Chemical protective elastomer materials free of a perfluoroalkyl substance and articles including the same

Abstract

Curable chemical protective elastomeric formulations and articles which include such formulations that are free of a perfluoroalkyl substance (PFAS-free) and include (a) a polythioether nucleophile component, (b) a liquid polyol component, and (c) at least one isocyanate as a cross-linking component. The formulations when cured provide chemical protection according to the National Fire Protection Association (NFPA) 1994 2022 ed. Class I and / or Class III requirements.

Description

CHEMICAL PROTECTIVE ELASTOMER MATERIALS FREE OF A PERFLUOROALKYL SUBSTANCE AND ARTICLES INCLUDING THE SAMECROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is based on and claims domestic priority benefits from U.S. Provisional Patent Application Serial No. 63 / 574,076 filed on April 3, 2024, the entire contents of which are expressly incorporated herein by reference.GOVERNMENT RIGHTS

[0002] This invention was made with support by the US Army - Natick under contract numbers W91 1 QY-22-C-0020 and W911 QY-24-P- 0077. The Government has certain rights in the invention.FIELD

[0003] The embodiments disclosed herein relate generally to durable solvent-borne or water-borne elastomeric materials free of a perfluoroalkyl substance (PFAS-free elastomers). The PFAS-free elastomers that embody the present invention may usefully be employed as a protective material, e.g., composite fabrics and / or films coated or impregnated with the PFAS- free elastomeric material and formed into useful articles such as ground covers, tent materials and articles of clothing (e.g., boots, clothing liners, gloves and the like) which provide personal protection against chemical, biological, radiological, and nuclear (CBRN) contamination threats.BACKGROUND

[0004] The proliferation of weapons of mass destruction presents a serious security threat to U.S. and allied personnel around the world.Military warfighters and first responders must be prepared to operate under a wide range of CBRN environments while having the capacity to rapidlyrespond to these potential threats. CBRN-protective articles, such as wearable clothing articles thereby offer a first line of defense for personnel to perform tasks in high-risk environments. Current CBRN articles offer excellent durability and protection from CBRN threats, however their bulk results in poor dexterity and elevated thermal burden. Furthermore, their barrier properties are largely due to environmentally hazardous perfluoroalkyl and polyfluoroalkyl substances (PFAS). There is no known commercially available non-fluorinated material that offers adequate protection against CBRN threats.

[0005] The tactility of current CBRN-protective materials, such as CBRN-protective gloves, must be improved to ensure optimal utility during the assessment, extrication, rescue, decontamination, and treatment at sites where CBRN terrorism agents (both liquid and vapor) may have been deployed. Due to the use of relatively thick butyl rubber (e.g., from about 10 to about 40 mil thick), current CBRN-protective gloves prevent the type of fine motor movement necessary to perform tasks during critical activities. Furthermore, with the increased prevalence of capacitive-based touch screen systems, the current butyl CBRN-protective gloves do not offer touch screen capability.

[0006] Thus, there is a need for novel barrier materials, especially for use with CBRN-protective articles, e.g., gloves, clothing, tenting material and the like, that allow for high levels of function without the trade-off between chemical protection, dexterity, tactility, or thermal burden. It is towards fulfilling such needs that the embodiments disclosed herein are directed.SUMMARY

[0007] Broadly, the embodiments disclosed herein are directed toward curable chemical protective elastomeric formulations and articles which include such formulations that are free of a perfluoroalkyl substance (PFAS-free). The PFAS-free formulations of the embodiments willnecessarily include (a) a polythioether nucleophile component, (b) a liquid polyol component, and (c) at least one isocyanate as a cross-linking component. The formulations when cured provide chemical protection according to the National Fire Protection Association (NFPA) 1994 2022 ed. for Class I and / or Class III requirements.

[0008] According to some embodiments, the polythioether nucleophile component is a liquid polysulfide polymer with thiol end groups having a weight average molecular weight of between about 500 and 10000 g / mol. The polythioether nucleophile component may have a thiol content between about 2.0 mol% and 7.0 mol%. A preferred polythioether nucleophile is a polycondensation product of bis(2-chloroethyl) formal with alkali polysulfide having a weight average molecular weight of between about 750 g / mol and about 1 150 g / mol.

[0009] The polyol component in certain embodiments may be a polycaprolactone or aliphatic alcohol having three or more nucleophilic hydroxyl groups, e.g., polyols having a weight average molecular weight of between about 120 g / mol to about 1200 g / mol. One preferred polyol component is a liquid polyester triol terminated by primary hydroxy groups having a hydroxyl value of between about 170 to about 196 KOH / g and a weight average molecular weight of about 900 g / mol.

[0010] The cross-linking component of some embodiments will include at least one isocyanate that is comprised of at least one trimeric aliphatic isocyanate. For example, at least one aliphatic diisocyanate selected from methylene diphenyl diisocyanate (MDI) and / or hexamethyl diisocyanate (HDI) may be employed in the formulations described herein.

