WO1990015897A1

WO1990015897A1 - Polyolefinic fibers having increased melting temperatures

Info

Publication number: WO1990015897A1
Application number: PCT/US1990/003164
Authority: WO
Inventors: Yash P. Khanna; Anne-Marie C. Reimschuessel; John P. Sibilia
Original assignee: Allied-Signal Inc.
Priority date: 1989-06-12
Filing date: 1990-06-05
Publication date: 1990-12-27

Abstract

A fiber having increased melting point comprising a polyolefin core coated with a polymer such as a polyamide.

Description

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POLYOLEFINIC FIBERS HAVING INCREASED MELTING TEMPERATURES

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to improved polyolefinic fibers. More particularly, this invention relates to such polyolefinic fibers formed from thermoplastic polymers such as polyolefins, polyesters and nylons having increased melting points.

2. Prior Art

Polyolefinic materials are well known materials of commerce which have experienced wide acceptance in forming shaped objects and film or sheet material. The use of such materials has extended to the fiber and fabric industries. For example, such fibers are described in U.S. Patent Nos. 4,457,985; 4,587,154; 4,567,092; 4,562,869; 4,559,862; 4,137,394; 4,356,138; 4,413,110; and U.S. Patent application Serial No. 359,020. A disadvantage of polyolefinic materials have been their relatively low melting points. This has reduced their applicability in applications where relatively high melting polymeric materials are required. In U.S. Patent No. 4,403,012 is described polyolefinic fibers which have melting points higher than the melting point of the polymer from which they were formed.

Bico ponent fibers are known in the art. For example. Textile World, June 1986 at page 29 describes sheath/core fibers which have an inner core of polyester and have an outer core of polypropylene or polyethylene. Also see Textile World, April 1986, page 31.

3icomponent textile filaments of polyester and nylon are known in the art, and are described in U.S. Pat. No. 3,489,641. According to the aforesaid patent, a yarn that crimps but does not split on heating is obtained by using a particular polyester. It is also known to employ as the polyester component of the bicomponent filament a polyester which is free from antimony, it having been determined that antimony in the polyester reacts with nylon to form a deposit in the spinneret which produces a shorter junction line, and thus a weaker junction line. Such products are claimed in U.S. Patent Application Serial No. 168,152, filed July 14, 1980.

It is also known to make bicomponent filaments using poly[ethylene terephthalate/5-(sodium sulfo) isophthalat=] copolyester as the polyester component. U.S. Patent No. 4,118,534 teaches such bicomponents.

It is also known to make bicomponent filaments in which the one component partially encapsulates the other component. U.S. Patent No. 3,607,611 teaches such a bicomponent filament.

It is also known to produce bicomponent filaments in which the interfacial junction between the two polymeric components is at least in part jagged. U.S. Patent No. 3,781,399 teaches such a bicomponent filament. Bicomponent filaments having a cross sectional dumbell shape are known in the art. U.S. Patent No. 3,092,892 teaches such bicomponent filaments. Other nylon/polyester bicomponent fibers having a dumbell cross sectional shape having a jagged interfacial surface are known, the polyester being an antimony-f ee copolyester having 5-(sodium sulfo) isophthalate units. U.S. Patent No. 4,439,487 teaches such fibers. The surface of such bicomponent filament is at least 75% of one of the polymeric components. Still other nylon/polyester bicomponent sheath/core fibers are described in Japan

Patent Nos. 49020424, 4804721, 70036337 and 68022350; and U.S. Patent Nos. 4,610,925; 4,457,974 and 4,610,928.

