Shape recovery and secondary-shape forming in polyurethane-shape memory polymer

The influence of the strain-holding conditions on shape recovery and secondary-shape forming was investigated. The results obtained are summarized as follows. (1) If strain is held at holding temperature T-h = T-g+20K in a short time, irrecoverable strain starts to appear at the holding time t(h)=0.5h and strain is not recovered at all at t(h)=8h. In the case of T-h = T-g+10K, irrecoverable strain appears in a short holding time if holding strain is large and the rate of secondary-shape forming S is 42% at t(h)=8h. (2) If strain of 50% is held at T-h = T-g+10K in a long time, strain becomes not to be recovered and S is 93% at t(h)=12h. In the case of T-h = T-g, the increasing rate of S increases if th is longer than 40h. If T-h is lower than T-g-10K for t(h)=72h, strain is recovered perfectly by heating and secondary-shape forming does not appear.