[0011] When employed in a water-borne formulation in accordance with embodiments of the formulation, the cyanate reactive groups of the at least one isocyanate will be blocked by a blocking agent selected from the group consisting of pyrazole derivatives and oxime derivatives, such as3,5-dimethyl- 1 H-pyrazole and / or methyl ethyl ketone oxime (MEKO). The applied formulation with the blocked isocyanate component may then be subjected to elevated temperatures for a time sufficient to vaporize the water carrier and unblock the isocyanate component to allow polymerization cross-linking of the formulation components. Curing temperatures of between about 100qC to about 175 °C, e.g., about 120 °C to about 165 °C and curing times of between about 5 minutes to about 12 or more hours may be employed.

[0012] These and other aspects of the embodiments disclosed herein will become more clear following consideration of the detailed descriptions thereof which follow.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Reference will be made to the accompanying drawing Figures, wherein:

[0014] FIGS. 1 and 2 are schematic illustrations of exemplary composite CBRN-protective articles in accordance with embodiments of this invention;

[0015] FIGS. 3A-3C are SEM photographs whereby FIG. 3A is a SEM analysis of a PFAS-free elastomeric material in accordance with an embodiment of the invention which showed no phase separation, FIG. 3B is a SEM photograph of a dispersion of silicon dioxide particles in a PFAS- free elastomeric film, and FIG. 3C is a SEM photograph showing silicon elemental analysis of the PFAS-free elastomeric film;

[0016] FIGS. 4A-4C are a series of photographs showing a glove prototype cast over conventional nitrile gloves (FIG. 4A), and a visual demonstration of the glove flexibility (FIGS. 4B and 40);

[0017] FIG. 5 is a graph containing decomposition plots of butyl rubber, neat PFAS-free material, and PFAS-free material containing with silicon dioxide particles;

[0018] FIG. 6 is a graph containing Tan(delta) curves for butyl rubber, neat PFAS-free material, and PFAS-free material containing with silicon dioxide particles;

[0019] FIG. 7 is a graph containing storage modulus curves for rubber, neat PFAS-free material, and PFAS-free material containing with silicon dioxide particles; and

[0020] FIG. 8 is an FID signal trace of butyl rubber and PFAS-free material with silicon dioxide particles during permeation test.DETAILED DESCRIPTION

[0021] Exemplary composite CBRN protective composite articles 10 and 10’ in accordance with embodiments of this invention are shown in FIGS. 1 and 2. The composite article 10 shown in FIG. 1 is in the form of a multilayer material comprised of a substrate 12 which includes a coating layer 14 of the PFAS-free elastomeric material according to the embodiments disclosed herein as an external surface thereof. The substrate 12 may be any film or synthetic fabric material. For example, when used as protective gloves, the substrate layer 14 may be a nitrile rubber layer. Optionally an inner layer 16 may be provided, e.g., as a liner material. The coating layer 14 of the PFAS-free elastomeric material may be of any thickness sufficient to achieve CBRN protective functions. For example, when employed as a CBRN protective glove material, the thickness of the coating layer 14 may be between about 5 mil to about 25 mil, preferably between about 10 mil to about 15 mil.

[0022] FIG. 2 depicts an embodiment of a CBRN protective material composite sheet 10’ which includes a fabric substrate 12’ which is impregnated (saturated) by the PFAS-free elastomeric material forming a matrix 14’ which encapsulates the fabric substrate 12’. Here again, an optional inner layer 16’ may be provided if desired. The thickness of the protective material composite sheet 10’ may be between about 5 mil to about 25 mil, preferably between about 15 mil to about 20 mil.

[0023] The PFAS-free formulations when cured can resist permeation for more than 10 hours when challenged with toluene in accordance with the methods described in the National Fire Protection Association (NFPA) 1994 2022 ed. for Class I and Class III materials (the entire content of which is expressly incorporated hereinto by reference). More specifically, permeation resistance testing has shown that the cured PFAS-free formulations in accordance with this invention provide sufficient protection to comply with the NFPA 1994 2022 ed. Class I and Class III requirements for toxic industrial chemicals (TICs) (toluene and dimethyl sulfate) and chemical warfare agents (sulfur mustard). When used as a material for CBRN-protective gloves, the cured PFAS-free elastomeric formulations as described herein are also touch screen compatible.I. The Curable PFAS-free Formulation

[0024] The precursor formulation of the PFAS-free elastomeric material in accordance with embodiments disclosed herein is a curable blend comprising a polythioether nucleophile component, a polycaprolactone triol component, and a trimeric aliphatic isocyanate component. When cured therefore the PFAS-free elastomeric material will be a random copolymerization reaction product of the polythioether nucleophile component, the polycaprolactone triol component, and the trimeric aliphatic isocyanate component that provides CBRN-protective attributes to substrates onto which the PFAS-free elastomeric material is applied. The curable mixture may contain a liquid blend of the curablecomponents in a solvent-based system or may be a dispersion of the curable components in water.A. The Polythioether Nucleophile Component

[0025] The uncured liquid PFAS-free formulation necessarily contains a liquid polysulfide polymer with thiol end groups (e.g., polythioether nucleophiles). Preferred are polythioether nucleophiles having a number average molecular weight of between about 500 and 10000 g / mol, typically between about 750 to 1 150 g / mol, for example about 1 100 g / mol. The preferred polythioether nucleophiles employed in the formulations will typically contain a thiol content between 2.0 and 7.0 mol%, preferably between about 6 mol% to about 7 mol%. The preferred polythioether nucleophiles will typically contain 1 .5 mol% or greater, for example up to about 2 mol% of a repeat units capable of branching.

