Patent Application
20210002438
The following relates to flexible textiles with penetration resistance and more specifically to flexible particle-laden elastomeric textiles with penetration resistance.
Needle stick injuries and other wounds caused due to penetration of sharp objects into the skin are a common form of workplace injuries. Similarly, materials and fabrics that are resistant to penetration of projectiles such as bullets and cuts from objects such as knives and shrapnel are of interest in a number of occupations including law enforcement, waste processing, and military combat. For instance, there is a growing demand for clothing that provides protection against stab threats in law enforcement and for gloves and arm-guards for personnel in recycling and hospital waste removal companies for protection against accidental needle-puncture.
Stab threats are categorized into two classes: puncture penetration by a sharp tip and cutting with a continuous sharp cutting edge. It is generally more difficult to make a resistant textile-armour to cutting as compared to puncture threats. Hypodermic needles, with a thin sharp tip and sloped cutting edges, belong to both categories. In general, protection against hypodermic needle puncture is provided by high thread-count fabrics due to their resistance to “windowing effect”. The “windowing” mechanism occurs when fibers are easily spread-apart and pushed-away by a sharp-tip penetrator without cutting the fabric. In general, areal density of fabric, yarn linear density and mechanical properties of fiber, number of filaments per yarn, fabric weave architecture, and the number of fabric plies affect the penetration resistance of the fabric target. Additionally, the boundary condition of fabric, geometry, type, mass, the speed of penetrator, and inter-yarn and fabric-projectile friction are among the other important factors which could affect the penetration resistance of multilayer textile structures against different types of penetrators.
There has been significant improvement in the manufacture of penetration-resistant materials in recent years. There is, however, still a strong need to improve the performance of protective clothing, especially to make them lighter and thinner with greater flexibility while still providing the same or better performance. Typically, soft penetration-resistant materials comprise of high-strength fabrics such as Kevlar® and ultra-high molecular weight polyethylene (UHMWPE). In order to prevent lethal injuries against different types of threats, several layers of fabric are stacked together which makes the final product relatively heavy and stiff. Various commercial products are available for puncture/stab protection, such as Kevlar Correctional™ from Dupont, which is made of high thread count Kevlar® fabric. However, this product is relatively expensive to manufacture and is not capable of providing sufficient ballistic protection. Coated fabrics, such as Twaron© Stab Resistant Material (SRM) made of Twaron© fabric coated with a silicon carbide polymer matrix composite provides a better stab resistance compared to untreated fabric. For instance, stab penetration work of a 12-layer stack of Twaron© fabric spray-coated with WC Co 83/17 cermet and Al2O3/AlSi 12 is about 1 J compared to 0.2 J for untreated Twaron© fabric, albeit with a significant weight increase. Another example is two-layer nylon coated UHMWPE fabric target with 80% higher puncture resistance than three-layer neat fabric target of equivalent areal density. Nylon coated UHMWPE fiber also shows 14-37% and 17-36% higher creep resistance and breaking force (respectively) compared with those of neat fiber at various temperatures. In another approach, flexible fabric with printed arrays of hard platelets of ceramic-polymer composite onto its surface has been used to fabricate a material called SuperFabric® in order to resist needle stick penetration. Here, the platelets that were bonded resisted puncture and cut threats. Nevertheless, the spaces between the plates were a weak point and multi-layer construction is needed to provide effective resistance.
Alternatively, non-Newtonian shear thickening fluids have also been used to fabricate flexible “Fluid Armour” that provides improved stab resistance. In one example, the fluid armour comprising a shear thickening fluid (STF) was impregnated into a high-performance fabric (e.g., Kevlar®, UHMWPE, or nylon) and was shown to provide about 40-100% higher energy absorption against puncture and stab threats compared to textile-only samples of comparable areal densities. In this example, it was shown that the penetration resistance of four-layer STF impregnated Kevlar® fabric is improved about 60 and 260% against 12- and 22-gauge hypodermic needles (respectively) compared to four-layer neat Kevlar®, albeit with a 15% increase in areal density and about 20% increase in thickness. Despite the high penetration resistance provided by the STF, STFs have a number of limitations. These include propensity to leak due to their liquid state, their hygroscopic nature which absorbs ambient moisture and degradation due to exposure to moisture.
One common method to make STFs for the manufacture of liquid body armour is to centrifuge colloidal silica (CS) with a liquid polymer, such as polyethylene glycol (PEG) or ethylene glycol (EG). As a result, water could be replaced with the liquid polymer and the remaining mixture consists of only silica particles and the polymeric liquid medium. The ballistic performance of one-, two-, and four-layer Twaron® fabric systems against high speed spherical projectiles was improved when the targets were still wet after impregnating in silica colloidal water suspension (SWS) up to 40 wt. % loading of particles. Beyond this particle concentration, the ballistic performance of the treated fabric system diminished below that of neat fabric and the effectiveness of such a treatment was found to be less significant on a 6-ply configuration of the same fabric. CS is also used as an effective reinforcing filler in polydimethylsiloxane (PDMS) and has been shown to have better wettability and easier processing than fumed silica. In one study, the difficulty of mixing high loading of monodispersed silica powder in PDMS was reported because of the high viscosity of this elastomer. On the contrary, an STF mixture of silica particles in EG medium with higher loading concentration provided better ballistic response because of higher inter-particle contacts. CS functionalized in isopropanol (IPA), methylethylketone (MEK), or methyltrimethoxysilane coupling agent could be dispersed better in PDMS which resulted in higher mechanical properties of the bulk PDMS composite because of increased filler-polymer and filler-filler interactions.
