Gelatinized and nongelatinized starch/pp blends: effect of starch source and carboxylic and incorporation

Due to the environmental impact caused by incorrect disposal and the non-biodegradability of synthetic polymers, the packaging sector seeks renewable raw materials. An alternative is the utilization of natural renewable polymer, such as thermoplastic starch (TPS), mixed with synthetics. However, the chemical incompatibility between these two materials leads to the use of a compatibilizer agent. Even though the compatibilizer effect of carboxylic acid on TPS blends have been studied, the correlation between the carboxylic acid and the starch source has not been investigated yet. Thus, this study focuses on the effects of added carboxylic acids (myristic (C14) and stearic (C18) acid) and the starch sources (corn, cassava, and potato) on the properties and microstructure of blends with TPS/PP (70/30). The results suggested that the compatibilizer effect of acids depends on the starch source and the length of the acid chain, where cassava blends with C14 showed better results. Acid insertion increased tensile strength and deformation at break, but reduced the elastic modulus, indicating a plasticizer effect. This behavior was related to the formation of amylose and lipid complexes (endogenous or added) during heating. Torque reduction and Tg displacement were also observed for acid blends. The SEM images showed two different morphological dispersions and a non-gelatinization effect due to the acid insertion. Results suggested that acids act differently according to the starch source.