The influence of shape-holding conditions on shape recovery of polyurethane-shape memory polymer foams

The thermomechanical properties of polyurethane-shape memory polymer (SMP) foams and the influence of shape-holding conditions on shape recovery were investigated experimentally. The results obtained can be summarized as follows. (1) By cooling the foam down to below the glass transition temperature T-g after compressive deformation above T-g, stress decreases and the deformed shape is fixed. By heating the shape-fixed foam up to above T-g under no load, the original shape is recovered. (2) The shape deformed above T-g is maintained for six months under no load at T-g - 60 K without depending on the maximum strain, and the original shape is recovered by heating thereafter. (3) If the deformed shape is held at high temperature, the original shape is not recovered. (4) The ratio of shape irrecovery increases in proportion to the holding strain, holding temperature and holding time.