Properties of reactively blended soy protein and modified polyesters

The compatibilizing effect of anhydride groups attached to a polyester was examined while blending soy protein and a biodegradable polyester. Three different polyesters grafted with anhydride functional groups were used as compatibilizers for blending with soy protein concentrate, soy flour, and soy isolate. The processing conditions for these blends in a twin screw extruder and injection-molding machine were evaluated and the physical and mechanical properties of these blends were determined. The concentrations of soy protein and compatibilizer were varied to achieve optimum mechanical properties, exploring the various limits of operating conditions. The dynamic mechanical properties were determined using a rheometric mechanical spectrometer (RMS-800). The enthalpy of fusion was determined using a differential scanning calorimeter. Blends containing compatibilizer gave enhanced tensile strength when compared to blends without compatibilizer. The morphology of these blends was investigated with the help of an optical microscope and X-ray diffraction was used for crystallinity studies. Water and oil absorption by these blends were determined for a period of 25 days.