Preparation and properties of rigid polyurethane foams containing modified cornstarches

Abstract

Abstract Rigid polyurethane foams were prepared containing 20% (based on weight of polyol) unmodfied or modified cornstarches. The cornstarches had been modified by breeding or conversion methods and included waxy, acid‐modified waxy, malto‐dextrin, and canary dextrin. Due to its more favorable role as an extender, canary dextrin was added to additional foam formulations at 10–40%. Foams containing dextrins responded to compressive stress as control foams with yield points before 10% deformation. Foams filled with the unmodified or waxy cornstarches did not give clearly defined yield points and were measured at 10% deformation. After 14 days under 70°C and ambient conditions, volume increases for the filled foams were 4.0–7.1% vs. 4.6% for the control. The foams filled with canary dextrin increased in volume 4.3%. With the addition of 40% canary dextrin, the volume increases for the foams were 4.4% under thermal conditions and 4.5% under humid conditions (38°C and 98% relative humidity). Under humid conditions for 14 days, the foams containing canary dextrin increased in weight as dextrin content increased (1.5, 3.2, 3.4, and 7.6% with 10, 20, 30, and 40% dextrin, respectively). with 40% canary dextrin in the foams, thermal conductivity was 0.0235 vs. 0.0242 W/mK (0.163 vs. 0.168 Btu in/ft 2 h°F) for the control.