Cold crystallization kinetics and spherulitic morphologies of SiO₂-MWNTs/polylactide composites

In order to investigate the effects of multi-walled carbon nanotubes (MWNTs) on the cold crystallization kinetics and spherulitic morphologies of polylactide (PLA), PLA and nano-SiO₂ modified MWNTs (SiO₂-MWNTs) which was surface-coated with nano-SiO₂ and grafted with silane couple agent were selected as matrix and modifying agent respectively to prepare SiO₂-MWNTs/PLA composites via solution blended process. DSC, polarized optical microscope, Jeziorny model and Johnson-Mehl-Avrami model were used to investigate the non-isothermal cold crystallization kinetics and spherulitic morphologies of composites. The results indicate that SiO₂-MWNTs can act as heterogeneous nucleating agent which decreases the cold crystallization temperature, increases the nucleation rate and the activation energy of crystal growth of SiO₂-MWNTs/PLA composites effectively. Cold crystallization process of SiO₂-MWNTs/PLA composites is mainly dominated by nucleation, and the addition of SiO₂-MWNTs can improve crystallization rate and crystallinity of the composites simultaneously. The spherulitic size of PLA which is cold crystallized is smaller than that of melt cooling crystallized. The influence of SiO₂-MWNTs content on cold crystallization spherulitic size is much smaller than that of it on melt cooling crystallization spherulitic size. The conclusions have guiding significance for optimizing the crystal structure and properties of PLA and preparing high-performance PLA composites.