CA1276064C

CA1276064C - Shaped polyethylene articles of intermediate molecular weight and high modulus

Info

Publication number: CA1276064C
Application number: CA000499202A
Authority: CA
Inventors: Sheldon Kavesh; Dusan Ciril Prevorsek
Original assignee: AlliedSignal Inc
Current assignee: Honeywell International Inc
Priority date: 1985-01-11
Filing date: 1986-01-08
Publication date: 1990-11-13
Anticipated expiration: 2007-11-13
Also published as: ES8701796A1; US4663101A; JPH0819563B2; AU593533B2; EP0472114A2; EP0472114B1; EP0187974A3; ES551405A0; AU5070185A; DE3587017D1; EP0472114A3; EP0187974A2; JPS61167010A; EP0187974B1; DE3588211T2; DE3588211D1; US5972498A; US5736244A; DE3587017T2

Abstract

SHAPED POLYETHYLENE ARTICLES OF INTERMEDIATE
MOLECULAR WEIGHT AND HIGH MODULUS

ABSTRACT
Solutions of intermediate molecular weight polymers from about 200,000 to about 4,000,000, such as polyethy-lene, in a relatively non-volatile solvent are extruded through an aperature at constant concentration and thereafter stretched at a ratio of at least about 3:1 prior to cooling to form a first gel. The first gels are extracted with a volatile solvent to form a second gel, and the second gel is dried to form a low porosity xerogel. Stretching occurs with any one or more of the first gel, second gel or xerogel. The polyethylene products produced by our process include products having a molecular weight between about 200,000 and about 4,000,000 a tenacity of at least about 13 grams/denier, a modulus of at least about 350 gram/denier, a porosity of less than 10% by volume, a crystalline orientation function of at least about 0.95, and a main melting temperature of at least about 140°C.

Description

- ~ ~7~

DESCRIPTION
SHAPED POLYETHYLENE ARTICLES OF
INTERMEDIATE MOLECULAR WEIGHT AND HIGH MODULUS
BAC~GROUND OF THE INVENTION
The present invention relates to intermediate 5 molecular wei~ht shaped polyethylene articles such as polyethylene fibers exhibiting relatively high tenacity, modulus and toughness, and 1:o products made therefrom.
- The polyethylene article is made by a process which includes the step of stretching a solution of 10 polyethylene dissolved in a solvent at a stretch ratio of at least about 3:1.
Polyethylene fibers, films and tapes are old in the art. An early patent on this subject appeared in 1937 (G.B. 472,051). However, until recently, the tensile 15 properties of such products have been generally unre-markable as compared to competitive materials, such as the polyamides and polyethylene terephthalate~
Recently, several methods have been discovered for preparing continuous low and intermediate molecular 20 weight polyethylene fibers of moderate tensile proper-ties. Processes for the production of relatively low molecular weight ibers (a maximum weight average molecular weight, Mw, of about 200,000 or less) have been described in U.S. Pat. Nos. 4,276,348 and 4,228,118 25 to Wu and Black, U.S. Pat. Nos. 3,962,205, 4,254,072, 4,287,149 and 4,415,522 to Ward and Cappaccio, and U.S.
Pat. No. 3,048,465 to ~urgeleit. U.S. Pat. No.
4,268,470 to Cappaccio and Ward describes a process for producing intermediate molecular weight polyolefin 3~ fibers (minimum molecular weight of about 300,0003.
The preparation of high strength, high modulus polyolefin fibers by solution spinning has been des-cribed in numerous recent publications and patents~
German Off. No. 3,004,699 to Smith et al. tAugust 21, 35 1980) describes a process in which polyethylene is first dissolved in a volatile solvent, the solution is spun and cooled to form a gel filamentr and, finally, the gel '~' .
~ 27~

filament is simultaneously stretched and dried to form the desired fiber. U.K. Patent Application No.

2,051,667 to P. Smith and P. J. Lemstra ~January 21, 1981) discloses a process in which a solution of a polymer is spun and the filaments are drawn at a stretch 5 ratio which is related to the polymer molecular weight, at a drawing temperature such that at the draw ratio used, the modulus of the filaments is at least 20 GPa - ~the application notes that to obtain the high modulus ~ values required, drawing must be performed below the 10 melting point of the polyethylene; in general, at most 135C). Kalb and Pennings in Poly~er Bulletin, Volume 1, pp. 879-80 (1979), J. Mat. Sci., VolO 15, pp. 2584-90 (1980) and Smook et alO in Polymer Mol., Vol 2, pp. 775-83 (1980) describe a process in which the polyethylene 15 is dissolved in a non-volatile solvent ~paraffin oil), the solution is cooled to room temperature to form a gel which is cut into pieces, fed to an extruder and spun into a gel filament, the gel filament being extracted with hexane to remove the parafin oil, vacuum dried and 20 stretched to form the desired fiber.
Most recently, ultra high molecular weight fibers have been disclosed. U.S. 4,413,110 to Kavesh and Prevorsek describes a solution spun fiber of from 500,000 molecular weight to about 81000~000 molecular 25 weight which exhibits exceptional modulus and tena-city. U.S. Pat. Nos. 4,430,383 and 4,422,993 to Smith and Lemstra also describe a solution spun and drawn fibers having a minimum molecular weight of about 800,000. V.S. Pat. No. 4,436,689 to Smith, Lemstra, 30 Kirschbaum and Pijers describes solution spun filaments of molecular weight greater than 400,000 (and an Mw/Mn <
5). In addition, ~.S. Pat. No. 4,268,470 to Ward and Cappacio also discloses high molecular weight polyolefin fibers.
In general, the known processes for forming poly-ethylene and other polyolefin fibers may be observed as belonging in one of two groups: those which describe ~;~7~

fibers of low average molecular weight (200,000 or less) and those which describe fibers of high average molecu-lar weight (800,000 or more)~ Between the two groups, there is a molecular weight range which has not been accessible to the prior art methods for preparing fibers 5 of high tensile properties.
There are advantages to the molecular weight ranges thus far mastered. Lower molecular weight polymers are generally synthesized and processed into fibers more - easily and economically than high molecular weight 10 fibers. On the other hand, fibers spun from high molecular weight polymers may possess high tensile prop-erties, low creep, and high melting point. A need exists for fibers and methods which bridge this gap, combining ~ood economy with moderate to high tensile 15 properties. Surprisingly, our process makes it possible to accomplish these results.
BRIEF DESCRIPTION OF THE INVENTION
_ The present invention is directed to novel shaped polyethylene articles having a weight average molecular 20 weight between about 200,000 and about 4,000,000, a crystalline orientation function of at least about 0.95, a tensile modulus of at least about 350 grams/denier, a tenacity of at least about 13 grams/denier, and a main melting temperature of at least about 140C (measured at 25 10C/minute heating rate by differential scanning calorimetry), said main melting temperature being greater than the main melting temperature of a shaped polyethylene article of substantially the same weight average molecular weight produced from a polymer 30 solution of substantially the same polymer concentra-tion, spun at substantially the same throughput rate and subjected to solution stretching at a ratio of less than about 3:1.
The present invention is directed to novel shaped 35 polyethylene articles having a weight average molecular weig`nt between about 200,000 and about 800,000, a crystalline orientation function of at least about 0.95, ~2~

