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Foamed polyurethane products were obtained from mixtures of polyolic and isocyanate compounds to which different amounts of water were added. The foaming process was carried out in a special homemade reactor that allows us to record continuously the change in volume and total pressure produced by the foam during its expansion period. From these measurements, the associated foaming work and power were derived. It is shown that the foaming power is joined with important internal system parameters such as surface tension, viscosity, bubble and water mole numbers, average bubble dimension, and coalescence kinetics. The closed/open nature of the bubbles during the expansion foaming period was experimentally investigated. The effect of the amount of water added on the foaming power and on the final apparent foam density was evaluated. The apparent density, which decreases as the amount of added water increases, reaches a critical value where the structural collapse occurs independently of the foaming temperature. A link between collapse criticality and the correspondent kinetic rate is suggested and discussed. |
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