Air Flow Measurement and Its Relations to Cell Structure, Physical Properties, and Processibility for Flexible Urethane Foam

Abstract

A slab stock urethane foam cell ideally resembles an elongated pentagonal dodeca hedron. The faces are bounded by ribs, and membranes stretch across the ribs during the expansion of the foam. The normal formation of the foam does not result in the rupture of all the membranes. Data are presented showing that Air Flow values for flexible polyether and polyester foams are affected profoundly by the membrane population and, to a smaller extent, by density and cell geometry. It is also shown that within a given bun Air Flow values may vary with both position and orientation. Air Flow val ues also vary considerably between different foams. Because variation in Air Flow values is related to cell structure, it can be related to certain physical properties. Examples of this are given for ball rebound, compression load deflection, flex fatigue, and color shad ing. A quantitative definition of operating range based on Air Flow values is demon strated for tin catalyst concentration in a polyether foam. As a result of these findings Air Flow is recommended as a new parame ter for describing flexible urethane foam cell structure.