Bi-layer materials based on thermoplastic corn starch, polylactic acid and modified polypropylene

Abstract

Currently, the development of environmentally friendly materials with suitable properties for industrial use has become of great importance. In this work, bilayer materials were developed by assembling thermoplastic- corn starch monolayers (TPS) combined with semi-crystalline polylactic acid (PLAs) monolayers and maleic anhydride grafted polypropylene (PPMA). The presence of a potassium sorbate solution was evaluated as interface material. Structural properties (FTIR and SEM), interactions with water (water vapor transmission rate, solubility in water and moisture content) and biodegradation of the materials were evaluated. FTIR spectra showed that potassium sorbate promotes chemical interactions between TPS monolayers (-OH group) and PLA monolayers (C = O group) or PPMA (C-O-C, C-O, C-H groups). For their part, SEM micrographs reveal that when adding potassium sorbate, higher interfacial adhesion develops between TPS and PPMA than between TPS and PLAs. As for the interactions with water, when using a PLA or PPMA monolayer, due to its hydrophobic characteristics, the high permeability to water vapour and the sensitivity to liquid water that starch-based materials present would be avoided. Finally, the biodegradation test showed that TPS biodegrades faster than other materials, followed by PLA. The results obtained are interesting since the addition of an adhesive material to assemble the low chemical affinity monolayers would be avoided. The developed materials exhibit great potential for application as packaging in the food industry.