shrunken some-what compared to the first gel ibers 33.
In a drying device 45; the second solvent is evaporated from the fibrous structure 41, forming essentially unstretched xerogel fibers 47 which are taken up on spool 52.
From spool 52, or fro~ a plurality of such spools if it is desired to oper~te the stretching line at a slower feed rate than the take up of spool 52 permits, the fibers are fed over driven f~ed roll 54 and idler roll 55 into a first heated tube 56, which may be rectangular, cylindrical or other convenient shape.
Sufficient heat is applied to the tube ~6 to cause the fiber temperature to be between 150-250C. The fibers are stretched at a relatively high draw ratio (e.g. 5:1) so as to form partially s~retched fibers 58 taken up by driven roll 61 and idler roll 62~ From rolls 61 and 62, the fibers are taken through a second heated tube 63, heated so as to be at somewhat higher temperature, e.g. 170-250C and are then taken up by driven take-up roll 65 and idler roll 66, operating at a speed suficient to impart a stretch ratio in heated tube 63 as desired, e.g. 1.8:1. The twice stretched fibers 68 produced ln this first embodiment are taken up on take-up spool 72.
With reference to the six process steps of the present invention, it can be seen that the solution forming step A is conducted in mixers 13 and 15. The extruding step B is conducted with device 18 and 23, and especially through spinnerette ~5. The cooling step C
is conducted in airgap 27 and guench bath 30O Extrac tion step D is conducted in solvent extraction device 37t The drying step E is conducted in drying device 45O The stretching step F is conducted in elements 52- -72, and especially in heated tubes 56 and 63. It will be appreciated, however, that various other parts of the system may also perform some stretching, even at temperatures substan~ially below those of heated tubes 56 and 63. Thus, for example, SO~R stretching (e.g.
2:1) may occur within quench bath 30, within solvent ex raction device 37, within drying device 45 or between solvent extraction device 37 and drying device 45.
~ second embodiment of the present invention is illus~rated in schematic form by ~igure 2. The solution forming and extruding steps A and B of the second embodiment are substantially the same as those in the first embodiment illus~rated in Figure l. Thus, polymer and first solvent are mixed in first mixing vessel 10 and conducted as a slurry in line 14 to intensive mixing device 15 operative to form a hot solution of polymer in first solvent. Extrusion device 18 impells the solution under pressure through the gear pump and housirlg 23 and then through a plurality of apperatures in spinnerette 27. T~e hot first gel fibers 28 pass through air gap 27 and quench ba'ch 30 so as to 20 form cool first gel fibers 33.
The cool first gel fibers 33 are conducted over driven roll 54 and idler roll 55 ~hrough a heated tube 57 which, in general, is lonqer than the first heated tube 56 illustrated in Figure l. The fibers 33 are drawn through heated tube 57 by driven take up roll 59 and idler roll ~n, so as to cause a relatively high stretch ratio (e.g. lOol)~ The ~nce stretched first gel fibers 35 are conducted into extraction device 37.
In the extraction device 37, the first solvent is extracted out of the gel fibers by second solvent and the fibrous structures 42 containing second solvent are conducted to a drying device 45. There the second solvent is evaporated from the ~i~rous structures; and xerogel ibers 48, being once-stretched, are taken up on spool 52.
Fibers on spool 52 are then taken up by driven feed roll 61 and idler 62 and pas~ed through a heated tube 63, operating at the relatively high ~emperature of between 170 and 270C. The fibers are taken up by driven take up roll 65 and idler roll 66 operating at a speed sufficient to impart a stretch in heated tube 63 as desired, e.g. 1.8:1. The twice-stretched fibers 69 produced in the second embodiment are then taken up on spool 72.
It will be appreciated that, by comparing the embodiment of Figure 2 with the embodiment of Figure 1, the stretching step F has been divided into two parts, with the irst part conducted in heated tube 57 per-formed on the first gel fibers 33 prior to extraction (D) and drying tE), and the second part conducted in heated tube 63, being conducted on xerogel fibers 48 subsequent to drying (E).
The third embodiment of the present invention is illustrated in Figure 3, with the solution forming step A, extru6ion step B, and cooling step C being sub-stantially identical to the first embodiment of Figure 1 and the second embodiment of Figure 2. Thus, polymer and first solvent are mixed in first ~ixing vessel 10 and conducted as a slurry in line 14 to in~ensive mixing device 15 operative to form a hot solution of polymer in firs solven~ ExtrusiOn device 18 i~pells the solution under pressure through the gear pump an~ housing 23 and then through a plurality of ~pertures in spinnerette 27. The hot first gel fibers 28 pass ~hrough air gap 27 and quench bath 30 ~o as to form cool first gel fibers 33.
The cool first gel fibers 33 are conducted over driven roll 54 and idler roll 55 through a heated tube 57 whichD in general, is longer than the first heated tube 56 illustrated in Figure 1. The length of heated tube 57 compensates D in general, for the higher velocity of fibers 33 in the third embodiment of Figure
3 compared to the velocity of xerogel fibers l47~
between takeup spool S2 and heated tube 56 in the first embodiment of Figure 1. The first gel fib~rs 33 are now ~æ~o~
taken up by driven roll 61 and idler ro~l 62, operative to cause the stretch ra~io in heated tu~e 57 to be as desired, e.g. 5:1.
From rolls ~1 and 62, the once-drawn first gel fibers 35 are conducted into modified heated tube 64 and drawn by driven take up roll 65 and idler roll 66.
