AbstractIn the industrial application of polyurethane resins to form surface coatings on wool fabrics, the prepolymer resin Synthappret is curred by reaction with water, either as steam or as atmoshpheric water vapor, to form the rubber network. This paper examines changes in the mechanical properties of the resin with cure conditions. It is shown for steam‐cured resin that the initial modulus, the equilibrium swelling in tetrachloroethylene, the Mooney‐Rivlin constantC1, and the average molecular weight of chain segments between crosslinks all reach constant values after 1 hr. However, the resin density and the Mooney‐Rivlin constantC2show a linear dependence on cure time with no indication of reaching an equilibrium value. It is concluded that although the network is substantially complete after 1 hr of steam cure, there is a continuing pattern of reorganization. The mechanical properties of resin produced by air curing, a much slower process, are consistent with those of a network which has had a longer period of reorganization. The density of air‐cured resin is significantly higher than that of resin prepared by steam curing. Stereoscan electron micrographs of the resin surface reveal a texture which coarsens with prolongation of cure time and also reveal a difference for the two methods
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