Tensile deformation behaviour of the polymer phase of flexible polyurethane foams and polyurethane elastomers

The change in micromorphology of the polymer phase (single strut) of a flexible polyurethane foam during deformation has been investigated by attenuated total reflection infrared spectroscopy - linear dichroism and by atomic force microscopy. Deformation and, therefore, orientation take place mainly in the soft rubbery phase. This two-phase elastic deformation process has been translated into a mathematical model, which correctly predicts the shape of a single-strut stress-strain curve. The theory also predicts the ultimate shape of stress-strain curves of polyurethane elastomers at various hard phase contents and of low-density polyethylene at various temperatures. Deviations from the elastic behaviour could be ascribed to yielding in combination with the rubbery behaviour.