Driven roll 65 is operated sufficiently fast to draw the fibers in heated tube 64 at the desired stretch ratio, ¦ e.g. 1.8:1. Because of the relatively high line speed in heated tube 64, required generally to match the speed of once-drawn gel fibers 35 coming off o~ rolls 61 and 62, heated tube 64 in the third embodiment of Figure 3 will, in general, be longer than heated tube 63 in either the second embodiment of Figure 2 or the first embodiment of Figure 1. While first solvent may exude from the fiber during stretching in heated tubes 57 and 64 (and be collected at the exit of each tube), the first solvent is sufficiently non-volatile so as not to evaporate to an appreciable extent in e~her of these heated tubesO
The twice-stretched first gel fiber 36 is then conducted through solvent extraction de~ice 37, where the second, volatile solvent extracts the first solvent out of the fibers~ The fibrous structures 43, contain-ing substantially only second solvent, ~e then dried i~drying device 45, and the twice-stretched fibers 70 are then taken up on spool 72.
It will be appreciated that, by comparing the third embodiment of Figure 3 to the first two embodi-ments of Figures 1 and 2, the stretchin~ step (F) isperformed in the third embodiment in tWD stages, both subsequent to cooling step C and prior ~ solvent extracting step D.
The process of the invention wi11 be further illustrated by the examples below.
~XAMPL,ES
The poly(vinyl alcohol) (PV-Oi-l) used in the follow-ing examples was prepared by the method of U.S. Patent A,463,138. The general procedures were as follows:
Poly(vinyl alcohol) A
S
The polymerization reactor consisted of a Pyrex~
cylindrical tube having a diameter of 50 mm and a height of 230 mm. The reactor had a tubular neck of 15 mm diameter topped with a vacuum valve. The reactor was placed in a vacuum jacketed Dewar flask filled wi-th methanol as a coolant which was cooled by a CryoCool cc-100 immersion cooler (Neslab Instruments, Inc~). A
medium pressure ultraviolet lamp was placed outside the Dewar flask about 75 mm frorn the reactor.
Commercial high purity vinyl acetate was refrac~
tionated in a 200-plate spinning band column~ The middle fraction having a boiling point of about 72.2~C
was collected and used as the monomer for preparing poly(vinyl acetate). The monomer was purified further by five cycles of a freeze-thaw degassing process in a hlgh vacuum. About three hundred grams of the purified and degassed vinyl acetate was transferred into the reactor which contained 14 mg of recrystallized azo~
bisisobutyronitrile. The initiator concentration was about 208 x 10 4 M.
The reactor was immersed in a methanol bath having a controlled temperature of -40C and irradiated with ultraviolet light over a period of 96 hours. The reac-tion mixture became a very viscous material. The unreacted monomer was distilled from the mixture under vacuum, leaving 87 grams of residue The latter was dissolved in ace-tone and then precipitated into hexane. The polymer formed was dried in a vacuum oven at 50C, yielding 54.3 grams (]~ conversion) of poly-(vinyl acetate). The intrinsic viscosity was determined to be 6.22 dL/g which corresponds to a viscosity average molecular weight of 2.7 x 106. The intrinsic viscosity measurement was conducted in tetrahydroEuran at 25C.
Alcoholysis of the poly(vinyl acetate) was accomplished by initially dissolving and stirring the poly(vinyl acetate) in about one liter of methanol. To this mixture was added 2.5 g of potassiu~ hydroxide dissolved in 50 mL of methanol, The mix~ure was stirred ¦ vigorously at room temperature. After ~bout 30 minutes, the mixture became a gel-like mass. The lat-ter was chopped into small pieces and extracted three times with methanol for removal of residual potassium salts~ The polymer was dried in a vacuum oven at 50C, yielding 24.5 grams of poly(vinyl alcohol)O
Reacetylation was accomplished by heating a 0.3 gram sample of the poly(vinyl alcohol) in a solution containing 15 mL of acetic anhydride, 5 mL of glacial acetic acid; and 1 mL of pyridine in a 125C bath under nitrogen for 4 hours. The solution formed was precipi-tated into ~ater, washed three times in water, redis-solved in acetone, reprecipitated into hexane, and dried. The intrinsic viscosity of the reacetylated poly(vinyl acetate) was 6.52 dL/g.
Poly(vinyl alcohol) B and C
The reactor employed in this Example was a quartz tube having a 1.5 liter capacity and 76 mm diam-eter. The ultraviolet apparatus was a Special Prepara-tive Photochemical Reactor, RPR-208 (The Southern New England Ultraviolet Company, Hamden, Connecticut)~
The reactor was immersed in a cooling bath surrounded by eight U-shape UV lamps.
A dry, nitrogen filled quartz reactor of the above-described type was charged with 508 g of purified vinyl acetate and 6.5 mg of azobisisobutyronitrile. The intiator concentration was about 8 x 10 molar. After four cycles of freeze-thaw operations the reactor was immersed in a methanol bath at -40C and irradiated with ultraviolet light for about 80 hours. After the unreacted monomer had been recovered vla standard dis-tillation procedures, the residue was dissolved in ace-tone forming l~S liters of solution~ One half of the acetone solution was precipitated into hexane as described in A~ above, while the other half was pre-cipitated into water. These two batches of poly(vinyl aceta~e) (B and C, respectively) had intrinsic vis-cosities c~ 6.3~ and 6.~7 dL/g, respectively, which corresponds to viscosity average molecular weights of 10 about 2.7 x 1o6 and about 2.9 x 106. The total conversion of monomer was 12%.
Both were then hydrolyzed to poly(vinyl alcohol) as described in A.
Poly(vinyl alcohol) D
The polymerization was performed according to the procedure described for ~ and C except that the irradiation time (length of polymerization) was 96 hours. The conversion of monomeric vinyl acetate was 13.8~ and the intrinsic viscosity was 7.26 dL/g, which corresponds to a viscosity average molecular weight of about 3.3 x 106. The weight average molecular weight of this polymer measured by a light scattering technique was found to be 3.6 x 10~.
