WO1996041042A1

WO1996041042A1 - Filled thermoplastic cut-resistant fiber

Info

Publication number: WO1996041042A1
Application number: PCT/US1996/008358
Authority: WO
Inventors: Robert B. Sandor; Gunilla E. Gillberg-Laforce; William F. Clear; John Flint; Leslie Lanieve; Scott W. Thompson
Original assignee: Hoechst Celanese Corporation
Priority date: 1995-06-07
Filing date: 1996-05-31
Publication date: 1996-12-19
Also published as: CA2221615C; CN1092254C; CA2221615A1; JPH11511209A; KR19990022515A; AU5967796A; TW307802B; CN1190444A; AU717702B2; BR9609091A; EP0845056A1

Abstract

A fiber having increased cut resistance is made from an isotropic polymer and a hard filler having an average particle size in the range of about 0.25 to about 10 microns and having a Mohs Hardness Value greater than about 3. The filler is included in an amount of at least about 0.1 % by weight. The preferred isotropic polymer is poly(ethylene terephthalate). The preferred filler is calcined alumina.

Description

FILLED THERMOPLASTIC CUT-RESISTANT FIBER

Related Application

This application is related to commonly assigned U.S. Application No. 08/243,344, filed May 16, 1994, still pending, and two divisional applications thereof.

Field of the Invention

This invention relates to fibers made from thermoplastic polymers containing hard fillers that have improved resistance to cutting.

Background of the Invention

Improved resistance to cutting with a sharp edge has long been sought. Cut-resistant gloves are beneficially utilized in the meat¬ packing industry and in automotive applications. As indicated by U.S. Patent Nos. 4,004,295, 4,384,449 and 4,470,251 , and by EP 458,343, gloves providing cut resistance have been made from yarn which includes flexible metal wire or which consists of high tensile strength fibers.

A drawback with gloves made from yarn that includes flexible metal wire is hand fatigue with resultant decreased productivity and increased likelihood of injury. Moreover, with extended wear and flexing, the wire may fatigue and break, causing cuts and abrasions to the hands. In addition, the wire will act as a heat sink when a laundered glove is dried at elevated temperatures, which may reduce tensile strength of the yarn or fiber, thereby decreasing glove protection and glove life.

Highly oriented fibers having high modulus and high tensile strength have better resistance to cutting than conventional semicrystalline polymers. Examples of these highly oriented polymers include polyaramides, thermotropic liquid crystalline polymers, and extended chain polyethylene. These also have shortcomings that limit their usefulness, including loss of properties at temperatures encountered in a drier (polyethylene), poor resistance to bleach (polyaramides), poor comfort, and high cost.

Improved flexibility and comfort and uncomplicated laundering are desirable in cut-resistant, protective apparel. Therefore, there is a need for a flexible, cut-resistant fiber that retains its properties when routinely laundered. Such a fiber may be advantageously used in making protective apparel, in particular highly flexible, cut-resistant gloves.

Thermoplastic polymers mixed with particulate matter have been made into fibers, but not in a way that significantly improves the cut resistance of the fiber, except for thermotropic liquid crystalline polymers. For example, small amounts of particulate titanium dioxide has been used in polyester fiber as a delustrant. Also used in polyester fiber is a small amount of colloidal silicon dioxide, which is used to improve gloss. Magnetic materials have been incorporated into fibers to yield magnetic fibers. Examples include: cobalt/rare earth element intermetallics in thermoplastic fibers, as in published

Japanese Patent Application No. 55/098909 (1980); cobalt/rare earth element intermetallics or strontium ferrite in core-sheath fibers, described in published Japanese Patent Application No. 3-130413 (1991 ); and magnetic materials in thermoplastic polymers, described in Polish Patent No. 251 ,452 and also in K. Turek et al., J. Magn. Magn. Mater. (1990), 83 (1-3), pp. 279-280.

Summary of the Invention

Fibers and yarns made from melt processable isotropic polymers can be made more resistant to cutting with a sharp edge by including a hard filler which is preferably distributed uniformly through the fiber. The hard filler has a Mohs Hardness Value of greater than about 3 and is present in an amount of at least about 0.1 % by weight. The average particle size is in the range of about 0.25 microns to about 10 microns. The fiber has improved resistance to cutting compared with a fiber made with the same polymer without the hard filler. This improvement is at least about 20% when measured by the Ashland

Cut Protection Performance test.

