VAPOR TRANSPORT IN POLYMERIC MEMBRANES - DESIGN AND DEVELOPMENT OF A SEMIPERMEABLE BARRIER FABRIC

The diffusion of selected organophosphorous vapors, carbon tetrachloride vapor and oxygen through polymeric membranes and composite fabrics was studied. The organophosphorous compounds employed were dimethyl methyl phosphonate and 2,2-dichlorovinyl methyl phosphate. Polyethylene teraphthalate (PET), polyvinyl chloride (PVC), cellulose acetate and polytetrafluoroethylene (PTFE) membranes were used. Composite fabrics included an active carbon impregnated polyurethane foam fabric, bi-membrane composites of PET and PVC and bi-membranes with an encapsulated active carbon layer. Diffusion parameters were evaluated by breakthrough time, diffusion rate and diffusion coefficients. Diffusion properties were measured using flame ionization and thermal conductivity detectors with a gas chromatograph.; Oxygen diffusion rates and coefficients did not vary significantly among the membranes and composites tested. Breakthrough times for the organophosphorous and carbon tetrachloride vapors varied greatly. Additions of a second membrane and a carbon layer for the membrane composites were observed to at least double the measured breakthrough times. Diffusion rates were affected more by vapor pressure than by the construction of the barrier. Diffusion coefficients were significantly reduced by composite construction. Membrane bilayer composites reduced the calculated diffusion coefficients by as much as an order of magnitude.; Vapor absorption by single membranes and the polyurethane foam fabric was measured using a static gravimetric technique and was evaluated in terms of a change in weight with time. It was determined that PET membranes had the greatest sorption capacity per unit volume ranging from 0.576 to 17.77 mg/cm('2)/cm('3). The low values obtained for the polyurethane foam, in the range of 0.068 to 1.513 mg/cm('2)/cm('3), were attributed to water poisoning of the active carbon which provided the absorption system for the fabric.; Membrane stability to vapor exposure was evaluated by effect on tensile properties, surface degradation and decrease in percent crystallinity. Thermal analysis indicated significant, greater than 70 percent, reduction in crystallinity for PET after vapor exposure. Scanning electron micrographs did not show any detectable surface effects.