The formation of stereocomplex in asymmetric blends of PLLGA and PDLA and the effect of stereocomplex on PLLGA crystallization

The isothermal and non-isothermal crystallization behaviors of asymmetric poly(L-lactic acid-co-glycolic acid) (PLLGA)/poly(D-lactic acid) (PDLA) blends was investigated at PDLA loadings of up to 10 wt%. A simple solvent-casting procedure, was developed for the preparation of PLLGA/PDLA stereocomplex crystallites dispersed in a PLLGA matrix. The formation of stereocomplexes in the PLLGA matrix was verified by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Non-isothermal crystallization measurement demonstrated that the addition of PDLA significantly accelerates the crystallization of PLLGA. Subsequent assessment of the influence of PDLA content on the isothermal crystallization kinetics of PLLGA by the Avrami equation confirmed that the crystallization rate of PLLGA is enhanced by the addition of PDLA contents, with a reduction in the half crystallization time (t(1/2)) and increase in the crystallization rate constant (k) values. A PDLA content of 17 wt% was found to particularly enhance the crystallization rate of PLLGA, from which it is inferred that the PLLGA/PDLA stereocomplex crystals act as effective nucleus to enhance the crystallization of PLLGA.