SUMMARY OF THE INVENTION The present invention is directed to polyolefin based fiber having increased melting points. More particularly, this invention relates to polyolefinic based fiber comprising a core formed from one or more polyolefins of fiber forming molecular weight and sheath formed from one or more materials selected from the group consisting of amorphous polymers having a glass transition temperature (Tg) greater than the melting point of the polyolefin forming said core, and crystalline and semicrystalline polymers having melting points (T ) greater than the melting point of the polyolefin forming said core. "Amorphous polymers", "crystalline polymers" and "semi crystalline polymers" are known in the art. [See for example, D.W. Van Dreuelen and P.J. Hoftyzer, Properties of Polymers",. Elsevier Scientific Publishing Company Amsterdam, Oxford and New York (1976)]. As used herein, a "fiber" is an elongated body, the length dimension of which is greater than the transverse dimensions of width and thickness. Accordingly, the term fiber includes single filament, ribbon, strip and the like, having regular or irregular cross-section. The fiber of this invention exhibits a higher melting point as compared to polyolefin fibers which do not include the polyamide sheath.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more fully understood and further advantages will become apparent when reference is made to the following detailed description of the invention and the accompanying drawings in which:

FIGs. 1, 2 and 3 represent Differential Scanning Calorimetry thermograms for polyethylene fiber and for polyethylene coated with polyethylene terephthalate, polyetherimide, polyphenylene sulfone, epoxy, nylon 6, nylon 66 and nylon 4,6.

DETAILED DESCRIPTION OF THE INVENTION The fiber of this invention comprises a polyolefin core coated with a polyamide sheath. The polyolefin core is formed from a polyolefin of "fiber forming molecular weight" . As used herein, "fibeb forming molecular weight" is a molecular weight at which the polymer can be melt spun into a fiber. Such molecular weights are well known to those of skill in the art and may vary widely depending on a number of know factors, including the specific type of polymer. In the preferred embodiments of the invention, the molecular weight of the polyolefin is at least about 5,000 and in the particularly preferred embodiments the molecular weight of the polyolefin is from about 8,000 to about 5,000,000. Amongst these particularly preferred embodiments, most preferred are those embodiments in which the polyolefin is of ultra-high molecular weight of from about 500,000 to about 5,000,000. Polyolefin useful in the practice of this invention may vary widely. The type of polyolefin is not critical and the particular polyolefin chosen for use in any particular situation will depend essentially on the physical properties and features desired. Thus, a multiplicity of linear thermoplastic polyolefin having wide variations in physical properties are suitable for use in this invention.

Illustrative of polyolefins useful in the practice of this invention are those formed by polymerization of olefins of the formula:

- C - CH.

wherein:

R. and R₂ are the same or different at each occurrence and are hydrogen, alkyl or phenyl. Such polyolefins include polystyrene, polyethylene, polypropylene, poly(1-octadecene) , polyisobutylene, poly{1-ρentene) , poly(2-methylst/rene) , ρoly(4- methylstyrene) , poly(l-hexene) , poly(l-pentene) , poly(4-methoxystryene) , poly(5-methyl-l-hexene) , poly(3-methyl-l-pentene) , poly(l-butene) , poly( 3- methyl-1-butene) , poly(3-phenyl-l-propene) , poly(3- methyl-1-butene) , poly(1-pentene) , poly(4-methyl-l- butene), ρoly(1-pentene) , poly(4-methyl-l- pentene), poly(1-hexene) , poly(5-methyl-l-hexene) , poly(1-octadecene) , and the like.

Preferred for use in the practice of this invention are polyolefins of the above referenced formula in which R, is hydrogen and R₂ is hydrogen or alkyl having from

1 to about 12 carbon atoms such as polyethylene, polypropylene, polyisobutylene, poly(4-methyl-l-pentene) , poly(1-butene) , poly(1-pentene) , poly(3-methyl-l-butene) , poly(1-hexene) , poly(5-methyl-l-hexene) , poly( 1-octene) , and the like.