Poly(vinyl alcohol~ E
A mixture containing 4.6 mg of azobisisobutyro-nitrile and 762 grams of pure vinyl acetate was placed in a Pyrex~ glass reactor tube of 85 mm diameter and 430 mm length (capacity 2 liters). After four freeze-thaw cycles of degassing, the mixture was immersed in a methanol bath at -30C and irradiated with ultraviolet light for 66 hours. After the unreacted monomer had been removed, the residue was dissolved in acetone and the solution obtained was added to hexane with stirring whereby the poly(vinyl acetate) was precipi~ated. There 35 was obtained 76.2 grams ~10% conversion) of polymer with an intrinsic viscosity of 6.62 dL/g which corresponds to a viscosity average molecuar weight of about 2~ x 10 .
The poly(vinyl acetate) was hydrolyzed in .
methanol as described for A. A sample of the poly(vinyl alcohol~ formed was reacetylated as described for Ao The intrinsic viscosity of the reacetylated polymer was found to be 6.52 dL/g ~hich is corresponding to a molecular weight of about 2.9 x 106O Thus, reacetyla-tion demonstrated that the poly(vinyl acetate) origi-nally formed was essentially linear. The batches of PV-OH prepared by these procedures are used in the following examples, with the identification, approximate molecular weight (weight average~ and aspects of preparation differing from the above tabulation and in Table I:
TABLE I
Spinning 15 PV~OH Mol Wt*Scale Process Features A 2.7x1065 g/run B 2.7x1065 g/run precipitated with water C 2.9x1065 g/run precipitated with hexane D 3.3x106 precipitated with hexane E 2.9x10 *The indicated molecular weights are for polyvinyl ace tate. The PV-OH molecular weights would be one-half these values.
Example 1 An oil-jacke~ed double helical tHELICONE~) mixer constructed by Atlantic Research Corporation was charged with a 6.0 weight percent solution of the PV-OH
labeled "A" in Table I having a molecular weight of approximately 1.3 million and 94 weight percent glycerin.
The charge was heated ~ith agitation at 75 rev/min to 190C under nitrogen pressure over a period of two hours. After reaching 190C, agitation was maintained for an additional two hours.
In Examples l-5 the solution was discharged into a syringe-type ræ~ extruder at the mixing tempera-ture (190C in this E~ample 1) and expelled through a 0.8 mm diameter aperture at a reasonably constant rate o 0.7 cm3/min.
The extruded uniform solution filament was quenched to a gel state by passage through a paraffin oil bath located at a distance of 5 cm below the spin-ning die. The gel filament was wound up continu-ously on a 2.5 cm (one inch~ diameter bobbin at the rateof 2.5 m/min (8 feet/min). The fibers were drawn at feed rate of 260 cm/min and a 2.~.1 ratio at room temperature.
The bobbin of gel fiber was then immersed in methanol to exchange this second solvent for glycerin ~and paraffin oil from the ~uench bath~. The methanol bath was changed three times over 48 hours. The fibrous product containing methanol was unwound from the bobbin and the methanol solvent evaporated at 25C for 5 minutes.
The dried (xerogel) fiber was 188 denier.
Part of this fiber was fed at sn cm/min into a hot tube (180 cm) (six eet) long blanketed with nitrogen and maintained at 230C. The fiber was stretched continu-ously 4.9/1 within the hot tube. The once-stretched fiber was then stretched in the same tube 1.54/1 at a tube temperature of 252C. The properties of the twice-stretched fiber were:
denier - 25 tenacity - 17.4 g/denier modulus - 446 g/denier elongation - 3.3 Example 2 A second part of the dried gel fiber of Example 1 was stretched in the 180 cm tube at 231C at a feed rate of 50 cm/min and a draw ratio of 5O33:1.
The properties of this once-stretched fiber were:
denier - 31 tenacity - 14.5 g/denier modulus - 426 g/denier elongation - 3.5%
Example 3 The procedures of ~xample 1 were repeated using the polymer labeled "A" in Table 1, but using ethylene glycol as solvent ~n place of glycerol, and with the mixing and extrusi~n conducted at 170C in-stead of 190C. ~he room temperature draw oE the gel fibers was at a 2:1 draw ra~o and the methanol ex-traction was conducted over 40 hours with the methanol replaced twice. A portion u~ the dried gel fiber was stretched in the 180 cm tube at 250C at a feed speed of 60 cm/min and a draw ratio of 5.g:1. The properties of the once~stretched fibers were:
denier ~ 22 tenacity - 10.6 g/denier modulus - 341 g/denier elongation - 3.5%
Examp~e 4 A second portion o~ the dried gel fiber of Example 3 was stretched twi~ in the 180 cm tube: first at 217C with a feed speed ~f 60 cm/min and a draw ratio of 4~83:1, second at ~40C with a feed speed of 60 cm/min and a draw ratio of 1~98:1. The properties of this twice-stretched fiber ~ere:
denier - 18 tenacity - 13 g/denier modulus - 385 g/denier elongation - 4.0%
Example 5 -Example 1 was repe~ted using the polymer labeled "B" in Table 1 as a 6% solution in glycerol at 210C mixed over 5-1/4 hour~ The spin rate was 0.4 cm3/min rather than the 0.7 cm3/min used in Examples 1 and 3. The room temperature draw was at a ~eed rate of 310 cm/min and a 1.98:1 ratio and the extraction was conducted over 64 hours, with the methanol changed twice.
