Experimental research on swelling and glass transition behavior of poly(methyl methacrylate) in supercritical carbon dioxide

• The volume change ratio of PMMA at 12 MPa has the most significant increment, instead of that at 20 MPa.
• Tg of PMMA decreased from 380.5 to 311.4 K withCO2 pressure 0.1–12 MPa, and increased from 311.4 to 323.1 K with 12–22 MPa.
• When CO2 pressure is beyond 12 MPa, hydrostatic pressure has a more significant effect on swelling ratio than swelling.
• The Tsat−pCO2Tsat−pCO2 curve has similar change with the Tg−pCO2Tg−pCO2 curve.

The glass transition temperature (Tg) reduction of polymer by plasticization is a paramount thermodynamic property in polymer/diluent systems, thus effecting microcellular foaming process. Experiment was conducted in a high-pressure cell furnished with an optical channel. In this research, the swelling ratios (ΔV/V0) of polymethyl methacrylate (PMMA) in carbon dioxide (CO2) with pressures ranging from 2 to 22 MPa were measured, thus the Tg data of PMMA was determined in the same pressure range. It was found that the swelling ratio increases with temperature but reaches the maximum at 12 MPa, instead of 22 MPa. And the glass transition temperature decreases from 380.5 to 311.4 K within the pressure range of 0.1–12 MPa but increases gradually to 323.1 K from 12 to 22 MPa. Additionally, the change of maximum saturation temperature as a function of CO2 pressures agrees well with Tg of the polymer-CO2 system.

Complete Tg–p profile for PMMA/CO2 system.Figure optionsDownload as PowerPoint slide