EXTRUDATES OF CORNSTARCH WITH UREA AND GLYCOLS - STRUCTURE MECHANICAL PROPERTY RELATIONS

Urea, various glycols and mixtures of these were tested as plasticizers for gelatinized cornstarch. Mixtures of cornstarch, urea and/or triethylene glycol, glycerol or propylene glycol were extruded into ribbons. Mechanical and structural properties of the ribbons were evaluated by tensile testing, DSC and NMR. Flexible ribbons were obtained only when enough urea or glycol was present to lower the glass transition temperature of the starch near or below room temperature. Ribbons containing high levels of urea were rather stiff, reflecting the low mobility of urea. Ribbons containing high levels of glycol were, in contrast, soft and weak. Samples extruded with mixtures of urea and glycols exhibited enhanced elongations at break. All samples became brittle at very low humidities and soft at high humidities.