Measurement of gas solubility and diffusivity in polylactide

The solubilities of carbon dioxide and nitrogen in a polylactide melt were determined at temperatures from 180 to 200 °C and pressures up to 28 MPa using a magnetic suspension balance (MSB). Both Sanchez–Lacombe (SL) and Simha–Somcynsky (SS) equations-of-state (EOS) were applied to predict the amount of volume swelling in the polylactide (PLA)/gas mixture due to gas dissolution. With the proper prediction of volume swelling from both SS-EOS and SL-EOS, the “corrected solubility” was determined based on the experimentally measured “apparent solubility” from the MSB. After measurement of the gas sorption curve in the PLA melt, the theoretical sorption model based on Fick's second law was adopted to extract the diffusion coefficients of carbon dioxide and nitrogen in polylactide at both 180 and 200 °C.