Thermal behaviour of metal soaps from biodegradable rubber seed oil

Abstract

Soaps are a class of surface active compounds derived from natural oils and fats. Double decomposition reactions permit the synthesis of metallic soaps, which are long-chain carboxylates of metal ions, from alkaline ones such as sodium, potassium or ammonium soaps. Metallic soaps are commercially important as they find use in diverse applications such as driers in paints or inks, components of lubricating greases, heat stabilizers for plastics (especially PVC), catalysts and water proofing agents, fuel additives and cosmetic products amongst others. Many of these applications are related to the thermal properties of these compounds and the thermal behaviour of metal soaps in terms of decomposition processes is of great importance. Rubber seed oil (RSO) which is an unsaturated triglyceride abundantly available in Nigeria, India and Australia is an excellent starting material for metal soaps. In this study rubber seed oil having 2.2% myristic acid, 7.6% palmitic acid, 10.7% stearic acid, 20.61% oleic acid, 36.62% linoleic acid, 22.5% linolenic acid was used in making barium, calcium, cadmium and zinc soaps. The thermal behaviour of soaps (Ba, Ca, Cd and Zn) of rubber seed oil for use as additives in the processing of poly(vinyl chloride) (PVC) was investigated by thermal gravimetry and differential scanning calorimetry. The stability of the soaps was examined by thermogravimetry up to 873 K at a constant heating rate of 10 °C min -1. The soaps were found to be thermally stable up to 473 K as they recorded less than 5% mass loss at this temperature with values of apparent activation energy for decomposition varying from 52 to 96 kJ mol-1. Differential scanning calorimetric studies of the soaps revealed melting and decomposition behaviour of metal soaps. © 2010 Akadémiai Kiadó, Budapest, Hungary.