US20130295808A1

US20130295808A1 - Nylon coated uhmwpe fibres with improved properties and apparatus for coating same

Info

Publication number: US20130295808A1
Application number: US13/858,705
Authority: US
Inventors: Dariush Firouzi; Daniel Foucher; Habiba Bougherara; Pradeep Agrawal
Original assignee: Ryerson University
Current assignee: Ryerson University
Priority date: 2012-04-09
Filing date: 2013-04-08
Publication date: 2013-11-07
Also published as: CA2811896A1

Abstract

A composition comprising an inner core of UHMWPE fibres having a molecular weight greater than 500,000 Daltons with a denier of from about 700 to about 3000, preferably from about 1000 to about 2500, more preferably from about 1500 to about 2000, most preferably from about 1500 to about 1800, with an overall thickness of 0.2 to 0.8 mm and a nylon coating.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is a nonprovisional of and claims priority to U.S. Patent Application Ser. No. 61/621,870, filed Apr. 9, 2012, which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

Ultra high molecular weight polyethylene (“UHMWPE”) is a polyolefin comprised of ethylene units and having an extremely high molecular weight per unit of polymer, typically greater than 500,000 Daltons. Like other polymers, UHMWPE can be formed into sheets, blocks and fibre threads. UHMWPE has several desirable properties including abrasion resistance, fatigue resistance, high strength, high toughness, resistance to water, the ability to float on water, good resistance to distortion, excellent electrical properties, high impact resistance and resistance to ultraviolet (UV) radiation. Such properties make UHMWPE ideal in applications such as artificial joints, industrial parts and other high-strength applications. There are however drawbacks to UHMWPE fibre including poor mechanical performance at temperatures above 90° C. or for applications where a load is applied for an extended period of time. This drawback may occur even at room temperature. Creep is defined as the progressive deformation of a material at constant load or stress. So called “creep” for UHMWPE can be as high as 10% in 90 hours when a 30% load is applied at room temperature (Strong, A. B., “Polymeric Reinforcing Fibers—Kevlar, Spectra and Others”, Composites Fabrication, January 1997, pages 9-13).
The prior art includes attempts to address the undesirable characteristics of UHMWPE. Some involve using metal alloys or copolymers of UHMWPE with other materials such as inorganic fillers, other polymers and the like. Others involve coating UHMWPE fibres, in particular, to introduce improved properties.
Pal, S. et al., (Trends Biomater. Artif. Organs, Vol. 18 (2), January 2005) attempted to address the deficiencies by applying a hydroxyapatite coating over alumina ceramic particulate reinforced UHMWPE composite biomaterials. A bioactive coating on this composite implant facilitates biological fixation between the prosthesis and the hard tissue, and increases the long-term stability and integrity of implants.
Silva, M. A. et al., (Biomed. Mater. 5 (2010) 035014 (9 pp) used titanium and titanium/hydroxyapatite coatings on UHMWPE to improve in vitro osteoblastic performance.
Pal, K. et al., (Trends Biomater. Artif. Organs, Vol. 19 (1), pp. 39-45 (2005) reported on the development and coating of porous UHMWPE plates. Beyond enhancing the biological response, this research shows some improvement in mechanical properties by coating a solution mixture of Sodium Carboxy Methyl Cellulose (SCMC)/Polyvinyl Alcohol (PVA)/Hydroxyapatite (HA) on UHMWPE.
Roy, S. and Pal, S. (Bull. Mater. Sci., Vol. 25 (7), December 2002, pp. 609-612 characterized silane coated hollow sphere alumina-reinforced UHMWPE composites. This research also developed a polymer (UHMWPE)-silane coated ceramic (Alumina) composite to characterize its mechanical properties.
Kane, S. et al., (Journal of Biomedical Materials Research Part A Vol. 92 (4) pp. 1500-1509 (2010) characterized the tribology of PEG-like coatings on UHMWPE. A cross linked hydrophilic coating similar to polyethylene glycol was covalently bonded to the surface of UHMWPE to improve the lubricity and wear resistance thereof for use in total joint replacements.
EP 2182101 A1 relates to a web of yarns comprising a first web of a high density polyethylene and a second web of elastomeric polymer fibres (including polyamide fibres).
U.S. Pat. No. 8,012,172 B2 relates to a high strength, abrasion resistance surgical suture of UHMWPE strands braided with polyester or nylon.
Japanese published patent application 05-282004 relates to UHMWPE coated with nylon and used in fishing line applications.
In spite of these attempts to improve the properties of UHMWPE fibres, there still exists a long-felt need for fibre or fabric comprising UHMWPE having high creep resistance, high strength, improved processability, reduced weight, and increased antiballistic properties.

