Thermal and mechanical properties and water absorption of guanidine hydrochloride-modified soy protein (11S)

Thermal and mechanical properties and water absorption of guanidine hydroch loride (GuHCl)-modified 11S soy protein and molded plastics made from it we re studied using differential scanning calorimetry (DSC), dynamic mechanica l analysis (DMA), mechanical tests, and scanning electron microscopy (SEM). The DSC results showed that the denaturation temperature of GuHCl-modified 11S solutions was higher than that of the control sample and the high conc entration GuHCl completely denatured 11S. Nonfreezing water of the modified 11S solution exhibited a minimum value at 0.9M GuHCl. Both DSC and DMA res ults showed that GuHCl was a plasticizer of 11S and the glass transition te mperature of modified 11S plastics decreased with increasing GuHCl concentr ation. Both the stress and strain of modified 11S plastics reached their hi ghest values at a 0.9 GuHCl concentration. The SEM observations supported t hese results. A water-absorption test showed an improvement in the water re sistance of 11S plastics with GuHCl modification. The water absorption had a minimum value at 0.9M GuHCl. The interaction between GuHCl molecules and 11S protein was found to have important effects on the thermal and mechanic al properties and the water absorption of 11S plastics. (C) 2000 John Wiley & Sons, Inc.