Isothermal and nonisothermal crystallization kinetics of poly(ε-caprolactone)/multi-walled carbon nanotube composites

Differential scanning calorimeter (DSC) and polarized optical microscopy (POM) have been used to investigate the isothermal and nonisothermal crystallization behavior of poly(epsilon-caprolactone) (PCL)/multi-walled carbon nanotube (MWNT) composites. PCL/MWNT composites have been prepared by mixing the PCL polymer with carboxylic groups containing multi-walled carbon nanotubes (c-MWNTs) in tetrahydrofuran solution. Raman spectrum of c-MWNT indicated the possible presence of carboxylic acid groups at both ends and on the sidewalls of the MWNTs. The TEM micrograph showed that the c-MWNT is well separated and uniformly dispersed in the PCL matrix. DSC isothermal results showed that the introduction of c-MWNT into the PCL initiates strongly heterogeneous nucleation, which induced a change of the crystal growth process. The activation energy of PCL significantly decreases by adding 0.25 wt% c-MWNT into PCL/c-MWNT composites and then increases as c-MWNT content increases. The result demonstrates that the addition of c-MWNT into PCL induces the heterogeneous nucleation at lower c-MWNT content and then inhibits the polymer chain transportation ability during crystallization at higher c-MWNT content. In this study, we have also studied the nonisothermal crystallization kinetics and melting behavior of PCL/c-MWNT composites at various cooling rates. The correlation among isothermal and nonisothermal crystallization kinetics and melting behavior of PCL/c-MWNT composites can be also discussed.