In the particularly preferred embodiments of this invention, the polyolefins of choice are those in which R, is hydrogen and R₂ is hydrogen or alkyl naving from i to about 8 carbon atoms such as polyethylene, polypropylene, poly(isobutylene) , ρoly(1-pentene) , poly(3-methyl-l-butene) , poly(1-hexene) , poly(4- methyl-1-pentene) , and poly(1-octene) . Amongst these particularly preferred embodiments, most preferred are those embodiments in which R, is hydrogen and R₂ is hydrogen or alkyl having from 1 to about 6 carbon atoms such as polyethylene, polypropylene, poly(4-methyl-l- pentene), and polyisobutylene, with polyethylene and polypropylene being the polyolefins of choice. In the most preferred embodiments of the invention, the polyolefin core is formed from a high molecular weight polyethylene filament, a high molecular weight polypropylene filament or a combination thereof. U.S.P. 4,457,985 generally discusses such high molecular weight polyethylene and polypropylene filaments, and the disclosure of this patent is hereby incorporated by reference to the extent that it is not inconsistent herewith. In the case of polyethylene, suitable filaments are those of molecular weight of at least 150,000, preferably at least one million and more preferably between two million and five million. Such extended chain polyethylene (ECPE) filaments may be grown in solution as described in U.S. Patent No. 4,137,394 to Meihuzen et al.. or U.S. Patent No. 4,356,138 of Kavesh et al., issued October 26, 1982, or a filament spun from a solution to form a gel structure, as described in German Off. 3,004,699 and GB 2051667, and especially as described in Application Serial No. 572,607.of Kavesh et al. filed

January 20, 1984 (see EPA 64,167, published Nov. 10, 1982). 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 units per 100 main chain carbon atoms, and that may also contain admixed therewith not more than about 50 wt% of one or more polymeric additives such as alkene-1-polymers, in particular low density polyethylene, polypropylene or polybutylene, copolymers containing mono-olefins as primary monomers, oxidized polyolefins, graft polyolefin copolymers and polyoxymethylenes, or low molecular weight additives such as anti-oxidants, lubricants, ultra-violet screening agents, colorants and the like which are commonly incorporated by reference. Depending upon the formation technique, the draw ratio and temperatures, and other conditions, a variety of properties can be imparted to these filaments. The tenacity of the filaments should be at least 15 grams/denier, preferably at least 20 grams/denier, more preferably at least 25 grams/denier and most preferably at least 30 grams/denier. Similarly, the tensile modulus of the filaments, as measured by an Instron tensile testing machine, is at least 300 grams/denier, preferably at least 500 grams/denier and more preferably at least 1,000 grams/denier and most preferably at least 1,200 grams/denier. These highest values for tensile modulus and tenacity are generally obtainable only be employing solution grown or gel filament processes. Many of the filaments have melting points higher than the melting point of the polymer from which they were formed.

Similarly, highly oriented polypropylene filaments of molecular weight at least 200,000, preferably at least one illion and more preferably at least two million may be used. Such high molecular weight polypropylene may be formed into reasonably well oriented filaments by the techniques prescribed in the various references referred to above, and especially by the technique of U.S. Serial No. 572,607, filed January 20, 1984, of Kavesh et al. and commonly assigned. Since polypropylene is a much less crystalline material than polyethylene and contains pendant methyl groups, tenacity values achievable with polypropylene are generally substantially lower than the corresponding values for polyethylene. Accordingly, a suitable tenacity is at least 8 grams/denier, with a preferred tenacity being at least 11 grams/denier. The tensile modulus for polypropylene is at least 160 grams/denier, preferably at least 200 grams/denier.

The amount of polyolefin included in the fiber of this invention may vary widely. In general, the amount of polyolefin in the fiber is not greater than about 99.5 percent by weight based on the total weight of the fiber. In the preferred embodiments of the invention the amount of polyolefin in the fiber may vary from about 99.5 to about 60 percent by weight based on the total weight of the fiber, and in the particularly preferred embodiments of the invention the amount of polyester in the fiber may vary from about 99 to about 85 weight percent on the aforementioned basis. Amongst these particularly preferred embodiments, most preferred are those embodiments in which the amount of polyester in the fiber is from about 99 to about 95 weight percent based on the total weight of the fiber.