[0026] One specifically preferred class of polythioether nucleophiles that may be employed successfully in the practice of this invention includes THIOPLAST™ polysulfides which are the polycondensation of bis-2- chloroethyl-)formal with alkali polysulfide which generates long-chain macromolecules which are cut to the required chain length by reductive splitting with sodium dithionite. The disulfide groups are at the same time converted into reactive thiol terminal groups. By introducing a trifunctional component (e.g., 1 ,2,3-trichloropropane) during synthesis a third thiol terminal group can be added to a specific number of molecules to determine the extent of cross-linking during the curing process. (See WO 2006 / 032034, the entire content of which is expressly incorporated hereinto by reference.) Of particular preference is THIOPLAST™ G4 polysulfide having a weight average molecular weight of less than about 1 ,100 g / mol commercially available from Nouryon Pulp and Performance Chemicals AB.

[0027] The amount of the polythioether nucleophile employed in the uncured liquid PFAS-free formulation according to embodiments of thisinvention will be between about 1 wt.% to about 20 wt. %, typically between about 2 wt.% to about 15 wt.%, based on total weight of the liquid PFAS- free formulation. For example, in a solvent-borne liquid formulation the polythioether nucleophile will be present in an amount of between about 5 wt.% to about 15 wt. %, typically between about 8 wt.% to about 12 wt.%, whereas in a water-borne liquid formulation, the polythioether nucleophile will be present in an amount of between about 1 wt.% to about 5 wt. %, typically between about 2 wt.% to about 4 wt.%, based on total weight of the liquid PFAS-free formulation.B. The Polyol Component

[0028] The liquid polyol component is most preferably a polycaprolactone or aliphatic alcohol having three or more nucleophilic hydroxy groups having a number average molecular weight of between about 120 g / mol to about 1200 g / mol, typically between about 700 g / mol to about 1000 g / mol, for example about 900 g / mol. The polyol component is preferably a polytriol, such as polycaprolactone triol or an aliphatic triol (e.g., trimethylol propane). Specific polyols that may be employed in the practice of this invention include, for example, liquid polyester triols terminated by primary hydroxy groups that have a hydroxyl value of between about 170 to about 196 KOH / g and a weight average molecular weight of about 900 g / mol. Preferred liquid polyols include CAPA® polyester polyols commercially available from Ingevity UK Ltd, especially CAPA® 3091.

[0029] The amount of the liquid polyol component employed in the uncured liquid PFAS-free formulation according to embodiments of this invention will be between about 5 wt.% to about 60 wt. %, typically between about 10 wt.% to about 40 wt.%, based on total weight of the liquid PFAS- free formulation. For example, in a solvent-borne liquid formulation the liquid polyol will be present in an amount of between about 25 wt.% to about 55 wt. %, typically between about 30 wt.% to about 40 wt.%, whereasin a water-borne liquid formulation, the liquid polyol component will be present in an amount of between about 5 wt.% to about 20 wt. %, typically between about 10 wt.% to about 15 wt.%, based on total weight of the liquid PFAS-free formulation.C. The Isocyanate Component

[0030] An isocyanate component is provided in the uncured liquid PFAS-free formulation to randomly cross-link the polythioether and polyol components. One or more dimeric or trimeric aliphatic isocyanates that are typically employed to form polyurethanes may be employed in the practice of this invention. For example, the isocyanate component may be virtually any aliphatic diisocyanate, such as methylene diphenyl diisocyanate (MDI) (e.g., SUPRASEC® 9615 methylene diphenyl diisocyanate commercially available from Huntsman International LLC), hexamethylene diisocyanate (HDI) (e.g., DESMODUR® low-viscosity HDI trimers commercially available from Covestro LLC, such as DESMODUR® N100A and DESMODUR® N3600), and polyisocyanates containing HDI trimers and modified with multifunctional alcohols (e.g., Coronate® HXLV commercially available from Tosoh Chemicals Company) and mixtures thereof. In practice, virtually any multi-functional aliphatic isocyanates (such as those based on hexamethylene diisocyanate biurets) can reasonably be expected to form materials of similar physical and chemical properties.

[0031] If employed in a water-borne formulation, the cyanate reactive groups of the dimeric or trimeric aliphatic isocyanate component must be blocked in order to allow it to remain effective as a cross-linking agent for the polythioether and polyol components when dispersed in water. The blocking agent may be, for example, a pyrazole derivative (such as 3,5- dimethyl-1 H-pyrazole), oxime derivatives (such as methyl ethyl ketone oxime, MEKO), aromatic alcohols (such as phenol derivatives), diethyl malonate, caprolactam derivatives and sodium bisulfite, provided that the blocking agent can be removed from the isocyanate component aboveabout 100 °C but below the substrate decomposition temperature (e.g., the melting or decomposition temperature of fibers providing a textile substrate for the PFAS-free formulation).

