Investigation On Cellulosic Shape Memory Polymeric Composites

In this thesis, we prepared two kinds of shape memory polymer composites based on cellulose. Cellulose is the most abundant biopolymer found in nature and offers many advantages such as renewability, biodegradability and biocompatibility. So as a reinforcing filler in composites, it has many advantages over other materials. Furthermore, the two kinds of shape memory polymer composites have good water-induced shape memory effect, biodegradability and biocompatibility. So composites developed in this thesis are especially attractive for potentially biomedical applications.Firstly, we prepared biodegradable and biocompatible water-induced shape-memory composites by introducing microcrystalline cellulose (MCC) into a poly(d,l-lactide)(PDLLA) matrix. We also analyzed the mechanism of the water-triggered shape-memory effect by considering the microstructure, water contact angle, water uptake, thermal properties and static and dynamic mechanical properties of the composites. We also investigated the shape memory effect of the composites upon exposure to water at37℃.We observed that the composite with an MCC content of35%(PDLLA-MCC-35) exhibited a good shape-memory effect upon exposure to water at37℃. The results of in vitro degradation analysis and cytotoxicity analysis demonstrated that the PDLLA-MCC-35composite exhibited good biodegradation and good cytocompatibility.Secondly, we use the sulfuric acid hydrolysis method to prepare nanocrystalline cellulose(NCC). Microcrystalline cellulose (MCC) was used as the starting material. A detailed study of the structure, topography, dimensions and thermal stability were performed.The results showed that we successfully prepared the NCC with a length of200nm and a width of10nm.Finally, we introduced nanocrystalline cellulose into polycaprolactone(PCL) and polyethylene glycol(PEG) matrix by chemical method. As NCC has a large number of hydroxyl groups, it can be used as crosslinking agent to crosslink the molecular chains of PCL and PEG, which were blocked end by diisocyanate. So the shape memory polymer nanocomposites network was obtained. As a result, we successfully prepared the PEG-PCL-NCC shape memory polymer nanocomposites. We also analyzed the microstructure, crosslink density, water contact angle, water uptake, crystallinity, thermal properties and static and dynamic mechanical properties, cytotoxicity, thermo-induced shape-memory and water-induced shape-memory properties of the composite. We found that the PEG[60]-PCL[4O]-NCC[10] composite exhibited a good thermo-induced and water-induced shape-memory effect. Futhermore, the PEG[60]-PCL[40]-NCC[10] composite possess good cytocompatibility.