SUMMARY OF INVENTION

In this application, the term UHMWPE, UHMWPE fibre and UHMWPE fibres are used interchangeably.
This invention relates to UHMWPE fibres coated with Nylon, preferably Nylon 6,6, Nylon 6,12, Nylon 6 or Nylon 5,10 resulting in an improved material and the process to coat the UHMWPE fibres. UHMWPE fibres used for this purpose typically have deniers of 600-2400, with each fibre consisting of between 200-400 filaments.
This invention also relates to the apparatus to apply said nylon coating to UHMWPE fibres. In one embodiment, the nylon is deposited on the UHMWPE fibres, preferably in the form of a nylon solution or molten nylon, such that the nylon is substantially uniformly deposited on the UHMWPE fibres through the use of a milled die, or the like, preferably said die is of a specific diameter, preferably said diameter is between 0.5-2.0 mm, and more preferably 1.0 mm. In one embodiment, a nylon solution from about 0.1 to about 20 wt % substantially dissolved nylon in a substantially alcoholic solution, preferably from about 3 to about 15 wt % and more preferably about 5 wt % is applied on to the UHMWPE fibres. In one embodiment, the UHMWPE fibres are passed through the nylon solution resulting in a nylon coating on said UHMWPE fibres. In one embodiment, the nylon coating comprises from about 5 to about 50 wt % of the overall UHMWPE fibre weight, preferably from about 10 to about 30 wt %, more preferably from about 15 to about 25 wt %, most preferably from about 20 wt %. The hybrid nylon coated/UHMWPE fibres have, among other properties and characteristics, improved mechanical properties and higher heat resistance compared to uncoated/neat UHMWPE. In one embodiment, the hybrid nylon/UHMWPE fibres have a density of from about 0.90 to about 1.11 g/mL, and preferably from about 0.98 to about 1.05 g/mL and can be woven into weaves, preferably panelled weaves for various applications including anti-ballistic applications such as a security vest or blast proof shield, as well as in automotive parts.
In one embodiment a process is provided in which a substantially alcohol soluble nylon solution is used to coat or encapsulate polymeric fibres such as UHMWPE. This results in an improvement to the fibre's properties such as mechanical/tensile strength, heat resistance and the like. The substantially alcohol soluble nylon is selected from nylon 6/6, nylon 6/12, nylon 6 and nylon 5,10 and the alcohol can be any lower alkanol such as methanol, ethanol, propanol, butanol or cyclohexanol.
In another embodiment, there is provided a process for coating UHMWPE with nylon, said process comprising:
Providing a nylon in a faun suitable for adherence to said UHMWPE, preferably a nylon solution or molten nylon, preferably in a concentration of about 0.1 to about 20% in alcohol or 100% molten nylon;
Allowing the contact of said nylon solution to said UHMWPE for a predetermined period of time to allow adherence of said nylon solution to said UHMWPE;
Allowing sufficient time for drying of said nylon solution to said UHMWPE; in one embodiment washing said coated UHMWPE, preferably with water.
In one embodiment, said process for coating said UHMWPE with nylon is conducted in a milled die having a predetermined diameter. Preferably said diameter is from about 1 mm to about 2 mm.
In one embodiment, the UHMWPE used herein has a molecular weight greater than about 500,000 Daltons to about 3,000,000 Daltons. In the nylon coated UHMWPE fibres, the nylon coating comprises from about 5 to about 50 weight % by weight of the UHMWPE, preferably 10-30 weight %, more preferably 15-25 weight % and most preferably 20-25 weight %. The nylon coated UHMWPE fibres thus produced have a density from about 0.9 to about 1.1 g/mL and more preferably from about 0.98 to about 1.05 g/mL.
In another embodiment, UHMWPE fibres having a nylon coating comprising from about 5 to about 50% by weight of UHMWPE fibres is provided. The coated fibres have improved mechanical/tensile strength and heat resistant properties compared to uncoated UHMWPE fibres.
In another embodiment, nylon coated UHMWPE fibres are provided having an increased creep resistance versus neat UHMWPE fibres.
In another embodiment, nylon coated UHMWPE fibres are provided having an improved tensile strength versus untreated UHMWPE, preferably from about 10% to about 100% increased tensile strength versus neat or untreated UHMWPE, most preferably about 22% increased tensile strength versus neat UHMWPE.
With respect to the apparatus, in one embodiment, there is provided a first station to house said uncoated UHMWPE, a coating station, to house said nylon solution to coat said UHMWPE preferably a memory station to remove excess solution, preferably a washing station, to wash said coating on said UHMWPE, and preferably a drying station, to dry said nylon coated UHMWPE.