[0032] The amount of the isocyanate component employed in the uncured liquid PFAS-free formulation according to embodiments of this invention will be between about 10 wt.% to about 70 wt. %, typically between about 15 wt.% to about 55 wt.%, based on total weight of the liquid PFAS-free formulation. For example, in a solvent-borne liquid formulation the isocyanate component will be present in an amount of between about 15 wt.% to about 35 wt. %, typically between about 20 wt.% to about 30 wt.%, whereas in a water-borne liquid formulation, the liquid isocyanate component (which must be blocked as described above) will be present in an amount of between about 30 wt.% to about 60 wt.%, typically between about 45 wt.% to about 55 wt.%, based on total weight of the liquid PFAS-free formulation.D. Additional Components

[0033] Virtually any additional component that is typically employed in polymeric formulations may be employed in the PFAS-free elastomeric formulations as described herein provided that the CBRN protection afforced by the PFAS-free elastomeric formulation when cured is not adversely affected. For example, pigments (such as carbon black and other colorants), fillers (such as fibrous and / or particulate reinforcement media, such as SiO2particulate fillers), processing aids (such as surfactants to aid in film formation), UV protection agents, flame retardants and like may be employed.

[0034] Catalysts may also be included in the formulation in order to catalyze the random copolymerization reaction of the PFAS-free formulation components. For example, in a solvent-borne liquid formulation, a dibutyltin dilaurate catalyst may be employed, whereas in a water-borneliquid formulation, a heterocyclic amidine catalyst may be employed. The catalysts are employed in an amount sufficient to catalyze the reaction between the PFAS-free formulation components, e.g., an amount of less than about 0.1 wt.%, typically less than about 0.01 wt.%, based on total weight of the PFAS-free formulation.

[0035] Typically, the total amount of all additional components will be less than about 20 wt.%, usually less than about 10 wt.%, based on the liquid total weight of the liquid PFAS-free formulation.II. Formulation Preparation and UseA. Solvent-Borne Formulation

[0036] The solvent-borne formulation is prepared by pre-blending the non-isocyanate components of the PFAS-free formulation in amounts as described above using any conventional blending equipment. Typical solvents that may be used include acetone, toluene, dichloromethane, or chloroform. The amount of solvent employed in the uncured solvent-borne PFAS-free formulation according to embodiments of this invention will be between 5 wt % to about 30 wt%, typically between 19 wt % and 25 wt% based on total weight of the liquid PFAS-free formulation. Once the non- isocyanate components are formed into a homogenous liquid pre-blend, the isocyanate(s) component(s) is(are) added into the liquid pre-blend in amounts as described above using any conventional blending equipment to thoroughly mix the same and form the solvent-borne formulation.

[0037] Once the solvent-borne formulation has been prepared, it may be applied onto a desired substrate and allowed to cure. Curing may be accomplished by an initial removal of solvent. The procedure for removal of the solvent will be dependent on the solvent type and the amount of solvent used. Typically, the solvent removal is accelerated using heat. Some embodiments of this invention may use multiple layers of the PFAS-freeformulation. In these cases the additional layers can be applied after the removal of the solvent, but before the PFAS-free material is fully cured. After the solvent is removed from the final layer of PFAS-free formulation material, reactions between the components of the PFAS-free formulation will occur to complete the curing process. These reactions occur in ambient conditions but can be accelerated via heat. Temperatures between 100 °C to about 175 °C, e.g., about 120 °C will reduce the time for the reaction to complete. When elevated temperatures are employed for curing, the typical times to achieve a full cure of the PFAS-free formulation is between about 8 hours to about 12 hours.B. Water-Borne Formulation

[0038] The water-borne PFAS-free formulation is prepared by mixing and homogenizing the components described above in a sufficient amount of water to achieve a uniform dispersion of the components in an aqueous phase. As noted previously, the isocyanate component must be blocked to allow for such aqueous dispersion.

[0039] The aqueous dispersion of the PFAS-free formulation may then be applied onto a substrate by any conventional technique, e.g., dipping, spraying, and the like. For example, if the substrate is a woven or non-woven textile fabric, the fabric may be continuously immersed in a bath containing the aqueous dispersion of the PFAS-free formulation so as to saturate the fabric with a desired amount thereof. The fabric saturated with the aqueous dispersion of the PFAS-free formulation may then be subjected to padding to remove excess formulation before being heat cured, e.g., curing of the fabric in a curing oven at an elevated temperature greater than room (20 'C) temperature but below the degradation temperature of the fabric substrate and for a time sufficient to vaporize the water carrier and unblock the isocyanate component to allow polymerization cross-linking of the formulation component. Curing temperatures of between about 100 °C to about 175 °C, e.g., about 120 °C toabout 165 °C and curing times of between about 5 minutes to about 12 or more hours may be practiced. The treated fabric may also be retreated multiple times to achieve the desired coating thickness of the PFAS-free elastomeric material on the fabric substrate.

[0040] The embodiments of this invention will be further understood by reference to the following Examples.EXAMPLESExample 1 - Solvent Borne PFAS-free Elastomeric Materials

[0041] Glove prototypes were prepared by dipping 1 1 mil nitrile gloves in a solution of the elastomer, silicon dioxide (an additive that increases tensile properties which is commercially available from Evonik Corporation USA under the trade name ACEMATT® OK 412), and carbon black (used as a colorant). The glove prototypes exhibited touch screen compatibility.

