Corn protein-based thermoplastic resins: Effect of some polar and amphiphilic plasticizers

Homogeneous blends of corn gluten meal (CGM) and "polar" plasticizers (wate r, glycerol) or "amphiphilic" plasticizers [octanoic and palmitic acids, di butyl tartrate and phthalate, and diacetyl tartaric acid ester of mono-digl ycerides (DATEM)] were obtained by a hat-mixing procedure. The glass transi tion temperature (T-g) of the blends was measured by modulated differential scanning calorimetry and dynamic mechanical thermal analysis, as a functio n of plasticizer type and content (0-30% dwb). The plasticizing efficiency (i.e., decrease of T-g) at equal molar content was found to be proportional to the molecular weight and inversely proportional to the percent of hydro philic groups of the plasticizer. The migration rate of the plasticizers in the polymer was related to their physicochemical characteristics. It was a ssumed that polar substances interacted with readily accessible polar amino acids, whereas amphiphilic ones interacted with nonpolar zones, which are buried and accessible with difficulty. The temperature at which a thermopla stic resin of plasticized CGM could be formed was closely connected to the T-g of the blend.