Effect of molecular weight of poly(L-lactic acid) on the stereocomplex formation between enantiomeric poly(lactic acid)s blendings

The effect of molecular weight of poly(L-lactic acid) on the stereocomplex formation between poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA) was investigated. Films of 1:1 blend were prepared from PLLA with molecular weight of 125, 180 and 209 kg/mol and PDLA with molecular weight of 150 kg/mol by a solution cast method. Thermal properties, crystalline structure and mechanical properties were measured by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (XRD) and tensile testing. Blending lowest molecular weight PLLA (M_w 125 kg/mol) with PDLA showed highest stereocomplex formation with melting temperature more than 50°C compared to that of homocrystallites. As the molecular weight of PLLA became higher, the stereocomplex formation was lower. Films with higher stereocomplex formation also had higher mechanical properties.