[0042] The PFAS-free elastomeric materials (sometimes referenced hereinafter as “PUv3”) represents a unique solution to an emerging problem, i.e., promising a high degree of protection against both liquid and vapor TIC and CWA challenges without relying on fluorinated components. Polysulfides are known chemically resistant materials. As will be detailed hereinbelow, blends of polyurethane, polythiourethane and polysulfide have been shown to possess good permeation resistance. Scanning electron microscopy (SEM) cross sectional analysis (FIG. 3A) of cryo-fractured neat PUv3 glove material reveals no phase separation of the resin components (polysulfide / polyol soft segments), instead showing that they seamlessly integrate into a homogenous film. The light-colored areas of silicon dioxidefilled films (FIG 3B) were identified as silicon using energy dispersive spectroscopy (EDS) SEM (FIG. 3C) with particle sizes ranging from 3.5-20 pm. Since warfighters would be most comfortable with a black glove,carbon black may be incorporated into the PFAS-free elastomeric formulation. While the chemical composition of the glove material will lend itself to discoloration after prolonged UV exposure, the final prototypes will be packaged in vacuum sealed mylar bags to minimize UV exposure; the butyl gloves currently used as the industry standard for CBRN Class I protection is packaged in a similar style of vacuum sealed bag.

[0043] Various glove scaffolds were initially explored for the base layer of the PFAS-free initial prototype glove material. Ultimately, a 1 1 -mil nitrile glove (AlphaTec® by Ansell) was selected as a scaffold as it demonstrated the best combination of substrate adhesion and tactile properties (FIGS. 4A-4C). While initial prototypes resulted in inadequate coatings on 1 ) the finger webbing (particularly between the thumb and index) and 2) material tackiness, the issues were resolved by 1 ) changing the dipping parameters to allow for a more even coating, and 2) applying a nanoclay posttreatment to reduce tackiness.

[0044] The initial prototype gloves had a thickness of 22 mil, fit well (on individuals with extra-large hands), permitted fine motor skills, and were touch screen compatible. To scale up the dipping process, negative molds of the (ceramic) hand molds were cast and with 15 molds being cast from epoxy. The scaled-up process will thereby allow the manufacture of approximately 50 gloves per batch.

[0045] Multiple prototyping experiments were subsequently conducted to develop a standard production procedure. The equipment used allowed the manipulation of variables important to the manufacturing process (e.g., dipping speed, retraction speed, multi-axis rotation, etc.) that could not be manipulated with the in-lab dipping machine. This equipment enabled rapid viability assessment of production procedures. The initial prototypes made by the prototyping experiments used pre-manufactured gloves as scaffolds for the PFAS-free elastomeric formulation. The scaffolds were put on standard ceramic forms and dipped into the PFAS-free elastomeric formulation material. This configuration was used to determine the optimal settings for the dipping procedure.

[0046] Additional experiments were performed using bespoke, natural rubber gloves as a scaffold instead of pre-manufactured gloves. The glove forms would follow a standard procedure for making dipped latex examination gloves. After the gloves were dried, but before the gloves were cured, they were dipped into the liquid PFAS-free elastomeric formulation. This method dramatically improved the fit of the gloves and the dexterity of the wearer. Other latex glove materials may be employed as a substrate for the layer of the liquid PFAS-free elastomeric formulation, such as nitrile, as well as other glove constructions, such as a supported-type gloves and different glove shapes.

[0047] The base PFAS-free solvent-borne elastomeric glove material formulation is shown in Table 1 below. It has been shown that chemical resistance is the result of the resin chemistry and is only slightly improved with the addition of silicon dioxide particles. Other additives may also be present, e.g. fillers such as carbon black, surfactants for film formation, and the like.Table 1. Glove Formulation

[0048] The PFAS-free glove material (PUv3) was tested against TICs (toluene), live CWAs (GD and HD), and low vapor pressure chemicals(DMS); the tested materials include: butyl rubber (7 mil), neat PUv3 (13 mil), and Pllv3 + silicon dioxide (13 mil). While the glove PFAS-free PUv3 material disclosed herein has approximately 2x the thickness of the butyl rubber tested, the thickness (13 mil vs 7 mil, respectively) is still approximately one-half that of butyl rubber used in CBRN Class A garments (< 25 mil). Testing has also confirmed that the PFAS-free PUv3 glove material outperformed both the 7 and 25 mil butyl rubber glove against all TICs and CWA simulants.

[0049] Table 2 below shows the permeation data from tests that were conducted in triplicate as per NFPA 1994 2022 ed. standards and analyzed after 1 and 6 hours. Since there are no requirements in NFPA 1994 2022 ed. for 6 hours of breakthrough testing, the 1 -hour requirements were applied. As shown in Table 2, all the glove materials were able to still pass the Class 1 requirements for GD at 6 hours, while only a few were able to pass for Toluene and DMS. The samples were compared to negative and positive controls (all of which conformed to accepted testing requirements), and the chemical retention of the materials were analyzed by extracting the samples with acetone after the 6-hour permeation tests.Table 2. Permeation test results show the PFAS-free PUv3 glove material meets Class I Standards (as per NFPA 1994 2022 ed.). Challenge Density for all solvents: 20 g / m2

