Effect of Different Shape-Memory Processing Methods on the Thermomechanical Cyclic Properties of a Shape-Memory Polyurethane

Shape-memory polymers are materials that are capable of changing their shape when an external stimulus is applied. This effect is called the shape-memory effect (SME) and takes place by means of a thermomechanical cycle called programming. The SME depends on the thermomechanical conditions at which programming is performed, and the influence of these conditions differs depending on whether the programming is performed with a strain- or stress-controlled protocol. This study focuses on finding the thermomechanical cycling conditions in stress-controlled programming (T _prog and σ_m) that stabilize the material in the fewest cycles while obtaining the best mechanical and shape-memory properties over the highest number of cycles. Using a T _prog above or below, the glass transition temperature makes a big difference in terms of shape recovery and the maximum stress is a key factor in the stabilization of shape-memory properties.