Experimental Research on Glass Transition Temperature of Polymers in Compressed CO2

Glass transition temperature (Tg) is an important characteristic parameter of polymers. The investigation of polymers' Tg in compressed CO2 is especially necessary for the application of supercritical fluids technique in polymer science. In this paper, based on creep compliance experimental principle, an apparatus for testing Tg of polymers in high pressure environment is established. Glass transition temperature of PET, PS, PVC and PMMA in atmosphere and in compressed CO2 has been tested. In the experiment processes, the equilibrium adsorption temperature is room temperature, and the equilibrium adsorption pressure ranges are as following: 0~3.5 MPa for PET, 0~11.0 MPa for PS, 0~9.0 MPa for PVC and 0~4.5 MPa for PMMA. The Tg obtained in atmosphere using this apparatus agree well with those in literature. This proves that the experimental method and the apparatus developed in this work are reliable and valid, so they can be applied to determine Tg of polymers at high pressure. From the results of Tg of polymers in compressed CO2, we can conclude that CO2 has distinct swelling and plasticizing effects on polymers, so that CO2 can make Tg of polymers decrease largely.