[0050] Neat and silicon dioxide-filled PUv3 films were evaluated for their permeation resistance against toluene and MEK to compare to butyl rubber (the industry standard for CWA-protection). As shown in Table 3 below, PUv3 resins outperformed butyl rubber in every experiment. This demonstrates that PUv3 provides superior protection against both TICs and CWA simulants. The resulting films were transparent (with a yellow hue) and highly flexible. Additionally, the touch screen capabilities of these films were evaluated by placing the films over the face of a smart phone (on top of a protective screen cover), and the phone was able to be operated seamlessly even when the operator was wearing an additional layer of nitrile gloves.Table 3. In-house permeation data for butyl rubber, nitrile base, PUv3 glove material (neat and with silicon dioxide). Challenge density = 20 g / m21.1 Physical Testing

[0051] Several physical and thermal tests have been conducted on films of the glove materials. The material has been characterized by thermal gravimetric analysis, dynamic mechanical analysis, tensile testing, and permeation after biaxial stretching.1.1.1 Thermal Gravimetric Analysis

[0052] The thermal degradation behavior of each material was analyzed using thermal gravimetric analysis (TGA). The samples were heated under a nitrogen atmosphere to OOC at a rate of 5°C / min. The resulting curves are plotted in FIG. 5 along with their associated onset points. Both polymers disclosed herein, i.e., Pllv3 and PUv3 with silicon dioxide particles, have similar onset temperatures meaning that the inclusion of the silicon dioxide particles does not affect the polymer’s inherent properties. Additionally, the final weight loss of PUv3 with silicon dioxide particles rests at approximately 19%. This comparatively large result is attributed to the resistance of silicon dioxide to decomposition.1.1.2 Thermal Gravimetric Analysis

[0053] The PUv3 glove materials, both neat and silicon dioxide-filled, were tested by Dynamic Mechanical Analysis (DMA) to compare storagemodulus and glass transition temperature (Tg) against butyl rubber. The experiment used a 30.0 pm dual screw film clamp to oscillate the sample at 1 Hz at a preload of 1 N. The temperature was ramped from -85 °C to 200 °C at a rate of 3°C / min. The tan(delta) peaks for each material are shown in Figure 6.

[0054] Butyl rubber has a much lower Tgthan PUv3, meaning it remains flexible at lower temperatures. Adding silicon dioxide particles to PUv3 did not change the Tgof the material by an appreciable amount. This data indicate the addition of silicon dioxide particles is not drastically affecting the inherent physical characteristics of the PUv3 polymer.

[0055] Error! Reference source not found, depicts the storage moduli for butyl rubber, PUv3, and Pllv3 with silicon dioxide particles. The PUv3 material has a higher storage modulus at temperatures below 5 °C, meaning it will feel stiffer in this temperature range. This is corroborated by the measured Tgin Error! Reference source not found.. At temperatures higher than this, Pllv3 and butyl rubber have comparable storage moduli and will behave similarly in terms of their flexibility. Adding silicon dioxide particles to PUv3 increases its storage modulus across all temperatures.1.1.3 Tensile Testing

[0056] The tensile properties of PUv3 and silicon dioxide-filled Pllv3 films were compared to butyl rubber using ASTM D412 at 20 inches / minute. The results are shown in Table 4 below.Table 4. Tensile properties of butyl rubber, PUv3, and PUv3 with silicon dioxide particles as determined by ASTM D412

[0057] The PUv3 material was not as elastic as butyl rubber. Adding silicon dioxide particles to the formulation further decreased its elasticity. In contrast, the tensile strength of neat PUv3 is comparable to butyl rubber and is much larger than butyl rubber with silicon dioxide particles.1.1.4 Permeation Resistance After Biaxial Stretching

[0058] Permeation tests were conducted for butyl rubber and Pllv3 with silicon dioxide particles. The challenge material for these tests was liquid toluene dispensed at an areal density of 20 g / m2. Ultra-pure nitrogen was used as the carrier gas at a flow rate of 50 seem. Prior to permeation testing, a swatch of the PUv3 with silicon dioxide particles was stretched to 25% of its elongation 5 times in both the x-axis and y-axis. The breakthrough point was defined as when the FID produced a signal of 2.5 mV or higher. The signal from the FID is plotted as a function of time in Error! Reference source not found.. Even after stretching, PUv3 material resists chemical permeation for about 3 hours longer than butyl rubber. This confirms the exceptional barrier properties of PUv3 with and without silicone dioxide particles and its potential as a replacement for the current industry standard glove material, butyl rubber.Example 2 - Water Borne PFAS-free Elastomeric Formulations2.1 PFAS-Free Textile Treatment Formulation

[0059] As described previously, the reaction product of the solvent- borne PFAS-free elastomeric formulations has demonstrated chemical resistance, but the isocyanate-based curatives used in the previously described polymer system are incompatible with water. Isocyanates can however be blocked with groups that stabilize them in otherwise reactive environments. The blocking groups are then caused to leave or deblock at high temperatures, reactivating the curative. In the embodiments described herein, 3,5-dimethyl-1 H-pyrazole (DMP) was employed as the blockinggroup due to its relatively low deblocking temperature (e.g., about 1 0 °C) and simple blocking reaction procedure. Blocking the isocyanate groups is especially important when considering the transition from lab-scale prototyping to larger scales of manufacturing. While exceptions exist, most textile manufacturing facilities use exclusively waterborne treatments. Thus, the water-borne PFAS-free formulations as described herein are especially well suited for use in treatment of fabrics to impart CBRN-protection to the resulting article.

