Structural and mechanical properties of flexible polyurethane foams cured under pressure

Flexible two-component polyurethane foam was synthesized under various extents of overpressure up to 2 bar. The influence of the pressure conditions on shrinkage and basic foam properties such as the relative density, microstructure, and ratio of open to closed pores as well as the elastic mechanical properties were investigated. The relationship between the relative foam density and the applied overpressure is shown to be rather linear. An abrupt change of the mainly open pore structure to essentially closed-cell foam was found in the narrow range between 50% and 60% relative density. A way to control the shrinkage properties of closed-cell foam via the extent and duration of overpressure applied during the foam synthesis was found and a hypothetic qualitative model describing the basic underlying mechanisms is given. Closed-cell flexible foam showing no effective shrinkage was produced this way. The achieved foam properties display an interesting potential for the application as e.g. gasket material.