Effect of gamma-irradiation on thermally stimulated depolarization current spectra of polyethylene-grafted-poly(Acrylic acid)

The graft copolymerization process of polyethylene (PE) with acrylic acid is performed using a Co-60-gamma irradiator, and the samples are irradiated at different doses, 30, 50, 70 and 100 kGy with a dose rate of 0.55 Gy/s. Global thermally stimulated discharge current (TSDC) spectrum of irradiated and non-irradiated PE-g-AAc has been investigated from RT to similar to 440K. The TSDC spectrum of non-irradiated PE-g-AAc exhibited two relaxation processes. The first process is located at similar to 329 K, and the second one is at similar to 390 K. These processes are called dipolar and space charge relaxation, i.e. alpha- and rho-relaxation, respectively. On the other hand, the position of these processes is shifted towards a higher temperature for irradiated samples. The activation energy for alpha-relaxation process of non-irradiated samples is similar to 0.21 eV, while for irradiated samples, it is 0.34 eV. The thermal sampling technique (TS) has been applied to decompose the global TSDC spectrum of all samples into its elementary peaks. The molecular parameters, such as activation energy (E-a), pre-exponential factor (tau(0)), enthalpy (Delta H), entropy (Delta S) and Gibbs free energy (Delta G), are estimated for all samples. The compensation phenomenon has been verified for all samples in different ways, such as plotting ln tau(0) against E-a or entropy versus enthalpy.