Shape memory polymers (SMPs) are a particular class of smart materials, which present the ability to undergo important changes of shape on the intervention of a triggering stimulus, and, amongst various type of stimuli (electric and magnetic fields, UV and infrared irradiation, moisture, solvent, pH change), temperature is the most frequently employed. SMPs have peculiar advantages, with respect to other shape memory materials (such as shape memory alloys, SMAs), such as their intrinsic lightness, low cost and easy processability, very large shape variations (up to about 100 times those typical of SMAs) and an easy tailoring of their thermo-mechanical properties, mainly for what concerns transition temperatures and stiffness. One of the main drawbacks of SMPs is the relatively low stress exerted during the recovery step which could represent a limiting factor for their use in the field of actuators. In this view, shape memory polymer-based composites (that is a SMP modified with a fibrous reinforcement) can represent an interesting and useful improvement.
In the present work, shape memory composites have been prepared with a woven-non-woven poly(butylene terephthalate) (PBT) impregnated with a cross-linked polycaprolactone (PCL) having well established shape memory properties. The cross-linking step has been carried out by means a mild sol-gel chemistry based on alkoxysilane functional groups present in the PCL structure. The subsequent characterization has shown that the PCL matrix still exhibits good shape memory properties indicating that the presence of the PBT as reinforcement didn't negatively influence these peculiar properties. On the other hand, the presence of a fibrous reinforcement improved in a significant way the stress exerted by the composites during the recovery (actuation) step suggesting their potential use as smart materials for mechanical actuation.