As a second essential component, the fiber of this invention includes a coating of one or more materials selected from the group consisting of amorphous polymers having a glass transition temperature (T ) greater than the melting point of the polyolefin forming said core, and crystalline and se icrystalline polymers having melting points (T ) greater than the melting point of the polyolefin forming said core. The coating material may vary widely and may be a thermoseting resins such as an alkyd, allylic, amino (melamine and urea, epoxy,phenolic, unsaturated polyester, silicon and urethane, or a thermoplastic polymer such as polyolefin, polyester, polyamides, and the like.

In the preferred embodiments of this invention, the coating is formed from one or more polyamides. The molecular weight of the polyamides may vary widely. For example, the polyamides may be a wax having a relatively low molecular weight i.e., 500 to 1,000 or more. The polyamide may also be of fiber forming molecular weight. Such polyamide for use in the practice of this invention are well known. Usually, the polyamide is of fiber forming molecular weight having a molecular weight of at least about 5,000. In the preferred embodiments of the invention the molecular weight of the polyolefins is from about 8,000 to about 1,000,000 and in the particularly preferred embodiments is from about 25,000 to about 750,000. Amongst the particularly preferred embodiments most preferred are those in which the molecular weight of the polyamide is from about 50,000 to about 500,000.

Illustrative of useful and preferred polyamides are those characterized by the presence of recurring carbonamide groups as an integral part of the polymer chain which are separated from one another by at least two carbon atoms. These polyamides are those prepared by reaction of diamines and devices having the recurring unit represented by the general formula:

-NHCORCONHR¹-

in which R is an alkylene group of at least about two carbon atoms, preferably from about 2 to about 10 carbon atoms, or aryl, preferably phenyl and R is R or aryl. Examplary of such materials are ρoly(hexamethylene adipamide) (nylon 6,6), ρoly(hexamethylene sebecamide) (nylon 6,10), poly(hexamethylene isophthalamide) , poly(hexamethylene terephthalamide) , poly(heptamethylene pimelamide) (nylon 7,7), poly(octamethylene suberamide) (nylon 8,8), poly(nonamethylene azela ide) (nylon 9,9), poly( ecamethylene azelamide) (nylon 10,9), ρoly(decamethylene sebacamide) (nylon 10,10), poly[bis(4- amino cyclohexyl)methanie-l,10_^-decanecarboxamide) ] (Quiana), poly(m-xylylene adipamide), poly(p-xylylene sebacamide), poly(2,2,2-trimethyl hexamethylene terephthalamide) , poly(piperazine sebacamide), poly(p-phenylene terephthalamide), poly(metaphenylene isophthalamide) and the like.

Other useful polyamides are those formed by polymerization of amino acids and derivatives thereof, as for example lacatams. Illustrative of these useful polyamides are ρoly(4-aminobutyric acid) (nylon 4), poly(6-aminohexanoic acid) (nylon 6), poly(7-aminoheptanoic acid) (nylon 7), poly(8-aminoocatonoic acid) (nylon 8), ρoly(9-aminononanoic acid) (nylon 9), poly(10-aminodecanoic acid) (nylon 10), ρoly(11-aminoundecanoic acid) (nylon 11), poly(12-aminododecanoic acid) (nylonl2) and the like. Preferred polyamides for use in the practice of this invention are polycaprolactam and poly(hexamethylene adipamide), and poly(tetramethylene adipamide) (nylon 4,6).

