Influence of long-term storage in cold hibernation on strain recoveryand recovery stress of polyurethane shape memory polymer foam

Abstract

In this paper, the effects of long-term storage in compressed coldhibernated elastic memory (CHEM) polyurethane foam, a kind of shape memorypolymer, are investigated experimentally. The foams were pre-strained at ahigh temperature, which was above the glass transition temperature, to 80%and 93.4%, respectively, and then cooled back to room temperature. Aftervarious periods of cold hibernation (up to two months), they were heated up atfixed length or against different constant loads. It is found that: (1) themaximum stress that the foam could exert at fixed length depends heavily onthe amount of pre-strain; (2) expansion rates of 380 and 1273% from thehibernated size against a 1 N load (pre-strained by 80 and 93.4%,respectively) are achievable. However, upon further increases in load, theexpansion is reduced dramatically. It appears that the tested CHEMpolyurethane foam retains its shape memory properties even after being storedin a compacted state for a long period. Complete strain recovery is attainablefor a hibernation period of up to two months.