Development of epoxy mixtures for application in aeronautics and aerospace†
This work describes a successful attempt toward the development of composite materials based on nanofilled epoxy resins for the realization of structural aeronautic components providing efficient lightning strike protection. The epoxy matrix is prepared by mixing a tetrafunctional epoxy precursor with a reactive diluent which allows the moisture content to be reduced and facilitates the nanofiller dispersion step. The reactive diluent also proves to be beneficial for improving the curing degree of nanofilled epoxy mixtures. It increases the mobility of reactive groups resulting in a higher cure degree than the epoxy precursor alone. This effect is particularly advantageous for nanofilled resins where higher temperature treatments are needed, compared to the unfilled resin, to reach the same cure degree. As nanofiller, different carbon nanostructured fiber-shaped fillers are embedded in the epoxy matrix with the aim of improving the electrical properties of the resin. The results highlight a strong influence of the nanofiller nature on the electrical properties especially in terms of electrical percolation threshold (EPT) and electrical conductivity beyond the EPT. Among the analyzed nanofillers, the highest electrical conductivity is obtained by using multiwalled carbon nanotubes (MWCNTs) and heat-treated carbon nanofibers (CNFs). The achieved results are analyzed by considering the nanofiller morphological parameters and characteristics with respect to the impact on their dispersion effectiveness.