Investigation of soy protein blends prepared by simultaneous plasticization and mixing

In this research, plasticization and mixing of soy protein concentrate (SPC) with poly(butylene adipate-co-terephthalate) (PBAT) were carried out simultaneously in a single-step compounding process. The effects of water content in SPC prior to compounding and SPC loading level on the plastic behavior of SPC were investigated. Compatibilizer was found to be indispensible to achieve high performance blends and displayed great influence on SPC phase morphology in blends. The influences of these three factors on the phase structure of PBAT/SPC blends and the structure-property relationship were investigated in detail. Critical water content in pre-compounding SPC and SPC loading level for the formation of percolated SPC structure were revealed.;In the compatibilized blend system, the plastic deformation of SPC was determined by the deformability which was controlled by plasticization of SP and shear stress exerted on SP which was controlled by SPC loading level in this study. One of the important advantages of processing SPC as plastic is that the SPC particles can be turned into elongated filaments which require smaller maximum packing density for the formation of percolated structure. The blends with SPC percolated structure displayed overall superior mechanical and physical properties compared with the blends consisting of ordinary particulate SPC filler.;At a given concentration, the interconnectivity of the SPC domains was directly determined by the aspect ratio of the SPC particles. The formation of full percolated structure depended on both SPC aspect ratio and SPC loading level. Quantitative analysis of the filler aspect ratio was also performed in this research. Detailed phase morphology of the blends was revealed by transmission electron microscopy (TEM), atomic force microscopy (AFM) and scanning electron microscopy (SEM). Study of dynamic rheology also confirmed the percolated network structure. Interestingly, a correlation between SPC loading level and water content in pre-compounding SPC existed and its influence in SPC phase structure and properties of the resultant blends were studied. Tensile and dynamic mechanical properties were greatly improved for those blends with superior percolated structures. Impact toughness and thermal properties of PBAT/SPC blends were also characterized. The molecular weight change of PBAT in blends and influence of processing on SP solubility were examined.