A new method of making a synthetic fiber or yarn more resistant to cutting with a sharp edge is also disclosed. The method comprises the steps of making a uniform blend of a melt processable isotropic polymer and a hard filler having a Mohs hardness value greater than about 3 and then spinning the polymer in the melt phase into fiber or yarn that has its cut performance as measured by the Ashland Cut Protection Performance improved by at least about 20%, and preferably by at least about 35%. The fibers and yarns described above can be made into fabrics that have improved resistance to cutting using any of the methods that are currently used for making fibers and yarns into fabrics, including weaving and knitting. The fibers and yarns can also be made into non-woven fabrics that have improved cut-resistance. Both the fabrics and the methods of making cut-resistant fabrics and the resulting fabrics are new.

Detailed Description of the Invention

As indicated above, a flexible cut-resistant fiber useful for the manufacture of protective apparel may be produced when a hard filler is included in the fiber. The fiber is made from an isotropic polymer. The term "isotropic" means polymers that are not liquid crystalline.

Preferably, the polymer is melt processable; i.e., it melts in a temperature range which makes it possible to spin the polymer into fibers in the melt phase without significant decomposition. The preferred method of making the fiber is by melt spinning. Preferred isotropic polymers are semi-crystalline. Semi¬ crystalline polymers that will be highly useful include poly(alkylene terephthalates), poly(alkylene naphthalates), poly(arylene sulfides), aliphatic and aliphatic-aromatic polyamides, polyesters comprising monomer units derived from cyclohexanedimethanol and terephthalic acid, and polyolefins, including polyethylene and polypropylene.

Examples of specific semi-crystalline polymers include poly(ethylene terephthalate), poly(butylene terephthalate), poly(ethylene naphthalate), poly(phenylene sulfide), poly(1 ,4-cyclohexanedimethanol terephthalate), wherein the 1 ,4-cyclohexanedimethanol is a mixture of cis and trans isomers, nylon-6, nylon-66, polyethylene and polypropylene. These polymers are all known to be useful for making fibers. The preferred semi-crystalline polymer is poly(ethylene terephthalate).

Polymers that cannot be processed in the melt can also be filled with hard particles, as for example cellulose acetate, which is typically dry spun using acetone as a solvent, or a polyaramide, such as the polymer of terephthalic acid and p-phenylenediamine, which is dry-jet, wet-spun from a concentrated sulfuric acid solution. The hard particles would be incorporated into the spinning processes for these polymers in order to obtain the filled fibers. Amorphous, non- crystalline polymers, such as the copolymer of isophthalic acid, terephthalic acid and bisphenol A (polyarylate) may also be filled and utilized in this invention by a melt spinning process.

An important aspect of this invention is the discovery that a flexible cut-resistant fiber may be made from a suitable polymer filled with a hard material that imparts cut resistance. The material may be a metal, such as an elemental metal or metal alloy, or may be nonmetallic. Generally, any filler may be used that has a Mohs Hardness value of about 3 or more. Particularly suitable fillers have a Mohs Hardness value greater than about 4 and preferably greater than about 5. Iron, steel, tungsten and nickel are illustrative of metals and metal alloys, with tungsten, which has a Mohs value ranging from about 6.5 to 7.5 being preferred. Non-metallic materials are also useful. These include, but are not limited to, metal oxides, such as aluminum oxide and silicon dioxide, metal carbides, such as silicon carbide and tungsten carbide, metal nitrides, metal sulfides, metal silicates, metal suicides, metal sulfates, metal phosphates, and metal borides. Other ceramic materials may also be used. Aluminum oxide, and especially calcined aluminum oxide, is most preferred. Titanium dioxide in general is less preferred.

