Dynamic mechanical properties of MWCNTs/epoxy composite for aerospace applications

The present paper analyzes the dynamic mechanical properties of multiwalled carbon nanotubes (MWCNTs)/epoxy composites for structural applications. The composites were prepared by dispersing MWCNTs into an epoxy resin based on TetraGlycidyl-MethyleneDiAniline (TGMDA) and both epoxy precursor and composite were cured with 4,4’-diaminodiphenyl sulfone (DDS). Morphological investigation indicates good levels of CNT dispersion into the epoxy mixture. The electrical behaviour of the formulated composites and their high values in the storage modulus and glass transition temperature are very promising in the field of aerospace applications. The epoxy matrix was obtained by mixing TGMDA with 1,4-Butandioldiglycidylether (BDDGE) monomer at a concentration of 80%: 20% (by wt) epoxide to flexibilizer. DDS was added at a stoichiometric concentration with respect to the epoxy rings. Epoxy blend and DDS were mixed at 120 °C and the MWCNTs were added and incorporated into the matrix by using a ultrasonication for 20 minutes (Hielscher model UP200S-24KHz high power ultrasonic probe). All the mixtures were cured by a two-stage curing cycles: a first isothermal stage was carried out at the lower temperature of 125 °C for 1 hour and the second isothermal stage at higher temperatures up to 180 °C or 200 °C for 3 hours. These samples are named TBD-CNT(X%)(Y °C) where X is the CNT percentage and Y is the temperature of the second stage. The AFM micrograph of TBD-CNT(0.64 %)(200°C) clearly shows that the nanofillers were well dispersed in the polymeric matrix, forming a homogeneous structure in which CNTs uniformly cover the entire surface. Similar results have been obtained for lower concentrations of MWCNTs and curing cycles up to 180°C. The obtained results demonstrate that the method used for CNT dispersion into the epoxy mixture was very efficient for this investigated composite. The addition of MWCNTs causes the formation of resin fraction whit a decrease in the cure degree, as evidenced by the presence of a lower transition in the spectrum of tan delta. The incorporation of a small concentration of MWCNTs causes an increase in the elastic modulus value with respect to the unfilled epoxy matrix. The reinforcement effect of MWCNTs in the storage modulus is strong enough to compensate the decrease of the hydrogen bonding in the regular packing of the polymer chains due to the nanoinclusions that space out the polar sulfone groups (the proximity of these groups should favour hydrogen bonding contributing to an increase in the storage modulus).