In one aspect, a penetration-resistant composite is described herein. The penetration-resistant composite includes a woven or non-woven substrate and an elastomeric binder covering at least a portion of the substrate. The elastomeric binder includes a polymeric base and particles dispersed within the polymeric base. The particles include one or more of amorphous silica particles, fumed silica particles, boron nitride particles, calcium chloride particles, aluminum oxide particles, calcium carbonate particles, graphite particles, metallic glass particles and silicon carbide particles. The particles have a concentration in a range of about 0 wt. % to about 80 wt. % of the elastomeric binder. The particles have a size in a range of about 1 nanometers to 100 micrometers.
In some embodiments, the particles have a concentration in a range of about 50 wt. % to about 80 wt. % of the elastomeric binder.
In some embodiments, the particle concentration is higher than a critical limit to cause jamming of the particles within the elastomeric binder when the composite is compressed.
In some embodiments, the polymeric base is selected from a class of chemicals including silicones, thermoplastic elastomers, natural or synthetic rubbers, fluoro or perfluoro elastomers and elastoolefins.
In some embodiments, the polymeric base comprises one or more of polydimethylsiloxane (PDMS), thermoplastic polyurethane (TPU), styrenic block copolymers (TPS), poly isoprene, butyl rubber, nitrile rubber and fluorosilicone rubber.
In some embodiments, the particles include one or more of silica (SiO2) and/or silicon carbide (SiC) particles.
In some embodiments, the particles are spherical, oval, elongated or sheet like.
In some embodiments, the substrate and the elastomeric binder form one layer of a plurality of layers of the composite.
In some embodiments, the substrate is woven, non-woven, or 0°/90° cross-plied of continuous fibres of aramid, nylon polypropylene, polyethylene, S-Glass, or polybenzobisoxazole (PBO), polyester, or cotton fibers.
In another aspect, a method of forming a penetration-resistant composite is described herein. The method includes mixing particles with a pre-polymer of an elastomeric binder to form a pre-polymer mixture, the particles including one or more of amorphous silica particles, fumed silica particles, boron nitride particles, calcium chloride particles, aluminum oxide particles, calcium carbonate particles, graphite particles, metallic glass particles and silicon carbide particles, each of the particles having a having a diameter in a range of about 10 nanometers to 50 micrometers. The method also includes infusing the prepolymer mixture into a substrate and curing the infused substrate using heat, air-drying or optical means to form the penetration-resistant composite.
In some embodiments, mixing the particles into the pre-polymer of the elastomeric binder includes mixing a colloidal silica with the particles and the elastomeric binder.
In some embodiments, the elastomeric binder includes PDMS and the particles have a concentration in a range of about 0 to about 80 wt. % of the elastomeric binder.
In some embodiments, mixing the particles with the pre-polymer of the elastomeric binder includes mixing an alcohol solvent with the pre-polymer mixture.
In some embodiments, the solvent is selected from a group of lower alkanols including methanol, ethanol, propanol, butanol and cyclohexanol.
In some embodiments, prior to mixing the particles with the elastomeric binder, the particles are mixed with a colloidal silica and treated with an alcohol solvent to form a particle mixture, and the particle mixture is mixed with the pre-polymer of the elastomeric binder.
In some embodiments, the method further includes, prior to infusing the prepolymer mixture in the substrate, performing a plasma treatment to the substrate.
In some embodiments, infusing the prepolymer mixture into the substrate includes soaking the substrate in the prepolymer mixture for about one minute.
In some embodiments, infusing the prepolymer mixture into the substrate further includes, after soaking the substrate in the prepolymer mixture, passing the substrate through a manual cold laminator to remove excess prepolymer mixture from the substrate.
In another aspects, articles including a penetration-resistant composite described herein are described herein.
In some embodiments, the article is a security vest, body armor, or blast proof shields or the like.
Other features and advantages of the present application will become apparent from the following detailed description taken together with the accompanying drawings. It should be understood, however, that the detailed description and the specific examples, while indicating preferred embodiments of the application, are given by way of illustration only, since various changes and modifications within the spirit and scope of the application will become apparent to those skilled in the art from this detailed description.
The drawings included herewith are for illustrating various examples of articles, methods, and apparatuses of the present specification. In the drawings:
Various apparatuses or processes will be described below to provide an example of each claimed embodiment. No embodiment described below limits any claimed embodiment and any claimed embodiment may cover processes or materials that differ from those described below. The claimed embodiments are not limited to materials or processes having all of the features of any one material or process described below or to features common to multiple or all of the materials described below. It is possible that a material or process described below is not covered by any of the claimed embodiments. Any embodiment disclosed below that is not claimed in this document may be the subject matter of another protective instrument, for example, a continuing patent application, and the applicants, inventors or owners do not intend to abandon, disclaim or dedicate to the public any such embodiment by its disclosure in this document.
At the outset, for ease of reference, certain terms used in this application and their meanings as used in this context are set forth. To the extent a term used herein is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in at least one printed publication or issued patent. Further, the present techniques are not limited by the usage of the terms shown below, as all equivalents, synonyms, new developments, and terms or techniques that serve the same or a similar purpose are considered to be within the scope of the present claims.
As one of ordinary skill would appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name only. In the following description and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus, should be interpreted to mean “including, but not limited to.”
The articles “the,” “a” and “an” are not necessarily limited to mean only one, but rather are inclusive and open ended to include, optionally, multiple such elements.