The particle size and particle size distribution are important parameters in obtaining good cut resistance while preserving fiber mechanical properties. In general, the hard filler should be in the form of particles, with a powder form being generally suitable. Flat particles (i.e. platelets) and elongated particles (needles) also work well. The average particle size is generally in the range of about 0.25 to about 10 microns. Preferably the average particle size is in the range of about 1 to 6 microns. The most preferred average particle size is about 3 microns. For particles that are flat (i.e. platelets) or elongated, the particle size refers to the length along the long axis of the particle (i.e. the long dimension of an elongated particle or the average diameter of the face of a platelet). The particles preferably should exhibit a log normal distribution. For making textile fibers (i.e. fibers having a denier in the range of about 1 .5. to 1 5 dpf), the particles should be filtered or sieved in such a way that particles larger than about 6 microns are excluded.

A minor percentage of the hard filler is used. The amount is chosen to yield enhanced cut resistance without causing a significant loss of tensile properties. Desirably, the cut resistance of the fiber or fabric made from the fiber will show improvements of at least about 20% using the Ashland Cut Protection Performance Test. Preferably the cut resistance will improve by at least about 35%, and most preferably will improve by at least about 50% in comparison with a fiber made of the same polymer but without the filler. The tensile properties of the fiber (tenacity and modulus) preferably will not decrease by more than about 50%, and more preferably will not decrease by more than about 25%. Most preferably, there will not be a significant change in tensile properties (i.e., less than about 10% decrease in properties). On a weight basis, the filler should be present in an amount of at least about 0.1 %. The upper limit of filler is determined mainly by the effect on tensile properties, but levels above about 20% by weight are generally less desirable. On a volume basis, the particle level concentration is preferably in the range of about 0.1 % to about 5% by volume, more preferably about 0.5% to about 3% by volume and most preferably about 2.1 % by volume. For the preferred embodiment (calcined alumina in PET), these ranges on a weight basis are about 0.3% to about 14% (preferred), about 1.4% to about 8.5% (more preferred), and about 6% (most preferred). In accordance with the present invention, filled fibers are prepared from a filled resin. The filled resin is made by any of the standard methods for adding a filler to a resin. For example, for a melt processable isotropic polymer, the filled resin is conveniently prepared in an extruder by mixing the hard filler with molten polymer under conditions sufficient to provide a uniform distribution of the filler in the resin, such as mixing in a twin screw extruder. The filler may also be present during the manufacture of the polymer or may be added as the polymer is fed into the extruder of fiber spinning equipment, in which case the blending and spinning steps are nearly simultaneous.

Since the filler is distributed uniformly in the polymer melt, the filler particles are also typically distributed uniformly throughout the fibers, except that elongated and flat particles are oriented to some extent because of the orientation forces during fiber spinning. Some migration of the particles to the surface of the fiber may also occur. Thus, while the distribution of particles in the fibers is described as "uniform", the word "uniform" should be understood to inclyjde non- uniformities that occur during the processing (e.g., melt spinning) of a uniform polymer blend. Such fibers would still fall within the scope of this invention. Any size fiber may be made according to the present invention. In the manufacture of fabrics and yarns, the fiber will generally have a denier in the range of about 1 to about 50 dpf, preferably in the range of about 1 .5 to about 15 dpf, and most preferably about 4 dpf. Cut-resistant monofilaments may also be made by including a hard filler. Monofilaments generally have a diameter of about 0.05 to about 2mm. The fibers are made by conventional fiber spinning processes. As previously stated, the preferred process is melt-spinning, but wet-spinning and dry-spinning may also be used.

The description above is written with respect to fibers. The term fiber includes not only conventional single fibers but also yarns made from a multiplicity of these fibers. In general, yarns are utilized in the manufacture of apparel, fabrics and the like.

Cut-resistant fabric may be made using a filled fiber in accordance with the present invention by using conventional methods, such as knitting or weaving, and conventional equipment. Non-woven fabrics can also be made. Such fabric will have improved cut resistance in comparison with the same fabric made using fiber manufactured from the same polymer without a filler. The cut resistance of the fabric will be improved by at least about 20% when measured using the Ashland Cut Protection Performance test. Preferably the cut resistance will improve by at least about 35%, and most preferably will improve by at least about 50%. Cut-resistant apparel may then be made from the cut-resistant fabric described above. For example, a cut-resistant safety glove designed for use in the food processing industries may be manufactured from the fabric. Such a glove is highly flexible and readily cleanable, being resistant to chlorine bleach and to the heat of a drier. Protective medical gloves may also be made using the cut- resistant fibers of this invention. Other uses of the fabrics and monofilaments include side curtains and tarpaulins for trucks, softsided luggage, commercial upholstery, inflatables, fuel cells, collapsible packaging, airline cargo curtains, firehose sheaths, cut- resistant aprons for use in metal packing, chaps, etc.

