Isothermal crystallization kinetics and melting behavior of PLLA/f-MWNTs composites

Poly(l-lactide) (PLLA) and functionalized multi-walled carbon nanotubes (f-MWNTs) were used to prepare PLLA/f-MWNTs composites via solution blending. The structure and morphology of f-MWNTs were characterized using FT-IR and SEM. The spherulitic morphologies, isothermal crystallization kinetics, and melting behavior of the resulting PLLA/f-MWNTs composites were investigated by POM and DSC, respectively. Both Avrami and Lauritzen–Hoffman kinetics models are used to quantitatively evaluate the crystallization half-time t _1/2, the nucleation constant K _g, and the work of chain folding q of PLLA and its composites. Temperature modulated DSC was used to investigate the mechanism of overlapped endothermic and exothermic peaks of PLLA/f-MWNTs composites. The results indicated that the SiO₂ coating on the MWNTs could react with coupling agent KH-550 leading to the formation of f-MWNTs, which can be evenly dispersed in PLLA matrix. A decrease of spherulite size and an increase of crystallization rate were observed from POM measurements for PLLA/f-MWNTs. The multiple melting behavior can be attributed to the melt-recrystallization process of PLLA/f-MWNTs composites at certain temperature.