a tensile modulus of at least about 350 grams/denier, a tenacity of at least about 13 grams/denier, and a main melting temperature of at least about 140C (measured at 10C/minute heating rate by differential scanning calorimetry), said main melting temperature being-5 greater than the main melting temperature of a shapedpolyethylene article of substantially the same weight average molecular weight produced ~rom a polymer - solution of substantially the same polymer concentra-~ tion, spun at substantially the same throughput rate and 10 subjected to solution stretching at a ratio of less than about 3:1.
The present invention is also drawn to novel shaped polyethylene articles having a weight average molecular weight between about 250,000 and 750,000, a crystalline lS orientation function o~ at least about 0.95, a tensile modu~us of at least about 500 grams/denier, a tenacity of at least about 15 grams/denier, and a main melting temperature of at least: about 141C (measured at 10C/minute heating rate by differential scanning 20 calorimetry), said main melting temperature being greater than the main melting temperature of a shaped polyethylene article of substantially the same weight average molecular weight produced from a polymer solution of substantially the same polymer concentra-25 tion, spun at substantially the same throughput rate andsubjected to solution stretching at a ratio of less than about 3:1.
~ he present invention also includes novel shaped polyethylene articles of substantially indefinite length 30 having a weight average molecular weight between about 250,000 and 750,000, a crystalline orientation function of at least about 0.95, a tensile modulus of at least about 750 grams/denier, a tenacity of at least about 18 grams/denier, and a main melting temperature of at least 35 about 141C (measured at 10C/minute heating rate by differential scannin~ calorimetry~, said main melting temperature being greater than the main melting ~7 Ei~

temperature of a shaped polyethylene article of substantially the same weight average molecular weight produced from a polymer solution of substantially the same polymer concentration, spun at substantially the same thro~ghput rate and subjected to solution S stretching at a ratio of less than about 3:1.
The present invention also includes novel shaped polyethylene articles of substantially indefinite length having a weight average molecular weight between about ~ 300,000 and 700,000, a crystallino orientation function 10 of at least about 0.95, a tensile modulus of at least about 750 grams/denier, a tenacity of at least about 20 grams/denier, and a main melting temperature of at least about 141C (measured at 10C/minute heating rate by differential scannin~ calorimetry), said main melting lS temperature being greater than the main melting temperature of a shaped polyethylene article of substantially the same weight average molecular weight produced from a polymer solution of substantially the same polymer concentration, spun at substantially the 20 same throughput rate and subjected to solution stretching at a ratio of less than about 3:1.
The present invention is also drawn to a shaped polyethylene article having a weight average molecular weight between about 200,000 and about 4,000,000 a 25 tensile modulus of at least about 350 grams/denier, a transverse microfibrillar spacing which is less than a trans~erse microfibrillar spacing of a shaped polyethylene article of substantially the same weight average molecular weight produced from a polymer 30 solution of substantially the same polymer concentra-tion, spun at substantially the same throughput rate and subjected to solution stretching at a ratio of less than about 3:1, a tenacity of at least about 13 grams/denier, and a main melting temperature of at least about 140C
35 measured at lO~C/minute heating rate by differential scanning calorimetry).
The present invention is also directed to novel ~2~6~

shaped polyethylene articles having a weight average molecular weight greater than about 200,000 and less than 500,000 a crystalline orientation function of at least about 0.95, a tensile modulus of at least about 350 grams/denier, a tenacity of at least about 13 5 grams/denier, and a main melting temperature of at least about 14~C (measured at 10C/minute heating rate by differential scanning calorimetry).
The present invention also includes a process for ~ producing shaped polyethylene articles, for example 10 fibers, which comprises the steps of:
(a) forming, at a first temperature, a solution of polyethylene in a first solvent, said polyethylene having a weight average molecular weight between about 20~,000 and 4,0U0,000 kilograms/kg mole;
(b) extruding said solution through an aperature to form a solution product, said solution product being at a temperature no less than said Eirst temperature;
~0 (c) stretching the solution product at a stretch ratio of at least about 3:1;
(d) cooling the solution product to a second temperature below the first temperature to form a first gel containing first solvent;
(e) extracting the first solvent from the first gel with a second solvent to form a second gel containing second solvent, substantially free of the first solvent;
(f) drying the gel containing the second solvent 3Q to form a xerogel substantially free of solvent; and, (g) stretching at least one of the first gel, the second gel and the xerogel, the total stretch ratio being sufficient to achieve a 35 polyethylene article having a tenacity of at least about 13 grams/denier, a porosity of less than 10~ by volume, and a modulus of at least about 350 grams/denier.

BRIEF DESCRIPTION OF THE ~RAWINGS
Figure 1 illustrates in schematic form the preferred embodiment of the apparatus used to produce the novel articles.
Figure 2 graphically depicts the effects of polymer 5 concentration and die draw ratio on fiber tenacity.
Figure 3 graphically shows the effects of polymer concentration and die draw ratio on the overall - stretchability of fibers.
DETAILED DESCRIPTION OF THE INVENTION
There are many applications which require load bearing elements of high strength, modulus, toughness, dimensional and hydrolytic stability.
For example, marine ropes and cables, such as the mooring lines used to secure tankers to loading stations 15 and the cables used to secure drilling platforms to underwater anchorage, are presently constructed of materials such as nylon, polyester, aramids and steel which are subject to hydrolytic or corrosive attack by sea water. Consequently, such mooring lines and cables 20 are constructed with significant safety factors and are replaced frequently. The greatly increased weight and the need for frequent replacement creates substantial operational and economic burdens.
The fibers and films of this invention exhibit 25 relatively high strength, high modulus and very good toughness. Also, they are dimensionally and hydrolytically stableO The fibers and films prepared by our unique process possess these properties in a heretofore unattained combination and are, therefore, 30 quite novel and useful materials. Consequently, our fibers and films offer significant advantages when employed as, for example, marine ropes and cables.
Other applications for the fibers and films of our invention include: reinforcement of thermoplastics, 35 thermosetting resins, elastomers, and concretes for uses such as pressure vessels, hoses, power transmission belts, sports and automotive equipmenti and, building ~L~7Ç~

