Effect of plasticizer composition on the properties of injection molded cassava starch-based bioplastics

Sustainability has led to an exponential increase in the interest for using renewable resources. The abundance of starch in nature has promoted the production of starch-based bioplastics through widespread industrial techniques employed for conventional polymers, such as injection molding (IM). This research specifically aims to assess the effect of different plasticizers (i.e., glycerol, glycerol/water) on the properties of cassava (Manihot esculenta) starch bioplastics obtained through IM. Through dynamic mechanical analysis (DMA) and tensile tests, viscoelastic and mechanical properties of the bioplastics at different plasticizer to starch ratios (30-40 %, w/w) were analyzed. Other properties, such as water uptake capacity (WUC) or soluble matter loss were studied and related to the structure of the materials analyzed via scanning electron microscopy and X-ray diffraction. The effect of relative humidity (RH) on dynamic mechanical response of bioplastics was explored. Mixed plasticizer fractions, including glycerol and water, gave rise to hardened materials with rougher surfaces that were dramatically softened at both low and high RH. The low WUC and uniform structure displayed by materials produced from cassava starch and 30 % of glycerol might be of interest for its application in food packaging due to their optimal performance with temperature at high RH (80 %).