Then, Sonja (2011) Self-healing polymeric materials for potential dental application / Sonja Then. PhD thesis, University of Malaya.
Abstract
Poly(urea-formaldehyde) (PUF) microcapsules that enclose dicyclopentadiene (DCPD) were successfully prepared by in situ polymerization. The effect of diverse process parameters and concentrations of ingredients on the product yield and quality was investigated. After optimizing the procedure high yields of microcapsules were obtained (up to 89%) which appeared in the form of a free-flowing white powder. The morphology of the microcapsules was observed by digital microscopy, optical microscopy (OM), and field emission gun scanning electron microscopy (FESEM). FTIR and 1H-NMR were employed to analyze the chemical structure and content of the core material. The thermal properties were characterized utilizing DSC and TGA. The microcapsules could be incorporated into another polymeric host material. In the event the host material cracks due to excessive stress or strong impact, the microcapsules would rupture to release the DCPD, which could polymerize to repair the crack, thus autonomously heal the material. To enhance the properties of the microcapsule shell, the urea was partially replaced with up to 5% melamine. Different microscopic techniques, FTIR spectroscopy and DSC were employed to examine the capsule shell, whereas the core content was confirmed by 1H-NMR. Capsules in the range of 50-300 μm were then embedded in a light curable dental composite matrix consisting of bisphenol-A-glycidyl dimethacrylate (Bis-GMA) and triethylene-glycol dimethacrylate (TEGDMA). Two different amounts (3 wt% and 6 wt%) of microcapsules were embedded into the dental host material and their performances were evaluated through mechanical tests. OM examination of the light-cured specimens showed a random distribution of the microspheres throughout the host material, whereas FESEM analysis revealed excellent bonding of the microcapsules to the host material. These characteristics are of utter importance for maintaining the very good mechanical properties of a dental composite with self-healing ability. Flexural strength, microhardness and nanoindentation hardness measurements proved that the addition of the microcapsules did not affect the mechanical properties of the virgin matrix material. The substitution of the urea with small amounts of melamine in the capsule shell has improved the hardness of the microcapsules and made it easier to mix with the viscous host material before light curing. Finally, the encapsulation of epoxy resins was studied. PUF microcapsules were prepared incorporating the commercially available Epikote 828 (diglycidylether of bisphenol-A, DGEBA) diluted in n-butyl glycidyl ether (BGE). Proton NMR spectroscopy verified the presence of the epoxy core. DSC result has shown the onset of degradation of PUF/epoxy microcapsules was above 170°C. FESEM showed that the PUF/epoxy microcapsules adhered well to the epoxy matrix resin. In summary, this research work scrutinized the microcapsule based self-healing system for the potential application in dental polymeric materials. The findings that were obtained during the course of this study are significant for the further development of a self-healing restorative composite.
Actions (For repository staff only : Login required)
![[img]](http://studentsrepo.um.edu.my/style/images/fileicons/application_pdf.png)