The dried fibers were stretched once in the 180 cm tube at 254C with a 39 cm/min feed rate and a 4.6.1 draw ratio. The properties of t~e once-stretched fibers were:
~2~
denier 23 tenacity - 19.2 g/denier modulus - 546 g/denier elongation - 4.5%
The results of Examples 1-5 are summarized in Table 2.
Polymer A A A A B
10 Solvent G G EG EG G
Spin Temp (P~) 190 190 170 170 210 Spin Ra~e (cm /min) 0.7 0.7 0.7 0-7 0~4 R.T. Draw Ratio 2.04 2~04 2.00 2.00 1.98 1st Stage Draw Temp 230 231 250 217 254 1st Stage Draw Ratio 4.90 5.33 5O90 4.83 4.60 2nd Stage Draw Temp 252 -- -- 240 --2nd Stage Draw Ratio 1.54 ~ 1.98 --Fiber Denier 25 31 22 18 23 Tenacity 17.4 14.5 10O6 13.0 19.2 Modulus 446 426 341 385 546 Elongation 3.3 3.5 3.5 4.0 4.5 G = glycerol EG = ethylene glycol A, B refer to the polymers of Table 1 Example 6 -Example 1 was repeated using a melt pump and one-aperture die in place of the syringe-type ram extru~
der. A 5.5% solution of polymer D in glycerin was used.
Thus, the bottom discharge opening of the Helicone~
mixer was fitted with a metering pump and a single hole capillary spinning die of 0.8 mm diameter and 20 mm length. The temperature of the spinning die was maintained ~t 190C as the solution was extruded by the metering pu~p through the die at a rate of 1.70 cm3/min, with a g m/~in take up speed. There was no room tem-perature draw~ The first stage draw was in a six feet s~ (180 cm) long tube purged with nitrogen with the first -2~-half at 75C, the second half at 220C. The feed speed was 99.4 cm/min, and the draw ratio was 2~6:1. The second stage draw was conducted with the first half of the same tube at 205C, the second half at 261C, the feed speed at 121.1 cm/min and the draw ratio oE 1.34:1.
The properties of the product fiber were 24 denier, 19 g/denier tenacity, 628 g~den~er modulus and 3.9%
elongation to breakO With appropriate modification of stretching equipment it is expected that higher draw ratios and, therefore, better properties will be achieved.
y
between takeup spool S2 and heated tube 56 in the first embodiment of Figure 1. The first gel fib~rs 33 are now ~æ~o~
taken up by driven roll 61 and idler ro~l 62, operative to cause the stretch ra~io in heated tu~e 57 to be as desired, e.g. 5:1.
From rolls ~1 and 62, the once-drawn first gel fibers 35 are conducted into modified heated tube 64 and drawn by driven take up roll 65 and idler roll 66.
Driven roll 65 is operated sufficiently fast to draw the fibers in heated tube 64 at the desired stretch ratio, ¦ e.g. 1.8:1. Because of the relatively high line speed in heated tube 64, required generally to match the speed of once-drawn gel fibers 35 coming off o~ rolls 61 and 62, heated tube 64 in the third embodiment of Figure 3 will, in general, be longer than heated tube 63 in either the second embodiment of Figure 2 or the first embodiment of Figure 1. While first solvent may exude from the fiber during stretching in heated tubes 57 and 64 (and be collected at the exit of each tube), the first solvent is sufficiently non-volatile so as not to evaporate to an appreciable extent in e~her of these heated tubesO
The twice-stretched first gel fiber 36 is then conducted through solvent extraction de~ice 37, where the second, volatile solvent extracts the first solvent out of the fibers~ The fibrous structures 43, contain-ing substantially only second solvent, ~e then dried i~drying device 45, and the twice-stretched fibers 70 are then taken up on spool 72.
It will be appreciated that, by comparing the third embodiment of Figure 3 to the first two embodi-ments of Figures 1 and 2, the stretchin~ step (F) isperformed in the third embodiment in tWD stages, both subsequent to cooling step C and prior ~ solvent extracting step D.
The process of the invention wi11 be further illustrated by the examples below.
~XAMPL,ES
The poly(vinyl alcohol) (PV-Oi-l) used in the follow-ing examples was prepared by the method of U.S. Patent A,463,138. The general procedures were as follows:
Poly(vinyl alcohol) A
S
The polymerization reactor consisted of a Pyrex~
cylindrical tube having a diameter of 50 mm and a height of 230 mm. The reactor had a tubular neck of 15 mm diameter topped with a vacuum valve. The reactor was placed in a vacuum jacketed Dewar flask filled wi-th methanol as a coolant which was cooled by a CryoCool cc-100 immersion cooler (Neslab Instruments, Inc~). A
medium pressure ultraviolet lamp was placed outside the Dewar flask about 75 mm frorn the reactor.
Commercial high purity vinyl acetate was refrac~
tionated in a 200-plate spinning band column~ The middle fraction having a boiling point of about 72.2~C
was collected and used as the monomer for preparing poly(vinyl acetate). The monomer was purified further by five cycles of a freeze-thaw degassing process in a hlgh vacuum. About three hundred grams of the purified and degassed vinyl acetate was transferred into the reactor which contained 14 mg of recrystallized azo~
bisisobutyronitrile. The initiator concentration was about 208 x 10 4 M.
The reactor was immersed in a methanol bath having a controlled temperature of -40C and irradiated with ultraviolet light over a period of 96 hours. The reac-tion mixture became a very viscous material. The unreacted monomer was distilled from the mixture under vacuum, leaving 87 grams of residue The latter was dissolved in ace-tone and then precipitated into hexane. The polymer formed was dried in a vacuum oven at 50C, yielding 54.3 grams (]~ conversion) of poly-(vinyl acetate). The intrinsic viscosity was determined to be 6.22 dL/g which corresponds to a viscosity average molecular weight of 2.7 x 106. The intrinsic viscosity measurement was conducted in tetrahydroEuran at 25C.