construction materials.
The polymer used in the present invention is crystallizable polyethylene. By the term ~Icrystal-lizable" is meant a polymer which is capable of exhibiting a relatively high degree of order when 5 shaped, attributable in part to its molecular weight and high degree of linearity. As used herein, the term polyethylene shall mean a predominantly linear - polyethylene material that may contain minor amounts of ~ chain branching or comonomers not exceeding 5 modifying lO units per 100 main chain carbon atoms, and that may also contain admixed therewith not more than about 25 wt~ of one or more polymeric additives such as alkene-l-polymers, in particular low density polyethylene, polypropylene or polybutylene, copolymers containing 15 mono-olefins as primary monomers, oxidixed polyolefins, graft polyolefin copolymers and polyoxyme~hylenes, or low molecular weight additives such as anti-oxidants, lubricants, ultra-violet screening agents, colorants and the like which are commonly incorporated therewith.
20 In the case of polyethylene, suitable polymers have molecular weights (by intrinsic viscosity) in the range of about 200,000 to about 4,000,000. This corresponds to a weight average chain length of 8,333 to 166,666 monomer units or 16,666 to 333,332 carbons. The 25 preferred weight average molecular weight of polyethylene used in our process is between about 200,000 (302 IV) and about 800,000 (8.4 IV~, more preferably between about 250,000 (3.7 IV) and 750,000 ~ (8.0 IV), and most preferably between about 300,000 (4.2 30 IV) and about 700,000 (7.6 IV). The IV numbers represent intrinsic viscosity of the polymer in decalin at 135C. In addition the polymers used in the present invention have a weight to number average molecular weight ratio (Mw/Mn) which is variable over a wide 35 range. We prefer to use polymers with a Mw/Mn ratio of t at least about 5:1 because polymers having a more narrow distribution range are more difficult to produce. In ~27~

g addition, we believe there may be unexpected advanta~es to using a higher ratio (i.e. ~ :1), particularly with a bimodal molacular weight distribution.
The first solvent should be a non-volatile solvent under the processing conditions. This is necessary in 5 order to maintain essentially constant concentration of solvent upstream and through the aperture (die or spinnerette) and to prevent non-uniformity in liquid content of the gel fiber or film containing first solvent. Preferably, the vapor pressure of the first 10 solvent should be no more than about one fifth of an atmosphere (20kPa) at 175C., or at the first temperature. Preferred first solvents for hydrocarbon polymers are aliphatic and aromatic hydrocarbons of the desired non-volatility and solubility for the polymer.
15 Preferred first solvents for polyethylene include paraffin or mineral oil.
The polymer may be present in t:he first solvent in a first concentration which is selected from a range from about 5 to about 25 weight percent. The optimum 20 concentration is dependent upon the polymer molecular weightO For a polymer of about 650,000 (Mw), the first concentration îs preferably about 5 to about 15 weight percent and more preferably about 6 to about 10 weight percent; however, once chosen, the concentration should - 25 not vary adjacent the die or otherwise prior to cooling to the second temperature. The concentration should also remain reasonably constant over time (i.eO, over the length of the iber or film).
The first temperature is chosen to achieve complete 30 dissolution of the polymer in the first solvent. The first temperature is the minimum temperature at any point between where the solution is formed and the die face, and must be greater than the gelation temperature for the polymer in the solvent at the first 35 concentration. For polyethylene in paraffin oil at 5 to 15 weight percent concentration, the gelation temperature is approximately 100-130C; therefore, a ~7~
--~o--preferred temperature can be between 180~C and 250C, or more preferably between 200 and 240C. While temperatures may vary above the irst temperature at various points upstream of the die face, excessive temperatures causative of polymer degradation should be 5 avoided. To assure complete solubility, a first temperature is chosen whereat the solubility of the polymer exceeds the first concentration, and is typically at least 100 percent greater. The second ~ temperature is chosen whereat the solubility of the 10 polymer is much less than the first concentration.
Preferably, the solubility of the polymer in the first solvent at the second temperature is no more than about 1~ percent of the first concentration. Cooling of the extruded polymer solution from the first temperature to 15 the second temperature should be accomplished at a rate sufficiently rapid to form a gel fiber which has 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 20 temperature to the second temperature should be at least about 50C/minute.
A critical aspect of our invention is the step of stretching ~solution stretching) the extruda~e (solution product) at a ratio of at least about 3:1 and up to 25 about 200:1. The preferred ratio of stretching depends upon the polymer molecular weight and the first concentration. For a polymer of about 650,000 (~w) at a first concentration between about 6% and about 10%, the preferred stretch ratio is between about 3:1 and about 30 50:1 and the most preferred ratio of stretching is between about 10:1 and about 50:10 Solution stretching, i.e., stretching the spun solution product prior to forming a gel therefrom, occurs between the aperture of the die and the quench bath (normally within the space 35 of a few inches). Stretching can be accomplished by regulating the spinning rate (measured by the length of product formed per unit time) through the die relative ~2~6~

to the angular velocity of the quench bath roller.
Solution stretching of at least about 3:1 results in the formation of a gel (upon cooling to the second temperature) which consist of continuous polymeric networks highly swollen with solvent. Each gel has 5 substantially uniform polymer density with polymer voids constituting less than 10% ~by volume), normally less than 5%, of the fiber. A solution stretch ratio of at least about 3:1 unexpectedly aids in forming high strength articles of intermediate molecular weight (cf.
10 U.S. 4,413,110). Within the limitations of the solution stretch ratio range, the higher the pump rate of polymer through the die or spinnerette, the lower the solution stretch ratio because of the degree of alignment (orientation) imparted by shear through the die or lS spinnerette~
The extraction with second solvent is conducted in a manner (ordinarily in a washer cabinet) that replaces the first solvent in the gel with second solvent without significant changes in gel structure. Some swelling or 20 shrinkage of the gel may occur, but preferably no substantial dissolution, coagulation or precipitation of the polymer occurs. When the first solvent is a hydro-carbon, suitable second solvents include hydrocarbons, chlorinated hydrocarbons, chlorofluorinated hydrocarbons 25 and others, such as pentane, hexane, heptane, toluene, methylene chloride, carbontetrachloride, trichlorotri-fluoroethane (TCTFE), diethyl ether and dioxane. The most preferred second ~olvents are methylene chloride (~.P. 39.8C) and TC~E (B.P. 47.5C). Preferred second 30 solvents are the non-flammable volatile solvents having an atmospheric boiling point below about 80C., more preferably below about 70C and most pre~erably below about 50C. Conditions of extractions should be chosen so as to remove the first solvent to a level of less 35 than 0.1 percent of the total solvent in the gel.
A preferred combination of the conditions is a first temperature between about 150C and about 250C, a ~2~