The amount of polyamide included in the fiber of the invention may vary widely and is usually from about 0.5 to about 50 percent by weight based on the total weight of the fiber. In the preferred embodiments of this invention, the amount of polyamide is from about 1 to about 35 weight percent based on the total weight of the fiber; and in the particularly preferred embodiments of the invention the amount of polyamide in the fiber is from about 2 to about 25 weight percent based on the total weight of the fiber. Amongst the particularly preferred embodiments, most preferred are those embodiments in which the amount of polyamides is from about 5 to about 20 percent by weight based on the total weight of the fiber. Various optional ingredients which are normally included in polyamide and/or polyolefin fibers may be incorporated into the fiber at an appropriate point during its manufacture. Such optional components include fillers, nucleating agents, colorants, anti-oxidants, stain resistant agents, anti-static agents, fire retardants and the like. These optional components are well known to those of skill in the art, accordingly, only the preferred optional components will be described herein in detail.

While certain cross-sections are preferred for certain uses, in general the cross-sectional shape of the fiber is not critical and can vary widely. The fiber may have an irregular cross section or a regular cross section. For example, the fiber can be flat sheets or ribbons, regular or irregular cylinders, or can have two or more regular or irregular lobes or vanes projecting from the center of axis of the fiber, such fibers are hereinafter referred to as "multilobal" fibers.

Illustrative of such multilobal fibers are trilobal, hexalobal, pentalobal, tetrolobal, and octalobal filament fibers.

The fibers of this invention may be foamed. Such foamed fibers can be prepared by using conventional foaming techniques, as for example U.S. Patent Nos. 4,562,022; 4,544,594; 4,380,594 and 4,164,603.

The fiber of this invention is conveniently manufactured by coating a polyolefin fiber or filament with one or more polyamides. Any convenient polymer coating technique can be employed. For example, the polyolefin fiber or filament can be coated with a polyamide in a solution coating process. For example, in such a process a polyamide can be dissolved in a suitable solvent. Such solvents include partially halogenated hydrocarbons such as l-bromo-3-chlorobenzene, l-bromo-2-ethoxybenzene, l-bromo-4-fluorobenzene, l-chloro-4-fluorobenzene, ethylene chlorohydrin, chlorobenzene, carbon tetrachloride, 1,3-dibromobenzene, 1,3-dichlorobenzene, 1,2-dichlorobenzene, isopropylchloride, chloral hydrate, n-propylchloride, sec-butylbromide, 1,2-dichloroethane, dichloromethane, chloroacetic acid, trichloroacetic acid, chloroform. 1,3-dichloropropanol, dichloroacetic acid, trichloromethanol, trifluoracetic acid, trifluoroethanol and the like; substituted and unsubstituted phenols such as phenol, o-cresol, m-cresol, p-cresol, o-nitrophenol, catechol, o-fluorophenol, m-fluorophenol, p-fluorophenol, o-chlorophenol, m-chlorophenol, p-chlorophenol, o-bromophenol, m-bromophenol, and the like; aromatic and aliphatic alcohols, and glycols as well as solutions thereof, such as benzyl alcohol, diethylene glycol, glycerol, methanol, hydrogen chloride/methanol,

2-butene-l,4-diol, higher primary alcohols such as

1-octanal, 1-decanol, 1-dodecanol, 1-heptanol and the like, solutions of alcohol soluble salts such as calcium chloride, magnesium chloride, and Ca(SCN)_ in methanol and the like; various organic and inorganic acids such as acetic acid, halogenated acetic acid, cyanoacetic acid, formic acid, nitric acid, sulfuric acid, phosphoric acid and the like; ketones such as acetone, diethyl succinate and the like; heterocycles amides and ureas such as N-acetylmorpholin, N,N-dimethyl acetamide, N,N-dimethyl fora ide, foramide, (alphafcγpyrrolidone, tetramethyl urea, hexamethyltrisophosphoamide, and the like; ethers such as tetrahydrofuran; aliphatic carbonates such as ethylene carbonate, propylene carbonate and the like; aliphatic sulfoxides such as dimethyl sulfoxide and the like; and other solvents such as hydrogen fluoride and sulfur dioxide. It should be appreciated that this listing of solvents is merely representative of useful solvents and is not exhaustive of useful solvents. Preferred solvents for use with polyamides are m-cresol, chlorophenol, formic acid, trifluoroethanol, acetic acid, trichloroacetic acid, ethylene carbonate, sulfuric acid, phosphoric acid, hexamethytrisphosphoa ide, dimethyl sulfoxide and sulfuric acid; and particularly preferred solvents for use in the practice of this invention with polyesters are phenol, phenol/ tetrachloroethane, phenol/2,4,6-trichlorophenol, chlorohydrate, chlorophenol, nitrobenzene, dimethyl sulfoxide, and halogenated aliphatic carboxylic acids.

