Thermal and mechanical properties and water absorption of sodium dodecyl sulfate-modified soy protein (11S)

The thermal and mechanical properties and water absorption of sodium dodecy l sulfate (SDS)-modified 11S soy protein and molded plastics made from it w ere studied using differential scanning calorimetry (DSC), dynamic mechanic al analysis (DMA), mechanical tests, and scanning electron microscopy (SEM) . The DSC results showed that both the temperature and enthalpy of thermal denaturation of modified 11S solutions decreased as the SDS concentration i ncreased. Nonfreezing water of the modified 11S solution had a minimum valu e at 1.0% SDS, The ordered structure of SDS-modified 11S protein was recove red and/or newly formed during the freeze-drying process. Both DSC and DMA results showed that SDS was a plasticizer of 11S,,and the glass transition temperature of modified 11S plastics decreased with increasing SDS concentr ation, Both the tensile strength and elongation of modified 11S plastics fi rst decreased and then increased as the SDS concentration increased, and 5. 0% SDS-modified 11S plastic had the highest tensile strength and elongation . The SEM observations supported these results. A water-absorption test sho wed a reduction in the water resistance of 11S plastics after SDS modificat ion. The rate of water absorption increased with increasing SDS concentrati on. The hydrophobic interaction between SDS molecules and 11S protein was f ound to have important effects on the thermal and mechanical properties and the water absorption of 11S plastics, (C) 2001 John Wiley &: Seas, Inc. J Appl Polym Sci 81: 166-175, 2001.