DEFORMATION AND FRACTURE-BEHAVIOR OF WHEAT-STARCH PLASTICIZED WITH GLUCOSE AND WATER

The mechanical properties of wheat starch and the effects of plasticizers upon them are studied in flexure at 293 K. For compositions low in water and glucose the material is glassy, with a flexural modulus between 0.7 and 5.0 GPa. The addition of water and glucose to wheat starch plasticizes the material through its glass transition into a rubbery state. The flexural moduli of the rubbery samples are in the range 50 to 200 MPa, which is indicative of a partially crystalline polymer. For starch-water mixtures the glass transition occur in the water content range 18 to 20%. The addition of glucose progressively shifts the glass transition to lower water contents. At strains below 0.04 brittle failure is only observed in the glassy samples. The surface morphology of the fractured samples shows features typical of pure synthetic glassy polymers.