Recycling of thermoset flexible polyurethane foams into solid polyurethane rubber

It was possible to recycle flexible polyurethane foam into solid polyurethane elastomers by compression molding at 230-250 degrees C. The solid elastomers were still cross-linked thermosets. Indentation hardness was comparable with the upper end of the range for commercial polyurethane elastomers, and increased with molding temperature, presumable due to formation of allophanate and biuret cross-links. Final moldings were inhomogeneous, due to poor fusion and lack of mastication, giving low tensile strength and elongation, and poor reproducibility. Glass transition temperatures, by DSC and DMA, were comparable with commercial polyurethane elastomers. Previous studies, in which the foam was converted to the elastomeric sheets, gave better results because the foam was not completely cured before remolding, or because it was blown with non-reactive physical blowing agent. In the present study on water-blown foam, formation of polyurea cross-links made it more difficult to open these bonds and remold the foam.