Abstract

Ximenia americana seed oil (XSO) and Balanites aegyptiaca seed oil (BSO) were soxhlet extracted and characterized. The iodine values were 158.3 and 102.6 gI₂ 100 g^-1 for XSO and BSO, respectively. The oxirane content for the epoxidized oil derivatives, EXSO and EBSO, were 4.9 and 4.1%, respectively. Kinetic studies of thermal degradation of poly (vinyl chloride), (PVC) in the temperature range, 170 to 190°C under nitrogen atmosphere were conducted in the presence of the oils and epoxidized derivatives. The effect of the oils was evaluated from the rate of dehydrochlorination at 1% degradation, R_DH and the time required for degradation to attain 1% conversion t_DH. The additives retarded dehydrochlorination rate of PVC. The mechanism of thermal stabilization of PVC by the oils was attributed to trapping of HCl through addition reactions of the latter with unsaturated fatty acids. The resultant order of stabilization was, EXSO > EBSO > XSO > BSO. The latter was consistent with the results of viscosity measurements on degraded polymer and from thermogravimetric studies. The order of stabilization was corroborated by the activation energies, (E_a) calculated from the rate constants of dehydrochlorination process. The highest value of 111.84 kJmol^-1 was obtained for PVC with 3 wt-% EXSO additive. In air, PVC was unstabilized by XSO and BSO and was adduced to dominant oxidative reactions of unsaturated fatty acids and consequent prevention of HCl-trapping addition reactions.

Key words: Thermal degradation, stabilization, poly(vinyl chloride), Ximenia americana, Balanites aegyptiaca, seed oils.