Alcoholysis of the poly(vinyl acetate) was accomplished by initially dissolving and stirring the poly(vinyl acetate) in about one liter of methanol. To this mixture was added 2.5 g of potassiu~ hydroxide dissolved in 50 mL of methanol, The mix~ure was stirred ¦ vigorously at room temperature. After ~bout 30 minutes, the mixture became a gel-like mass. The lat-ter was chopped into small pieces and extracted three times with methanol for removal of residual potassium salts~ The polymer was dried in a vacuum oven at 50C, yielding 24.5 grams of poly(vinyl alcohol)O
Reacetylation was accomplished by heating a 0.3 gram sample of the poly(vinyl alcohol) in a solution containing 15 mL of acetic anhydride, 5 mL of glacial acetic acid; and 1 mL of pyridine in a 125C bath under nitrogen for 4 hours. The solution formed was precipi-tated into ~ater, washed three times in water, redis-solved in acetone, reprecipitated into hexane, and dried. The intrinsic viscosity of the reacetylated poly(vinyl acetate) was 6.52 dL/g.
Poly(vinyl alcohol) B and C
The reactor employed in this Example was a quartz tube having a 1.5 liter capacity and 76 mm diam-eter. The ultraviolet apparatus was a Special Prepara-tive Photochemical Reactor, RPR-208 (The Southern New England Ultraviolet Company, Hamden, Connecticut)~
The reactor was immersed in a cooling bath surrounded by eight U-shape UV lamps.
A dry, nitrogen filled quartz reactor of the above-described type was charged with 508 g of purified vinyl acetate and 6.5 mg of azobisisobutyronitrile. The intiator concentration was about 8 x 10 molar. After four cycles of freeze-thaw operations the reactor was immersed in a methanol bath at -40C and irradiated with ultraviolet light for about 80 hours. After the unreacted monomer had been recovered vla standard dis-tillation procedures, the residue was dissolved in ace-tone forming l~S liters of solution~ One half of the acetone solution was precipitated into hexane as described in A~ above, while the other half was pre-cipitated into water. These two batches of poly(vinyl aceta~e) (B and C, respectively) had intrinsic vis-cosities c~ 6.3~ and 6.~7 dL/g, respectively, which corresponds to viscosity average molecular weights of 10 about 2.7 x 1o6 and about 2.9 x 106. The total conversion of monomer was 12%.
Both were then hydrolyzed to poly(vinyl alcohol) as described in A.
Poly(vinyl alcohol) D
The polymerization was performed according to the procedure described for ~ and C except that the irradiation time (length of polymerization) was 96 hours. The conversion of monomeric vinyl acetate was 13.8~ and the intrinsic viscosity was 7.26 dL/g, which corresponds to a viscosity average molecular weight of about 3.3 x 106. The weight average molecular weight of this polymer measured by a light scattering technique was found to be 3.6 x 10~.
Poly(vinyl alcohol~ E
A mixture containing 4.6 mg of azobisisobutyro-nitrile and 762 grams of pure vinyl acetate was placed in a Pyrex~ glass reactor tube of 85 mm diameter and 430 mm length (capacity 2 liters). After four freeze-thaw cycles of degassing, the mixture was immersed in a methanol bath at -30C and irradiated with ultraviolet light for 66 hours. After the unreacted monomer had been removed, the residue was dissolved in acetone and the solution obtained was added to hexane with stirring whereby the poly(vinyl acetate) was precipi~ated. There 35 was obtained 76.2 grams ~10% conversion) of polymer with an intrinsic viscosity of 6.62 dL/g which corresponds to a viscosity average molecuar weight of about 2~ x 10 .
The poly(vinyl acetate) was hydrolyzed in .
methanol as described for A. A sample of the poly(vinyl alcohol~ formed was reacetylated as described for Ao The intrinsic viscosity of the reacetylated polymer was found to be 6.52 dL/g ~hich is corresponding to a molecular weight of about 2.9 x 106O Thus, reacetyla-tion demonstrated that the poly(vinyl acetate) origi-nally formed was essentially linear. The batches of PV-OH prepared by these procedures are used in the following examples, with the identification, approximate molecular weight (weight average~ and aspects of preparation differing from the above tabulation and in Table I:
TABLE I
Spinning 15 PV~OH Mol Wt*Scale Process Features A 2.7x1065 g/run B 2.7x1065 g/run precipitated with water C 2.9x1065 g/run precipitated with hexane D 3.3x106 precipitated with hexane E 2.9x10 *The indicated molecular weights are for polyvinyl ace tate. The PV-OH molecular weights would be one-half these values.
Example 1 An oil-jacke~ed double helical tHELICONE~) mixer constructed by Atlantic Research Corporation was charged with a 6.0 weight percent solution of the PV-OH
labeled "A" in Table I having a molecular weight of approximately 1.3 million and 94 weight percent glycerin.
The charge was heated ~ith agitation at 75 rev/min to 190C under nitrogen pressure over a period of two hours. After reaching 190C, agitation was maintained for an additional two hours.
In Examples l-5 the solution was discharged into a syringe-type ræ~ extruder at the mixing tempera-ture (190C in this E~ample 1) and expelled through a 0.8 mm diameter aperture at a reasonably constant rate o 0.7 cm3/min.
The extruded uniform solution filament was quenched to a gel state by passage through a paraffin oil bath located at a distance of 5 cm below the spin-ning die. The gel filament was wound up continu-ously on a 2.5 cm (one inch~ diameter bobbin at the rateof 2.5 m/min (8 feet/min). The fibers were drawn at feed rate of 260 cm/min and a 2.~.1 ratio at room temperature.