second temperature between about minus 40C and about 40C and a cooling rate between the first temperature and the second temperature at least about 50C/minute.
Most preferably, the first solvent does not experience a phase change at the second temperature. It is preferred 5 that the first solvent be a hydrocarbon, when the polymer is a polyolefin such as intermediate molecular weight polyethylene. The first solvent should be - substantially non-volatile, one measure of which is that its vapor pressure at the first temperature should be 10 less than 20kPa, and more preferably less than 2kPa.
In choosing the first and second solvents, the primary desired difference relates to volatility as discussed above. It is also preferred that the polymers be less soluble in the second solvent at about 40C than 15 in the first solvent at about 150C. Once the gel containing second solvent is formed, the second gel is then dried under conditions where the second solvent is removed leaving the solid network of polymer substan-tially intactO By analogy to silica gels, the result;ng 20 material is called a "xerogel" meaning a solid matrix corresponding to a solid matrix of a wet gel, ~ith the liquid having been replaced by gas ts-g., by in inert gas such as nitrogen or by air). The term "xerogel" is not intended to delineate any particular type of surface 25 area, degree of porosity or p~re size.
Stretching may be performed upon the gel after cooling to the second temperature, or during or after extraction. Alternatively, stretching of the xerogel may be conducted, or a combination of gel stretching and 30 xerogel stretching may be preformed. Stretching after gelation most preferably is conducted in two or more stages. The first stage of stretching may be conducted at room temperature or at an elevated temperature, ordinarily at a temperature between about 115C and 135C. Preferably, stretching is conducted in the last of the stages at a temperature between about 120C and 155C. Most preferably, the stretching is conducted in ~7~

the last of the stages at a temperature between about 13~C and 150C.
The stretching which occurs subsequent to gelation is another critical aspect of our invention~ Stretching subsequent to gelation can be accomplished during 5 quenching, washing, and/or drying of the gels, and can also be accomplished by a xero~el stretching step. As noted above, stretching subse~uent to gelation most - preferably occurs in at least two stages. The amount of acceptable stretching subsequent to gelation at various 10 stages of the process is as follows: stretching of the gels is normally at least about 1.5:1; stretching of the xerogel in a first stage, preferably occurring between 115C and 135C, is generally more than about 2:1; and stretchin~ of the xerogel in a second stage, preferably 15 occurring between about 130C and 155C, is normally about 1.5:1.
With a solution stretch ratio of at least about 3:1 and at least one subsequent stretching operation, the overall stretch ratio of the product is between about 20 30:1 and about 500:1 or more. The total combined stretch ratio (of the solution product, the gel and/or the xerogel) of at least about 30:1 produces novel articles exhibiting a unique combination of proper-ties. Furthermore, the stretching steps of the process 25 are interrelated in such a fashion that an increase in the solution stretch ratio is coupled with a decrease in the subsequent gel and/or xerogel stretch ratios. The Examples described hereinbelow illustrate how the stretch ratios are interrelated in obtaining particular 30 improved fiber properties.
The intermediate weight polyethylene articles, such as fibers, produced by the present process are novel in that they exhibit a unique combination of properties: a tensile modulus at least about 350 grams/denier 35 (pre~erably at least about 500 grams/denier, more preferably at least about 750 grams/denier, and most preferably at least about 1,000 grams/denier), a 6~

tenacity at least about 13 grams/denier (preferably at least about 15 grams/denier, more preferably at least about 18 grams/denier and most prefe~ably at least about 20 grams/denier), a main melting temperature (measured at lO~C/minute heating rate by differential scanning 5 calorimetry) of at least about 140C, preferably at least about 141C, and wherein said main melting temperature is greater than the main melting temperature of a shaped polyethylene article of substantially the same weight average molecular weight produced from a 10 polymer solution of substantially the same polymer concentration, spun at substantially the same throughput rate and subjected to solution stretching at a ratio of less than about 3:1, a porosity of less than 10~ by volume (normally less than 5%), and a crystalline 15 orientation function (f)~ of at least about 0.95.
Preferably, the article has an ultimate elongation ~UE) at most of about 7 percent, and more preferably not more than about 5 percent. In addition, the articles have a high toughness and uniformity. Moreover and very 20 importantly, the products produced by our process exhibit a transverse microfibrillar spacing less than that which would occur in an article of the same molecular weight having been produced by a process which subjects a solution product to a solution stretch of 25 less than about 3:1.
The crystalline orientation function is a measurement of the degree of alignment of the axis of the polymer crystals with the maior axis of the product. It has been shown that the higher the 30 crystalline orientation function the higher the tensile strength of the product. The crystalline orientation function is mathematically calculated from the equation reported by R.S. Stein, J. PolyO Sci., 31, 327 (1958) :

f = 12 ~3 < cos ~>2 _ 1) where a = the angle between the major axis of the ~%7~i~64 product and the major axis of the crystals in the product. Perfectly oriented crystals, i.e. crystal having a major axis parallel to the major axis of the product, would exhibit an f = 1 . For polyethylene fibers produced by our novel process, the crystalline 5 orientation function is at least about 0.95.
We have also employed infra-red techniques to determine the overall orientation function for a polyethylene product produced by our processO This technique is reported in detail in R.J. Samuels, 10 Structure of Polvmers and Properties, John Wiley and . _ _ Sons, New York, 1974~ pp. 63~82.
The degree of crystallinity of the product is related to the tensile strength in a similar fashion as the orientation factor. Crystallinity of the product 15 can be measured by a variety of methods including x-ray diffraction, heat of fusion and density measurement and is at least about 0.70 or higher. By x-ray diffraction, we measured the degree of crystallinity of a fibrous product produced by our process to be about 0.65.
~lowever, density measurements of the same fiber indicate a degree of crystallinity of about 0.77. See Example 13.
An important and unique property of products produced by our process is the transverse microfibrillar 25 spacing. Products produced by our process exhibit microstructure (transverse microfibrillar spacing) below about 150A that appears to be sensitive to the critical process variables and may have a direct role in the final properties of the product. The spacing between the microfibrils i.e., the transverse microfibrillar spacing, is unique in that an article produced by employing a solution stretch of at least about 3:1 exhibits a transverse microfibrillar spacing less than that which would exist in a shaped polyethylene article of substantially the same weight average molecular weight produced from a polymer solution of substantially the same polymer concentration, spun at substantially ~27~