As used herein, the terms “approximately,” “about,” “substantially,” and similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. It should be understood by those of skill in the art who review this disclosure that these terms are intended to allow a description of certain features described and claimed without restricting the scope of these features to the precise numeral ranges provided. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and are considered to be within the scope of the disclosure.
The term “particles” used herein refers to micro- or nanoscale particles that vary in type from the elastomeric matrix with which they are mixed. For instance, as described below, the particles generally have a size (e.g. diameter) in a range of about 1 nanometer to about 100 micrometers. The particles may be spherical, oval, elongated or sheet-like.
One object of the present disclosure is to provide a penetration-resistant composite material. The composite is generally flexible and includes a substrate and an elastomer configured to coat and/or impregnate at least a portion of the substrate. The elastomer includes micro- and/or nano-sized particles.
Generally, the substrate is flexible. For example, the substrate may be a flexible textile consisting of a network of natural or artificial woven or non-woven fibers. In some embodiments, the substrate may be but is not limited to high-density polyethylene (HDPE) woven fabrics. In other examples, the substrate may include but is not limited to an ultra-high molecular weight polyethylene fiber, an ultra-high molecular weight polypropylene fiber, an aramid fiber, an ultra-high molecular weight polyvinyl alcohol fiber or mixtures thereof. In other embodiments, typical textile-based resistant materials may comprise of high-strength fibers (HSFs) such as aramid, S-glass, ultra-high molecular weight polyethylene (UHMWPE), polypyridobisimidazole (PIPD), and polyphenylene benzobisoxazole (PBO).
The substrates described herein are generally coated and/or impregnated with one or more polymeric and non-polymeric materials. For instance, the substrates may be coated with a low modulus, elastomeric material (i.e. an elastomeric binder).
Generally, elastomeric materials and/or elastomeric formulations are also described for coating the substrate. In some embodiments, the elastomeric materials are selected from a class of materials including but not limited to silicones, thermoplastic elastomers, natural or synthetic rubbers, fluoro or perfluoro elastomers and elastoolefins. The elastomeric materials and/or elastomeric formulations have a polymeric base, such as but not limited to a polydimethylsiloxane base or a polyurethane base.
Generally, the elastomers include one or more micro- and/or nano-sized particles such as but not limited to one or more of amorphous silica particles, fumed silica particles, boron nitride particles, calcium chloride particles, aluminum oxide particles, calcium carbonate particles, graphite particles, metallic glass particles, silicon carbide particles or the like. The micro- and/or nano-sized particles generally have a size (e.g. diameter) in a range of about 1 nanometers to about 100 micrometers, or a range of about 10 nanometers to 50 micrometers.
In some embodiments, the particles include silica (SiO2) and/or silicon carbide (SiC) particles.
In some embodiments, the particles may have a concentration in a range of about 0 wt % to about 80 wt % when mixed with the elastomeric material, or in a range of about 10 wt % to about 80 wt % when mixed with the elastomeric material, or in a range of about 30 wt % to about 80 wt % when mixed with the elastomeric material, or in a range of about 50 wt % to about 80 wt % when mixed with the elastomeric material. In some embodiments, the elastomeric materials may include high concentrations of particles mixed therein. For instance, the particles may have a concentration of about or more than 50 wt % when mixed with the elastomeric material, a concentration of about or more than 60 wt % when mixed with the elastomeric material, a concentration of about or more than 70 wt % when mixed with the elastomeric material, or a concentration of about 80 wt % when mixed with the elastomeric material.
Another object of the present disclosure is to provide a method of forming a penetration-resistant composite material.
In some embodiments, the methods of forming the composite include coating and/or impregnating and/or infusing a substrate (e.g. HDPE woven fabrics) with a mixture comprising an elastomer and particles. For instance, the mixture of the elastomer and the particles can be formed using colloidal silica (CS) and PDMS. Herein, colloidal silica generally refers to a suspension of fine amorphous, nonporous, and typically spherical silica particles, or the like, in a liquid phase. The liquid phase may include but is not limited to water.
In some embodiments, mixing particles describe herein with a pre-polymer of an elastomeric binder to form a pre-polymer mixture includes mixing particles including one or more of amorphous silica particles, fumed silica particles, boron nitride particles, calcium chloride particles, aluminum oxide particles, calcium carbonate particles, graphite particles, metallic glass particles or silicon carbide particles. The particles generally have a diameter in a range of about 10 nanometers to 50 micrometers.
After mixing the particles with the elastomeric material, the methods described herein include coating, or impregnating or infusing the prepolymer mixture into a substrate. For instance, impregnating or infusing the prepolymer mixture into a substrate may include soaking the substrate in the prepolymer mixture to provide for the prepolymer mixture to coat at least a portion of the substrate and/or to soak into the woven and/or nonwoven fibres of the substrate.
After coating, or impregnating or infusing the prepolymer mixture into the substrate, the methods described herein include curing the infused substrate. The infused substrate may be cured using heat, air-drying, optical means or any other technique to cure an elastomer described herein.
In some embodiments, the substrates may undergo a treatment process prior to being coated and/or impregnated with the elastomer. For instance, in some embodiments, the substrate may undergo a plasma treatment process prior to being coated and/or impregnated with the elastomer. The plasma treatment process may include exposing the substrate to an oxygen plasma.
