Isothermal and Nonisothermal Cold Crystallization Behaviors of Asymmetric Poly(l-lactide)/Poly(d-lactide) Blends

Abstract

Isothermal and nonisothermal cold crystallization behaviors of asymmetric poly(l-lactide) (PLLA)/poly(d-lactide) (PDLA) blends at PDLA loadings of 0–20 wt % were investigated in this work. Formation of the stereocomplex in the blends was confirmed by differential scanning calorimetry and wide-angle X-ray diffraction. For both neat PLLA and its blends, the overall isothermal cold crystallization rates increase with increasing crystallization temperature; moreover, the overall isothermal cold crystallization rates of PLLA are faster in the blends than in neat PLLA, indicative of the nucleating agent effect of the stereocomplex formed in the blends. Crystallization mechanism and crystal structure of PLLA remain unchanged despite the PDLA loading. For the nonisothermal cold crystallization, the crystallization process of PLLA is accelerated by increasing both heating rate and the PDLA loading up to 10 wt %. The Ozawa equation failed to fit the crystallization process, while the Tobin equation could describe it well in the relative degree of crystallization range of 0–75%.