Phase Behaviors of PU/SPI Green Composites Using SAXS Profiles

Abstract

ABSTRACTA series of polyurethane (PU) green composites have been synthesized with varying amounts, namely 0, 2, 4, 8, and 12 wt% of soya protein isolate (SPI) by two methods. In the first method, castor oil (CO) and toluene‐2,4‐diisocyanate (TDI) molar ratio is CO/TDI : 1/1 with varying amounts of the SPI content. In the second method, the molar ratio of TDI is calculated by considering the –OH groups of both CO and SPI. We made the assumption that, in the first method, SPI acts as a filler and in the second method SPI is one of the coreactants in PU formation. The mechanical properties of the fabricated PU/SPI green composites are evaluated; and it is found that the tensile strength increases up to 8 wt% of SPI, and a further increase in SPI leads to reduction in the tensile strength. The small angle x‐ray scattering profiles have been used to evaluate the arrangement of amorphous (A) and crystalline (C) regions in the PU/SPI green composites in a scale of about 700 Ǻ by considering the variation in scattered intensity with scattering angles ranging from 0.3° to 1.5°. For this purpose, a linear paracrystalline model is used. In this study, the exponential distribution of phase lengths gives a good agreement between the measured and computed data on the basis of a linear paracrystal model. It is observed that there are significant changes in the distribution of phase lengths due to changes in the composition and chemical structure of PU/SPI composites obtained by methods 1 and 2.