Extrusion and Characterization of Soy Protein Film Incorporated with Soy Cellulose Microfibers

A biodegradable alternative material to synthetic plastics was explored in this study through the extrusion of soy protein isolate (SPI) composite films containing soy cellulose microfibers (SMF). SMF were isolated from soy pods and stems using a chemo-mechanical method. The fibers produced through successive treatments were characterized by microscopy, x-ray diffraction, and Fourier transform infrared analysis. SMF/SPI composite films (0.08 to 0.3 mm thick), containing different concentrations of cellulose fibers, were produced using a single-screw extruder (0.625 '' screw; 24 : 1 L/D ratio; 100-120 min(-1); 120 to 150 degrees C barrel temperature) and characterized. Homogenous films with uniform distribution of SMF were obtained with the highest concentration of 0.5% w/w SMF/SPI. Increasing fiber content resulted in the formation of aggregates. As with other protein films, mechanical properties of the extruded pristine SPI and composite films were negatively affected by humidity. At the optimal concentration of 0.25% w/w SMF/SPI, films exhibited improved mechanical performance at elevated relative humidity (84%) when compared to the pristine SPI films.