Influence of moisture in polyurethane shape memory polymers and their electrically conductive composites
Date of Issue2007
School of Mechanical and Aerospace Engineering
This dissertation presents a systematic study on the influence of moisture in polyurethane shape memory polymers (SMPs) and their electrically conductive composites. It was found that Tg of the SMP decreases by about 40 °C after immersion in water. This phenomenon is caused by the weakening of the hydrogen bonding between N-H and C=0 groups due to the absorbed water. Furthermore, the water absorbed into the SMP can be separated into two parts, free water and bound water. Each part was quantified in the course of this study. The bound water in the SMP significantly reduces T in an almost linear manner, while the effect of free water is negligible. Based on these findings three new features of the polyurethane SMPs were proposed: SMPs with functionally gradient Tg , water actuated shape recovery, and porous SMPs using water as a non-toxic foaming agent. Electrically conductive polyurethane SMPs were fabricated by filling the SMP with conductive carbon powders. Their microstructure, electrical conductivity, response upon uniaxial tensile, dynamic mechanical properties and shape memory properties were characterized experimentally both at dry and wet states. Good electrical conductivity and the shape memory effect were observed. It was demonstrated that shape recovery can be activated by directly passing an electrical current.