Playing with process conditions to increase the industrial sustainability of poly(lactic acid)-based materials

Abstract

Polylactic acid (PLA) is an important polymer for the replacement of oil-based polymers in the biomedical field as well as for degradable single use polymeric materials. To fully exploit the potential of this sustainable polymer in our society either physical (blending) or chemical (e.g. crosslinking) modification is desired. Many experimental studies exist regarding PLA mechanical or thermal property enhancement, but the (time dependent) molecular scale information is largely lacking. In the present work, it is demonstrated that coupled matrix-based Monte Carlo simulations allow understanding of which molecules are modified and how, selecting the PLA chemical modification route to highlight the in silico design potential. Model validation is performed for two case studies: (i) PLA modification with conventional radical initiator (benzyl peroxide; BPO) in the absence and presence of crosslinking agent (CA) pentane-1,5 diyl diacrylate (PDA) and (ii) PLA modification via γ-irradiation. Specific emphasis is on obtaining a better understanding of the impact of the viscous melt conditions on the reaction outcome, either favoring crosslinking or lowering the chain length via β-scission. It is illustrated that optimal melt reaction conditions exist to obtain a given molecular scale driven PLA chemical modification pathway. The most effective approach is in this context a tuned initial CA concentration. The present work contributes to the enlargement of the application range for PLA, as more dedicated molecular control will enable the production of PLA with sufficiently high melt strengths, acceptable brittleness degrees, and sufficiently high crystallization rates.