Example 1 Poly(ethylene terephthalate) fibers incorporating tungsten powder filler are described below. Tungsten has a Mohs Hardness value of about 6.5 to 7.5. Tire yarn grade poly(ethylene terephthalate) (PET), having an intrinsic viscosity of about 0.95 when measured in o-chlorophenol, was obtained from Hoechst Celanese Corporation, Somerville, New Jersey in the form of pellets. A master batch was made by blending the polymer with 10% tungsten powder on a weight basis in a twin screw extruder. The tungsten had an average particle size of about 1 micron. The polymer pellets and tungsten were both dried before blending. The master batch was blended with additional PET in a twin screw extruder to yield blends having 1 % and 4% tungsten on a weight basis. The samples were melt spun by forcing the molten blend first through a filter pack and then through a spinneret. The yarn was subsequently drawn off a heated feed roll at 90°C, then drawn over a heated shoe, and finally subjected to a 2% relaxation at 225 ^CC. The yarn was plied for testing of properties. The data are summarized in Table 1. One of the 10% tungsten-loaded fibers was also analyzed for tungsten to ensure that the filler was not filtered out. The analysis of the fiber shows about 8.9% by weight tungsten in the fiber.

Tensile properties. The tenacity, elongation and modulus were measured using ASTM test method D-3822.

Cut resistance. The fiber was first knitted into fabric for the testing of cut resistance. The areal density of yarn in the fabric was measured in ounces/square yard (OSY in Tables 1 and 2). The cut resistance of the fabric was then measured using the Ashland Cut Performance Protection ("CPP") test. The test was carried out at TRI/Environmental, Inc., 9063 Bee Cave Road, Austin, Texas 78733- 6201 . In the test, the fabric sample is placed on the convex surface of a mandrel. A series of tests is carried out in which a razor blade loaded with a variable weight is pulled across the fabric until the fabric is cut all the way through. The distance the razor blade travels across the cloth until the blade cuts completely through the cloth is measured. The point at which the razor blade cuts through the fabric is the point at which electrical contact is made between the mandrel and razor blade. The distance required to make the cut is plotted on a graph as a function of the load on the razor blade. The data are measured and plotted for cut distances varying from about 0.3 inches to about 1 .8 inches. The resulting plot is approximately a straight line. An idealized straight line is drawn or calculated through the points on the plot, and the weight required to cut through the cloth after one inch of travel across the cloth is taken from the plot or calculated by regression analysis. The interpolated values of the weight required to make a cut after one inch of blade travel across the cloth are shown in Tables 1 and 2 as "CPP", an abbreviation for Cut Protection Performance. Finally, for purposes of comparing the data for different areal densities of cloth sample, the CPP value is divided by the areal density of the cloth (OSY) to compensate for variations in areal density. This value is shown as CPP/OSY in Tables 1 and 2.

Example 2 In these experiments, PET fiber samples were filled with alumina powder, which was sold commercially under the trademark MICROPOLISH^® II as a polishing abrasive. Two different alumina powders were used having average particle sizes of about 0.05 microns and about 1 .0 microns. Both were obtained as deagglomerated powders from Buehler, Ltd., Waukegan Road, Lake

Bluff, Illinois 60044. The 0.05 micron alumina was gamma alumina with a cubic crystal structure and a Mohs Hardness Value of 8. The 1 .0 micron material was alpha alumina having a hexagonal crystal structure and a Mohs Hardness Value of 9. The two alumina powders were blended with PET using the same method as in Example 4 to yield filled PET samples containing alumina at levels of about 0.21 %, 0.86%, 1 .9% and 2.1 % by weight. Measurements of fiber properties and cut resistance were made using the same methods as in Example 1. The data are presented in Table 2.

The data in Tables 1 and 2 show that there is an improvement in cut resistance of at least about 10-20% at all levels of filler used in these experiments. Both sets of data incorporate filler in the fiber at levels of about 0.07% to about 0.7% on a volume basis. The fiber properties do not appear to significantly degrade with these amounts and sizes of particles.

