Effect of average particle size and distribution on the performance of copolymer polyols

Copolymer (graft) polyols with varying particle size distribution were evaluated in a typical molded seating foam formulation. Three separate studies were conducted. In the first study, a graft polyol with a wide particle size distribution was fractionated by ultracentrifugation. The second and third studies used narrowly dispersed graft polyols of different average particle size and their blends. For the second study, the average particle sizes for the blend components were 0.26 and 7.6 mum (where the 7.6 mum component contained primarily 9 mum "large" particles). For the third study, they were 0.15, 1.4 and 3.0 mum. A three-component mixture experiment was designed for the third study, and the data was analyzed by model fitting. In the second study, cell opening increased and foam physical properties improved as the fraction of small particles in the bimodal blend increased. For the three-component mixture study, we report optimal blend compositions for cell opening, selected mechanical properties and flammability performance (WSS302(double dagger)). Optical microscopy of the foam cell structure and dynamic mechanical analysis (DMA) were conducted in order to explain the above results in terms of the interaction of the copolymer particles with the foam cell structure and polyurethane-urea matrix.