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 (T_m) of the homocrystal and the stereocomplex. However, PLLA and PDLA are easier to separate when being molded at below the T_m of the stereocomplex. The stereocomplex had a higher melting temperature (T_m) (more than 50°C) and a higher crystallization temperature (T_c) (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.