Design of Shellac-Based Film with Improved Mechanical Properties through Composite Formation with Clay
The objective of this study was to explore the effect of clay on mechanical and related properties of shellac (SHL) films. The SHL was dissolved in ammonia solution, and then casted into the film. For SHL-clay composite film, bentonite (BTN) which is popular clay in pharmaceuticals, was added and well dispersed before casting. The SHL and SHL-BTN composite films were then comparatively characterized. The results showed that SHL-BTN composite films were stiffer than SHL films since the modulus was 3 times higher. However, the percent elongation was lower, suggesting the more fragility of composite film. The drawback of composite film was solved by adding of polyethylene glycol. The percent elongation of composite film, puncture strength and modulus were higher than those of SHL film. However, BTN may be dispersed in the film without any interaction of shellac molecules since the FTIR spectrum of SHL-BTN composite film did not change as compared to physical mixture of SHL and BTN. The knowledge gained should provide an alternative way of modification of shellac properties for coating.