Effect of molecular weight on crystallization behavior of poly (lactic acid) under isotherm and non‐isotherm conditions

Abstract The effect of molecular weight on the crystallization behavior of poly(lactic acid) (PLA) both isothermally and non‐isothermally was studied using differential scanning calorimetry and polarized optical microscopy. Two distinct crystal forms (α and α′) were investigated under normal conditions of crystallization for different molecular weights. Using microscopy, the growth rate of spherulites was measured and the nucleation rate was estimated. Heterogeneous nucleation and morphology with a variant α and α′ forms have been proposed. Spherulites from low molecular mass PLA contained more interlamellar amorphous phase. In addition, the results showed more rapid crystallization of α′ than the α form in isothermal conditions.