In some embodiments, the particles may be mixed with or include a colloidal silica during mixing of the particles with the prepolymer. Mixing or including the particles with or as a colloidal silica may provide for dispersing the particles into the prepolymer of the elastomer and may provide for a higher percentage of particles to disperse within the elastomer when compared to mixing a dry powder of the particles. For instance, mixing particles with a colloidal silica during mixing of the particles with the prepolymer, or mixing particles with a colloidal silica prior to mixing the mixed particles and colloidal silica with the prepolymer, may provide for improved dispersion and/or improved yields of particles in the prepolymer when compared to mixing a dry powder of the particles with the prepolymer.
In some embodiments, mixing the particles with the pre-polymer of the elastomeric binder includes mixing an alcohol solvent with the pre-polymer mixture.
In some embodiments, the solvent is selected from a group of lower alkanols including methanol, ethanol, propanol, butanol and cyclohexanol.
In some embodiments, the solvent is an organic solvent.
In some embodiments, prior to mixing the particles with the elastomeric binder, the particles are mixed with a colloidal silica and treated with an alcohol solvent to form a particle mixture, and the particle mixture is mixed with the pre-polymer of the elastomeric binder.
In some embodiments, prior to infusing the prepolymer mixture in the substrate, performing a plasma treatment to the substrate.
In some embodiments, infusing the prepolymer mixture into the substrate includes soaking the substrate in the prepolymer mixture for about one minute.
In some embodiments, infusing the prepolymer mixture into the substrate further includes, after soaking the substrate in the prepolymer mixture, passing the substrate through a manual cold laminator to remove excess prepolymer mixture from the substrate.
In some embodiments, curing the infused substrate forms a layer of the penetration-resistant composite, and the method further comprises stacking two or more layers of the infused substrate and forming the penetration using a compression mold press.
In some embodiments, the composite may be coated with a nylon coating to form a light-weight flexible protective material.
In some embodiments, the composite may be coated with a shear thickening fluid (STF) material to form a light-weight flexible protective material.
The composites described herein may be included in an article to provide penetration resistance to the article. For instance, the article may include a garment such as but not limited to a security vest, body armor, or blast proof shields, a protective element such as but not limited to gloves, or the like.
In some embodiments, the composites described herein show up to or about a 90% increase in specific penetration resistance force (SPRF) to hypodermic needles compared to the neat fabric. Resistance to penetration is dependent on the concentration of the micro- and/or nanoparticles (e.g. hard silica particles) in the elastomeric matrix. Furthermore, by adding particles such as but not limited to silicon carbide nanoparticles to CS and mixing the CS with an elastomer such as but not limited to PDMS such that the particles have a concentration of about 80 wt. % of the total mixture, the SPRF can be increased to about 110% compared with that of one-layer neat fabric. In some embodiments, when forming the penetration-resistant composite, the particles may have a concentration that is higher than a critical limit, where the critical limit causes the particles to jam against one another. At high particle concentrations, there may be sufficient density of particles within the elastomer to form a of percolation network of particles that form upon impact which could distribute the load over a larger area, offer higher resistance to impact and prevent failure of the material. The PDMS provides a thin elastomeric layer between the particles that is quickly compressed to limit at the initial stages of impact. Further compression leads to the formation of percolation networks that then arrest further deformation and distribute the load. Interestingly, similar formation of percolation networks has been observed in highly particle loaded liquids. Here, instead of compressive forces, shear is used to initiate the formation of percolation networks of particles that could instantaneously “jam” the liquid and create a semi-solid like state in a phenomenon termed “shear jamming”.
In some embodiments, composites described herein can be stacked in layers (e.g. in two or more layers). For instance, in some embodiments a two-layer stack of the same treated fabric can provide a 190% higher SPRF while being 40% less in thickness as compared to a five-layer stack of neat fabric having the same areal density. In some embodiments, the two-layer stack was able to completely prevent the penetration of a 21 G needle at a speed of 50 cm/min (according to ASTM standards) in about one-third of the performed experiments while a five-layer stack of neat fabric, was easily penetrated. These results demonstrate that impregnation of textiles with high concentrations of nano-sized hard particles in an elastomeric matrix can be an attractive method for the manufacture of needle stick penetration-resistant garments.
In some embodiments, composite materials comprising plasma-treated ultra-high molecular weight polyethylene (UHMWPE) fabric that has been dip-coated into a nanoparticle-laden elastomeric mixture are described herein. The elastomeric mixture comprises of SiC nanoparticles of 0.5 μm diameter and a polyurethane (PU)-based polymer. The nanoparticles may be loaded at various weight percentages, such as but not limited to 0, 30, and 50 wt. %.
In some embodiments, the maximum penetration resistance force of a single-layer uncoated UHMWPE fabric may increase up to about 218% due to the loading of nanoparticles.
In some embodiments, two- and five-layer stacks of coated fabric may show up to about 57 and 340% higher spike-puncture and hypodermic-needle resistance, respectively, when compared to a 7-layer stack of neat fabric.
In some embodiments, two- and five-layer stacks of coated fabric may be more flexible and about 21-55% thinner compared to a 7-layer stack of neat fabric (of comparable areal density).
In one example, penetration tests and characterization were performed for exemplary composites.
