Shape xity and shape recovery of polyurethane shape-memory polymer foams

The thermomechanical properties of polyurethane shape memory polymer (SMP) foams were investigated experimentally. The results obtained can be summarized as follows. (1) By cooling the foam after compressive deformation at high temperature, stress decreases and the deformed shape is Ž xed. Stress decreases markedly in the region of temperature below the glass transition temperature Tg during the cooling process. (2) By heating the shape-Ž xed foam under no load, the original shape is recovered. Strain is recovered markedly at the temperature region in the vicinity of Tg. (3) The ratio of shape Ž xity is 100 per cent and that of shape recovery 98 per cent. Neither ratio depends on the number of cycles. (4) Recovery stress increases by heating under constraint of the Ž xed shape. Recovery stress is about 80 per cent of the applied maximum stress. Relaxed stress at high temperature is not recovered. (5) The shape deformed at high temperature is maintained for six months under no load at Tg7 60K without depending on maximum strain, and the original shape is recovered by heating thereafter. (6) If the deformed shape is kept at high temperature, the original shape is not recovered. The factors in uencing the shape irrecovery are the holding conditions of strain, temperature, and time.