The bobbin of gel fiber was then immersed in methanol to exchange this second solvent for glycerin ~and paraffin oil from the ~uench bath~. The methanol bath was changed three times over 48 hours. The fibrous product containing methanol was unwound from the bobbin and the methanol solvent evaporated at 25C for 5 minutes.
The dried (xerogel) fiber was 188 denier.
Part of this fiber was fed at sn cm/min into a hot tube (180 cm) (six eet) long blanketed with nitrogen and maintained at 230C. The fiber was stretched continu-ously 4.9/1 within the hot tube. The once-stretched fiber was then stretched in the same tube 1.54/1 at a tube temperature of 252C. The properties of the twice-stretched fiber were:
denier - 25 tenacity - 17.4 g/denier modulus - 446 g/denier elongation - 3.3 Example 2 A second part of the dried gel fiber of Example 1 was stretched in the 180 cm tube at 231C at a feed rate of 50 cm/min and a draw ratio of 5O33:1.
The properties of this once-stretched fiber were:
denier - 31 tenacity - 14.5 g/denier modulus - 426 g/denier elongation - 3.5%
Example 3 The procedures of ~xample 1 were repeated using the polymer labeled "A" in Table 1, but using ethylene glycol as solvent ~n place of glycerol, and with the mixing and extrusi~n conducted at 170C in-stead of 190C. ~he room temperature draw oE the gel fibers was at a 2:1 draw ra~o and the methanol ex-traction was conducted over 40 hours with the methanol replaced twice. A portion u~ the dried gel fiber was stretched in the 180 cm tube at 250C at a feed speed of 60 cm/min and a draw ratio of 5.g:1. The properties of the once~stretched fibers were:
denier ~ 22 tenacity - 10.6 g/denier modulus - 341 g/denier elongation - 3.5%
Examp~e 4 A second portion o~ the dried gel fiber of Example 3 was stretched twi~ in the 180 cm tube: first at 217C with a feed speed ~f 60 cm/min and a draw ratio of 4~83:1, second at ~40C with a feed speed of 60 cm/min and a draw ratio of 1~98:1. The properties of this twice-stretched fiber ~ere:
denier - 18 tenacity - 13 g/denier modulus - 385 g/denier elongation - 4.0%
Example 5 -Example 1 was repe~ted using the polymer labeled "B" in Table 1 as a 6% solution in glycerol at 210C mixed over 5-1/4 hour~ The spin rate was 0.4 cm3/min rather than the 0.7 cm3/min used in Examples 1 and 3. The room temperature draw was at a ~eed rate of 310 cm/min and a 1.98:1 ratio and the extraction was conducted over 64 hours, with the methanol changed twice.
The dried fibers were stretched once in the 180 cm tube at 254C with a 39 cm/min feed rate and a 4.6.1 draw ratio. The properties of t~e once-stretched fibers were:
~2~
denier 23 tenacity - 19.2 g/denier modulus - 546 g/denier elongation - 4.5%
The results of Examples 1-5 are summarized in Table 2.
Polymer A A A A B
10 Solvent G G EG EG G
Spin Temp (P~) 190 190 170 170 210 Spin Ra~e (cm /min) 0.7 0.7 0.7 0-7 0~4 R.T. Draw Ratio 2.04 2~04 2.00 2.00 1.98 1st Stage Draw Temp 230 231 250 217 254 1st Stage Draw Ratio 4.90 5.33 5O90 4.83 4.60 2nd Stage Draw Temp 252 -- -- 240 --2nd Stage Draw Ratio 1.54 ~ 1.98 --Fiber Denier 25 31 22 18 23 Tenacity 17.4 14.5 10O6 13.0 19.2 Modulus 446 426 341 385 546 Elongation 3.3 3.5 3.5 4.0 4.5 G = glycerol EG = ethylene glycol A, B refer to the polymers of Table 1 Example 6 -Example 1 was repeated using a melt pump and one-aperture die in place of the syringe-type ram extru~
der. A 5.5% solution of polymer D in glycerin was used.
Thus, the bottom discharge opening of the Helicone~
mixer was fitted with a metering pump and a single hole capillary spinning die of 0.8 mm diameter and 20 mm length. The temperature of the spinning die was maintained ~t 190C as the solution was extruded by the metering pu~p through the die at a rate of 1.70 cm3/min, with a g m/~in take up speed. There was no room tem-perature draw~ The first stage draw was in a six feet s~ (180 cm) long tube purged with nitrogen with the first -2~-half at 75C, the second half at 220C. The feed speed was 99.4 cm/min, and the draw ratio was 2~6:1. The second stage draw was conducted with the first half of the same tube at 205C, the second half at 261C, the feed speed at 121.1 cm/min and the draw ratio oE 1.34:1.
The properties of the product fiber were 24 denier, 19 g/denier tenacity, 628 g~den~er modulus and 3.9%
elongation to breakO With appropriate modification of stretching equipment it is expected that higher draw ratios and, therefore, better properties will be achieved.
y
Claims (29)
1. A process comprising the steps:
(a) forming a solution of a linear polyvinyl alcohol having a weight average molecular weight at least 500,000 in a first solvent which is non volatile under processing conditions at a first concentration between about 2 and about 15 weight percent polyvinyl alcohol, (b) extruding said solution through an aperture, said solution being at a temperature no less than a first tempera-ture upstream of the aperture and being substantially at the first concentration both upstream and downstream of said aperture, (c) cooling the solution adjacent to and downstream of the aperture to a second temperature below the temperature at which a rubbery gel is formed, forming a gel containing first solvent of substantially indefinite length, (d) extracting the gel containing first solvent with a second, volatile solvent for a sufficient contact time to form a fibrous structure containing second solvent, which gel is substantially free of first solvent and is of substantially indefinite length;
(e) drying the fibrous structure containing second solvent to form a xerogel of substantially indefinite length free of first and second solvent; and (f) stretching at least one of:
(i) the gel containing the first solvent, (ii) the fibrous structure containing the second solvent and, (iii) the xerogel, at a total stretch ratio sufficient to achieve a tenacity of at least about 10g/denier and a modulus of at least about 200 g/denier.
