Study On Radiation Crosslinking And Shape-memory Effects Of Polycaprolactone

The characteristics of radiation crosslinking and shape-memory behaviors for polycaprolactone (PCL) and its blends were investigated systematically in this dissertation. Firstly, PCLs with different molecular weight were cross-linked by Y -radiation at different temperature conditions. The radiation cross-linking feature was examined by Soxhlet extractor with toluene and analyzed using Charlesby-Pinner equation. It was concluded that the cross-linking degree was relative to molecular weight and radiation dose, and, the relation between sol fraction and dose followed the Charlesby-Pinner equation. The higher temperature is useful to radiation crosslinking, the higher the temperature, the lower gelation dose, radiation crosslinking Gc increases, po/qo decreases. Radiation caused the tensile strength and elongation of all the samples drop. The DSC diagrams demonstrated that radiation caused the crystallinity increased and the melting temperature of PCL decreased. The DMA analysis indicated that radiation cross-linking raised heat deformation temperature of PCL and presented a rubbery state, whereas rendered enough strength at temperatures higher than melting point and provided enough force to recover the deformation. The shape memory results revealed that only those specimens that had a sufficiently high cross-linking degree (gel content is higher than about 10%) were able to show the typical shape memory effect, a large recoverable strain, and a high final recovery rate. The response temperature of the recovery effect (about 55℃) was related to the melting point of the samples.The mechanism of shape memory effects of radiation crosslinking PCL was analysed and demonstrated from the structure of assemble state, chemical thermodynamics and Maxwell-Wiechert viscoelastic model.Secondly, the enhanced effects of polyfunctional polyester acrylate(PEA) on radiation crosslinking of PCL were studied. The influences of the usage of PEA, the size of functional group, radiation dose on radiation crosslinking law, dynamic mechanical properties, crystallization, shape memory behaviors of PCL were investigated, respectively. It was proved that radiation crosslinking of PCL after applying PEA wasn't in correspondence with the classic Charlesby-Pinner equation, but followed Chen-Liu-Tang relation. The efficiency of radiation crosslinking of PCL was distinctively improved after applying PEA. The more the usage andfunctional group number, the more gel content and the more distinctive the radiation crosslinking effects. On the basis of this, the mechanism of enhancing radiation crosslinking of PEA was proposed and discussed. The DMA analysis indicated that enhanced radiation cross-linking better raised heat deformation temperature of PCL. The shape memory results revealed that the enhanced crosslinked PCL presented 100% recoverable deformation and more quick recovery rate. The nonisothermal crystallization kinetics analysis demonstrated that the way of crystalline growth of radiation crosslinked PCL belonged to heterogeneous nucleation and single-dimension growth model. By using an evaluation method proposed by Kissinger, activation energies of nonisothermal crystallization for radiated PCLs with different radiation dose have been evaluated to be between 64 kJ/mol and 54 kJ/mol.Lastly, the radiation crosslinking of PCL and polydimethylvinylsiloxane (PDMVS) blends was also studied. It was concluded that the radiation crosslinking of PCL/PDMVS) blends also followed Charlesby-Pinner equation. PDMVS played a promoting role in crosslink reaction during radiation. As the usage of PDMVS increases, the gelation dose and the ratio of degradation to cross-linking (po/qo) decreases, the efficiency of radiation crosslinking is raised. The Yong's modulus of radiation crosslinked PCL/PDMVS blends decreases with the increase of PDMVS under the melting point temperature of PCL, and increases with the increase of PDMVS above the melting point temperature of PCL. The properly crosslinked PCL/PDMVS blends exhibited fine shape memory effects, the ratios of deformation recovery is above 95%.