the same throughput rate and subjected to solution stretching at a ratio of less than about 3:1. From some preliminary small angle x-ray scattering investigations conducted with fiber products, we believe that products produced by our process will have a transverse 5 microfibrillar spacing of less than about 50 ~. Our small angle scattering investigations were carried out using Cu radiation (1.54 A, Ni filtered). In the - procedure, the x-rays, directed normal to the major axis of the fiber, impact the fiber and are scattered ~ver an 10 angle 2 ~ <5. The intensity (I) of the scattered x-rays are detected over the entire angle 2 9 using a linear position sensitive proportional counter. The intensity (I) is plotted versus the angle to establish a peak intensity (indicated at a specific angle) which is 15 characteristic of the transverse microfibrillar spacing (the spacing being calculated from Braggs Law ~ = 2d sin ~ , which is assumed to be correct).
As indicated in the Examples below, tradeoffs between various properties can be made in a controlled 20 fashion with the present process.
Figure 1 illustrates in schematic form the preferred embodiment of the apparatus used to produce novel fibers, wherein the stretching steps include solution filament stretching and stretching at least two 25 Of the gel containing the first solvent, the gel containing second solvent; and, the xerogel. As shown, a first mixing vessel 10 is fed with the intermediate molecular weight polymer 11 such as polyethylene of weight average molecular weight ~etween ab~ut 200,000 30 and about 4,000,000, and is also fed with a firstr relatively non-volatile solvent 12 such as paraffin oil. First mixing vessel 10 is equipped with an agitator 15. The residence time of polymer and first solvent in first mixing vessel 10 is sufficient to form 35 a slurry. The slurry is removed from first mixing vessel via line 14 to a preheater 15. The residence time and temperature in preheater 15 are sufficient to dissolve between about 5~ and 50~ of the polymer. From the preheater 15, the solution is fed to an extrusion device 18 containing a barrel 19 within which is a screw 20 operated by motor 22 to deliver polymer solution at reasonably high pressure to a gear pump in housing 23 at 5 a con~rolled flow rate. Motor 24 is provided to drive gear pump 23 and extrude the polymer solution, still hot, through a spinnerette at 25 comprising a plurality of aperatures, which may be circular, x-shaped or oval shaped, or in any of a variety of shapes having a relatively small major access in the plane of the spinnerette when it is desired to form fibers, and having a regtangular or other shape when an extended major access in the plane of the spinnerette when it is desired to form films or tapes.
An aperture of circular cross section (or other cross section without a major axis in the plane perpen-dicular to the flow direction more than about 8 times the smallest axis in the same plane, such as oval, y- or x-shaped aperture) is used so that both gels will be ~ fiber gels, the xerogel will be a xerogel fiber and the product will be a fiber. The diameter of the aperture is not critical, with representative apertures being between about 0O25 mm and about 5 mm in diameter (or other major axis). The length of the aperture in the flow direction should normally be at least about 10 times the diameter of the ape~ture (or other similar major access), preferably at least 15 times and more preferably at least 20 times the diameter (or other similar major access).
The temperature of the solution in the preheater vessel 15, in the extrusion device 18 and at the spinnerette 25 should all equal or exceed a first temperature (e.g., about 200C) chosen to exceed the gelation temperature (approximately 100 to 130C for 35 polyethylene and paraffin oil). The temperature may vary (fluctuating between about 200C and 220C) or maybe constant (e.g., about 220C~ from the preheater ~Z~ 4 vessel 15 to the extrusion device 18 to the spinnerette 25. At all points, however, the concentration of polymer in the solution should be substantially the same. The number of aperatures in thus the numbers of fibers formed, is not critical, with convenient number 5 of fibers being 16, 19, 120 or 240.
From the spinnerette 25, the polymer solution passes through an airgap 27, optionally enclosed and - filled with an inert gas such as nitrogen, and optionally provided with a flow of gas to facilitate 10 coolingO A plurality oE solution fibers 28 containing first solvent pass through the airgap 27 and into a quench bath 30 so as to cool the fibers, both in the airgap and in the quench bath 30 to a second temperature at which the solubility of the polymer in the first solvent is relatively low, such that the polymer solution forms a gel. Prior to gelation, solution fiber stretching occurs in the airgap 27 at a ratio of at least about 3:1. This high stress draw of the solution fibers prior to gelatlon is critical in achieving the ultimate properties of the fibers.
Rollers 31 and 32 in the quench bath operate to feed the fiber through the quench bath and operate in relation to the solution fiber rate of extrusion (determined by the length of extruded fiber per unit time) at an angular velocity sufficient to stretch the solution filament at a ratio of at least about 3:1 prior to gelation. As between rollers 31 and 32, it is contemplated that stretching of the gel filament may be desired. Normally, the degree of stretch imparted between roll 31 and 32 to the gel fiber would be more than about 1.5:1. In the event that stretching of the gel fiber between rollers 31 and 32 is desired, some of first solvent may exude out of the fibers and can be collected as a layer in quench bath 30. From the quench bath 30, the cool first solvent containing gel fibers (first gel fibers) 33 passed to a solvent extraction device 37 where a second solvent, being of relatively ~27~

low boiling point, such as trichlorotrifluoroethane, is fed in through line 38. The solvent outflow through line 40 contains second solvent and substantially all of the first solvent from the cool first gel fibers 33.
The polymer is now swollen by the second solvent. Thus, 5 second solvent containing gel fibers (second gel fibers) 41 conducted out of the solvent extraction device 37 contain substantially only second solvent, and relatively little first solvent. The second gel fibers - 41 may have shrunken somewhat compared to the first gel 10 fibers 33, but otherwise have substantially the same polymer morphology.
In a drying device 45, the second solvent is evaporated from the second gel fibers 41 forming essentially unstretched xerogel fibers 47 which are 15 taken up on spool 52.
From spool 52, or from a plurality of spools if it is desired to operate a stretching line at a slower feed rate than the take up line of spool 52 permits, the fibers are fed over driven feed roll 54 and idler roll 20 55 into a first heated tube 56 which may be rectangular r cylindrical or any other convenient shape. Sufficient heat is supplied to the tube 56 to cause the internal temperature to be between about 115C and 135C. The fibers may be stretched at this stage if desired. In - 25 this embodiment stretching would occur at a relatively high ratio (generally more than about 2:1, preferably about 3:1) so as to form partially stretched fibers 58 taken out by a driven roll 61 and idler roller 62. From rolls 61 and 62, the fibers are taken through a second 30 heated tube 63, heated so as to be at somewhat higher temperature, e.g., 130C to about 155C, and are then taken up by driven takeup roll 65 and idler roll 66.
The driven takeup roll 65 is capable of operating at a sufficient speed to impart a desired stretch ratio to 35 the gel fibers in heated tube 63 (normally more than about 1.1.1, preferably between about 1.2:1 and about 1.7:1). The twice stretched fiber 68 produced in this ~2~

embodiment are taken up on takeup spool 72.
With reference to Figure 1, the seven process steps of the invention can be seen. The solution forming step (a) is conducted in preheater 15 and extrusion device 18. The extrusion step tb) is conducted with device 18 5 and 23, and especially through spinnerette 25. The solution product stretching step (c) is generally conducted in the airgap 27, and the coollng and quenching step (d) i5 conducted in the airgap 27 and in ~ the quench bath 30. Extraction step (e) is conducted in 10 solvent extraction device 37. The drying step (f) is conducted in the drying devlce 45. The stretching step (g) is preferably conducted in elements 52-72, and especially in heated tubes 56 (Zone 1) and 63 (Zone 2). It will be appreciated however, that various other 15 parts oE the system may also perform some stratching, even at temperatures substantially below those of heated tubes 56 and 63. As noted before, stretching may occur within the quench bath 30, ~ithin the solvent extraction device 37, within drying device 45 and/or between 20 solvent extraction device 37 and drying device 45.