[0060] Table 5 below shows the base PFAS-free formulations employed in the described experiments below:Table 5. PFAS-free Water-Borne Formulation

[0061] The components of the waterborne PFAS-free formulation in Table 5 above were mixed and homogenized in an aqueous phase until a uniform consistency of the suspension was reached. Fabric swatches of woven Operational Camouflage Pattern (OOP) 1 :1 nylon-cotton blend (50 / 50 NyCo) fabric were then immersed in the liquid suspension until the swatches were fully saturated. Pressure was applied to the saturated swatches via a padder to ensure that the suspension fully impregnated the fabric swatches and was consistent across the thickness of the swatch. Padding of the saturated fabric swatches also served to remove excess aqueous PFAS-free formulation from the fabric.

[0062] The saturated swatches were then subjected to an elevated temperature of 165 °C for 5-10 minutes to vaporize the residual water remaining after padding and begin the curing process for the PFAS-free elastomeric formulation. This procedure was repeated 2 more times to apply a total of three coats to each fabric swatch. The thus treated fabric swatch was then heated at 120 °C for 12 hours after the final coat to complete the curing process for the PFAS-free elastomeric formulation. The fully cured fabric swatches were then subjected to various testing protocols as descried below.2.2 Permeation Testing

[0063] The treated fabric swatches as described above were tested for permeation against toxic industrial chemicals (TICs) and live chemical warfare agents (CWAs). For comparison, the same permeation tests were conducted on samples of a commercial, PFAS-containing composite textile certified as a NFPA 1994 2022 ed. Class 3 barrier material.

[0064] All tests were conducted in triplicate as per the NFPA 1994 2022 ed. Class 3 standard and analyzed after 15 minutes and 1 hour of exposure to the challenge agent. As shown in Table 6 below, all the treated textiles passed the Class 3 requirements for TICs (DMS) and CWAs (HD). The PFAS-free composite material in accordance with the invention provided greater permeation resistance against toluene than the commercial composite, and substantial permeation resistance against dimethyl sulfate (DMS) and sulfur mustard (HD) at a challenge of 10 g / m2.Table 6. Permeation results (challenge density for all reagents: 10 g / m2)2.3 Physical Testing

[0065] Woven OCP 50 / 50 NyCo finished with the waterborne, PFAS- free chemically resistant formulation was tested for puncture resistance (ASTM F1342, standard probe), burst strength (ASTM D751 -19 Proc. A), MVTR (ASTM E96), and evaporative resistance and total heat loss (modified ASTM F1868, methods B and C).2.3.1. Puncture Strength

[0066] The resistance to puncture was measured using an ADMET tensile tester. The machine was outfitted with a 22 lb. load cell and puncture probe type A, which moved at 20 in / min. The average peak load across 8 - 9 experiments is compared to that of a commercial Class 3 material in Table 7 below. As is shown therein, the average peak loads for each textile are within one standard deviation of each other— therefore, the puncture resistance of treated fabric according to the embodiments described herein is directly comparable to a commercial Class 3 material.Table 7. Puncture resistance Data2.3.2. Burst Strength

[0067] Swatches of fabric treated with the PFAS-free waterborne suspension according to the invention were analyzed for burst strength in a ring clamp / ball burst rupture test. The 1 -inch diameter probe moved perpendicular to the test sample at a rate of 12 in / min until the fabric ruptured. The average peak force at rupture across 5 samples is compared to a commercial Class 3 material and the NFPA 1994 2022 ed. Class 3 requirement in Table 8 below.Table 8. Ball burst strength data

[0068] As can be seen, the textiles treated with the PFAS-free waterborne suspension had a burst strength lower than the commercial Class 3 material but exceeding the NFPA 1994 2022 ed. Class 3 requirement. It should also be noted that the commercial Class 3 material tested was a three-layer composite whereas the PFAS-free waterborne treated material in accordance with the invention was a single-layer coated fabric. Despite this difference, the inventive material still performed within specifications for NPFA 1994 Class 3 garments and adequately resisted rupture.2.3.3. Moisture / Water Vapor Transmission Rate Testing

[0069] The breathability of the PFAS-free water borne material was quantified with MVTR testing as per ASTM E96 at a temperature of 26 °C and a relative humidity of 65%. Moderate MVTRs were observed with the inventive material as compared to a commercial Class 3 material and also showed substantial improvement over the solvent-borne formulations used in Class 1 glove coatings described previously (noted as the “Class 1 Glove Material”). These results are shown in Table 9 below.Table 9. ASTM E96 MVTR results for a series of samples2.3.4. Evaporative Resistance and Total Heat Loss Testing

[0070] Additional breathability metrics, evaporative resistance and total heat loss, were measured through sweating guarded hotplate testing. The standard procedures referenced in NFPA 1994 2022 ed., ASTM F1868 methods B and C, were modified to fit smaller sample sizes (20” squares down to 5” squares ). During these experiments, the test plate temperature was set to 35 °C and samples were kept in a 21 °C, 65% relative humidity environment. The PFAS-free water-borne treated textile according to the invention had a lower total heat loss than the commercial Class 3 material, but it still exceeded the NFPA 1994 2022 ed. Class 3 requirement. These results are presented in Table 10 below.Table 10. Evaporative resistance values from modified ASTM F1868 testing**********

[0071] While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope thereof.