In another embodiment nylon coated UHMWPE fibres can be woven into a weave, preferably paneled weaves and this weaved material can function as part of an anti-ballistic material useful in systems such as a security vest system, body armour, blast shield or the like. The uses of the nylon coated UHMWPE fibres are not limited to the above.
For ballistic applications, without being bound to any theory, STFs in materials such as Kevlar demonstrate a non-Newtonian flow behaviour observed as an increase in viscosity with increasing shear rate or applied stress (Barnes, 1989; Maranzano and Wagner, 2001; Lee and Wagner, 2003). This transition from a flowing liquid to a solid-like material is due to the formation of shear induced transient aggregates, or “hydro-clusters” that dramatically increase the viscosity of the fluids (Bender and Wagner, 1995; Maranzano and Wagner, 2002, Bossis and Brady, 1989; Catherall et al., 2000).
The use of STFs in body armour or anti-ballistic vests takes advantage of the property that at higher shear rates, the viscosity of the composite spikes and transiently turns rigid, offering an enhanced stab and ballistic resistance when compared to non-STF body armour.
Suspension of silica particles in liquid polymers has been widely investigated, analyzed and often reported in literature regarding STFs. Most existing studies on STF-fabrics focused on spherical or rod-like silica particles (Egres, 2005). Extensive analysis of ballistic properties of several STF systems was conducted by the U.S. Army Research Laboratory and Wagner's group with assistance of fractions (wt. %) of colloidal silica particles (120 nm average diameter) that were suspended in polyethylene glycol with different molecular weights (200, 300, 400, or 600 g/mole) and impregnated with Kevlar® fabrics. The results illustrated significant improvement in ballistic properties of Kevlar/STF composite material as compared to neat Kevlar®. Additionally, the addition of STF was shown to cause little or no increase in the thickness or stiffness of the fabrics.
In addition to stab and ballistic resistance, dramatic improvements in puncture resistance were observed under high and low speed loading conditions, while slight increase in cut protection were also observed. The tests were performed under different conditions on impregnated Kevlar® fabrics with STFs that were generated by dispersing functionalized colloidal silica particles (500 nm) in 200 g/mol polyethylene glycol at a volume fraction of approximately 52% (Wagner et al., 2001). Comparative research was conducted with colloidal silica (446 nm av. Dia-40% wt.) suspended in ethylene glycol.
In another embodiment, there is provided a weaved material comprising a nylon coated UHMWPE further comprising a shear thickening fluid (STF). In one instance, resulting in an anti-ballistic material that is further substantially resistant to impacts, such as but not limited to knife and bullet impacts or the like. Preferably the weaved material is substantially lighter than traditional aramid fibres incorporating a STF. In one embodiment the resulting weave is from about 30 to about 50% of the weight of traditional aramid fibres using STF. This results in a substantially lighter weave and the positive attributes associated therewith.
In yet another embodiment, there is provided an improved STF comprising silica and a glycol. In one embodiment the STF comprises fumed silica and polyethylene glycol. In another embodiment the STF comprises fumed silica and polypropylene glycol. In yet another embodiment, the STF comprises crystalline silicon dioxide and polyethylene glycol. In yet still another embodiment, the STF comprises colloidal silica and polyethylene glycol. In one embodiment the amount of silica in the glycol is at least 30%. The prior art STFs when reaching a concentration level of at least 30% experience degradation and instability. The current invention overcomes the degradation and instability associated with the prior art STFs.
In yet another embodiment of the invention, there is provided a process to manufacture a STF, comprising:
Blending a first quantity of silica in a predetermined amount of glycol for a period of time to allow substantially full dispersion of said silica in said glycol,
Adding a second quantity of silica to said predetermined amount of glycol under sonication conditions, preferably sonication with a water bath, preferably to allow substantially full dispersion of said silica in said glycol.
Preferably said sonication water bath is at room temperature.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing the tensile strength of neat UHMWPE at room temperature.

