Study on the Thermo-Mechanical and Biodegradable Properties of Shellac Films Grafted with Acrylic Monomers by Gamma Radiation

Shellac (SL) films were prepared by casting and were grafted with various acrylic monomers of different functionalities using gamma radiation. Different formulations of shellac with varying concentrations (3, 5 and 7%) of these acrylic monomers such as 2-hydroxyethyl methacrylate (HEMA), 2-ethylhexyl acrylate (EHA) and 1,4-butanediol diacrylate (BDDA) in methanol were prepared. The pure shellac and other treated films were then irradiated under gamma radiation (Co-60) at different doses (0.5-5 kGy) at a dose rate of 3.5 kGy/h where 1 Gy = 1 J/kg = 100 rads. The mechanical properties like tensile strength (TS) and elongation at break (Eb) of the prepared films were studied. The mechanical properties of the irradiated shellac films demonstrated superior values. Among the formulations, shellac grafted with BDDA (SL-g-BDDA) showed the highest TS and Eb values which were 543 and 168% higher than those of raw shellac films, respectively. The water uptake behavior of raw and treated films was also studied. The raw film showed 11% water uptake but HEMA containing film showed 67%. In the soil burial test, HEMA containing shellac film was rapidly degraded than other raw, EHA and BDDA grafted films. Thermal properties indicated that grafting of acrylic monomers decreased the melting temperature of the pure shellac films.