Morphology of water-blown flexible polyurethane foams

Abstract

A series of four water-blown flexible polyurethane foams was produced in which the water content was varied from 2 to 5 pph at a constant isocyanate index of 110. A portion of each foam was thermally compression molded into a plaque. The morphology of the foams and plaques was investigated using DMS, DSC, FTIR, TEM, SEM, swelling, WAXS, and SAXS. A high degree of phase separation occurs in these foams and the degree of phase separation is independent of water (hard segment) content. In the foam with the lowest water content the morphology is similar to that of typical segmented urethane elastomers. Small hard segment domains are present with a correlation distance of roughly 7.0 nanometers. When the water content is increased a binodal distribution of hard segments appears. There are the small hard segment domains typical of segmented urethane elastomers as well as large hard segment aggregates greater than 100 nanometers in diameter. The large domains are thought to be aggregates of polyurea that precipitated during the manufacture of the foam. The foam making process successfully incorporated the trifunctional polyols into a network indicating a high degree of polymerization for the hydroxyl-isocyanate reaction. Unreacted isocyanate is present in the foams a month after curing. It is believed to be trapped in the large urea aggregates. WAXS patterns of the foams suggest hard segment ordering that may be of a paracrystalline nature but certainly lacking in true crystallinity.