Example 3

A series of experiments was run using tungsten particles of several different particle sizes (0.6 - 1.6 microns) as fillers in PET at concentrations of 0.4 - 1.2 volume %. The tungsten-filled PET was spun into yarn, which was subsequently knitted into fabric for testing. Cut resistance was again measured by the Ashland Cut Protection

Performance Test, using the modified procedure described below. The CPP values were divided by the areal densities of the cloth to correct for the fact that the tests were carried out on different densities of cloth. The data are presented in Table 3.

Cut Protection Performance (CPP) The Ashland CPP Test was run as described at the end of Experiment 1 , but a calibration against a standard with a known CPP value was used to correct the results. The calibration standard was 0.062 inch neoprene, style NS-5550, obtained from FAIRPRENE, 85

Mill Plain Road, Fairfield, CT 06430, which has a CPP value of 400 gms. The CPP value was measured for this standard at the beginning and end of a series of tests, and an average normalization factor was calculated that would bring the measured CPP value of the standard to 400 gms. The normalization factor was then used to correct the measured data for that series of tests. Also, in caculating the CPP value, a plot of the logarithm of the distance required to cut the fabric vs. the load on the razor blade was utilized, as it was more linear.

Example 4

A series of experiments was run using calcined aluminum oxide as the filler for the fiber. The experiments were run using the same procedure as used in Examples 1-3, but with a broader range of particle sizes (0.5 - 3 microns) and a wider range of concentrations

(0.8 - 3.2 volume %) than in Example 2.

The calcined aluminum oxide used in the experiments was obtained from Agsco Corporation, 621 Route 46, Hasbrouck, N.J.

07604, and is in the form of platelets, referred to as Alumina #1 .

The CPP values were measured using the procedure described at the end of Example 3. The CPP/OSY values were then calculated as described above. These data are presented in Table 4. It can be seen from the data in the tables that the CPP/OSY values are affected by all of the variables listed (i.e., particle size, particle concentration, areal density, and the fiber dpf). At the high areal densities (OSY), the CPP/OSY values fall off significantly. Thus comparisons are preferably made for tests in fabrics having similar areal densities.

Nevertheless, it can be seen from the data in Table 4 that at a level of 2.4 volume % (6.8 weight%), with a particle size of 2 microns, the CPP/OSY values for fabrics made from textile fibers (2.8 dpf) and having areal densities of less than about 10 ounces per square yard were greater than about 100. (Sample Nos. 22-24 and 30). This is much more than a 50% increase over the average CPP/OSY value of about 53 that was measured for unfilled PET fiber of comparable fiber size and areal density (the three Controls in Table 1 ). The average CPP/OSY values for all the tungsten filled PET samples of Table 3 (70) and all the aluminum oxide filled PET samples of Table 4 (75) are also significantly higher than the average of the controls.

It is to be understood that the above described embodiments of the invention are illustrative only and that modification throughout may occur to one skilled in the art. Accordingly, this invention is not to be regarded as limited to the embodiments disclosed herein.

Table 1. Cut Resistance of PET Filled with Tungsten

Particle

% Tungsten Size

No. Wt. Volume (microns) dfif T/E/M¹ CPP² OSY³ CPP/OSY

Control 1 .. - 3.1 6.8/6.7/124 421 7.1 59

Control 2 - - 5.0 - 384 6.8 56

Control 3 _ - 5.0 - 589 13.0 45

1-1 1 % 0.07% 1 micron 6.0 6.3/9.0/128 540 9.1 59

1-2 1 % 0.07% 1 micron 5.6 565 7.3 77

1-3 4% 0.29% 1 micron 6.0 7.2/1 1.6/109 643 7.0 92

1-4 4% 0.29% 1 micron 5.9 7.0/12.5/100 620 7.3 85

1-5 10% 0.72% 1 micron 1 1.6 6.3/10.0/123 697 7.5 93

1-6 10% 0.72% 1 micron 7.4 4.1/22.9/75 759 8.5 90

1 -7 10% 0.72% 1 micron 6.0 - 670 7.6 89

'Tenacity (gpd), Elongation (%), Modulus (gpd), measured using ASTM test method D-3822. ²Cut Protection Performance, measured using the Ashland CPP test. ³0unces per Square Yard.

