Effect of molecular weight of Poly(ethylene glycol) on plasticization of Poly (L-lactic acid)

Poly(L-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 (epsilon(b) = 32%) in PLLA/PEG5-15% where PEG5-15% represents 15 wt% of PEG with the MW of 5 kg/mol while epsilon(b)s of PLLA/PEG-15% where PEG-15% represents 15 wt% of PEG with other MW PEGs were similar to 300%. WAXD results confirmed that PLLA in quenched PLLA/PEG-15% blends crystallized into mixtures of alpha'-form and alpha-form crystals during heating. DSC analysis showed that two cold crystallization temperature (T(cc)s) were observed in PLLA/PEG5-15% while only one T-cc was observed in PLLA/PEG2-15% and PLLA/PEG8-15%, indicating that PLLA/PEG5-15% formed separated alpha'-form and alpha-form crystals while the other two blends formed mixed alpha'-form and alpha-form crystals. The competition between phase separation and PLLA crystallization determined the final structures and physical properties of PLLA/PEG blends.

Automated summary

In this study, poly(L-lactic acid) (PLLA) was plasticized with poly(ethylene glycol) (PEG) to improve its brittleness, and the effects of PEG molecular weight and content on the properties of PLLA/PEG blends were systematically studied. The competition between phase separation and PLLA crystallization was found to determine the final structures and physical properties of PLLA/PEG blends, with different PEG contents and molecular weights influencing the crystallization form and mechanical properties of the blends.