Crystallization kinetics and melting behaviors of poly(l-lactide)/graphene oxides composites

Poly(l-lactide)/graphene oxides (PLLA/GOs) composites containing different concentrations of GOs were prepared. Polarized optical microscope (POM) was used to characterize the isothermal crystallization morphologies of both neat PLLA and PLLA/GOs composites. Differential scanning calorimetry (DSC) was used to investigate the isothermal and nonisothermal crystallization and subsequent melting behaviors of the PLLA in different samples. Our results showed that GOs exhibited great role in improving the crystallization ability of the PLLA. During the isothermal crystallization process, addition of the only 0.1 wt% GOs accelerated the crystallization of the PLLA greatly. However, further increasing the concentration of the GOs was unfavorable for the crystallites perfection of the PLLA matrix, resulting in the decrease of equilibrium melting point accordingly. During the nonisothermal crystallization process, the crystallization behavior of the PLLA was found to be greatly dependent upon both the cooling rates and the concentration of the GOs. The corresponding crystallization kinetics was investigated and analyzed. Interestingly, it was observed that even if the cooling rate was increased up to 10 °C/min, the composites with high concentration of the GOs still show high crystallinity. This is very significant from a viewpoint of whether enhancing processing efficiency or preparing new PLLA material with excellent physical properties.