Low-Permeability Coating for Nitrile Rubber
Navy SBIR FY2008.1

Sol No.: Navy SBIR FY2008.1
Topic No.: N08-042
Topic Title: Low-Permeability Coating for Nitrile Rubber
Proposal No.: N081-042-0106
Firm: Rethink Technologies, Inc.
15 West Main Street
Cambridge, New York 12816-1118
Contact: Roger Faulkner
Phone: (518) 677-2080
Web Site: www.rethink-technologies.com
Abstract: This research will develop a coating for the nylon/NBR fly-through cover (FTC) to reduce water permeation into the missile tube. The point-to-point variability of permeation of our novel coating will be reduced compared to the MTM coating. The currently variable permeation of water compromises the mechanical integrity of the sea-wetted FTC by softening localized regions of the FTC. We will design a tape or film that will be adhered to the surface of the fly-through cover before compression molding. The tape or film will be designed to withstand at least 160 inflation/deflation cycles. We will investigate elastomeric layers and low permeability plastic films bonded inside elastomeric layers. We will investigate two commercially available elastomers as elastomeric permeation barriers. We will prepare compounds with and without platy nanofillers. We will then take the best elastomer compounds and make thermoplastic vulcanizates (TPVs) based on these elastomers in combination with low permeability plastics. Such coatings will be tested for mechanical and permeability properties. Lastly, multilayer structures comprised of the elastomeric compound or compounds, sandwiched with a highly permeation-resistant plastic film layer will be prepared and evaluated. Plastics with permeability from 20-500 times lower than the elastomeric barrier layers will be investigated.
Benefits: There are numerous applications in which electronics or cables need to be protected from water. In some cases, the life expectancy for undersea cables is determined by the time that the sheathing protects the cable from saturation by water. Similarly, alcohol permeation (especially methanol and ethanol) through polymeric fuel hoses and other automotive fuel system components is increasingly problematic as organic vapor emission limits are tightened. Methanol permeabilities are generally correlated with water permeability, and often methanol is the fastest permeating component of standard fuel mixtures (such as CM15) which are used to test automotive fuel system components. Therefore, reducing methanol permeation is highly significant for meeting some automotive fuel hose specs. In some cases, metallic layers can be used to provide a nearly perfect moisture and methanol barrier; often however, due to a need for high flexibility or because of potential corrosion of metals, there is a need for a more flexible, polymer-based protective film. Although polychlorotrifluoroethylene (PCTFE) is well established as a clear packaging material for moisture-sensitive pharmaceuticals, it has not so far been applied to cable sheathing nor as a permeation resistant layer in fuel hoses and/or other fuel system components. Development of a practical method to adhere films of PCTFE to elastomer films such as FKM and NBR is expected to translate into the capability of deploying PCTFE in elastomer-based cables and fuel hoses, and other components where the superior barrier properties of PCTFE to water and methanol in particular will be very useful. In addition to the potential applications of elastomer/PCTFE composite films as methanol permeation barriers, the purely elastomeric films based on nanocomposites of butyl rubber or high fluorine FKM have numerous potential applications as moisture barriers for corrosion protection of metals. The FKM-based solutions have potential applications in high altitude aircraft coatings (due to the combination of high permeation resistance to water, rubbery low modulus which reduces the importance of mismatched coefficients of thermal expansion with metallic substrates, and high UV and ozone resistance). Both the butyl rubber-based coatings and the FKM-based coatings have high potential as nontoxic antifouling coatings for ship hulls and water intake pipes (to resist barnacles and zebra mussel attachment, in particular). It has been found that there is an ideal surface energy density for an polymer to resist attachment by barnacles, around 22 dynes/cm. This is well-matched by silicone rubber, butyl rubber, and some grades of fluoroelastomer. Most current non-toxic antifouling paints designed to inhibit barnacle attachment are made of silicone rubber, which does not protect the substrate from sea water corrosion very well. Butyl rubber or FKM-based coatings, especially high moisture permeation resistant versions based on platy nanocomposite fillers, have high potential for improving the degree of corrosion protection for these anti-fouling paints and coatings.