Effect of soy protein isolate resin modifications on their biodegradation in a compost medium

This study presents the effect of Phytagel® and stearic acid modification of soy protein isolate (SPI) based ‘green’ resins on their biodegradation in composting environment. The composting process was monitored for up to 10 weeks and the degradation of the resins was characterized by weight loss, attenuated total reflectance infrared spectroscopy, differential scanning calorimetry and sol–gel analysis. The changes in the resin surface topography and microstructure during composting were also characterized using scanning electron microscopy (SEM). The gel fraction in SPI resin reduced significantly as a function of composting time indicating its fast degradation within 21 days. The stearic acid modified SPI resin (SAM-SPI) degraded at a slower rate than the SPI resin and Phytagel® modified SPI (PM-SPI) resin degraded at the slowest rate. Based on the spectroscopic analysis and differential scanning calorimetric studies, it was found that stearic acid was among the main residue in the case of SAM-SPI resin after composting and Phytagel® in the case of PM-SPI resin. The results of this study suggest that the biodegradation and hence, the service life of the SPI based resins can be controlled by changing the concentration of stearic acid or Phytagel® in the SPI resin.