Effects of silicon surfactant in rigid polyurethane foams

The rigid polyurethane foams (RPUFs) have been fabricated from high functional crude 4,4'-di-phenylmethane diisocyanate (CMDI) and polypropylene glycols (PPGs) for a wide range of surfactant concentration with an environmently friendly blowing agent (HFC 365mfc). Cream time, gel time, and tack-free time increased with the addition of surfactant. Foam density decreased rapidly to a minimum at 0.5 pphp (part per hundred polyol) surfactant due to the increased blowing efficiency with surfactant. Surface tension rapidly decreased to an asymptotic value at 2 pphp surfactant. In accordance with this, cell size decreased and closed cell content increased rapidly to constant values at low surfactant concentrations (< 1 pphp). The decrease of cell size was accompanied by the decrease of thermal conductivity to give a linear relatiohship between the two implying that the series model of heat transfer is applicable.