___ XEROGEL YARN PREPARATION
An oil jacketed double Helical (Helicone~) mixer, - 25 constructed by Atlantic Research Corporation, was charged with 10 wt% linear polyethylene, 89.5 wt%
mineral oil (Witco "Kaydol'~ , and 0.5 wt% antioxidant ~If ~Shell "Ionol"~.
The linear polyethy~ene was Allied Corporation 30 FD60-018 having an intrinsic viscosity (IV) of 3.7 measured in decalin at 135C, a weight average molecular weight of 284,000 kg/mol and an Mw/Mn of approximately 10. The charge was heated with agitation at 60 rpm to 240C. The bottom discharge opening of the Helicone 35 mixer was adapted to feed the polymer solution first to a gear pump and then to a l9-hole spinning die. The holes of the spinning die were each of 0.040"

~27~

diameter. The gear pump speed was set to deliver 15.2 cm3/min of polymer solution to the die. The extruded solution filaments were stretched 39.8:1 in passing through a 2" air gap into a water quench bath at 15C
wherein the filaments were quenched to a gel state.
The gel "yarn" was passed into a washer cabinet in which the mineral oil content of the gel filaments was extracted and replaced by trichlorotrifluoroethane (TCTFE) at 35C. The gel yarn was stretched 1.14:1 in traversing the washer. The extracted gel yarn was 10 passed into a dryer cabinet where the TCTFE was evaporated from the yarn at 60C. The dried yarn was stretched 1.14:1 at 60C as it exi~ed the dryer cabinet. The extracted and dried xerogel yarn of 173 denier was wound onto a roll at 63~2 meters/min.
~5 HOT STRETCHING
The roll of xerogel yarn from Example 1 was transferred to a two zone stretch bench. Each zone 20 consisted of a 10-ft long heated tube maintained at uniform temperature and under nitrogen blanketing. The xerogel yarn was fed into the first stage at 16 m/min.
Other stretch conditions and the properties of the yarns obtained are given in Table 2.

Table 2 ZONE TEMPSI C STRETCH RATIOS
Example #1 #2 ~1 ~2 2 120 136 3.0 1.5 3 120 135 3.0 1.~

4 120 145 2.9 1.6 5 120 145 2.9 1.7 6 125 140 3.0 1.5 7 129 145 2.75 1.35 8 129 145 2.75 1.45 9 130 145 3.0 1.5 ~ ~7~;~6~

Table 2 ~con't) Modulus ~ UE W-t-B*
ExamRle Denier Tenacity __~/d J/g _ _ _ _ _ _ 2 47 14 490 5.5 ~3 3 52 13 460 6.0 46 4 40 13 470 7.2 59 6 34 14 550 5.6 46 7 40 12 3~0 9.2 77 8 38 12 410 8.2 66 9 31 15 490 ~.7 83 *W-t-b is the work needed to break the fiber.

The melting temperatures of the yarns of examples 6 and 9 were determined using a Perkin-Elmer DSC-2 Dif ferential Scanning Calorimeter. Samples of about 3.2 mg were heated in argon at the rate of 10C/min. The yarns showed a doublet endotherm in duplicate runs:

Example 6 142C (main) + 146C
Example 9 140C ~main) + 148C

-XEROGEL YARN PREPARATION AND HOT STRETCHING
The xerogel yarns of the following examples were prepared from solutions of polyethylene (Mitsui~HI-ZEX
14SM-60) having a 7.1 IV (a weight average molecular weight ~ 649,000 kq/mole) and an Mw/Mn of approximately 8. The xerogel yarns were prepared essentially as in Example 1 except that the spinning solution concentra-tions, the pumping rate, the stretch of the solution yarns and the stretch oi- the gel yarns were varied as illustrated in Table 3. The gel yarn stretch ratios employed in Examples 10-31 were generally the highest that could be employed consistent with either of two constraints: breakage of the yarn, or physical limitations of the apparatus used. In general, physical 76~
~23-limitations of the apparatus limited the gel yarn stretch ratio that could be employed with yarns spun with a solu~ion stretch of above about 20:10 There~ore, the gel yarn stretch ratios recited in the Examples shou~d not be construed as fundamental limitations of the process as higher gel stretch ratios can be employed.

Table 3 Stretch Ratios Solution Pumping Conc., R~teSolution Gel Example Wt~ cm /minYarn Yarn 6 38 1.1 9.02 11 6 38 3.1 4.5 12 6 15.2 8.8 3.39 13 6 15.2 8.8 3.39 14 6 15.229.0 1.85 6 15.246.6 1.15 16 8 38 1.1 9.62 17 8 15.23.16 5.61 18 8 15.28.65 3.4 19 8 150236.8 1,46 38 1.09 8.44 21 10 29.23.25 7.3 22 10 12.88.74 7.43 23 10 16.419.4 2.78 24 12 38 1.1 8.94 12 15.218.1 2.97 26 12 15.226.7 2.02 27 12 15.238.2 1.41 28 15 15.6 1.1 8.6 29 15 15.618.2 3.0 150226.7 2.0 31 15 15.638.6 1.39 Table 3 (con't) Leaving Stretch R tios Example Dryer @ 120C@ 145COverall 1.24 3.0 1.35 50 11 1.3 3.75 1 D 4 95 12 1.22 2.9 1,~ 147 13 1.22 2.9 1.5 158 14 1.14 3.6 1.4 308 1.14 3.5 1.4 299 16 1.25 3.3 1.2 52 17 1.26 4O5 1.3 131 la 1.20 ~I.0 1.3 184 19 1.14 5.5 1.4 472 . 1.24 2.75 1.4 44 21 1.17 3.0 1.5 126 22 1.14 2.75 1.4 285 23 1.14 3.g 1.5 36~
24 1.31 2.75 1.4 50 1.14 3.0 1.5 276 26 1.14 2.8 1.4 241 27 1.14 3.5 1.~ 301 28 1.19 2.5 1.2 34 29 1O14 2.25 1.4 196 1.14 2~25 1.5 205 - 25 31 - 1.14 3.0 1.3 239 The xerogel yarns were hot stretched as in Examples - 2-9. Zone No. 1 temperature was maintained at 120C and Zone No. 2 temperatures was 145C. The stretch ratios and the properties of the yarns obtained are given in Table 4.

Table 4 Tenacity Modulus % W-t-~l Example Denier g/d g/d UE J/g_ M21ting TemPs C*
119 24 1100 3.5 47 11 65 26 1380 3.7 54 1~ 41 30 134~ 3.7 63146, 151 13 46 29 1030 4.4 73 14 20 29 1480 3.3 58146, 151 19 24 1040 4.1 56~34, 146, 148 - 16 187 24 1100 3.5 46146, 151 17 90 19 730 4~4 49 18 50 30 1380 4.0 69 19 16 30 1180 4.5 74146, 151 289 24 1~40 3.9 50 21 84 31 1280 4.6 80146, 151 22 45 28 1030 4.4 66 23 33 28 860 4.8 74 24 291 24 1290 3.5 47 43 28 1050 5.2 81lA2, 150 26 4~ 28 870 6.1 90 27 44 27 840 6.5 96144, 149 28 510 21 ~80 4.3 47 29 ~2 20 640 5.~ 61 84 20 680 6.3 64 .- 25 *Main melting peak is underlined lW-t-b is the work needed to break the fiber.

