An investigation of the utilisation of African locustbean seed oil in the preparation of alkyd resins

Abstract

Preparation of alkyd resins using phthalic anhydride and glycerol modified with African locustbean seed oil was investigated. The oil was solvent extracted with petroleum spirit (60–80°C). The oil content of the seed ranged from 15 to 20%. Three grades of alkyds formulated to contain 27% (I), 50% (II) and 60% (III) oil were prepared using a recipe containing various amounts of phthalic anhydride, glycerol and African locustbean seed oil employing the alcoholysis method. The progress of reaction was monitored by determining the acid value of the aliquot of the reaction mixture at regular time intervals. The acid value decreased as the reaction progressed. The rate of decrease was higher at the initial stages of reaction and depended on the amount of reactants. Kinetic study showed that the initial stages of the reaction followed a second-order rate law, after which deviation was observed. The extent of reaction as determined at this region ranged from 57.9 to 63.5%, indicating an appreciable degree of conversion. The average degree of polymerisation at this point ranged between 2 and 3, and this suggests formation of low molecular weight species and branching at short intervals along the alkyd chains. The second-order rate constants for the linear portion were 6.05×10−5 , 12.51×10−5 and 5.98×10−5 g (mg KOH)−1 min−1 for samples I, II and III, respectively. The oil is essentially a semi-drying oil.