Study of Effect of NCO/OH Molar Ratio and Molecular Weight of Polyol on the Physico-Mechanical Properties of Polyurethane Plaster Cast

Abstract

Abstract: Polyurethane plaster cast was an open weave fabric bandage, prepared by coating polyurethane prepolymer on raschel knitted fiberglass and polyester fabric. Curing takes place by coming in contact with water to form hard rigid cast. Polyurethane prepolymers were synthesized by reacting molar excess of diphenyl methane diisocyanate (MDI) with polypropylene glycol (PPG) at 60°C for 2 hours. This effect of different NCO/OH molar ratio and molecular weight of polyol on the tack free time, setting time, diametral compression strength, percent elongation and tensile strength of polyurethane plaster cast were investigated.. It was observed that with increase in NCO/OH molar ratio, tack free time and setting time of the cast decreases, whereas diametral compression strength increases. Tensile strength was determined in universal testing machine and was found to increase with increasing NCO/OH ratio while opposite trend was observed in case of percent elongation. With increase in polyol molecular weight, tack free time and setting time of the cast increases, whereas diametral compression strength decreases. Blended polyols i.e. PPG 1000 with PPG 400 in 50/50 ratio gives tensile strength and diametral compression strength in between their unblended counterparts. In comparison to fiberglass cast, polyester cast has higher percent elongation and diametral compression strength. Key words: Polyurethane plaster cast Prepolymer Fiberglass cast Polyester cast