Abstract: The degradation behavior of three different types of lac films (seedlac, shellac, and bleached lac) was studied in terms of weight loss rate. Each type of lac film under investigation could be degraded naturally and the degradation rate increased with increasing soil moisture content and temperature but decreased with increasing soil pH. A dynamic model describing their degradation respectively was established. Under the same conditions, the degradation half-lives of bleached lac, seedlac and shellac decreased sequentially. Moreover, their pre- and post-degradation samples were characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and capillary viscosimeter, and the results showed that these three types of lac films presented no considerable changes in their molecular structure but revealed significant changes in their morphology and tissue and exhibited a remarkable decrease in their relative molecular weights after degradation.

Key words: lac, degradation, weight loss, relative viscosity