Abstract
A suitably modified resin film infusion (RFI) process was used for manufacturing carbon fiber-reinforced composites (CFRCs) impregnated with a resin containing nanocages of glycidyl polyhedral oligomeric silsesquioxane (GPOSS) for enhancing flame resistance and multi-wall carbon nanotubes (MWCNTs) to contrast the electrical insulating properties of the epoxy resin. The effects of the different numbers (7, 14 and 24) of the plies on the equivalent direct current (DC) and alternating current (AC) electrical conductivity were evaluated. All the manufactured panels manifest very high values in electrical conductivity. Besides, for the first time, CFRC strings were analyzed by tunneling atomic force microscopy (TUNA) technique. The electrical current maps highlight electrically conductive three-dimensional networks incorporated in the resin through the plies of the panels. The highest equivalent bulk conductivity is shown by the seven-ply panel characterized by the parallel (σ//0°) in-plane conductivity of 16.19 kS/m. Electrical tests also evidence that the presence of GPOSS preserves the AC electrical stability of the panels.
Highlights
To fully apply composite materials in wide extent in aircraft vehicles, several drawbacks still need to be overcome, such as a suitable electrical conductivity to better cover several functions and continuous enhancement of fire safety in aviation materials
No peaks were observed in the second run, the sample was considered totally cured (DC = 100%) and the exothermic heat (∆H) during the first run was assumed as the total heat of reaction of the uncured material (∆HT )
New carbon fiber-reinforced composites (CFRCs) are proposed with the aim to have a load-bearing structure with functional
Summary
To fully apply composite materials in wide extent in aircraft vehicles, several drawbacks still need to be overcome, such as a suitable electrical conductivity to better cover several functions (e.g., lightning strike and electromagnetic compatibility issues) and continuous enhancement of fire safety in aviation materials. Many functions can be conferred to aeronautical composites by proper use of nanotechnology, for example by embedding nanostructured materials with exceptional properties, like carbon nanotubes (CNTs), in aeronautical grade epoxy resins before or during the manufacturing processes [11,12,13,14,15,16]. The introduction of secondary nanoscale reinforcements (e.g., graphene, carbon nanotubes or nanoclay distributed in polymer matrix or fiber sizing) into the fiber-reinforced composites may contribute to further improvements. Zhou et al showed that the addition of secondary CNT nano reinforcement into epoxy matrices ensures a strong increase of the composite strength [17]. In the Polymers 2019, 11, 1865; doi:10.3390/polym11111865 www.mdpi.com/journal/polymers
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