FIG. 2 is a graph showing the tensile strength of coated UHMWPE at room temperature.

FIG. 3 is a graph showing a creep test of neat UHMWPE at 50° C.

FIG. 4 is a graph showing a creep test of coated UHMWPE at 50° C.

FIG. 5 is a cross-section schematic of coated UHMWPE of the present invention.

FIG. 6 is a graph showing a creep test of neat UHMWPE at 25° C., 50° C. and 70° C.

FIG. 7 is a graph showing a creep test of coated UHMWPE at 25° C., 50° C. and 70° C.

FIG. 8 is a schematic of coating apparatus for use in the present invention, according to one embodiment.

FIG. 9 is a diagram of the coating apparatus for use in the present invention, according to one embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the FIGS. 1 and 2 and Table 1, which show the results of tensile tests conducted on untreated and nylon coated UHMWPE, respectively. As can be seen, at room temperature, there is a 18% improvement in breaking force with the nylon coated UHMWPE. At 50° C., there is a 21% improvement. Similarly at 70° C., there is a 10% improvement and at 100° C., there is a 26% improvement. At 125° C., there is a 100% improvement as uncoated
UHMWPE cannot be used beyond 100° C. Therefore not only is there an improvement in tensile strength, but there is also an improvement in heat resistance of the UHMWPE.

TABLE 1

Mechanical Properties of Nylon Coated and neat UHMWPE fibres at different temperatures.

Referring now to FIGS. 3 and 4, the creep test results of nylon coated and untreated UHMWPE, respectively. The force used was fixed at 195 Newtons with the initial moving speed at 50 mm/min. It is evident from this test that there is less creep associated with the nylon coated UHMWPE than with the untreated UHMWPE at higher temperature. Furthermore, it can be seen that the creep resistance for the nylon coated UHMWPE is improved over the untreated UHMWPE.
Referring now to FIG. 5, it can be seen that the UHMWPE is evenly coated with nylon such that the coating is substantially even throughout the length of the UHMWPE.
Referring now to FIGS. 6 and 7, and Table 2, a comparison of the creep results for the neat and nylon coated UHMWPE demonstrate the dramatic improvement in creep resistance at higher temperature. As can be seen, there is slight improvement at 25° C., 49% improvement at 50° C. and 58% improvement at 70° C.

TABLE 2

Improving creep resistance of coated UHMWPE
versus neat UHMWPE at different temperatures

In one embodiment there is provided a process for preparing a nylon 6/6 or nylon 6/12 coated UHMWPE fibre. The nylon has a molecular weight of about 100,000 to about 150,000, preferably about 120,000 g/mol and is applied by first dissolving the nylon in a lower alkanol such as methanol, ethanol, propanol, etc., preferably methanol, in the presence of an alkaline earth salt, preferably calcium chloride. The concentration of nylon in alcohol is from about 0.1 to about 0.3 M, most preferably about 0.2 M. The ratio of nylon to calcium chloride to methanol in the solution is most preferably about 1:4:20. Preferably, the solution is heated to substantially disclose the calcium chloride and nylon, preferably to reflux in order to substantially dissolve the calcium chloride and nylon. The UHMWPE fibre is drawn through a nylon solution and then through a manufactured, milled die having an orifice of about 1 to about 2 mm in diameter, used to remove the excess nylon. This step is then followed by a water wash, preferably deionized water, to remove the salt and preferably to cause the nylon to constrict and encapsulate the UHMWPE fibre. As the coated nylon UHMWPE fibre dries in one embodiment via room temperature, and in another embodiment under heating, the nylon further contracts on the UHMWPE fibre preferably from a tight coating. Alternatively, the UHMWPE fibre is drawn through molten nylon forming a uniform coating of nylon on the UHMWPE fibre. In another embodiment, the alcoholic nylon solution can be sprayed onto the UHMWPE fibre and air or oven-dried to form a nylon coated UHMWPE fibre. In another embodiment, multiple fibres of UHMWPE can be drawn through the nylon solution to form multiple nylon encapsulated UHMWPE fibres. The thus formed nylon coated UHMWPE fibre is optionally wound on a spool for subsequent weaving.
In another embodiment, the nylon material is deposited on the UHMWPE fibres, preferably such that the nylon material is substantially uniformly deposited on the UHMWPE fibres. The nylon coating comprises from about 5 to about 50 weight % of the overall UHMWPE fibre weight, preferably from about 10 to about 30 weight %, more preferably from about 15 to about 25 weight % and most preferably from about 20 to about 25 weight %. Preferably, the UHMWPE fibre inner core has a diameter from about 0.2 to about 0.8 mm and most preferably about 0.6 mm and the nylon shell is most preferably about 0.3 mm in thickness.
FIGS. 8 and 9 provide a typical process and apparatus to apply said coating to said UHMWPE. In another embodiment, the nylon coated UHMWPE fibres so produced by the above processes has a density of about 0.9 to about 1.1 g/mL and most preferably of about 0.98 to about 1.05 g/mL. The coated fibres will have a denier of between 700 to about 3000, preferably from about 1000 to about 2500, more preferably from about 1500 to about 2000, most preferably from about 1500 to about 1800 deniers. The nylon coated UHMWPE woven fibre can be weaved into panels suitable for use in, for example, anti-ballistic applications such as security vests, body armour and blast proof shields. The inclusion of an optional shear thickening fluid (STF) provides a nylon coated UHMWPE material that is resistant to knife and bullet impacts and is 30-50% lighter in weight than comparable aramid fibres using a shear thickening fluid. This results in a security vest that is lighter in weight and more comfortable for the wearer.
In another embodiment and with reference to FIGS. 8 and 9, an apparatus (10) is provided for coating UHMWPE fibres (20) comprising a coating portion (30) for coating the fibres (20) a die 20-1 for removing excess nylon solution, a washing portion (40) for washing off the salt from the applied nylon solution and a drying portion (50) for drying the coated fibres (60). The coating portion (30) is preferably under an inert atmosphere, preferably nitrogen. The washing portion (40) preferably uses water. The drying portion (50) preferably uses warm air to dry the coated fibres (60).

