THE DEFORMATION AND FAILURE BEHAVIOR OF WHEAT-STARCH PLASTICIZED WITHWATER AND POLYOLS

The mechanical properties of starch plasticized with water and glycero l or xylitol have been studied in flexure at room temperature. The add ition of a polyol lowers the glassy modulus and the glass transition t emperature of the starch. With the addition of polyols, the fall in mo dulus with increasing water content at the glass transition becomes le ss sharp and shifts to lower water contents. The high strain deformati on shows that all samples fracture at a water content below 10% (wet w eight basis), a proportion of which tears at water contents in the ran ge 9%-10% and no fracture occurs in samples above about 10% water. Mic roscopy shows that there is evidence of permanent plastic deformation in fractured samples as the water content is increased to 10% water, a lthough there is a negligible change in fracture stress and strain.