Chiang Mai Journal of Science

Biodegradable plastics have become interesting alternative materials in packaging applications, because of their lower environmental impacts. Among these, polylactide (PLA) has played a key role, pertaining to many of its excellent properties. However, its commercialization as packaging materials for products sensitive to light, gas, or temperature changes, such as fresh vegetables and fruits, is challenging, due to its moderate gas transmission rates, and lower mechanical properties, compared to conventional plastic products. One effective method to solve this problem is the adding of inorganic fillers to the PLA resin to improve its properties. In this study, PLA bio-composite films have been developed by introducing low-cost silica particles as a reinforcing agent. To effectively achieve property enhancements, compatibility between the 2 components needs to be improved. Surface modification of the inorganic silica particles is conducted by coating with poly (lactic acid-grafted-chitosan) copolymer (PCT). Commercial silica particles (c-silica), with average particle size of 1-5 mm, were coated with PCT copolymer, employing a phase inversion emulsification (PIE) technique. After the coating process, the average size of the modified particles (m-silica) decreases to 17 nm, as the coated PCT layers on the particle surfaces prevent agglomeration of the silica particles by providing steric repulsion. The resulting m-silica and c-silica are then used in the preparation of PLA/silica bio-composite films by varying silica types and their contents from 0-5.0 wt%. Thermal and mechanical properties, light transmission, and gas permeability of the 2 bio-composite systems, are compared.  PLA/m-silica exhibit greater tensile behaviors at all particle compositions. Variations in CO2/O2 permeability of bio-composite films can be optimized by changing the silica compositions. At 5.0 wt% of m-silica, the highest decrease in light transmission at 4, 8, and 16% for UV-A, UV-B, and visible regions, respectively, are observed.  The resulting PLA/m-silica bio-composite films have high potential for use as smart packaging for fresh vegetables and fruits.