In the most preferred embodiments of the invention solvents for use with polyamides are m-cresol, chlorophenol, formic acid and trifluoroethanol; and most preferred solvents for use with polyesters are phenol and phenol/tetrachloroe hane.

The amount of polymer contained in the solution may vary widely, the only requirement being that the same polymer will precipitate from the solution when treated in the second step of the process. In general, the amount of polymer in the solution is at least about 0.01 weight percent, based on the total weight of the solution. The upper concentration of polymer in the solution is not critical, and is dictated primarily by the solubility of the polyamide in the particular wolfent. In the preferred embodiments of the invention, the amount of polymer in the solution is at least about 0.01 weight percent based on the total weight of the solution, and in the particularly preferred embodiments of the invention the amount of polymer contained in said solution is at least about 0.5 weight percent on the aforementioned basis. Amongst the particularly preferred embodiments of the invention, most preferred are those embodiments in which the amount of polymer in the solution is at least about 1 weight percent based on the total weight of the solution.

After contacting the polyolefin fiber with the polyamide solution the contacted fiber is removed from contact and the solvent removed from the adhering solution by a conventional method. Illustrative of such methods are evaporation under atmospheric or reduced pressure.

Adhesion of the sheath to the polyolefin core may be improved by surface modification prior to coating. Illustrative of useful surface modification treatments are chemical etching, corona discharge and plasma treatment. The polyolefin fibers or filaments can be formed by any suitable fiber or filament forming technique. For example, polyolefin fibers may be formed by conventional processes such as melt, solution, dry and gel spinning techniques. Illustrative of suitable fiber spinning processes and melt spinning techniques and apparatus for carrying out these processes are those described in "Man Made Fibers Science and Technology", Vol. 1-3, H.F. Mark et al., Interscience New York, 1968; "Encyclopedia of

Polymer Science and Technology", Vol. 3; Fundamentals of

Fiber Formation by Androzej Ziabuke, Wiley and Sons, New

York, New York (1976); "Encyclopedia of Polymer Science and Technology", Vol.3, pps. 326-381 and U.S. Patent Nos.

4,454,196 and 4,410,473. In the preferred embodiments of the invention polyolefin fibers are formed using the techniques of U.S. Patent Nos. 4,413,110; 4,535,027;

4,535,027; 4,137,394 and 4,356,138; and German Off 3,004,699, GB No. 2051667 and EPA 64,197 all of which are incorporated herein by reference.

The fibers of this invention can be employed in the many applications that polyolefin and polyamide fibers are used. These fibers are particularly useful in the fabrication of ballistic-resistant articles such as those described in U.S. Patent Nos. 4,403,012; 4,650,710; 4,457,985; 4,613,535; 4,737,402 and 4,748,064 all of which are hereby incorporated by reference.

The following examples are presented to more particularly illustrate the invention and should not be construed as limitations.

EXAMPLE I

Solutions of nylon 6, nylon 6,6 and nylon 4,6 were prepared in trifluoroethanol (TFE) at about 10 wt% concentration. A sample of polyethylene yarn manufactured and sold by Allied-Signal Inc. under the trademark

Spectra^R 1000 was soaked in each of these solutions and then the solvent in the solution adhering to the yarn was stripped off by vacuum drying.