It is seen from the data of Examples 10-31 that yarn tenacity, modulus, elongation, toughness and melting temperatures may be regulated through a choice of solution concentration, solution stretch ratio, gel stretch ratio and xerogel stretch ratios. The yarn 35 properties are also functions of polymer I~ and the respective stretch temperatures and speeds. The final product of Example 13 was characterized by x-ray ~7~

diffraction, heat of fusion, density, and infra-red dichroic measurements at 720 and 730 cm 1. The results are as follows:
a) density (Kg/m3): 961 b) heat of fusion (cal/g): 59.6 c) x-ray crystallinity index: 0.65 d) crystalline orientation function (f~) 0.992 e) overall infra-red fiber orientation function:
~.84 The tenacity data of Examples 10-31 are shown plotted vs. solution stretch ratio in Figure 3.
Examples 10, 16, 20, 24 and 28 are comparative examples of fiber samples not subject to a solution stretch of at least about 3:1. Surprisingly, it is apparent from the plot that for this 7.1 IV polymer essentially the same tenacity-solution stretch ratio relation.ship applies for polymer concentrations of from 6 wt% to 10 wt~o In Figure 4, the overall stretch ratios obtained in Examples 10-31 are shown plotted vs. solution stretch ratio and as a function of polymer concentration. Very surprisingly, the stretchability (overall stretch ratio) increased with increasing polymer concentration over the concentration range 6 wt%-10 wt%. This feature is contrary to reports in the literature which clearly 25 indicate that as concentration levels increase, the ovsrall stretchability of the fiber should decrease.
See Smith, Lemstra & Booij, Journal of Polymer Science, Poly. Phys. Ed., 19, 877 (1981). While the causes of the opposite effect indicated by our results as compared 30 to the results reported in Smith st al., su~ra, are not entirely clear, it appears that this opposite effect results from the sequence of processing steps employed in our process (which produces a more uniform fiber).
Our results indicate that solution stretching at a 35 ratio of at least 3:1 tends to cause molecular disentanglement. Because this feature competes with the opposing tendency of greater entanglement with increasing polymer concentration, we believe that -` ~276~

optimum overall stretchability occurs at intermediate solution stretch ratios and intermediate first concentrations.

The xerogel yarns of the following examples were prepared from a 6 wt% solution of polyethylene (Hercules HB-301) having a 9.0 IV, approximately 998,000 Mw, and an Mn/Mm of approximately 8. The yarns were spun essentially as in Example 1 except that the solution yarns and gel yarns were stretched as recited in Table 5. Pumping rate was 38 cm3/min in Examples 32 and 33 and was 17.3 cm3/min in Examples 34-36.
The xerogel yarns were hot stretched as in Examples 2-9. 2One No. 1 temperature was maintained at 135C and 15 zone No. 2 tsmperature was 150C. Feed speed to the first hot stretch zone was 12 m/min in ~xample 32, 24 m/min in Example 33 and 16 m/min in Examples 34-36. The stretch ratios and the properties of the yarns obtained are also given in Table 5.
Table 5 - _ Stretch Rat os _ _ Solutlon Gel Leaving Zone Nb~l Zone N~.2 Example Yarn Yarn ~y~_ @ 135C @ 150C Overall 32 1.08 8.14 1.3 3.25 1.2 45 33 1.08 8.14 '.3 2.5 1~2 34 - 25 34 12.95 3.65 1.15 3.0 1.2 196 35 19.8 2.38 1.15 3.0 1.25 203 36 40~0 1.18 1.15 3.0 1.25 203 Tenacity Modulus % W-t-B*
30 ~xampleDenier g/d q/d UE j/~
32 151 22 1120 2.9 35 33 14~ 25 1160 3.3 43 34 28 31 1360 3.7 63 26 32 1370 3.7 64 36 21 29 1040 4.2 65 *W-t-b is the work needed to break the fiber.

~276~6~

The following examples illustrate that the maximum attainable solution stretch and the effects of solution stretch are dependent on polymer molecular weight, 5 solution concentration and spinning throughput rate.
In these examples, polyethylene solutions were prepared as in Example 1 except that the polymer was of 26 IV, approximately 4~5 X 106 Mw, and Mw/Mn of ~ approximately 8. The solutions were spun through a 16 hole spinning die whose holes were of 0.040" diameter.
The pumping rate was 16 cm3/min in Examples 37-39 and 41, 32 cm3/min in Example 40, and 48 cm3/min in Examples 42-47.

Table 6 Stretch Ratios Solution Gel Zone No.l Zone No.2 Example Yarn Yarn @ 135C_ @ 150C Overall 37 0.61 6.78 5.25 2.0 43 3811.21 5.6 4.75 2.0 64 20 393.05 3.1 5.5 2.0 104 405.56 1.0 4.75 3.0 79 4110,0 1.0 4.5 2.5 112 4211.0 (BROKE)------------------------------431.08 3.7 5.75 2.25 52 ~ 25 441.48 2.58 5.0 2.5 48 452.25 1.95 S.35 2.5 59 463.82 1.0 5.0 2.75 52 474,0 (BROKE)-------------------------------7G~

Table 6 (con't) Modulus %UE W-t-B*
Denier Tenacitv g/d _ ~/9 38 g2 32 2250 2.4 --39 62 33 2090 2.5 --~0 59 31 1690 2.7 --42 --_________________ ~ 43 138 32 163~ 2.5 --44 130 35 1710 2.8 --99 32 1580 2.6 --46 108 28 1160 3.3 --47 - -_-__________________~__ 15 *W-t-b is the work needed to break the fiber.

Claims

1. A process for producing shaped polyethylene articles which comprises the steps of:
(a) forming, at a first temperature, a solution of polyethylene in a first solvent, said polyethylene having a weight average molecular weight between about 200,000 and 4,000,000 kilograms/kg mole;
(b) extruding said solution through an aperture to form a solution product, said solution product being at a temperature no less than said first temperature;
(c) stretching the solution product at a stretch ratio of at least about 3:1;
(d) cooling the solution product to a second temperature below the first temperature to form a first gel containing first solvent;
(e) extracting the first solvent from the first gel with a second solvent to form a second gel containing second solvent, substantially free of the first solvent;
(f) drying the gel containing the second solvent to form a xerogel substantially free of solvent; and, (g) stretching at least one of the first gel, the second gel, and the xerogel, the total stretch ratio being sufficient to produce a polyethylene article having a tenacity of at least about 13 grams/denier, a porosity of less than 10% by volume and a modulus of at least about 350 grams/denier.

2. The process of claim 1 wherein the solution product is stretched at a ratio of at least about 10:1.

3. The process of claim 1 wherein the total stretch ratio is at least about 30:1.

4. The process of claim 2 wherein the total stretch ratio is at least about 30:1.

5. The process of claim 1 wherein the concentration of polyethylene in the first solvent is between about 5 and about 75 percent by weight.

