ABSTRACT
Model poly(styrene-acrylonitrile) (SAN) dispersions were prepared in ethylene oxide-capped polyether triols by two different methods, and evaluated in a high solids, high resilience (HR) molded foam formulation. The first preparation method involved blending of two nearly monodisperse dispersions of different average particle size. The second method involved preparation of a polydisperse dispersion, and fractionating particles of various sizes by ultracentrifugation, thus eliminating process chemistry as a variable. However, while the particle size distribution of the centrifuged dispersions varied significantly, the method did not cleanly isolate large and small particles. Foam tightness was measured using a force to crush test. A standard set of physical properties was also measured.
Foam tightness strongly correlated with the particle size distribution, and specifically with the relative number of large (> 5 pm) particles. Dispersions containing predominately small particles produced relatively open foam (low force to crush), while even a relatively small proportion (< 20 vol. % of solids population) of large particles resulted in significantly tighter foam (high force to crush). Tear, elongation and compression sets of foams prepared with the blended dispersions correlated directly with the blend composition, while hardness varied only slightly with the particle size distribution. Only slight variations of foam physical properties with particle size distribution were found using the centrifuged dispersions.
