Fibre reinforced composites have been gaining wide acceptance in a variety of applications within the transport and aerospace sectors. The performances of these composites have a tendency to suffer when the material is exposed to adverse environments for long periods of time. This research focuses on the reinforcement of existing epoxy systems used in aerospace composite with nanofillers such as polyhedral oligomeric silsesquioxane (POSS) and functionalised carbon nanotubes (CNTs). The thermo-mechanical properties, cure kinetics, moisture properties and electrical conductivity have been investigated. Two epoxy systems with different curing agents were investigated: diglycidyl ether of bisphenol A cured with an amine and an anhydride curing agent. The incorporation of an amine functionalised POSS into the epoxy-amine system and an epoxy functionalised POSS into the epoxy-anhydride were investigated. The results showed that in both systems, the addition of POSS increased the Tg, cross-link density, final char yield at 800°C, whilst reducing the maximum moisture absorption when compared to the unmodified resin. In a composite system, the addition ofPOSS displayed an improvement in the reduction of moisture absorption. The addition of carboxyl-functionalised CNTs into the epoxy-anhydride system increased the electrical conductivity reaching an optimised percolation threshold at 2 wt-% addition. Improvements in the thermo-mechanical properties and cross-link density were also observed. The addition of CNTs in a composite system also displayed an improvement in both the electrical and thermal conductivity with little changes in the Tg and degradation temperature. A combination of POSS and CNT was also incorporated into the epoxy-anhydride system and was found that at small quantities (0.5 wt-% CNT with 0.5 wt-% POSS) the electrical conductivity reached values close to samples with 1 wt-% CNT. This suggests that the addition of both POSS and CNT are complementary and beneficially increases the dispersion within the matrix. Molecular modelling was also carried out in parallel to the experimental work and it can be applied to predict the properties of epoxies. The simulations were performed on cross-linked networks of diglycidyl ether of bisphenol A (DGEBA) and a dimethyl-methylene bis( cyclohexylamine) curing agent using condensed-phased optimised molecular potentials for atomistic simulation studies (COMPASS). The Tg and the effect of water on the Tg was calculated and the results were found to be in close agreement with experimental findings.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:665470 |
| Date | January 2014 |
| Creators | Tang, Winnie |
| Publisher | University of Surrey |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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