(a) forming a solution of a linear polyvinyl alcohol having a weight average molecular weight at least 500,000 in a first solvent which is non volatile under processing conditions at a first concentration between about 2 and about 15 weight percent polyvinyl alcohol, (b) extruding said solution through an aperture, said solution being at a temperature no less than a first tempera-ture upstream of the aperture and being substantially at the first concentration both upstream and downstream of said aperture, (c) cooling the solution adjacent to and downstream of the aperture to a second temperature below the temperature at which a rubbery gel is formed, forming a gel containing first solvent of substantially indefinite length, (d) extracting the gel containing first solvent with a second, volatile solvent for a sufficient contact time to form a fibrous structure containing second solvent, which gel is substantially free of first solvent and is of substantially indefinite length;
(e) drying the fibrous structure containing second solvent to form a xerogel of substantially indefinite length free of first and second solvent; and (f) stretching at least one of:
(i) the gel containing the first solvent, (ii) the fibrous structure containing the second solvent and, (iii) the xerogel, at a total stretch ratio sufficient to achieve a tenacity of at least about 10g/denier and a modulus of at least about 200 g/denier.
2. The process of claim 1 wherein said aperture has an essentially circular cross-section; said gel containing first solvent is a gel fiber; said xerogel is a xerogel fiber;
and said thermoplastic article is a fiber.
and said thermoplastic article is a fiber.
3. The process of claim 1 wherein said first temperature is between about 130°C and about 250°C; said second temperature is between about 0°C and about 50°C;
the cooling rate between said first temperature and said second temperature is at least about 50°C/min; and said first solvent is an alcohol.
the cooling rate between said first temperature and said second temperature is at least about 50°C/min; and said first solvent is an alcohol.
4. The process of claim 3 wherein said first solvent has a vapor pressure less than 80 kPa at said first temperature and said second solvent has an atmospheric boiling point less than 80°C.
5. The process of claim 1 wherein said first solvent has a vapor pressure less than 80 kPa at said first temperature and said second solvent has an atmospheric boiling point less than about 80°C.
6. The process of claim 1 wherein said first solvent is a hydrocarbon polyol or alkylene ether polyol having a boiling point (at 101 kPa) between about 150°C
and about 300°C.
and about 300°C.
7. The process of claim 6 wherein said first solvent is glycerol.
8. The process of claim 1 wherein said total stretch ratio is between about 3/1 and about 70/1.
9. The process of claim 2 wherein said total stretch ratio is between about 3/1 and about 70/1.
10. The process of claim 1 wherein said stretching step (f) is conducted in at least two stages.
11. The process of claim 10 wherein a first stretching stage is of the gel containing the first solvent.
12. The process of claim 11 wherein a second stretching stage is of the gel containing the first solvent.
13. The process of claim 11 wherein a second stretching stage is of the xerogel.
14. The process of claim 10 wherein at least two stretching stages are performed on the xerogel.
15. The process of claim 1 wherein the stretching is primarily performed on the xerogel.
16. The process of claim 1 wherein at least a portion of stretching is performed at a temperature between about 120°C and about 275°C.
17. The process of claim 16 wherein the stretching is performed in at least two stages with the latest stage performed at a temperature of between about 150°C
and about 250°C.
and about 250°C.
18. The process of claim 17 wherein said latest stage is performed on the xerogel.
19. The process of claim 1 wherein said linear polyvinyl alcohol has a weight average molecular weight of between about 1,000,000 and about 4,000,000.
20. The process of claim 19 wherein said linear polyvinyl alcohol has a weight average molecular weight of between about 1,500,000 and about 2,500,000.
21. A polyvinyl alcohol fiber of weight average molecular weight at least about 500,000 and having a tenacity of at least about 10 g/denier, a tensile modulus of at least about 200 g/denier and a melting temperature of at least about 238°C.
22. The polyvinyl alcohol fiber of claim 21 having a melting temperature of at least about 245°C.
23. The polyvinyl alcohol fiber of claim 21 being of weight average molecular weight of at least about 750,000.
24. The polyvinyl alcohol fiber of claim 21 having a tenacity of at least about 14 g/denier and a tensile modulus of at least about 300 g/denier.
25. A polyvinyl alcohol fiber of weight average molecular weight at least about 750,000 and having a tenacity of at least about 10 g/denier and a tensile modulus at least about 300 g/denier.
26. The polyvinyl alcohol fiber of claim 21 or 22 or 25 having a tenacity of at least about 17 g/denier and a tensile modulus of at least about 400 g/denier.
27. The polyvinyl alcohol fiber of claim 25 having a tensile modulus of at least about 550 g/denier.
28. The polyvinyl alcohol fiber of claim 21 or 22 or 25 being of weight average molecular weight of between about 1,000,000 and about 4,000,000.