EXAMPLES

The present invention is further illustrated by the following specific examples which should not be construed as limiting the scope or content of the invention in any way.

Example 1

Preparation of the Nylon Solution

Anhydrous Calcium chloride (CaCl₂) microbiology reagent grade from BDH was supplied by VWR. Methanol was reagent grade and nylon 6,6 pellets were purchased from Sigma-Aldrich having a molecular weight of 120,000 g/mol.
According to the method described by Benhui et al., J. Polym. Sci., Vol. 12 (1), 1992, hereby incorporated by reference, CaCl₂was added to methanol and heated to reflux for overall 10 minutes. Then nylon was added gradually and the resulting mixture was heated to reflux for several hours. The optimum mixture ratio for nylon, calcium chloride and methanol was 1:4:20.

Example 2

5 wt % Nylon 6,6 in Methanol

To a 2 L round bottom flask equipped with a reflux column and heated externally with an oil bath on a heater/stirrer hotplate, was added 1300 mL of anhydrous methanol. Slowly, 260 g of CaCl₂was added to the same flask using a powder addition funnel. The CaCl₂dissolved in the methanol, and the reaction was exothermic. The sample began to self reflux (80° C.) and was maintained at this temperature with the oil bath. 65 grams of Nylon 6,6 (Sigma Aldrich) was then added slowly to the flask over a period of 3 hours. The partially dissolved Nylon was refluxed in the methanol/CaCl₂solution for a further 24 hours which resulted in all the nylon 6,6 being dissolved. The final ratio of the reactants was 1:4:20 Nylon/CaCl₂/MeOH.

Example 3

4.80 wt % Nylon 6,6 in Ethanol

To a 250 mL round bottom flask equipped with a reflux column and heated externally with an oil bath on a heater/stirrer hotplate, was added 125 mL of anhydrous ethanol. Slowly, 25.5 g of CaCl₂was added to the same flask using a powder addition funnel. The CaCl₂dissolved in the methanol, and the reaction was exothermic. The sample began to self reflux (80° C.) and was maintained at this temperature with the oil bath. 6 grams of Nylon 6,6 (Sigma Aldrich) was then added slowly to the flask over a period of 3 hours. The partially dissolved Nylon was refluxed in the methanol/CaCl₂solution for a further 24 hours which resulted in all the nylon 6,6 being dissolved. The final ratio of the reactants was 1:4.25:20.83 Nylon/CaCl₂/EtOH.

Example 4

5 wt % Nylon 6,12 in Methanol

To a 2 L round bottom flask equipped with a reflux column and heated externally with an oil bath on a heater/stirrer hotplate, was added 700 mL of anhydrous methanol. Slowly, 140 g of CaCl₂was added to the same flask using a powder addition funnel. The CaCl₂dissolved in the methanol, and the reaction was exothermic. The sample began to self reflux (80° C.) and was maintained at this temperature with the oil bath. 35 grams of Nylon 6,12 (Sigma Aldrich) was then added slowly to the flask over a period of 3 hours. The partially dissolved Nylon was refluxed in the methanol/CaCl₂solution for a further 24 hours which resulted in all the nylon 6,12 being dissolved. The final ratio of the reactants was 1:5:20 Nylon/CaCl₂/MeOH.

Example 5

Typical Preparation of Nylon Coated UHMWPE

Nylon 6,6 having a molecular weight of about 100,000 to about 150,000, preferably about 120,000 g/mol was applied to UHMWPE by first dissolving the nylon in a lower alkanol such as methanol, ethanol, propanol, etc., preferably methanol, in the presence of salt, preferably calcium chloride. The concentration of nylon in alcohol is from about 0.1 to about 0.3 M, most preferably about 0.2 M. The ratio of nylon 6,6 to calcium chloride to methanol in the solution is most preferably about 1:4:20. Preferably, the solution is heated to reflux in order to dissolve the calcium chloride and nylon 6,6. The UHMWPE fibre is drawn through a drawn through a nylon solution and then through a manufactured, milled die having an orifice of about 1 to about 2 mm in diameter, used to remove the excess nylon. This step is then followed by a water wash, preferably deionized water, to remove the salt and to cause the nylon to constrict and encapsulate the UHMWPE fibre. As the nylon dries via room temperature air or under heating, it further contracts on the UHMWPE fibre holding tightly by mechanical means. Alternatively, the UHMWPE fibre is drawn through molten nylon forming a uniform coating of nylon on the UHMWPE fibre. In another embodiment, the alcoholic nylon solution can be sprayed onto the UHMWPE fibre and air or oven-dried to form a nylon coated UHMWPE fibre. In another embodiment, multiple fibres of UHMWPE can be drawn through the nylon solution to form multiple nylon encapsulated UHMWPE fibres. The thus formed nylon coated UHMWPE fibre is optionally wound on a spool for subsequent weaving.

