Abstract
Shape memory properties of PET (polyethylene-terephthalate) foams have been evaluated for two different foam densities. Samples were subjected to multiple memory-recovery cycles along three different directions to measure the effect of foam anisotropy on static mechanical and shape memory properties. The memory cycle was performed by uniaxial compression tests at room temperature. Despite these severe conditions, PET foams demonstrated very good shape memory behavior with shape recovery always higher than 90%. Due to cycling, the mechanical performance of foam samples is partially reduced, mainly along the extrusion direction of the foam panels. Despite this loss of static performance, shape memory properties are only partially affected by thermo-mechanical cycles. The maximum reduction is 10% for shape fixity and 3% for shape recovery. The experimental results are particularly interesting considering that compression tests were undertaken at room temperature. Indeed, PET foams seem to be optimal candidates for self-repairing structures.
Highlights
Shape memory polymers (SMPs) are a very interesting and well-known class of stimuli-responsive materials which have attracted a great deal of attention due to their ability to restore an equilibrium shape upon certain stimulus such as temperature, electricity, pH, ionic strength and light [1]
Because of the shape anisotropy induced by the extrusion process of PET foam panels, different behaviors are expected by testing shape memory along the extrusion direction and the two transverse ones
Uniaxial compression tests and thermo-mechanical cycles were carried out along three mutually orthogonal directions on PET foams to evaluate the anisotropy of shape recovery and residual stiffness after thermo-mechanical cycling
Summary
Shape memory polymers (SMPs) are a very interesting and well-known class of stimuli-responsive materials which have attracted a great deal of attention due to their ability to restore an equilibrium shape upon certain stimulus such as temperature, electricity, pH, ionic strength and light [1]. Foam structures improve the shape memory behavior of bulk polymers mainly in terms of compression rate [2,3]. PET foams exhibit good shape-memory properties by performing the memorizing step in cold conditions This is quite a rare occurrence in the world of SMPs as typically these polymers are strongly damaged when deformed in a rigid state. Because of the shape anisotropy induced by the extrusion process of PET foam panels, different behaviors are expected by testing shape memory along the extrusion direction and the two transverse ones. Memory-recovery cycles were performed by means of compression at room temperature (cold compression) and subsequent hot recovery This thermo-mechanical cycle was repeated three times for each principal direction of the initial foam panel
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