Effect of Molecular Weight of Poly(ethylene glycol) on Plasticization of Poly(ʟ-lactic acid)

Abstract Poly(ʟ-lactic acid) (PLLA) is a sustainable, biodegradable polymer, but the inherent brittleness impedes its potential application. In this study, we use poly(ethylene glycol) (PEG) to plasticize PLLA and systematically study the effect of molecular weight (MW) and content of PEG on the thermal and mechanical properties of PLLA/PEG blends. We observed a surprisingly big drop of elongation at break (eb =32%) in PLLA/PEG5-15% where PEG5-15% represents 15 wt% of PEG with the MW of 5 kg/mol while ebs of PLLA/PEG-15% where PEG-15% represents 15 wt% of PEG with other MW PEGs were ∼300%. WAXD results confirmed that PLLA in quenched PLLA/PEG-15% blends crystallized into mixtures of α′-form and α-form crystals during heating. DSC analysis showed that two cold crystallization temperature (Tccs) were observed in PLLA/PEG5-15% while only one Tcc was observed in PLLA/PEG2-15% and PLLA/PEG8-15%, indicating that PLLA/PEG5-15% formed separated α′-form and α-form crystals while the other two blends formed mixed α′-form and α-form crystals. The competition between phase separation and PLLA crystallization determined the final structures and physical properties of PLLA/PEG blends.