Isothermal crystallization kinetics of multi-walled carbon nanotubes-graft-poly(ε-caprolactone) with high grafting degrees

The isothermal crystallization kinetics of poly(epsilon-caprolactone) (PCL) grafted on multi-walled carbon nanotubes (MWNTs-g-PCL) with high grafting degrees were studied and compared with those of neat PCL and a PCL/MWNTs blend. The Avrami exponent n altered from 3.0 for the neat PCL to nearly 2.0 for the grafting polymers. The grafting polymers exhibit a significantly faster crystallization rate but lower crystallinity than the neat PCL and PCL/MWNTs blend. In the grafting polymers, MWNTs exert both stronger nucleation and confinement effects on the crystallization of PCL than those for the PCL/MWNTs blend. The grafting density affects crystallization of PCL more severely than the molecular weight of the grafting PCL. The crystallization activation energy of the grafting polymers is smaller than that of the PCL/MWNTs blend but larger than that of the neat PCL. The grafted PCL chains are over-crowded and highly stretched, and the PCL crystals lie on the surface of MWNTs with the b-axis basically perpendicular to the surface.