Dependency of the shape memory properties of a polyurethane upon thermomechanical cyclic conditions

The relationship between the shape memory properties and thermomechanical cyclic conditions was investigated with a type of shape memory polyurethane (SMPU). The thermal and dynamic mechanical properties of the polyurethane were examined by using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). It was found that the SMPU exhibited good shape memory effects (SMEs) at deformation temperatures ranging from T-g to T-g + 25degreesC. The strain recovery ratios increased with the increase of deformation speed and with the decrease in maximum strain. The recovery ratios also increased with increasing fixing speed. Therefore, in practical applications, in order to obtain better SMEs, the SMPU should be cooled to its frozen state as soon as possible after being deformed at a high temperature. The 'fixity' dramatically increased with the decrease in fixing temperature. To obtain optimal SMEs, the polymer has to be reheated up to the temperature at which the polymer deformed. In addition, the recovery ratios of the SMPU could increase slightly with the increase of recovery time. (C) 2004 Society of Chemical Industry.