Example 6

Preparation of Nylon Coated UHMWPE

A spooled sample of UHMWPE (1200D UHMWPE, tenacity=32 cN/dtex, modulus=1100 g/denier, elongation<4%, Montaki Canada Inc.) was placed in line on the prototype coating machine. The UHMWPE fibre was then pulled through a holding tank (25×2×2 in) containing a methanolic solution of 5% by weight of Nylon 6,6 for approximately 6 seconds. The fibre was drawn with a DC motor operating at 60 RPM, with a traveling speed of fiber of 0.1 m/s. The wet coated fibre was then directed into a cone shaped die (with 1 mm hole diameter) to remove excess Nylon material which was then returned to the holding tank. The coated fibres were next drawn through a distilled deionized water tank to remove the CaCl₂. This process helped collapse the nylon 6,6 tightly around the UHMWPE fibre. After 10 m, the coated fibres were allowed either to air dry or with blown with air for 5-7 minutes. The coated fibre was then spooled onto a second spool.

Example 7

Preparation of Fumed Silica Shear Thickening Fluid Using PEG

In a beaker, 15% by weight of a Fumed silica powder (14 nm, Aldrich) was blended with mechanical stirring into 85 g of a low molecular weight liquid polyethylene glycol (PEG, Mw=200 g/mol, Aldrich). Stirring was continued for 30 minutes at which time the silica powder was fully dispersed in the liquid polymer. To increase the loading, the beaker with the dispersion was placed in a sonicator water bath (VWR Ultrasonic water bath, 35 KHz, temperature controlled to 25° C.). With sonication, the weight % of the dispersion was slowly increased to a final loading level of 36% by adding additional small quantities (1 gram) of the fumed silica over a 5 hour period.

Example 8

Preparation of Fumed Silica Shear Thickening Fluid Using PPG

In a beaker, 15% by weight of a Fumed silica powder (14 nm, Aldrich) was blended with mechanical stirring into 83 g of a low molecular weight liquid polypropylene glycol (PPG, Mw=400 g/mol, Aldrich). Stirring was continued for 30 minutes at which time the silica powder was fully dispersed in the liquid polymer. To increase the loading, the beaker with the dispersion was placed in a sonicator water bath (VWR Ultrasonic water bath, 35 KHz, temperature controlled to 25° C.). With sonication, the weight % of the dispersion was slowly increased to a final loading level of 36% by adding additional small quantities (1 gram) of the fumed silica over a 5 hour period.

Example 9

Preparation of Crystalline Silicon Dioxide Shear Thickening Fluid

In a beaker, 20% by weight of a crystalline silicon dioxide powder (10-20 nm, Aldrich) was blended with mechanical stirring into 20 g of a low molecular weight liquid polyethylene glycol (PEG, Mw=200 g/mol, Aldrich). Stirring was continued for 30 minutes at which time the silica powder was fully dispersed in the liquid polymer. To increase the loading, the beaker with the dispersion was placed in a sonicator water bath (VWR Ultrasonic water bath, 35 KHz, temperature controlled to 25° C.). With sonication, the weight % of the dispersion was slowly increased to a final loading level of 40% by adding additional small quantities (2 grams) of the fumed silica over a 3 hour period.

Example 10

Preparation of Colloidal Silica Shear Thickening Fluid

In a test tube, 45% by weight of colloidal silica that had previously been dried from an aqueous solution was blended with mechanical stirring into 25 g of a low molecular weight liquid polyethylene glycol (PEG, Mw=200 g/mol, Aldrich). Mixing was continued in a Vortex Mixer for 30 minutes at which time the silica powder was fully dispersed in the liquid polymer. The weight % of the dispersion was slowly increased to a final loading level of 45% by adding additional small quantities (1 gram) of the silica over a 10 hour period.