Materials and Methods
In one example, colloidal silica (LUDOX® TM-50) was a 50 wt. % suspension in H2O, with specific surface area approximately 140 m2/g, 1.4 g/mL at 25° C., and pH=9 was purchased from Sigma-Aldrich, Canada. The amorphous silica powder (SiO2) had diameter of 400 nm, specific surface area of 35 m2/g, true density of 1800-2400 kg/m3, and bulk density smaller than 900 kg/m3 was purchased from US Research Nanomaterials, Inc. Houston, USA, and the silicon carbide (SiC) particles had a diameter of 0.5 μm and specific surface area of 4-8 m2/g was purchased from Panadyne Inc. Montgomeryville, USA. The PDMS polymer was purchased as Sylgard® 184 which is a silicone elastomer kit from Dow Corning Corporation, USA. The kit comprises of Base/Curing Agent to be mixed in a 10 (base):1 (curing agent) ratio by weight. Sylgard® 184 is highly flexible with low water absorption and high thermal stability over a wide temperature range (−45 to 200° C.), which makes it an ideal choice for our application. A high-density polyethylene (HDPE) plain weave fabric with an areal density of 285 g/m2, thickness of 0.5 mm, and thread count of 60×60 was used in this study.
Sample Fabric Preparation
CS was first added gradually to the pre-polymer base part of Sylgard® 184 to make the composite base mixture. Different compositions corresponding to silica particle loadings of 20, 35, and 47 wt. % of the final mixture (i.e. the total weight of particles, pre-polymer, and curing agent) were prepared. The maximum loading of silica that could be completely hand-mixed with the pre-polymer base was limited to about 47 wt. % of the total mixture. The well-stirred dispersion was then mixed with the required amount of cross-linking curing agent (10 pre-polymer base:1 curing agent ratio by weight) and stirred for 15 minutes. The HDPE fabric was cut to 5 cm×10 cm samples and then soaked in the mixture for one minute. A sharp edge scraper was used at the same time to facilitate the coating process by forcing the mixture into the fabric samples. Finally, the fabric was passed through a manual cold laminator with a gap size of 0.7-0.8 mm to remove excess material. The samples were cured in an oven at 80° C. for a period of seven hours. In order to achieve silica particle loadings greater than 47 wt. % of the mixture, a different manufacturing method was developed. Here, the CS was functionalized by gradually mixing isopropanol (IPA) solvent at room temperature so the weight ratio of ISP to water in CS was 0.4. The pre-polymer base part was then dispersed gradually into the solution of CS and IPA and stirred. The uniform mixture was mixed with the cross-linking curing agent and stirred for an additional 15 minutes to produce a final composition of 65 wt. % silica particles—35 wt. % PDMS or 80 wt. % silica particles—20 wt. % PDMS. The fabrics were then coated with the mixture and cured similar to the previous samples. Additionally, an alternate method was developed by adding amorphous silica powder to CS in order to explore the effect of mixing different particles. In this method, amorphous silica powder was added to the CS in order to increase the loading of particles to 75% of the weight of CS (1:2 weight ratio of 25 nm silica and 400 nm silica). IPA was then added gradually as the weight ratio of IPA to water in CS is 0.4. In the second step, the required pre-polymer and cross-linking agent were added to make a uniform mixture of 80 wt. % particles—20 wt. % PDMS. The fabrics were then soaked, coated, rolled, and heated like previous samples. Similar to the synthesis process of the latter sample, instead of using amorphous silica powder, 0.5 μm SiC particles were added to CS in order to make a final sample of 80 wt. % particles—20 wt. % PDMS.
Needle-Stick Penetration Test
A needle-stick penetration test apparatus was designed and fabricated according to ASTM F2878-10 standard (
Flexibility Test
The flexibility of the fabric was characterized on 5 cm×10 cm sample pieces (
Image Analysis
Scanning electron microscopy (SEM) analysis was carried out using a VEGA-LSU TESCAN VP to study the damage mechanism of the fabrics. The samples were coated with a gold material to prevent charge build-up. The diameter of the monodispersed spherical silica particles in CS was measured to be 25±5 nm from images taken by JEOL 1200EX TEMSCAN Transmission Election Microscope (TEM).
Results
An initial needle penetration test was conducted in order to demonstrate the effectiveness of the nanoparticle-elastomer composite. The images in
In comparison, the needle with a 10 N pre-load was not able to pierce through the two-layer stack of the coated fabric and instead was bent slightly. This dramatic difference in performance occurs despite the coated fabric stack having 40% lower thickness and the same flexibility as the five-layer neat fabric stack and warranted further investigation to characterize this phenomenon.
Effect Particle Concentration on Penetration Force, Flexibility, and Areal Density
Various single-layer samples of different particle loading were tested and compared to study the effect of particle concentration (from 0% to 80%) on the penetration resistance, flexibility, and areal density of the fabric. The effect of mixing two different types of particles (silica and SiC) in the PDMS mixture was also studied. Additionally, SEM image analysis was performed to infer the failure mechanism. The average thickness of the fabric samples was found to increase by 20-80% due to the coating, while the average increase in areal density was approximately 120-180%. Two exceptions were the coated samples with 35 and 47 wt. % silica particles in PDMS mixture which showed about 220-270% increase in areal density compared with the neat fabric.
The results of penetration tests performed on one-layer neat and treated fabric samples are shown in
Maximum penetration force, average energy dissipation, and bending-angle histogram plots of one-layer neat and coated samples are presented in
It can be seen from the results that one-layer neat fabric provides a maximum force of 1.8±0.5 N against needle-stick penetration. The peak resistance force increased to 3.3±0.6 N after coating the fabric with PDMS only. The penetration resistance force gradually increased to 3.6±0.7 N for 20 wt. % silica loaded PDMS coating to 5.1±0.6 N for a 47 wt. % silica loaded PDMS coating. However, this increase, especially in the case of 20, 35 wt. %, was not significantly different from the PDMS only coating. Interestingly, the fabrics coated with 65 and 80 wt. % silica loaded PDMS coating showed significantly higher increase in penetration force of 6.1±0.7, and 7.6±1.2 N respectively as compared with the PDMS coated fabric indicating that the particle loading plays a major role in increasing the penetration resistance at higher loading levels.
