Influence of polycaprolactone-triol addition on thermal stability of soy protein isolate based films

Abstract

The influence of polycaprolatone-triol (PCL-T) on the thermal degradation properties of soy protein isolate (SPI)-based films was studied by thermogravimetry and infrared spectroscopy under nitrogen atmosphere. The results showed that in the absence of PCL-T the thermal degradation began between 292 °C (pure SPI films) and ca. 264 °C (SPI/SDS films with more than 20% of SDS), and these values decreased further to the range 250–255 °C for SPI/SDS/PCL-T films. At the same time, the temperature of maximum degradation rate ( T max) decreased from 331 °C (pure SPI film) to ca. 280 °C for SPI/SDS/PCL-T films with 39% PCL-T content. This behavior was also confirmed by the activation energy ( E) values associated with the thermal degradation process. Apparently, the low thermal stability of PCL-T as compared to other film constituents, along with its plasticizer characteristics, is responsible for the decreased stability of SPI/SDS/PCL-T films. The FTIR spectra of gas products evolved during the thermal degradation indicated the formation of OH, CO 2, NH 3 and other saturated compounds, suggesting that the reaction mechanism involved simultaneous scission of the C(O)–O polyester bonds and C–N, C(O)–NH, C(O)–NH 2 and –NH 2 bonds of the protein.