Thermomechanics of shape memory polymer nanocomposites

Shape memory polymers (SMPs) have the capacity to recover large strains when pre-deformed at an elevated temperature, cooled to a lower temperature, and reheated. The thermomechanical behavior of SMPs can be tailored by modifying the molecular structure of the polymer, or by using the polymer as a matrix for multiphase composites. Here we study the thermomechanics of a SMP polymer and its composites made by adding nano-scale SiC reinforcements. Our experimental study focuses on the thermomechanical behavior in three-point flexure. The results show that the SMP nanocomposites have a higher elastic modulus and are capable of generating higher recovery forces as compared to the SMP resin. When pre-deformed at a temperature well above the glass transition temperature, T-g, the stress-strain response at the pre-deformation temperature governs the relationship between the recovery stress/strain and the corresponding constraining strain/stress. When pre-deformed at a temperature below T-g, the recoverable stress/strain is not governed by the stress-strain response at the pre-deformation temperature. Rather, a peak recovery stress, which is less than the pre-deformation stress, appears at a temperature near T-g. Ramifications of the results on future research efforts and emerging applications of SMPs and their composites are discussed. (C) 2003 Published by Elsevier Ltd.