Effect of molecular weight on isothermal crystallization kinetics of multi-walled carbon nanotubes-graft-poly(ε-caprolactone)

Three multi-walled carbon nanotubes-graft-poly(epsilon-caprolactone) (MWNTs-g-PCL) samples with different PCL chain lengths but the same grafting density were prepared and isothermal crystallization kinetics of MWNTs-g-PCLs were studied. These samples enable us to study the effect of chain length on crystallization kinetics independently without the interference of grafting density. The result shows that MWNTs can exert both nucleation and confinement effects on crystallization of the grafted PCL. The nucleation effect leads to a higher T-c and T-m a faster crystallization rate and a smaller crystal size of the grafting polymers. On the other hand, the confinement effect results in restricted crystal growth, lower crystallinity and larger crystallization activation energy of MWNTs-g-PCLs, as compared with the neat PCL. The crystallization behavior of the grafting polymers also varies greatly with the molecular weight of the grafted PCL chains. It is observed that the Avrami exponent, crystal size and crystallization activation energy decrease gradually as the chain length decreases, showing that the confinement effect of MWNTs becomes stronger and the crystal growth is restricted more severely in the grafting polymer with a shorter chain length. As revealed by the reduced grafting density, the PCL chains are more crowded and stretched when the grafted PCL chains are longer, leading to a smaller half-crystallization time and thus a faster crystallization rate. (C) 2013 Elsevier Ltd. All rights reserved.