Multiscale Carbon Fibre Composites with Epoxy-Graphite Nanoplatelet Matrices

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Abstract

This thesis reports the effects of incorporating graphite nanoplatelets (GNPs) to epoxy-carbon fibre (CF) laminates to produce multiscale composites. A grade of epoxy resin typical for the application in aerospace engineering, triglycidyl-p-aminophenol (TGPAP), was used in this work cured with 4,4’-diaminodiphenyl sulfone (DDS). To improve the processability of TGPAP, a diluent, the diglycidyl ether of bisphenol F (DGEBF), was added to formulations. Compositions of TGPAP/DGEBF/DDS were optimised using response surface methodology (RSM) with the target response being to obtain high glass transition temperature (Tg) and low resin viscosity. From RSM, the optimum values were obtained at 55.6 wt. % of DGEBF and a stoichiometric ratio of 0.60. Before addition into epoxy, GNPs were treated either covalently using 3-aminopropyltriethoxysilane (APTS) or non-covalently using a commercial surfactant, Triton X-100 (abbreviated as A-GNPs and T-GNPs, respectively). After treatment, XPS analysis showed a new peak at 100 eV for A-GNPs indicating silicon and the C/O ratio increased from 11.0 to 26.2 for T-GNPs relative to unmodified GNPs (U-GNPs), suggesting attachment of the modifier molecules had occurred. Nanocomposites (NCs) were prepared by incorporate GNPs into epoxy using mechanical mixing. Rheological percolation threshold of GNP-epoxy suspensions were determined using oscillatory-shear rheometry as 3.9 wt. % for AR-GNPs, 3.6 wt. % for U-GNPs, 3.2 wt. % for A-GNPs and 3.5 wt. % for T-GNPs, suggesting surface treatment improved dispersion. At 4 wt. % of GNPs, flexural strain of NCs was decreased relative to neat epoxy by 46% for AR-GNPs, 48.6% for U-GNPs, 4.6% for A-GNPs and 30.8% for T-GNPs but flexural moduli showed small increases of 6.1-7.4%. Fracture toughness (K1C) also improved. For example, the K1C increased from 0.80 ± 0.04 MPa.m1/2 for neat epoxy to 1.32 ± 0.01 MPa.m1/2 for NCs containing 6 wt. % of U-GNPs possibly due to the branching of cracks resulting from the embedded GNPs. Due to their mechanical performance, A-GNPs were used to fabricate epoxy/CF/A-GNPs multiscale composites. Multiscale composites showed inferior properties relative to a comparable conventional composite in flexural testing, interlaminar shear strength (ILSS) and interlaminar fracture toughness mode II (G11C) due to weaker bonding at the matrix-CF interface. However, multiscale composites showed ~40% higher capability than conventional composite to absorb energy during impact due to greater interfaces formed by the inclusion of A-GNPs into the system.

Keyword(s)

Epoxy/CF Mutliscale composites; Eppoxy/GNPs nanocomposite; Graphene nanoplatelets; Graphite nanoplaletets

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