EFFECT OF MELAMINE ON THE FOAM KINETICS OF POLYURETHANE MODEL SYSTEM - II - EFFECT OF MELAMINE PARTICLES ON FILM FORMATION

To study the influence of the flame-retardant melamine on foam propert ies of a polyurethane model system, single, vertical liquid foam films were studied. The presence of particles gives the possibility to obse rve the complete circulation in the film. The films of the model syste m have been found to be mobile films showing marginal regeneration. Fi lm formation was combined with surface-tension measurements on the poo l surface. The changes in the surface tension of the pool were measure d and the amount of surfactant diffused from the surface of the pool t o the surface of the film were calculated. This quantity was found to be a few percent of the moles necessary for equilibrium coverage. The fresh film surface is nearly independent of the pool surface and the m eniscus behaves as a slit, producing a film with a nearly surfactant-f ree surface. Two characteristic phenomena were observed during film fo rmation from a suspension containing 25 pphp melamine ultrafine: (1) T he convective currents are slower in the melamine-filled film than in the corresponding melamine-free lamellae. (2) No surface tension diffe rence was seen on the surface of the pool after film formation. It see ms that the melamine hinders the surface diffusion. (C) 1998 John Wile y & Sons, Inc.