Example 11

Preparation of STF Materials for Testing

Uncoated UHMWPE STF
UHMWPE woven fabric (1200D) was cut into 20×20 cm square layers. Each layer of UHMWPE was impregnated with STF samples (see above examples) by dipping into a plastic container containing the STF gel for about 30 seconds. The excess STF was squeezed out by q plastic rod. The fabrics were then hung for 12 hours for complete drying. Two test specimens were prepared by stacking 5 layers of the square layers, and heat sealed in a 3.75 mil thick nylon/polyethylene bag (3 mil PE/0.75 mil nylon) outer shell. This shell was only to keep the STF treated layers together for testing.
Nylon Coated UHMWPE STF
UHMWPE woven fabric (1200D) were cut into 20×20 cm square layers. Each layer was impregnated with a 5% by weight Nylon 6,6/MeOH solution for about 30 seconds. The excess Nylon material was squeezed out between woven segments by the means of plastic rod. The fabrics were then hung for 12 hours for complete drying. Next, each layer of coated UHMWPE was impregnated with STF samples (see above examples) by dipping into a plastic container with the STF for about 30 seconds. The excess STF was squeezed out by a plastic rod. The fabrics were then hung for 12 hours for complete drying. Two test specimens were prepared by stacking 5 layers of the square layers, and heat sealed in a 3.75 mil thick nylon/polyethylene bag (3 mil PE/0.75 mil nylon) outer shell. This shell was used only to keep the STF treated layers together for testing.
Kevlar STF
A woven Kevlar (Dupont) fabric was cut into 20×20 cm square layers. Each layer of coated UHMWPE was impregnated with STF samples (see examples) by dipping into a plastic container with the STF for about 30 seconds. The excess STF was squeezed out by a plastic rod. The fabrics were then hung for 12 hours for complete drying. Two test specimens were prepared by stacking 5 layers of the square layers, and heat sealed in a 3.75 mil thick nylon/polyethylene bag (3 mil PE/0.75 mil nylon) outer shell. This shell was used only to keep the STF treated layers together for testing.

Example 12

Dynamic Stab Testing of Neat Kevlar, Neat UHMWPE and the STF Impregnated Kevlar and UHMWPE Fabrics

Testing on all samples was carried out based on modified version of NIJ standard 0115.00. One NIJ-specific impactor, the spike, was used. The stab targets were placed on multi-layer foam backing, as specified by the NIJ standard. The impactor (with a weight of 2.3 Kg) was then dropped from a fixed height (50 cm) to the target. The depth of penetration into the target is quantified in terms of the number of witness paper layers penetrated by the impactor.

TABLE 3

Mass and areal density of testing samples impregnated with STF

		Total	Weight	Total Areal	STF Areal
Sample		Weight	of	Density	Density
No.	Description	(g)	STF (g)	(g/cm²)	(g/cm²)

1	Kevlar	89.50	0	.0458	0
2	UHMWPE	44.60	0	.0227	0
3	Kevlar/STF₁	128.17	38.67	.0656	.0198
4	UHMWPE/STF₁	58.75	14.27	.0301	.0074
5	Kevlar/STF₂	122.83	33.33	.0628	.0170
6	UHMWPE/STF₂	56.23	11.75	.0288	.0661

STF₁(Mixture of 60 wt % PEG and Silicon Dioxide with diameter of 10-20 nm)
STF₂(Mixture of 60 wt % PEG and fumed silica with diameter of 14 nm)

As can clearly be seen, the weight of UHMWPE/STF is significantly lower than the Kevlan/STF.

TABLE 4

Experimental results of drop tower testing for spike SP

					Penetra-
			Penetration		tion
Sample		Energy	Depth	Energy	Depth
No.	Description	E1 (J)	(mm)	E2 (J)	(mm)

1	Kevlar	24	40	36	100
2	UHMWPE	24	95	36	100
3	Kevlar/STF₁	24	0	36	0
4	UHMWPE/STF₁	24	30	36	100
5	Kevlar/STF₂	24	0	36	0
6	UHMWPE/STF₂	24	80	36	100

STF₁(Mixture of 60 wt % PEG and Silicon Dioxide with diameter of 10-20 nm)
STF₂(Mixture of 60 wt % PEG and fumed silica with diameter of 14 nm)

Example 13

Quasi-Static Testing of Neat and Nylon 6,6 Coated UHMWPE STF Samples

To complement the drop tower tests, quasi-static stab tests to measure the index puncture resistance force with uncoated and coated UHMWPE test samples were also performed (Table 6). Samples were prepared as discussed above. The spike impactor was mounted to the upper grip of a tensile tester (TestResources). The test was performed according to ASTM D4833. A machined ring clamp attachment consisting of concentric plates with an open internal diameter of 45±0.025 mm, capable of clamping the fabric without slippage. The sample was centered and secured between the holding plates. The test was performed at machine speed of 5 mm/min until the puncture tip completely ruptured the test specimen. The puncture blades and spike were machined according to the NIJ standard (National Institute of Justice: 0115.00). Nylon 6,6/UHMWPE fabrics showed a 67% improvement to the neat fabric at room temperature.

