Effect of metakaolin content on mechanical and water barrier properties of cassava starch films

Abstract

The development of biodegradable polymers has seen considerable growth in recent decades, in particular biopolymer films based on cassava, potato and corn starch for packaging applications. Unfortunately, these biopolymers have weak thermomechanical properties. Their reinforcement with mineral materials could improve the physicochemical properties. This work aims to assess the effect of the metakaolin content on the mechanical and water barrier properties of cassava starch-based films plasticized with glycerol. Bioplastics containing different amount by mass of metakaolin have been developed through the casting-evaporation method. Mixtures containing 0, 5, 10 and 15 wt% of metakaolin (MKB) were identified as BP (Bioplastic), BPMKB5 (Bioplastic reinforced with 5 wt% of MKB), BPMKB10 (Bioplastic reinforced with 10 wt% of MKB) and BPMKB15 (Bioplastic reinforced with 15 wt% of MKB), respectively. The results of physico-chemical analyses revealed a significant improvement in the mechanical tensile strength and hydric properties of the obtained biocomposites. Increasing the content of metakaolin resulted in more rigid bioplastics by increasing both Young's modulus and stress at break. However, the elongation at break decreased. Also, the coefficients of permeability, diffusion and solubility declined with increasing metakaolin content. The level of 10 wt% metakaolin was suitable for obtaining a bioplastic with moderate rigidity and ductility. This level of metakaolin resulted in less brittle bioplastics with acceptable mechanical strength for use in food packaging. Therefore, the valorization of metakaolin in biodegradable food packaging likely to replace synthetic polymers was possible.