We demonstrate the new features of a polyurethane shape memory polymer: water-driven actuation and recovery in sequence (i.e., programmable). Hydrogen bonding is identified as the reason behind these features. In addition, the absorbed water is quantitatively separated into two parts, namely, the free water and bound water. Their individual contribution on the glass transition temperature is identified.

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It was observed that the polyurethane shape memory polymer (SMP) loses its shape fixing capability after being exposed in the air at room temperature for several days. A significant indication for this change is the continuous decrease of the glass transition temperature (T g ) of polyurethane. Accompanying the decrease of T g , the uniaxial tensile behaviour also changes. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) tests were carried out to find the cause behind this phenomenon. Moisture was concluded as the main reason. A mathematical expression was obtained for the relationship between T g and the moisture. Moreover, the polyurethane shape memory polymer can fully regain its original properties after being heated at temperatures above 180 • C, which is the melting temperature of this SMP.

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Bamboo fibers demonstrate enormous potential as the reinforcement phase in composite materials. In this study, in order to find suitable NaOH concentration for bamboo fiber treatment, bamboo fibers were treated with 2 wt.%, 6 wt.% and 10 wt.% NaOH solutions for 12 h, respectively. We determined that 6 wt.% NaOH treated bamboo fibers were optimal for the fabrication of bamboo fiber composites by single fiber tensile test, single fiber pull-out test, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The short length bamboo fibers treated with 6 wt.% NaOH solutions were well dispersed in the epoxy matrix by a new preparation method. The effect of fiber content and fiber length on the mechanical behavior of bamboo fiber reinforced epoxy composites was investigated. The results confirmed that fracture toughness and flexural modulus of the composites monotonically increased with fiber length and content. However, for all samples, composites showed negligible difference on the flexural strength. The fracture surfaces of the composites were observed by SEM, revealing that fiber breakage, matrix cracking, debonding, and fiber pull out were major failure types. In addition, thermogravimetric analysis (TGA) was carried out to investigate the thermal behavior of both bamboo fibers and composites.

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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 T g 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 T g , 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.