INTERACTION OF CO2 GAS WITH SILICONE ELASTOMER AT HIGH AMBIENT PRESSURES

Interaction of high-pressure CO2 gas with a silicone elastomer, and to a lesser extent, with a nitrile rubber and a PTFE have been investigated. Sorptive dilations of the polymers were measured with the help of custom-made piezoelectric ultrasonic transducers under gas pressures of up to ca. 22 MPa at 42-degrees-C. The gas mass sorption was determined by a vibrating reed probe. For the silicone elastomer system the dilation isotherm mimics the sorption isotherm. The partial molar volume (PMV) of the absorbed CO2 gas in the silicone elastomer has been computed. A significant drop in the PMV value is observed when the CO2 gas becomes supercritical. In the transition region, the transmission of ultrasonic signals through the specimen indicated the formation of discrete small (estimated as about 60-mu-m in diameter) high density zones of CO2 in the rubber matrix. The plasticization effects of the absorbed high pressure CO2 gas have been identified from the interpretation of the changes in the acoustic longitudinal modulus obtained from ultrasonic transmission measurements. The effects of rapid gas decompression on the structural integrity of the various polymers have also been determined. Significant inflation of certain specimens occur toward the later stages of the decompression cycle. The initiation and development of internal cracks or bubbles was followed by monitoring the ultrasonic signal attenuation.