Bridging nano- to macro-mechanical properties of an aerospace-grade mono-component epoxy reinforced with carbon nanotubes

The use of carbon nanoparticles as fillers of composite materials is investigated as possible solution for a large number of challenges in the aerospace field, ranging from advanced structures with multiple functionalities to electromagnetic shielding and sensing. In particular, the current trend is to create multifunctional composite structures to carry out tasks generally performed by several elements, with the additional critical objective of replacing heavy assembled systems with lightweight composite structures. Multi-walled carbon nanotubes (MWCNTs) are well known as reinforcing nanoparticles that enhance the mechanical properties of neat resins, particularly epoxy resin. Different methods and approaches can be found in the literature to fabricate composite structures reinforced by MWCNTs, mostly involving two-component epoxy resin systems. For all applications, a good dispersion of the nanoparticles in the polymer matrix is crucial to obtain the expected results. Unlike two-component resins, mono-component systems show a strong temperature dependent viscosity, but have the limit that, due to the premixed amine curing elements, crosslinking reactions occur if too much heat is transferred to the resin. In this study we present an investigation of the mechanical and thermal properties, from the nano- to the macro-scale, of an aerospace-grade monocomponent epoxy system (RTM6) reinforced with different weight percentage of multi-walled carbon nanotubes. The nanoindentation technique was used to determine the hardness and the modulus at the nanoscale of the MWCNT-reinforced epoxy system, whereas tensile tests were performed to determine the ultimate strain and the elastic modulus at the macro-scale. In addition, the thermal properties of the composite systems were investigated by measuring the thermal expansion coefficient so to determine the effects of the MWCNTs on the dimensional stability of the RTM6 composite structures