Free-Radical Maleation of Polylactide in Supercritical Carbon Dioxide

In this research, maleic anhydride (MA) was covalently grafted onto both polylactide (PLA) film and powder in a supercritical carbon dioxide (scCO2) medium. This demonstrates that this free-radical initiated grafting process can be utilized not only for producing master batches of maleated graft copolymer powder and pellets, but also for grafting MA onto pre-formed polymer samples.

In scCO2 grafting, carbon dioxide serves as an inexpensive and environmentally benign reaction medium which readily dissolves the reactive monomer and initiator. Furthermore, scCO2 simultaneously swells the PLA polymer phase for improved monomer penetration.

The effects of run time and two different free-radical initiators were compared in order to determine the optimal run conditions for grafting. The resulting copolymer was characterized by FTIR, NMR, and DSC in order to verify grafting and sufficient removal of excess MA monomer. To increase the signal obtained through spectroscopy, the graft copolymer was reacted with benzylamine in acetone and purified by reprecipitation prior to analysis.