Showing papers by "Laura Monica Gorghiu published in 2005"

Kinetic approach on stabilization of LDPE in the presence of carnosic acid and related compounds. I. Thermal investigation

Abstract: Carnosic acid and similar compounds exhibit antioxidant behavior in a polyethylene matrix. Thermal resistance of LDPE was investigated at three temperatures (190, 200, and 210°C) by isothermal chemiluminescence. The main kinetic parameters: oxidation induction period (ti), half oxidation time (t1/2), maximum oxidation time (tmax), and propagation rate of oxidation (voxmax) were calculated. The inhibition of thermal degradation is proved by the values of these parameters relative to unstabilized polymer: the induction times of stabilized low density polyethylene are of one order of magnitude greater that raw polyethylene, and half oxidation periods are three to five times longer than initial LDPE. Thermal aging of protected low density polyethylene occurs at a much slower rate in comparison with unmodified LDPE. The depletion of stabilizers was also evaluated and the kinetic characteristics (the half-life and the rate constant of consumption for each antioxidant) at three concentrations of all tested additives (0.125, 0.25, 0.50, and 0.75% w/w) were determined. The effectiveness of stabilization was depicted by two values of activation energies calculated from oxidation induction times and maximum oxidation periods. Some considerations on stabilizing mechanism are presented. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1571–1577, 2005

Synergistic effects of EB irradiation and heat on EVA electrical insulators

Abstract: Radiation/thermal degradation is discussed as a successful endurance check. EVA samples were subjected to electron beam irradiation at 12, 30, 60 and 90 kGy. Heat treatment was performed in air at 120 °C for 72 h and 120 h. Chemiluminescence (CL) investigations on EVA specimens were carried out at 200, 210 and 220 °C. Several kinetic parameters such as oxidation induction time (ti), half-oxidation time (t1/2), maximum oxidation rate ( v ox max ), maximum time of thermal oxidation (tmax) and other chemiluminescence features were obtained from the time dependencies of the CL intensity. While the ageing factors of processed EVA samples reveal a constant value for two testing temperatures (200 and 210 °C), the co-operative factors that describe a combined (synergistic) degradation present higher than unity values, either for the oxidation rates or for the maximum CL intensity measured for all irradiation doses. They increase linearly with dose.