Effect of cardanol-based plasticizers on thermoplastic cassava (Manihot esculenta) starch properties

Thermoplastic cassava starch films were synthesized using native cassava starch plasticized with glycerol and cardanol-based plasticizers at 70:30, 80:20, and 90:10 ratios. Cardanol-based plasticizers were cardanol, epoxidized cardanol, and cardanol polyol. The effectiveness of the synthesis of epoxidized cardanol and cardanol polyol was assessed by Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (NMR) spectroscopy. The starch bioplastics were extruded in 3 mm filaments and characterized by tensile testing, water absorption, humidity and thermogravimetric analysis. Results showed a strong effect of the concentration of cardanol-based co-plasticizers on the mechanical properties with 20-fold increase in modulus, 4-fold increase in tensile strength, and half decrease in elongation. The moisture content was also significantly decreased in increasing co-plasticizer content. SEM micrographs showed a good compatibility, but also some voids. No significant difference, however, was observed for the water absorption properties. Thermal resistance was also improved for cardanol and epoxidized cardanol films.