This work describes a successful attempt toward the development of composite materials based on\ud
nanofilled epoxy resins for the realization of structural aeronautic components providing efficient\ud
lightning strike protection. The epoxy matrix is prepared by mixing a tetrafunctional epoxy precursor with\ud
a reactive diluent which allows the moisture content to be reduced and facilitates the nanofiller\ud
dispersion step. The reactive diluent also proves to be beneficial for improving the curing degree of\ud
nanofilled epoxy mixtures. It increases the mobility of reactive groups resulting in a higher cure degree\ud
than the epoxy precursor alone. This effect is particularly advantageous for nanofilled resins where\ud
higher temperature treatments are needed, compared to the unfilled resin, to reach the same cure\ud
degree. As nanofiller, different carbon nanostructured fiber-shaped fillers are embedded in the epoxy\ud
matrix with the aim of improving the electrical properties of the resin. The results highlight a strong\ud
influence of the nanofiller nature on the electrical properties especially in terms of electrical percolation\ud
threshold (EPT) and electrical conductivity beyond the EPT. Among the analyzed nanofillers, the highest\ud
electrical conductivity is obtained by using multiwalled carbon nanotubes (MWCNTs) and heat-treated\ud
carbon nanofibers (CNFs). The achieved results are analyzed by considering the nanofiller morphological\ud
parameters and characteristics with respect to the impact on their dispersion effectiveness
The focus of this study is to design new nano-modified epoxy formulations using carbon nanofillers, such as carbon nanotubes, carbon nanofibers and graphene-based nanoparticles (CpEG), that reduce the moisture content and provide additional functional performance. The chemical structure of epoxy mixture, using a non-stoichiometric amount of hardener, exhibits unique properties in regard to the water sorption for which the equilibrium concentration of water (C ) is reduced up to a maximum of 30%. This result, which is very relevant for several industrial applications (aeronautical, shipbuilding industries, wind turbine blades, etc), is due to a strong reduction of the polar groups and/or sites responsible to bond water molecules. All nanofillers are responsible of a second phase at lower glass transition temperature (Tg). Compared with other carbon nanofillers, functionalized graphene-based nanoparticles exhibit the best performance in the multifunctionality. The lowest moisture content, the high performance in the mechanical properties, the low electrical percolation threshold (EPT) have been all ascribed to particular arrangements of the functionalized graphene sheets embedded in the polymeric matrix. Exfoliation degree and edge carboxylated groups are responsible of self-assembled architectures which entrap part of the resin fraction hindering the interaction of water molecules with the polar sites of the resin, also favouring the EPT paths and the attractive/covalent interactions with the matrix.
The aim of this work is the identification of the best strategy for improving thermal, fire resistance and electrical conductivity of an epoxy resin for aeronautic applications. The effect of DodecaPhenyl POSS (DPHPOSS), Epoxycyclohexyl POSS (ECPOSS), Glycidyl POSS (GPOSS) and TriglycidylCyclohexyl POSS (TCPOSS) to act as flame retardants of the resin was evaluated. Flame retardancy tested by the limiting oxygen index (LOI) indicated that GPOSS has meaningful effects on the flame retardancy of the epoxy mixture. The incorporation of 5 wt% of GPOSS into the epoxy matrix resulted in a LOI value of 33 with respect to 27 of the pure epoxy mixture. The trend observed by LOI tests was confirmed by mass loss calorimetry measurements: a decrease from 540 kW m-2 down to 327 kW m-2 was observed in the peak of heat release rate (PHRR). LOI and PHRR values were compared with those obtained for the same resin replacing the 4,4′-diaminodiphenyl sulfone (DDS) with the bis(3-aminophenyl) phenylphosphineoxide (BAPPO) and the bis(3-aminophenyl) methyl phosphine oxide (BAMPO). BAMPO and BAPPO proved to be more effective than POSS compounds to increase LOI values. Carbon nanotubes (CNTs), embedded inside the epoxy resin to enhance electrical conductivity, are found to affect significantly fire properties of epoxy systems mainly by preventing the epoxy systems from forming intumescent charring
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