Structure-property relationship in polyurethane elastomers containing starch as a crosslinker

Polyurethane elastomers were synthesized using polypropylene glycol (PPG 2000) as the polyol and starch as the multifunctional crosslinker in varying concentrations. Thermal and mechanical properties were measured by DSC, DMA and tensile tests. The morphology was examined by SEM. The swelling behavior of the polyurethanes in various solvents was investigated and the solubility parameter was determined. All these properties mere compared with those of polyurethanes containing 1,1,1-trimethylol propane (TMP) as the crosslinker. Starch-based polyurethanes exhibited better mechanical properties. The effect of varying the starch:TMP ratio on the mechanical strength was also studied. With increasing starch content, the tensile strength and elongation increased. The starch-based PUs exhibited two glass transitions, whereas TMP-based PUs exhibited one T-g. No significant difference in the T(g)s of the two PUs was observed. The activation energy of St-PU calculated from DMA was 69 kcal/mol. Soil degradation tests indicated greater biodegradability in polyurethanes containing starch than in those containing TMP.