The work done by the needle penetrator was calculated from the area under the force-displacement curve up to a penetration of 10 mm through the target sample. The energy dissipation was increased over the neat fabric by 91, 155, 222, 345, 380, and 514% by treating one-layer fabric with PDMS and 20, 35, 47, 65, and 80 wt. % silica loading mixtures, respectively. The maximum penetration force increases to 9.4±1.9 N by incorporating amorphous silica powder (400 nm diameter) along with CS (25 nm) to make a uniform mixture of 80 wt. % particles—20 wt. % PDMS. As a result, the penetration resistance force and average energy dissipation during penetration of this sample increased by about 420 and 180% respectively, compared with one-layer neat fabric. Replacing 400 nm silica powder in the latter sample with 0.5 μm diameter SiC powder to the same particle concentration resulted in the highest penetration resistance force (9.8±1.4 N) among all one-layer target samples. The performance of this sample shows 440 and 180% improvement in the penetration resistance force and average energy dissipation, respectively, compared with one-layer neat fabric. Overall, the penetration resistance force and average energy absorbed of the neat fabric improved by increasing the particle concentration from 20 to 80 wt. % in the coating mixture.
The effect of particle addition is even clearer when force and the energy absorbed are normalized to the areal density. The specific penetration resistance force (SPRF) and Specific Energy Absorbed (SEA) which are normalized by the areal density of the corresponding one-layer samples are plotted as shown in
In order to understand the phenomena further, SEM images of the coated samples were taken before and after puncture and shown in
The after-puncture images of the coated samples (
Reduction in yarn mobility within the fabric has been attributed in the past to the superior penetration resistance of some STF-textile structures. It was also reported that yarn pull-out force increases, and breakage of fibers became more significant compared to fiber slippage and “windowing effect”. A similar effect could contribute to the improved penetration resistance of the current coated samples as a higher loading of hard silica particles is likely to provide more effective coupling mechanism that would increase fiber-fiber and fiber-particle load transferring and suppresses yarn mobility. One explanation for the increase in penetration resistance especially at high particle loading would be due to “elastic jamming” of particle fillers in PDMS. At high particle loading, there is sufficient density of particles that could allow formation of percolation network of particles that form upon impact which could distribute the load over a larger area, offer higher resistance to impact and prevent failure of the material. The PDMS provides a thin elastomeric layer between the particles which is quickly compressed to limit at the initial stages of impact. Further compression leads to the formation of percolation networks that then arrest further deformation and distribute the load. Interestingly, similar formation of percolation networks has been observed in highly particle loaded liquids. Here, instead of compressive forces, shear is used to initiate the formation of percolation networks of particles that could instantaneously “jam” the liquid and create a semi-solid like state in a phenomenon termed “shear jamming”.
Effect of Multiple Layers of Stacked Fabrics on Penetration Resistance
As it may be required to use multiple layers of treated or neat fabric layers in an end-product, it is important to examine the penetration resistance of a stack of fabric layers against hypodermic needles. Therefore, a two-layer stack of treated fabric and a five-layer stack of neat fabric layers of matched areal density were tested and compared. For this comparison, the coated samples with 80 wt. % particle loading which have the highest penetration resistances were chosen. The corresponding penetration force-displacement graphs are presented in
A comparison based on the areal density is shown by the histogram in
The effectiveness of using elastomeric composites reinforced with hard nanoparticle fillers to improve the penetration resistance of fabrics to hypodermic needles is demonstrated here. A novel technique is developed to disperse nano-sized fillers in PDMS using colloidal silica (CS) up to a loading of 80 wt. % particles in the elastomeric mixture using isopropanol (IPA) solvent. In addition, amorphous silica or silicon carbide powder was added to CS in order to improve the performance of the final products. Needle penetration tests were performed to determine the penetration resistance and energy dissipation of the treated fabric. Low concentration of silica particles dispersed in PDMS mixture was found to be not an effective solution to improve the specific penetration force (SPRF) and specific energy absorbed (SEA) of the neat fabric sample. There was a significant improvement in the penetration resistance of coated samples when the concentration of hard silica particles dispersed in the PDMS mixture was 65 wt. % and greater. This may be due to the onset of “elastic jamming” phenomenon or the formation of percolating network of connected particles at these percentages. The highest penetration resistance was obtained from a two-layer stack of coated sample with a mixture of 80 wt. % of “25 nm silica and 0.5 μm SiC” particles in PDMS. There was about 200% improvement in penetration resistance force compared to a five-layer stack of neat fabric (on the basis of equivalent areal density), while having similar flexibility and a thickness that was 40% less than the five-layer stack of neat fabric.
In another example, penetration tests and characterization was performed for other exemplary composites.
Materials
The UHMWPE plain woven fabric (Spectra® 900) with an areal density of 230 g/m2, 1,200 denier, 1,333 dtex, and thread count of 21×21 yarns per inch was supplied by Barrday, Inc., Canada. The silicon carbide (SiC) particles from Panadyne Inc. Montgomeryville, USA had a nominal diameter of 0.5 μm and specific surface area of 4-8 m2/g. A polyurethane-based elastomer (Brush-On® 40 kit) was purchased from Smooth-On, Inc., Macungie, USA. The kit comprises of A and B components to be mixed in a 1:1 ratio by weight. An organic solvent (mineral spirit) was purchased from Recochem Inc., Canada.