Table2. Cut Resistance of PET Filled with Alumina

% Alumina Particle Size

No. Wt. Volume (microns) dpf T/E/M¹ CPP² OSY³ CPP/OSY

2-1 0.21 % .07% 1 micron 1 1 4 6.7/10.3/1 12 547 7.2 76

2-2 0.21 % .07% 1 micron 5.6 7.4/12.4/104 463 7.5 62

2-3 0.86% 0.30% 0.05 5.6 7.4/14.0/1 10 501 7.3 69 micron

2-4 0.86% 0.30% 0.05 5.7 6.9/12.8/110 497 6.7 73 micron

2-5 1.9% 0.67% 1 micron 1 1.8 5.8/12.0/108 683 8.2 83

2-6 1.9% 0.67% 1 micron 5.6 7.4/10.9/108 478 6.7 71

2-7 2.1 % 0.74% O.Oδmicron 5.4 6.6/1 1.6/1 17 496 6.7 74

2-8 2.1 % 0.74% 0.05 5.9 5.4/12.8/100 431 6.2 69 micron

'Tenacity (gpd), Elongation (%), Modulus (gpd), measured using ASTM test method D-3822. Cut Protection Performance, measured using the Ashland CPP test. ³0unces per Square Yard.

TABLE 3. Cut Resistance of PET Filled with Tungsten

PARTSIZE is Particle size, measured in microns.

CONC is the concentration of hard particles, measured as a volume % in PET.

DPF is the fiber denier in dpf.

TENACITY, ELONG, and MODULUS are the fiber tensile properties, measured by ASTM test method D-3822.

OSY is the areal density of the knitted fabrics, measured in ounces per square yard.

CPP is the CPP value measured by the Ashland CPP test.

CPP/OSY is the ratio of the CPP value to the areal density (OSY).

* - measured by the method described in Example 1. TABLE 4. Cut Resistance of PET filled with Alumina

PARTSIZE is Particle size, measured in microns.

CONC is the concentration of hard particles, measured as a volume % in PET. DPF is the fiber denier in dpf.

OSY is the areal density of the knitted fabrics, measured in ounces per square yard. CPP is the CPP value measured by the Ashland CPP test. CPP/OSY is the ratio of the CPP value to the areal density (OSY). * - measured by the method described in Example 1.

Claims

We claim:

1. A cut-resistant fiber comprising an isotropic melt-processable polymer and a hard filler distributed uniformly in said fiber,, said filler having a Mohs Hardness value greater than about 3; said filler having an average particle size in the range of about 0.25 microns to about

10 microns; said filler being present in an amount of at least about 0.1 % by weight; said filler being operative to increase the cut resistance as measured by the Ashland Cut Protection Performance test by at least about 20% compared with a fiber comprising said polymer without said filler.

2. A cut-resistant fiber as recited in Claim 1 , wherein the cut resistance of said fiber is increased by at least about 35% compared with a fiber comprising said polymer without said filler.

3. A cut-resistant fiber as recited in Claim 1 , wherein the cut resistance of said fiber is increased by at least about 50% compared with a fiber comprising said polymer without said filler.

4. A cut-resistant fiber as recited in Claim 1 , wherein said hard filler has a Mohs Hardness value greater than about 5.

5. A cut-resistant fiber as recited in Claim 1 , wherein the average particle size of said hard filler is in the range of about 1 to about 6 microns.

6. A cut-resistant fiber as recited in Claim 1 , wherein the average particle size of said hard filler is about 3 microns.

7. A cut-resistant fiber as recited in Claim 5, wherein said hard filler is a non-metal selected from the group consisting oi metal oxides, including aluminum oxide and silicon dioxide, metal carbides, metal nitrides, metal sulfides, metal silicates, metal suicides, metal sulfates, metal phosphates, metal borides, and mixtures thereof, except that said hard filler is not titanium dioxide.

8. A cut-resistant fiber as recited in Claim 7 wherein said hard filler is included in said fiber in an amount of about 0.1 % to about 5% on a volume basis.

9. A cut-resistant fiber as recited in Claim 7 wherein said hard filler is included in an amount of about 0.5% to about 3% on a volume basis.

