Greatly accelerated crystallization of poly(lactic acid): cooperative effect of stereocomplex crystallites and polyethylene glycol

Stereocomplex crystallite (SC) between enantiomeric poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA), with largely improved thermal resistance and mechanical properties compared with PLLA and PDLA, is a good nucleating agent for poly(lactic acid) (PLA). The effects of SC and/or polyethylene glycol (PEG) on the crystallization behaviors of PLA were investigated. The non-isothermal and isothermal crystallization kinetics revealed that SC and PEG can separately promote the crystallization rate of PLA by heterogeneous nucleation and increasing crystal growth rate, respectively. However, their promoting effect is limited when used alone, and the modified PLA cannot crystallize completely under a cooling rate of 20 °C/min. When SC and PEG are both present, the crystallization rate of PLA is greatly accelerated, and even under a cooling rate of 40 °C/min, PLA can crystallize completely and get a high crystallinity owing to the excellent balance between simultaneously improved nucleation and crystal growth rate.