Injection molding and characterization of polylactide stereocomplex

Poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) were hand mixed 50/50 which removed the need for melt mixing of PLLA with PDLA prior to injection molding to produce a stereocomplex. Various characterization techniques were employed to study the mechanical properties, rheological properties, and crystallization behavior of the materials. High stereocomplex content was obtained by molding PLLA and PDLA at a temperature between the melting temperature (Tm) of the homocrystal and the stereocomplex. However, PLLA and PDLA are easier to separate when being molded at below the Tm of the stereocomplex. The stereocomplex had a higher melting temperature (Tm) (more than 50 °C) and a higher crystallization temperature (Tc) (more than 25 °C) than the neat PLLA. Rheological measurements at 200 °C revealed that the PLLA50/PDLA50 showed a much higher mechanical strength (G′) than PLLA, which was attributed to stereocomplex formation by injection molding. Furthermore, PLLA50/PDLA50 greatly enhanced the elongation-at-break of PLLA. Finally, this novel process provided a unique processing route for preparing high degree stereocomplex crystallites that has not previously been reported.