Claims

WHAT IS CLAIMED IS:1 . A curable chemical protective elastomeric formulation comprising the following components:(a) a polythioether nucleophile component,(b) a liquid polyol component, and(c) at least one isocyanate as a cross-linking component, wherein the formulation is free of a perfluoroalkyl substance, and wherein the formulation when cured provides chemical protection according to National Fire Protection Association (NFPA) 1994 2022 ed. Class I and / or Class III requirements.

2. The formulation according to claim 1 , wherein the polythioether nucleophile component is a liquid polysulfide polymer with thiol end groups.

3. The formulation according to claim 2, wherein the polythioether nucleophile component has a number average molecular weight of between about 500 and 10000 g / mol.

4. The formulation according to claim 2, wherein the polythioether nucleophile component has a thiol content between about 2.0 mol% and 7.0 mol%.

5. The formulation according to claim 1 , wherein the polythioether nucleophile is a polycondensation product of bis(2-chloroethyl) formal with alkali polysulfide.

6. The formulation according to claim 5, wherein the polythioether nucleophile component has a number average molecular weight of between about 750 and 1 150 g / mol.

7. The formulation according to claim 1 , wherein the polyol component is a polycaprolactone or aliphatic alcohol having three or more nucleophilic hydroxy groups.

8. The formulation according to claim 7, wherein the polyol component has a number average molecular weight of between about 120 g / mol to about 1200 g / mol.

9. The formulation according to claim 7, wherein the polyol component is a liquid polyester triol terminated by primary hydroxy groups that have a hydroxyl value of between about 170 to about196 KOH / g and a number average molecular weight of about 900 g / mol.

10. The formulation according to claim 1 , wherein the at least one isocyanate comprises at least one trimeric aliphatic isocyanate.1 1 . The formulation according to claim 1 , wherein the at least one isocyanate comprises at least one aliphatic isocyanate selected from the group consisting of methylene diphenyl diisocyanate (MDI), hexamethyl diisocyanate (HDI), and trimers of HDL12. The formulation according to claim 11 , wherein the at least one isocyanate is blocked by a blocking agent selected from the group consisting of pyrazole derivatives and oxime derivatives.

13. The formulation according to claim 12, wherein the blocking agent is 3,5-dimethyl-1 H-pyrazole and / or methyl ethyl ketone oxime (MEKO).

14. The formulation according to claim 1 , further comprising:(d) at least one additional component selected from the group consisting of catalysts, pigments, fillers, processing aids, UV protection agents and flame retardants.

15. The formulation according to claim 14, wherein the at least one additional component comprises a particulate SiO2.

16. The formulation according to claim 15, wherein the catalyst is a dibutyltin dilaurate catalyst or a heterocyclic amidine catalyst.

17. The formulation according to claim 1 , wherein the formulation is solvent-borne or water-borne.

18. A composite article comprising a substrate and a cured coating of the chemical protective elastomeric formulation in contact with the substrate.

19. The composite article according to claim 18, wherein the substrate is a fabric, and wherein the cured coating saturates the fabric.

20. A method of making a chemical protective composite article comprising:(i) providing a substrate,(ii) applying the curable chemical protective elastomeric formulation to the substrate, and(iii) curing the elastomeric formulation to provide a chemical protective composite article exhibiting chemical protection according to National Fire Protection Association (NFPA) 1994 2022 ed. Class I and / or Class III requirements.21 . The method according to claim 20, wherein the formulation is solvent-borne or water-borne.

22. The method according to claim 21 , wherein the formulation is solvent-borne and wherein the step (iii) comprises removing the solvent from the formulation and allowing the formulation to cure.

23. The method according to claim 21 , wherein the formulation is water-borne, and wherein step (ii) comprises saturating the fabric substrate with the waterborne formulation, and wherein step (iii) comprises removing excess water-borne formulation from the substrate obtained in step (ii) and curing the formulation at an elevated temperature.

24. The method according to claim 23, wherein the at least one isocyanate is blocked by a blocking agent selected from the group consisting of pyrazole derivatives, oxime derivatives, aromatic alcohols, diethyl malonate, caprolactam derivatives and sodium bisulfite, and wherein the elevated temperature of step (iii) is sufficiently high to remove the blocking agent to thereby unblock the at least one isocyanate component to allow polymerization cross-linking of the formulation components but is below a degradation temperature of the substrate.

25. The method according to claim 23, wherein step (iii) comprises (iiia) subjecting the saturated substrate to padding to fully impregnate the substrate with the elastomeric formulation and to remove excess formulation therefrom, then subsequently (iiib) curing the elastomeric formulation at an elevated temperature.

26. The method according to claim 25, wherein step (iiia) comprises impregnating the substrate with the water borne elastomeric formulation and removing excess formulation therefrom by padding, prior to practicing step (iiib).

27. The method according to claim 24, wherein the elevated temperature is between about 100 °C to about 175 °C.

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