The influences of UV-photocrosslinking on crystallite structure and nonisothermal crystallization kinetics of polyethylene (PE) were investigated by optical microscope (OM) and differential scanning calorimetry (DSC) at different cooling rates, respectively. The observation of crystallite structure showed that, due to crosslinking of molecular chains of PE, the PE spherulites grow more imperfectly with increasing gel content. The Avrami analysis modified by Jeziorny was applied to describe the nonisothermal crystallization process of virgin PE and photocrosslinked PE (XLPE) samples. The values of half-time of crystallization t1/2 and the parameter Zc showed that the crystallization rate increased with increasing cooling rates for both XLPE and virgin PE, but the crystallization rate of XLPE is lower than that of virgin PE at the same cooling rate. The activation energies were estimated by the Kissinger method, and the values were 176.7 and 197.1 kJ/mol for virgin PE and XLPE, respectively, indicating that UV-photocrosslinking might hinder the overall nonisothermal crystallization process of PE. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
The influences of UV-induced photodegradation on the nonisothermal crystallization kinetics of polypropylene (PP) were investigated by differential scanning calorimetry. The Avrami analysis modified by Jeziorny, Ozawa method, and a method modified by Liu were employed to describe the nonisothermal crystallization process of unexposed and photodegraded PP samples. Kinetics studies reveal that the rates of nucleation and growth may be affected differently by photodegradation. A short-term UV-irradiation may accelerate the overall nonisothermal crystallization process of PP, but a long-term UV-irradiation should impede it. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006