Fabric Preparation—Plasma Treatment
UHMWPE fabric was cut to 12 cm×18 cm and then put in a capacitively coupled systems plasma chamber (PE-25, Plasma Etch, Inc.) with a radio frequency (RF) source at 50 kHz and vacuumed at around 18×10−2 Torr. Oxygen was then fed into the chamber (50 cc/min) for 60 sec during gas stabilization phase. The oxygen feed was then closed before the RF power is applied for 5 minutes with power of 300 W. The plasma treatment was found to increase the adhesion of UHMWPE to coating materials.
Coating Preparation
Organic solvent (mineral spirit) was added to the pre-polymer base part of Brush-On® 40 kit so the weight ratio of solvent to part-A (i.e., a cross-linking agent) is 3.5 and mixed thoroughly for 2 hr. SiC particles (0.5 μm in diameter) were then added to the mixture to 30 and 50 wt. % of the final mixture (i.e. the total weight of particles and parts-A&B of the polyurethane-based elastomer) and mixed for 3 hr. Paste-like part-B of the elastomer kit was then added to the well-dispersed mixture and stirred thoroughly for 30 minutes. At this point, the mixture has a low viscosity which makes it feasible for immersion (dip) coating process without additional equipment. The plasma-treated fabric samples were soaked (dipped) in the mixture for 15 seconds and hang-dried under a fume hood for five hours. Using this technique, the material pickup of fabric samples from a same coating mixture is fairly equivalent although the samples were not squeezed after the dip process. One general advantage of dip coating technique is that fibers are not stressed/distorted during such process.
Spike-Puncture and Needle-Penetration Tests
Spike-puncture penetration tests were performed according to EN 388:2015 “European Standard for Protective gloves against mechanical risks” protocols which is also suggested by American National Standard Institute/International Safety Equipment Association (ANSI/ISEA) 105-2016 standard. Using a SHIMADZU tensile tester with 500 N load cell, a steel stylus-like spike (
Each test was repeated at least ten times on five similar samples to ensure consistency of the results and the maximum resistance force was recorded from force-vs-displacement curves. In a similar fashion, multiple-layer stacks of fabric were tested. Target samples were then categorized into different levels based on their penetration resistance according to ANSI/ISEA 105-2016 standards. ANSI/ISEA 105-2016 categorizes resistant textiles for hand protection based on their maximum resistance force against puncture (other than hypodermic needles) into five levels (Table A.1 in Appendix). Hypodermic needle penetration tests were performed similar to and in accordance with ASTM F2878—10 standards. Briefly, the fabric sample was held (sandwiched) firmly between the supporting fixture and another plate with the same open internal diameter of 20 mm. The fabric target was then punctured by the needles at a speed of 500 mm/min. A fresh 25 G 1″ (BD305125) hypodermic needlestick was used for each test and repeated at least ten times on five similar samples to ensure consistence of the results and the maximum resistance force was recorded from force-vs-displacement curves. Target samples were then categorized into different levels based on their penetration resistance according to ANSI/ISEA 105-2016 standards. ANSI/ISEA 105-2016 categorizes resistant textiles for hand protection based on their maximum resistance force against 25 G hypodermic needles into five levels (Table A.2 in Appendix).
Flexibility Test and Coefficient of Friction Determination
Flexibility tests were performed similar to our previous work based on the principles of ASTM D1388. The objective of this test is to compare the rigidity of 1-layer and multiple-layer target samples before and after coating. A 5 cm×10 cm piece of each sample was cut and encapsulated inside a thin polyethylene bag and a 20 g weight was attached to its leading edge at mid-point. With 6.2 cm length of the sample held firmly on the edge of table, its bending angle (BA) is then measured from captured images. Higher bending angle from this test means higher flexibility of the fabric sample. Static coefficient of friction of neat fabric (before and after plasma treatment) along weft direction were calculated according to ASTM D1894-14 using a SHIMADZU tensile tester with 500 N load cell (Method-C of apparatus for assembly).
Image Analysis and Contact-Angle Measurement
The images were taken using a handheld digital microscope (CELESTRON, LLC, California, USA). Scanning electron microscopy (SEM) analysis was done using a VEGA-LSU TESCAN VP. The SEM samples were coated with a thin gold layer to prevent charge build-up. Optical contact angle measurements were done using a DataPhysics OCA-35 instrument to analyze wettability of fabric surface before and after oxygen-plasma treatment. A drop of Milli-Q® ultrapure water (dosing rate of 2 μL/s) were applied using the instrument's electronic syringe unit on the surface of sample and the corresponding contact angle was recorded. Each test was repeated five times at different places of the fabric samples.
