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

Polyurethane elastomers were synthesized using polypropylene glycol (PPG 20 00) 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 behavi or of the polyurethanes in various solvents was investigated and the solubi lity parameter was determined. All these properties mere compared with thos e of polyurethanes containing 1,1,1-trimethylol propane (TMP) as the crossl inker. Starch-based polyurethanes exhibited better mechanical properties. T he effect of varying the starch:TMP ratio on the mechanical strength was al so studied. With increasing starch content, the tensile strength and elonga tion increased. The starch-based PUs exhibited two glass transitions, where as 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 biodegradabi lity in polyurethanes containing starch than in those containing TMP.