Gas permeation properties of poly(lactic acid)

The need for the development of polymeric materials based on renewable reso urces has led to the development of poly(lactic acid) (PLA) which is being produced from a feedstock of corn rather than petroleum. The present study examines the permeation of nitrogen, oxygen, carbon dioxide, and methane in amorphous films of PLA cast from solution. The properties of PLA are compa red to other commodity plastics and it is shown that PLA permeation closely resembles that of polystyrene. At 30 degreesC, N-2 permeation in PLA is 1. 3 (10(-10) cm(3) (STP) cm/cm(2) s cmHg) and the activation energy is 11.2kJ /mol. For oxygen the corresponding values are 3.3 (10(-10) cm(3) (STP) ca/c m(2) s cm Hg) and 11. 1 kJ/mol. The values for carbon dioxide permeation ar e 1.2 (10(-10) cm(3) (STP) cm/cm(2) s cmHg) and 6.1 kJ/mol. For methane val ues of 1.0 (10(-10) cm(3) (STP) cm/cm(2) s cmHg) and an activation energy o f 13.0 kJ/mol are found. Studies with pure gases show that polymer chain br anching and small changes in L:D stereochemical content have no effect on p ermeation properties, Crystallinity is found to dominate permeation propert ies in a biaxially oriented film. The separation factor for a CO2/CH4 mixed gas system is measured between 0 and 50 degreesC and does not deviate sign ificantly from the calculated ideal separation factor; at 0 degreesC the se paration factor is 16, a value that suggests continued studies of PLA as a separation medium are warranted. (C) 2001 Elsevier Science B.V. All rights reserved.