Properties of soy protein isolate/polycaprolactone blends compatibilized by methylene diphenyl diisocyanate

Blends of soy protein isolate with 10, 20, 30, 40, and 50% polycaprolactone (SPI/PCL) alone or with addition of 0.5, 1.0, 2.0 and 5.0% methylene diphe nyl diisocyanate (MDI) were prepared by using an intensive mixer at 160 deg reesC for 10 min, and then milled through a 1 mm sieve. The blends and SPI were compression-molded at 150 degreesC for 5 min, cooled to 30 degreesC, a nd removed from the mold. Thermal and mechanical properties and water absor ption of the blends were studied by a differential scanning calorimeter (DS C), a dynamical mechanic analyzer (DMA), an Instron, a water absorption tes t, and a scanning electron microscope (SEM). The glass transition temperatu re (T-g) of SPI was found to decrease with increasing PCL contents in the b lends containing 2 wt% MDI. For 50/50 (SPI/PCL) blends, the T-g of SPI decr eased with increases in MDI content. Both DSC and DMA results showed that c ompatibility between SPI and PCL was improved with the addition of MDI. Mec hanical properties of the 50/50 (SPI/PCL) blends increased with increasing MDI concentrations. Strength of the SPI/PCL blends with 2 wt% MDI decreased , and elongation of the blends increased with increasing PCL concentration. Water resistance of the blends was improved significantly by increasing PC L concentration and by incorporating MDI. (C) 2001 Elsevier Science Ltd. Al l rights reserved.