Studies on nonisothermal crystallization of HDPE/POSS nanocomposites

The nonisothermal crystallization of HDPE/POSS nanocomposites (POSS content varying from 1 to 10 wt%) was studied using differential scanning calorimetry (DSC) technique. The Ozawa approach failed to describe the crystallization behaviour of nanocomposites, whereas the modified Avrami analysis could explain the behaviour of HDPE/POSS (90:10) nanocomposite only. The value of Avrami exponent n for HDPE/POSS (90:10) nanocomposite ranged from 2.5 to 2.9 and decreased with increasing cooling rate. It is postulated that the values of n close to 3 are caused by spherulitic crystal growth with heterogeneous nucleation while simultaneous occurrence of spherulitic and lamellar crystal growth with heterogeneous nucleation account for lower values of n at higher cooling rates. A novel kinetic model by Liu et al. was able to satisfactorily describe the crystallization behaviour of HDPE/POSS nanocomposites. Presence of POSS did not cause significant change in the activation energy for the transport of polymer segments to the growing crystal surface. POSS molecules exhibit nucleation activity only at 10 wt% loading in HDPE and are not effective nuclei at lower loadings.