THERMALLY STIMULATED SHAPE MEMORY BEHAVIOR OF POLYMERS WITH PHYSICAL CROSSLINKS

The shape memory effect of polymers was investigated for the purpose of improving the processing conditions of their preparation and broadening the list of polymers for shape memory applications. Emphasis was put on the possibility of using polymers with physical crosslinks as shape memory materials and their structure-function relationships. Segmented block polyurethanes and polyethylene/nylon 6 graft copolymers were used as examples of polymers with physical crosslinks. It was found that these copolymers can really be used as thermally stimulated shape memory materials with large recoverable strain and high final recovery rate. The main advantage of using copolymers is their improved processing conditions as compared with polymers with chemical crosslinks. As only physical crosslinks are introduced, all conventional processing techniques for thermal plastics can be used, and the materials become easily reusable. The results indicate that the high crystallinity of these copolymers at room temperature and the formation of stable physical crosslinks are the two prerequisites for these polymers to exhibit shape memory effect. The successful use of block and graft copolymers imply the possibility of using polymers of various structure and properties as shape memory materials.

Thermomechanical and Shape Memory Properties of SCF/SBS/LLDPE Composites

A thermally triggered shape memory polymer composite was prepared by blending short carbon fiber（SCF） into a blend of poly（styrene-b-butadiene-b-styrene） triblock copolymer（SBS）/linear low density polyethylene（LLDPE） prior to curing. These composites have excellent processability compared with other thermosets. The dynamic mechanical analysis（DMA） and differential scanning calorimetry（DSC） were investigated to assess the thermomechanical properties of the SCF/SBS/LLDPE composite. Scanning electron microscope（SEM） imaging of the samples was performed to show the distribution of the SCF in the composite. The study specifically focused on the effect of SCF on the shape memory behavior of the SCF/SBS/LLDPE composite. The results indicated that the large amount of SCF significantly improved the mechanical property of the polymer composites while not damaging the shape memory performance. The SCF/SBS/LLDPE composites exhibited excellent shape memory behavior when the SCF content was less than 15.0 wt%. Moreover, the shape fixity ratio and shape recovery time of the SCF/SBS/LLDPE composites increased with the SCF content.