6. The process of claim 1 wherein the concentration of polyethylene in the first solvent is between about 6 and about 15 percent by weight.

7. The process of claim 1 wherein the concentration of polyethylene in the first solvent is between about 6 and about 10 percent by weight.

8. The process of claim 1 wherein the polyethylene has a weight average molecular weight between about 200,000 and about 800,000.

9. The process of claim 1 wherein the polyethylene has a weight average molecular weight between about 250,000 and about 750,000.

10. The process of claim 1 wherein the polyethylene has a weight average molecular weight between about 300,000 and about 700,000.

11. The process of claim 1 wherein the total stretch ratio is sufficient to produce a polyethylene article having a crystalline orientation function of at least about 0.95.

12. The process of claim 1 wherein stretching at least one of the first gel, second gel, and xerogel occurs in at least two stages.

13. The process of claim 1 wherein stretching at least one of the first gel, second gel, and xerogel comprises the steps of stretching the first gel or second gel, and the xerogel.

14. The process of claim 1 wherein stretching at least one of the first gel, second gel, and xerogel comprises the step of stretching the xerogel.

15. The process of claim 14 wherein stretching at least one of the first gel, second gel, and xerogel further comprises the step of stretching the xerogel in at least two stages.

16. The process of claim 14 further comprising the step of stretching the xerogel in a first stage at a ratio of at least about 2:1 and stretching the xerogel in a second stage at a ratio of at least about 1.1:1.

17. The process of claim 15 wherein the xerogel is stretched in a first stage at a temperature between about 115°C and about 135°C and the xerogel is stretched in the second stage at a temperature of between about 130°C and about 155°C.

18. A shaped polyethylene article having a weight average molecular weight between about 200,000 and about 800,000 kg/kg mole, a crystalline orientation function of at least about 0.95, a tenacity of at least about 13 grams/denier, and a main melting temperature of at least about 140°C (measured at 10°C/minute heating rate by differential scanning calorimetry), said main melting temperature being greater than the main melting temperature of a shaped polyethylene article of substantially the same weight average molecular weight produced from a polymer solution of substantially the same polymer concentration, spun at substantially the same throughput rate and subjected to solution stretching at a ratio of less than about 3:1.

19. The shaped polyethylene article of claim 18 wherein the polyethylene article has a weight average molecular weight between about 250,000 and about 750,000 a tensile modulus of at least about 500 grams/denier, and a tenacity of at least about 15 grams/denier.

20. The shaped polyethylene article of claim 18 wherein in the main melting temperature is at least about 141°C.

21. The shaped polyethylene article of claim 19 wherein the polyethylene article has a a tensile modulus of at least about 750 grams/denier, and a tenacity of at least about 18 grams/denier.

22. The shaped polyethylene article of claim 20 having a weight average molecular weight between about 300,000 and about 700,000, a tensile modulus of at least about 750 grams/denier and a tenacity of at least about 20 grams/denier.

23. The shaped polyethylene article of claim 20 wherein the tensile modulus is at least about 1000 grams/denier and the tenacity is at least about 20 grams/denier.

24. The shaped polyethylene articles of claim 18 further having an ultimate elongation of less than about 7%.

25. The shaped polyethylene article of claim 18 further having an ultimate elongation of less than about 5%.

26. The shaped polyethylene article of claim 18 further having a crystallinity of at least about 70%.

27. The shaped polyethylene article of claim 18 in the form of a fiber.

28. Yarn comprising polyethylene fiber of claim 27.

29. An article of manufacture comprising a polyethylene article having a weight average molecular weight between about 200,000 and about 800,000 kg/kg mole, a tensile modulus of at least about 350 grams/denier, a tenacity of at least about 13 grams/denier, a crystalline orientation function of at least about 0.95, and a main melting temperature of at least about 140°C (measured at 10°C/minute heating rate by differential scanning calorimetry), said main melting temperature being greater than the main melting temperature of a shaped polyethylene article of substantially the same weight average molecular weight produced from a polymer solution of substantially the same polymer concentration, spun at substantially the same throughput rate and subjected to solution stretching at a ratio of less than about 3:1.

30. The article of manufacture of claims 29 wherein the article of manufacture is a composite article.

31. The article of manufacture of claim 30 wherein the shaped polyethylene article is a fiber.

32. The shaped polyethylene article of claim 18 wherein the porosity is less than 10% by volume.

33. The process of claim 1 wherein the porosity is less than about 5%.

34. The process of claim 1 wherein cooling the solution product comprises quenching the solution product in a quench bath.

35. The process of claim 1 wherein cooling the solution product occurs at a rate greater that about 50°C/min.

36. The shaped polyethylene article of claim 18 wherein the article has a weight average molecular weight of less than 500,000.

37. A shaped polyethylene article produced by the process of claim 1.

38. The article of manufacture of claim 29 wherein the porosity is less than 10% by volume.

39. The article of claim 27 wherein the fiber has-a weight average molecular weight of less than 500,000.

40. A shaped polyethylene article having a weight average molecular weight between about 200,000 and about 4,000,000 kg/kg mole a tensile modulus of at least about 350 grams/denier, a transverse microfibrillar spacing which is less than a transverse microfibrillar spacing of a shaped polyethylene article of substantially the same weight average molecular weight produced from a polymer solution of substantially the same polymer concentration, spun at substantially the same throughput rate and subjected to solution stretching at a ratio of less than about 3:1, a tenacity of at least about 13 grams/denier, and a main melting temperature of at least about 140°C measured at 10°C/minute heating rate by differential scanning calorimetry.

41. An article of manufacture comprising the shaped polyethylene article of claim 40.

42. A shaped polyethylene article having a weight average molecular weight of at least about 200,000 and less than 500,000 kg/kg mole, a tenacity of at least about 13 grams/denier, a tensile modulus of at least about 350 grams/denier, and a main melting temperature of at least about 140°C measured at 10°C/minute heating rate by differential scanning calorimetry.

43. A shaped polyethylene article of claim 42 wherein the main melting temperature is at least about 141°C.

44. An article of manufacture comprising the shaped polyethylene article of claim 42.

45. A shaped polyethylene article having a weight average molecular weight between about 200,000 and about 4,000,000 kg/kg mole, a crystalline orientation function of at least about 0.95, a tensile modulus of at least about 350 grams/denier, a tenacity of at least about 13 grams/denier, and a main melting temperature of at least about 140°C (measured at 10°C/minute heating rate by differential scanning calorimetry), said main melting temperature being greater than the main melting temperature of a shaped polyethylene article of substantially the same weight average molecular weight produced from a polymer solution of substantially the same polymer concentration, spun at substantially the same throughput rate and subjected to solution stretching at a ratio of less than about 3:1.

46. The process of claim 1 wherein the solvent is a liquid at the second temperature.