The effectiveness of adding epoxidized neem oil (ENO) in poly(vinyl chloride) (PVC) to enhance heat stability was investigated. Neem oil, of vegetable extract, was characterized for its fatty acid profile and other properties. The virgin oil was epoxidized at 60°C with peroxymethanoic acid (performic acid) generated in situ in the reaction mixture by reacting hydrogen peroxide and methanoic acid. ENO was characterized by FTIR and NMR studies, and the degree of epoxidation was measured with iodine value and oxirane oxygen content. Solubility parameters of neem oil and ENO were estimated. Thermal degradation of PVC-containing ENO was studied using the static heat stability test and artificial aging at temperatures of 100, 110, 120, and 130°C. Results were compared with the samples prepared with conventional heat stabilizers systems used in PVC, such as Ca/Zn stearates and mixtures of both Ca/Zn stearates and ENO. The changes in elastic modulus of the ENO/PVC combination and the conventionally stabilized Ca/Zn system during aging were kinetically modeled, and the rate constants for the degradative influence of modulus were determined. The activation energies and preexponential factors for the degradative process were obtained from Arrhenius plots and their relationship through a compensation effect was found. In general, ENO was found to be an effective retarder of the degradation of PVC; use of 10 phr level of ENO showed the least degradation with the highest activation energy. A synergistic effect of ENO and Ca/Zn stearate system was also observed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
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