10. A cut-resistant fiber as recited in Claim 7, wherein said hard filler is included in an amount of about 2.1 % by volume.

1 1 . A cut-resistant fiber as recited in Claim 9, wherein said hard filler is calcined aluminum oxide.

12. A cut resistant fiber as recited in Claim 5, wherein said hard filler is a metal or metal alloy.

13. A cut-resistant fiber as recited in Claim 12, wherein said hard filler is included in an amount of about 0.1 % to about 5% by volume.

14. A cut-resistant fiber as recited in Claim 12, wherein said hard filler is included in an amount of about 0.5% to about 3% by volume.

15. A cut-resistant fiber as recited in Claim 12, wherein said hard filler is included in an amount of about 2.1 % by volume.

16. A cut-resistant fiber as recited in Claim 14, wherein said hard filler is selected from the group consisting of iron, steel, nickel, tungsten and mixtures thereof.

17. A cut-resistant fiber as recited in Claim 1 , wherein said isotropic melt-processable polymer is selected from the group consisting of poly(alkylene terephthalates), poly(alkylene naphthalates), poly(arylene sulfides), aliphatic polyamides, aliphatic-aromatic polyamides, polyesters of cyclohexanedimethanol and terephthalic acid, and polyolefins.

18. A cut-resistant fiber as recited in Claim 1 , wherein said isotropic melt-processable polymer is selected from the group consisting of poly(ethylene terephthalate), poly(butylene terephthalate), poly(ethylene naphthalate), poly(phenylene sulfide), poly(1 ,4- cyclohexanedimethanol terephthalate), nylon-6, nylon-66, polyethylene, and polypropylene.

19. A cut-resistant fiber as recited in Claim 1 , wherein said isotropic melt-processable polymer is poly (ethylene terephthalate).

20. A cut-resistant fiber as recited in Claim 9, wherein said isotropic melt-processable polymer is poly (ethylene terephthalate).

21. A cut-resistant fiber as recited in Claim 1 1 , wherein said isotropic melt-processable polymer is poly (ethylene terephthalate).

22. A cut-resistant fiber as recited in Claim 10, wherein said hard filler is calcined aluminum oxide and said isotropic melt-processable polymer is poly (ethylene terephthalate).

23. A cut-resistant fiber as recited in Claim 16, wherein said isotropic melt-processable polymer is poly (ethylene terephthalate).

24. A method of making a fiber or yarn having increased cut resistance, comprising the steps of

(a) making a uniform blend of at least about 0.1 % by weight of (1 ) a hard filler having a Mohs Hardness value greater than about 3 and a particle size in the range of about 0.25 microns to about 10 microns, and (2) an isotropic melt-processable polymer selected from the group consisting of poly(ethylene terephthalate), poly(butylene terephthalate), poly(ethylene naphthalate), poly(phenylene sulfide), poly(1 ,4-cyclohexanedimethanol terephthalate), nylon-6, nylon-66, polyethylene and polypropylene; and (b) spinning said uniform blend into a fiber or yarn having a cut resistance increased by at least about 20% compared with a fiber or yarn made from said isotropic polymer without said hard filler, as measured by the Ashland Cut Performance protection test.

25. A method of making a fabric having increased cut resistance, comprising the steps of

(a) making a fiber or yarn according to the method of Claim 24, and

(b) fabricating said fiber or yarn into a fabric having a cut resistance increased by at least about 20% compared with a fabric made from said isotropic polymer without said hard filler, as measured by the Ashland Cut Performance Protection test.

26. A cut-resistant fiber comprising a polymer that is not melt- processable and a hard filler distributed uniformly in said fiber, said filler having a Mohs Hardness value greater than about 3; said filler having an average particle size in the range of about 0.25 microns to about 10 microns; said filler being present in an amount of at least about 0.1 % by weight; said filler being operative to increase the cut resistance as measured by the Ashland Cut Protection Performance test by at least about 20% compared with a fiber comprising said polymer without said filler.

27. The cut-resistant fiber recited in Claim 26, wherein said polymer that is not melt processable is a polyaramide.

28. The cut-resistant fiber recited in Claim 27, wherein said polyaramide is the polymer of p-phenylenediamine and terephthalic acid.