Characterization of Natural Resin Shellac by Reactive Pyrolysis-Gas Chromatography

Abstract

Shellac is one of the thermosetting resins of animal origin secreted by the lac insect Kerria lacca which parasitically grows on some types of trees-such as mulberries commonly found in India, Thailand, Myanmar and south area of China. Shellac has been used as thermoplastics, adhesives and sealants, insulating materials and coating materials in various fields such as industrial material, medicine and food ingredient due to its various unique properties such as thermoplasticity, oil-resistibility, cohesiveness and insulating ability along with its non-poisonous nature [1]. Shellac is provided as a refined form of the stic-lac resin (raw shellac, just collected from twigs of the trees) consisting of resin (70–80%), wax (6–7%), coloring matter (4–8%) and others (15–25%) such as debris and moisture. The resin portion constituting the backbone of shellac is a complex mixture of polyesters consisting of a number of closely related sesquiterpene acids of the cedrene skeleton, mainly jararic acid and laccijalaric acid, and hydroxy-fatty acids, mainly threo-aleuritic acid, which can be separated into about 30% of soft resin (single ester) and about 70% of hard resin (polyesters consisting of several resin acid components) [1]. The chemical composition of shellac which affects its mechanical and thermal properties often varies to some extent depending on nature of the host trees on which the insect grows, the species of the insect and the environmental conditions. Therefore, it is important to know the subtle differences in the chemical composition of shellac.