Dimensionally-stable polyurethane sponge and sponge-forming prepolymer

摘要

An MDI based polyurethane foam having cellulose foam properties is produced by mixing together an aqueous phase which can optionally contain reinforcing fibers and surfactants and a resin phase comprising a prepolymer derived from a poly(oxy C2-4 alkylene)diol, an MDI containing isocyanate product having a functionality greater than 2.0 made of a mixture of MDI and isocyanate containing derivatives of MDI, and a monomeric polyol cross-linking agent having 3 or 4 hydroxyl equivalents per mole. The preferred polyol is trimethylolpropane and the preferred diol is Carbowax 1000. The diol and the polyol, such as trimethylolpropane, are present in a mole ratio in the range of 4:1 to 8:1 while the ratio of the isocyanate equivalents to the total hydroxyl equivalents is in the range of 3:1 to 4:1. The isocyanate containing product comprises more than 50% by weight of the prepolymer and Isonate 143L is the preferred isocyanate product. The foam has a minimal swell when wet and it does not curl upon drying.