Melt preparation and nucleation efficiency of polylactide stereocomplex crystallites

A melt blending procedure was developed for the preparation of poly(l-lactide) (PLLA)/poly(d-lactide) (PDLA) stereocomplex crystallites dispersed in a PLLA matrix. All PLLA/PDLA blends were prepared in a batch melt mixer with ≥95% PLLA. Three PDLA homopolymers with a range of molecular weights were used as the minority (≤5%) component. The presence of the stereocomplex in the PLLA matrix was verified by differential scanning calorimetry (DSC) and optical microscopy. The effectiveness of the in situ formed stereocomplex crystallites for nucleating PLLA crystallization was evaluated using self-nucleation and non-isothermal DSC methods. With only 3 wt% of the 14 kg mol−1 PDLA, nucleation efficiencies near 100% could be obtained. In addition, fast crystallization kinetics were observed in isothermal crystallization experiments at 140 °C. The stereocomplex crystallites were much more effective at enhancing the crystallization rate of PLLA compared to talc, a common nucleating agent.