29. The polyvinyl alcohol fiber of claim 21 being of weight average molecular weight between about 1,500,000 and about 2,500,000.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US432,044 | 1982-09-30 | ||
| US06/432,044 US4440711A (en) | 1982-09-30 | 1982-09-30 | Method of preparing high strength and modulus polyvinyl alcohol fibers |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1214909A true CA1214909A (en) | 1986-12-09 |
Family
ID=23714516
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000436574A Expired CA1214909A (en) | 1982-09-30 | 1983-09-13 | High strength and modulus polyvinyl alcohol fibers and method of their preparation |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US4440711A (en) |
| EP (1) | EP0105169B1 (en) |
| JP (1) | JPS59130314A (en) |
| CA (1) | CA1214909A (en) |
| DE (1) | DE3376855D1 (en) |
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|---|---|---|---|---|
| US4551296A (en) * | 1982-03-19 | 1985-11-05 | Allied Corporation | Producing high tenacity, high modulus crystalline article such as fiber or film |
| JPS5929146A (en) * | 1982-08-09 | 1984-02-16 | Kuraray Co Ltd | Preparation of water curable extrusion molded product |
| US4713290A (en) * | 1982-09-30 | 1987-12-15 | Allied Corporation | High strength and modulus polyvinyl alcohol fibers and method of their preparation |
| US4883628A (en) * | 1983-12-05 | 1989-11-28 | Allied-Signal Inc. | Method for preparing tenacity and modulus polyacrylonitrile fiber |
| EP0146084B2 (en) * | 1983-12-12 | 1995-05-10 | Toray Industries, Inc. | Ultra-high-tenacity polyvinyl alcohol fiber and process for producing same |
| JPH0696807B2 (en) * | 1984-11-02 | 1994-11-30 | 東レ株式会社 | High-strength, high-modulus polyvinyl alcohol fiber manufacturing method |
| JPH0670283B2 (en) * | 1984-11-02 | 1994-09-07 | 東レ株式会社 | Method for producing high-strength, high-modulus polyvinyl alcohol fiber |
| JPS61252313A (en) * | 1984-11-02 | 1986-11-10 | Toray Ind Inc | Polyvinyl alcohol yarn having improved knot strength and production thereof |
| JPS61215711A (en) * | 1985-03-19 | 1986-09-25 | Toray Ind Inc | Polyvinyl alcohol multifilament yarn having high tenacity and modulus |
| JPH06102848B2 (en) * | 1985-06-10 | 1994-12-14 | 東レ株式会社 | Ultra high strength polyvinyl alcohol fiber |
| JPS61202496U (en) * | 1985-06-11 | 1986-12-19 | ||
| JPH0343265Y2 (en) * | 1985-06-11 | 1991-09-10 | ||
| JPS61202489U (en) * | 1985-06-11 | 1986-12-19 | ||
| JP2687333B2 (en) * | 1985-06-12 | 1997-12-08 | 東レ株式会社 | Polyvinyl alcohol tire cord |
| US4619988A (en) * | 1985-06-26 | 1986-10-28 | Allied Corporation | High strength and high tensile modulus fibers or poly(ethylene oxide) |
| US5202431A (en) * | 1985-07-08 | 1993-04-13 | Fidia, S.P.A. | Partial esters of hyaluronic acid |
| US4851521A (en) * | 1985-07-08 | 1989-07-25 | Fidia, S.P.A. | Esters of hyaluronic acid |
| NL8502315A (en) * | 1985-08-23 | 1987-03-16 | Stamicarbon | ARTICLES OF HIGH STRENGTH AND MODULUS POLYVINYL ALCOHOL AND METHOD FOR MANUFACTURING THE SAME |
| JPH076087B2 (en) * | 1985-10-03 | 1995-01-25 | 株式会社クラレ | High strength and high modulus PVA fiber and method for producing the same |
| JPS62105704A (en) * | 1985-11-05 | 1987-05-16 | Bridgestone Corp | Radial tire |
| US4889174A (en) * | 1985-11-05 | 1989-12-26 | Bridgestone Corp. | Pneumatic radial tires |
| ES2023813B3 (en) | 1985-11-07 | 1992-02-16 | Akzo Nv | REINFORCING ELEMENT OF SYNTHETIC MATERIAL FOR USE IN REINFORCED CONCRETE, MORE PARTICULARLY PRE-STRESSED CONCRETE, REINFORCED CONCRETE PROVIDED WITH SUCH REINFORCEMENT ELEMENTS AND PROCESS FOR MANUFACTURING REINFORCED ELEMENTS, AND REINFORCED CONCRETE. |
| US4681792A (en) * | 1985-12-09 | 1987-07-21 | Allied Corporation | Multi-layered flexible fiber-containing articles |
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| NL142204B (en) * | 1965-02-01 | 1974-05-15 | Tno | PROCESS FOR MANUFACTURING ARTIFICIAL WIRES FROM HEAT-SENSITIVE POLYMERS AND WIRES THEREFORE OBTAINED. |
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| US4360488A (en) * | 1979-08-13 | 1982-11-23 | Imperial Chemical Industries Limited | Removal of solvent from gels of poly(hydroxybutyrate) and shaped articles formed therefrom |
-
1982
- 1982-09-30 US US06/432,044 patent/US4440711A/en not_active Expired - Lifetime
-
1983
- 1983-08-22 DE DE8383108258T patent/DE3376855D1/en not_active Expired
- 1983-08-22 EP EP83108258A patent/EP0105169B1/en not_active Expired
- 1983-09-13 CA CA000436574A patent/CA1214909A/en not_active Expired
- 1983-09-30 JP JP58182960A patent/JPS59130314A/en active Granted
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| JPH0375644B2 (en) | 1991-12-02 |
| EP0105169A2 (en) | 1984-04-11 |
| US4440711A (en) | 1984-04-03 |
| JPS59130314A (en) | 1984-07-26 |
| EP0105169A3 (en) | 1985-09-18 |
| EP0105169B1 (en) | 1988-06-01 |
| DE3376855D1 (en) | 1988-07-07 |
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