Effects of multi-walled carbon nanotubes grafted polycaprolactone on crystallization behavior and thermal stability of poly(L-lactic acid)

The hydroxylated multi-walled carbon nanotubes (MWCNTs-OH) initiated the ring-opening polymerization of ε-caprolactone (ε-CL), and polycaprolactone (PCL) grafted MWCNTs-OH (MWCNTs-OH-g-PCL) was prepared. The MWCNTs-OH-g-PCL/poly(L-lactic acid) (PLLA) composites were obtained by solution blending which had different contents of MWCNTs-OH-g-PCL. The grafted product was characterized by FTIR. It is found that MWCNTs-OH-g-PCL exhibits a carbonyl (C=O) stretching vibration peak in PCL at near 1 720 cm^-1, indicating that the grafted product is synthesized successfully. The effects of MWCNTs-OH-g-PCL on the crystallization behavior and thermal stability of PLLA homopolymers were investigated by DSC, polarized optical microscope (POM) and TGA. The results show that the crystallinity and the optimum temperaturerate of isothermal crystallization of the MWCNTs-OH-g-PCL/PLLA composites increase by the heterogeneous nucleation of MWCNTs-OH-g-PCL and the plasticization of PCL. The results also show that the grafting amounts of PCL in the MWCNTs-OH-g-PCL is 66%, and the decomposition temperature of the MWCNTs-OH-g-PCL/PLLA composites increases by about 30℃.