TABLE 5

Quasi-static testing of Neat and Nylon 6,6 Coated UHMWPE
test samples

		Index Puncture
	Sample	Resistance Force (N)

	Neat UHMWPE/STF	14
	Nylon 6,6 Coated	43
	UHMWPE/STF
	Percent Improvement %	~67

Claims

1. A composition comprising an inner core of UHMWPE fibres having a molecular weight greater than 500,000 Daltons with a denier of from about 700 to about 3000, preferably from about 1000 to about 2500, more preferably from about 1500 to about 2000, most preferably from about 1500 to about 1800, with an overall thickness of 0.2 to 0.8 mm and a nylon coating.

2. The composition of claim 1 wherein the UHMWPE fibres coated with nylon, has a diameter of 0.5-2.0 mm preferably, 0.8-1.0 mm.

3. The composition of claim 2 wherein the nylon coating comprises from 5 to 50% wt of the fibre, preferably 10 to 30% wt, more preferably 15 to 25% wt, most preferably about 20% wt.

4. The composition of claim 3 wherein the UHMWPE fibres has a diameter of 0.6 mm and an outer nylon coating of 0.3 mm.

5. The composition of claim 1 wherein the nylon coating comprises nylon selected from the group consisting of nylon 6,6, nylon 6,12, nylon 6 and nylon 5,10.

6. The composition of claim 2 wherein the nylon coating comprises nylon selected from the group consisting of nylon 6,6, nylon 6,12, nylon 6 and nylon 5,10.

7. The composition of claim 4 wherein the nylon coating comprises nylon selected from the group consisting of nylon 6,6, nylon 6,12, nylon 6 and nylon 5,10.

8. The composition of claim 1 with a density of from about 0.9 to about 1.1 g/mL.

9. The composition of claim 2 with a density of from about 0.9 to about 1.1 g/mL.

10. The composition of claim 3 with a density of from about 0.9 to about 1.1 g/mL.

11. The composition of claim 4 with a density of from about 0.9 to about 1.1 g/mL.

12. A process for preparing a coated UHMWPE fibre using an alcohol soluble nylon selected from the group of nylon 6,6, nylon 6,12, nylon 6, and nylon 5,10 and the alcohol is selected from the group of lower alkanols selected from the group consisting of: methanol, ethanol, propanol, butanol and cyclohexanol.

13. The process according to claim 12 wherein the nylon solution is a nylon in alcohol solution, wherein there is 0.1 to 20% wt of nylon in the solution, preferably 3 to 15% wt and more preferably about 5% wt of nylon in the solution.

14. A process for preparing a coated UHMWPE fibre comprising

a. contacting a UHMWPE fibre (or fibres) with a nylon alcoholic solution prepared in the presence of a salt selected from the group consisting of CaCl₂which is contacted with UHMWPE fibres for a predetermined period of time to allow coating of said UHMWPE,

b. washing said coated UHMWPE fibre to substantially remove CaCl₂from said coated UHMWPE fibre and further precipitate the nylon on the UHMWPE fibre,

c. drying said coated UHMWPE fibre.

15. The process of claim 14 wherein said nylon alcoholic solution has a nylon concentration of about 0.1 M to 0.3 M and preferably 0.2 M.

16. The process of claim 15 wherein said nylon alcoholic solution is selected from a nylon 6,6 methanolic solution or a nylon 6,6 methanolic solution, preferably in a ratio of 1:4:20 Nylon, Calcium Chloride, methanol.

17. The process of claim 16 wherein the UHMWPE fibres are passed (dip coated) through a 0.5-2 mm die, wherein said die is coated with the nylon alcoholic solution.

18. The process of claim 16 wherein said washing is conducted in distilled deionized water, to remove CaCl₂and further precipitate the nylon on the fibres.

19. The use of the composition of claim 1 in an anti-ballistic material.

20. The nylon coated UHMWPE fibre prepared by the process of claims 12, further coated with a Shear Thickening Fluid (STF) resulting in a light antiballistic material preferably 30% to 50% lighter then traditional aramid STF coated material.

21. The nylon coated UHMWPE fibre prepared by the process of claim 13, further coated with a Shear Thickening Fluid (STF) resulting in a light antiballistic material preferably 30% to 50% lighter then traditional aramid STF coated material.

22. The nylon coated UHMWPE fibre prepared by the process of claim 14, further coated with a Shear Thickening Fluid (STF) resulting in a light antiballistic material preferably 30% to 50% lighter then traditional aramid STF coated material.