Results
An initial spike penetration test was conducted on as-received and coated plasma-treated UHMWPE fabric samples to show the effectiveness of the coating process. The images of the samples before and after puncture under a maximum pre-set load of 100 N is shown in
In order to understand the results better, the material was microscopically analyzed. The SEM images of untreated UHMWPE fabric with only PU coating are shown in
The water contact angle of as-received UHMWPE fabric was 120.7±3.6° which can be considered as a hydrophobic material. However, when a droplet of water was dropped on the surface of UHMWPE fabric which was treated with plasma for ⅙, ½, 1, 2, 3, 4, and 5 min, the water instantly spread over the surface of fabric indicating complete wetting of plasma-treated UHMWPE fabric. The change of contact angle confirms the remarkable change in surface properties from an inert material to one that has polarizable groups and open dangling bonds that could be beneficial for wettability and adhesion of coatings to the UHMWPE fabric (
Puncture Test Results
A single-layer neat plasma-treated UHMWPE fabric and single-layer samples of plasma-treated UHMWPE fabric coated with 0, 30, 50 wt. % concentration of SiC were tested to study the influence of the nanoparticle loading on puncture resistance against a spike threat. The typical force-displacement curves of 1-layer plasma-treated neat and coated plasma-treated UHMWPE fabric against spike penetration are shown in
After the first peak, there is a sudden drop in the force in all three coated samples followed by an increase till the force reaches a second peak. The first peak and the sudden drop can be correlated to the point when the conical tip of the spike completely passed through the sample. The increase in the penetration force after the first peak can be attributed to the resistance from distant fibers near the impact zone. The average resistance force at the second peak-load (maximum resistance force) is 45.7±4.5, 67.3±8.3, and 105.7±9.3 N when the concentration of SiC in the PU mixture is 0, 30, and 50 wt. % respectively. The improvement in maximum resistance force as the concentration of SiC increased is because the fibers are more coupled with an increase in SiC and thus can exert more frictional force to the impactor. The load drops after the second peak as the conical tip of the spike completely penetrates through the fabric and adjacent fibers provide minimal further resistance. The plasma-treated neat UHMWPE fabric shows only a single peak of 33.2±8.7 N. In this case, unlike the coated fabric samples, the distant fibers do not exert a force to the spike penetrator when the failed fibers are pushed aside. This behavior can be attributed to the lower fiber-to-fiber and fiber-to-impactor frictional forces when the UHMWPE fabric was not coated.
From the images of damage area on coated UHMWPE fabrics (
Additionally,
Multiple layers of neat and coated fabric samples were tested to investigate the effectiveness of the coating material based on areal densities, flexibility, and thickness. For this purpose, several layers of fabric samples were stacked together and tested against spike penetration. The histogram of maximum resistance force, areal density, and flexibility of plasma-treated neat and coated UHMWPE fabric samples of different stacked layers is presented in
Also, from Table 1, the average thickness of 7-layer stack of neat fabric reduced by about 21-55% compared to 2-layer and 5-layer of coated samples of comparable areal density. From Table 1, 1-layer neat fabric has the lowest rigidity while 1-layer coated fabric with 50 wt. % SiC in PU mixture has the highest. Comparing the flexibility of multi-layer stacks of fabric samples with comparable areal density, it was found that the 7-layer stack of neat fabric was less flexible than 5-layer stack of coated samples with 0 and 30 wt. % of SiC in PU mixture and even the 2-layer stack of coated fabric with 50 wt. % SiC in PU mixture.
Apart from areal density, flexibility and thinness are equally important factors in the manufacture of protective gloves. Therefore, a figure of merit was formulated that represents the ratio of percentage increase in penetration resistance to percentage increase in thickness of different multi-layer neat and coated samples over a single layer of neat UHMWPE fabric and can be used to evaluate the performance of the various compositions and combinations that were fabricated. This figure of merit was found to be 0.74, 1.35, 1.68, and 2.49, respectively, for 7-layer neat, 5-layer coated with PU, 5-layer coated with 30 wt. % SiC, and 2-layer coated with 50 wt. % SiC. They show that addition of SiC nanoparticles increase the penetration resistance significantly more as compared with any increases in thickness of the overall coated fabric. Hence, the coated sample with 50 wt. % SiC in PU mixture provides the optimal performance, which is Level-5 resistance, acceptable thickness and flexibility among all the samples.
Hypodermic Needlestick Penetration
Single and multiple layers of neat and coated fabric samples of plasma-treated UHMWPE fabric were tested to study the impact of coating (0, 30, and 50 wt. % concentration of SiC) on penetration resistance against a needlestick threat. The typical force-displacement curves of 1-layer plasma-treated neat and coated plasma-treated UHMWPE fabric against needlestick penetration are shown in
Maximum resistance force, bending angle, and areal density histogram plots of 1-layer and multiple-layer neat and coated fabric samples are presented in
Here, this example shows the impact of coating UHMWPE fabric with a mixture of SiC and polyurethane (PU) to provide spike and hypodermic penetration resistance. A dip coating process to incorporate nanoparticle-elastomer mixtures with up to 50 wt. % particle loading was demonstrated. Spike puncture tests performed on coated fabric show a significantly higher resistance than neat fabric and the resistance increased with increase in SiC content. The penetration resistance of coated fabric was significantly higher than the neat fabric even when different stacks of target samples of comparable areal density were compared. A 5-layer stack of coated fabric with a mixture of 30 wt. % SiC in PU showed about 57% higher resistance and better flexibility compared to a 7-layer stack of neat fabric of the comparable areal density with 21-55% less thickness. The higher resistance of coated samples can be attributed to a combination of penetration of the coating into the fabric, better adhesion coating material with the fibers and the effect of the loaded nanoparticles in exerting more frictional force to the impactor. We also showed that plasma-treatment is a crucial preparation process for UHMWPE fabric to improve the adhesion and integration of coating material to the fabric. Non-uniform coatings and poor penetration and puncture resistances were obtained without plasma treatment. Similarly, the resistance of coated fabrics against hypodermic needle was superior to the neat fabric. The combination of SiC nanoparticles with PU elastomer provides an interesting solution in increase the puncture resistance while not affecting the needle penetration significantly. In the future, this property could be used in ballistic textiles (such as UHMWPE) which have rather weak resistance against puncture threats in order to improve their robustness and all-round performance.
While the above description provides examples of one or more methods or systems, it will be appreciated that other methods or systems may be within the scope of the claims as interpreted by one of skill in the art.