The amount of nylon coated on the surface of each sample and the melting point, T , of each coated sample m was determined by Differential Scanning Calorimetry (DSC). In these experiments, a Dupont 9900 thermal analyzer with a model 910 DSC was used. About 6 mg of the polyethylene yarn was lightly crimped in an aluminum cup, such that the sample was free to shrink i.e., unconstrained during melting. The analysis was carried out in an inert atmosphere using a heating rate of

10 C/min. The results of these experiments are set forth in FIG 1 and in the following Table I. In the Table, "PE * is polyethylene.

TABLE I

Exp Wt%

No. Sample Coating Main T_m, C l PE - 147

2 PE/Nylon 6 35 156

3 PE/Nylon 4,6 35 157

4 PE/Nylon 6,6 35 156

EXAMPLE II

A series of experiments were carried out to evaluate the effect of coating concentration on the increase in melting point of the polyethylene. In these experiments, the polyethylene yarns were coated with varying amounts of nylon 4,6 and evaluated as set forth in Example I. In some of these experiments, the polyethylene yarns were put under a tension of 1 g/denier, and the coating was applied, The tension was taken off only after the coating had dried. The results of these experiments are set forth in FIG. 2 and the following Table II. In the Table, "PE" is polyethylene and "N4,6" is nylon 4,6. TABLE II

Ξxp Wt% No. Sample Coating Tension Main Tin, C

1 PE - - 148.3

2 PE/N 4,6 1 - 149.1

3 PE/N 4,6 9 - 156.0

4 PE/N 4,6 16 - 156.9

5 PE/N 4,6 38 - 156.6

6 PE/N 4,6 6 + 157.0

7 PE/N 4,6 6 + 156.6

8 PE/N 4,6 37 156.4

EXAMPLE III

Using the procedure of Example I, polyethylene yarn was coated with self hardening epoxy (neat), polyethylene terephthalate (PET) (5% solution in m-cresol), polyethersulfone (PES) (5% solution in MeCl_) and polyetherimide (PEI) (5% solution in MeCl₂) . The amount of coating was estimated by comparing the weights of the coated and uncoated PE yarns. The melting point of each coated fiber was determined by Differential Scanning Calorimetry DSC. The results are set forth in the following Table III and in FIG. 3.

TABLE III

Exp Wt% NO . Sample Coating Main T_m, C

PE - 147

2 PE/Epo: 20 149+156

3 PE/PES 7 149+156

4 PE/PET 9 149

5 PE/PEI 12 151+155

Claims

WHAT IS CLAIMED IS:

1. A fiber comprising a polyolefin core coated with of one or more coating materials selected from the group consisting of amorphous polymers having a glass transitio temperature (Tg) greater than the melting point of the polyolefin forming said core, and crystalline and semicrystalline polymers having melting points (Tm) great than the melting point of the polyolefin forming said cor in an amount effective to increase the melting point of said fiber to a temperature greater than the melting poin of the polyolefin forming said core.

2. A fiber according to claim 1 wherein said polyolefin core is coated with one or more polyamides.

3. A fiber according to claim 2 wherein said polyamides are selected from the group consisting of poly(hexamethylene adipamide) and polycaprolactam..

4. A fiber according to claim 1 wherein the amount of said coating material is from about 0.5 to about 50 wt based on the total weight of the fiber.

5. A fiber according to claim 4 wherein said amount is from about 1 to about 35 wt%.

6. A fiber according to claim 8 wherein said amount is from about 2 to about 25 wt%.

7. A fiber according to claim 5 wherein said amount is from about 5 to about 20 wt%.

8. A fiber according to claim 1 wherein said polyolefin is selected from the group consisting of polyolefins formed by polymerization of olefins of the formula:

^R1^R2^C CH,

wherein:

R₁ and R₂ are the same or different at each occurrence and are no hydrogen, alkyl or phenyl.

9. A fiber according to claim 11 wherein:

R. and R_ are the same or different at each occurrence and are hydrogen or alkyl having from 1 to about 12 carbon atoms.

10. A fiber according to claim 1 wherein said polyolefin is polyethylene.