Synergistic toughening on hybrid epoxy nanocomposites by introducing engineering thermoplastic and carbon-based nanomaterials

In this study, epoxy-anhydride thermoset was initially modified with polyethersulfone (PESU) at 0-15 wt% loading. The various mass ratios at 0.50 wt% total content of graphene nanoplatelets (GNPs)/carbon nanotubes (CNTs) were further introduced to comprehensively study the simultaneous incorporation of different tougheners on morphological, thermal, and mechanical properties of engineering thermoplastic modified epoxy. The binary blend of PESU/epoxy reveals two-phase morphologies due to reaction induced phase separation, showing particulate morphology at 5 wt% PESU and co-continuous morphology at 10-15 wt% PESU. It was found that the presence of PESU at 5 wt% not only improved thermal stability but also provide the optimum mechanical properties, showing 35% and 40% increasing in tensile strength and fracture toughness, respectively. From fracture surface analysis, crack deflection from the PESU dispersed particles was observed as a main toughening mechanism for this binary blend. With introducing GNPs and/or CNTs, hybrid nanocomposite based on 5 wt% PESU modified epoxy matrix showed similar morphology and thermo-mechanical properties to the binary blends. Additionally, the remarkable Young's modulus were observed in all hybrid PESU/carbon-based nano fillers toughened epoxy composites. PESU and GNPs dispersed phase contribute greatly in enhancing fracture toughness (K-Ic) of hybrid PESU/nanofillers system. K-Ic of PESU/epoxy blends with 0.5 wt% GNPs was measured at 0.86 MPa m(1/2), counting as similar to 60% and similar to 18% improvement from pristine epoxy and 0.5 wt% GNPs modified neat epoxy, respectively. Apart from crack deflection of PESU, GNPs cluster effectively deviates and bifurcates the crack path, indicating the synergistic effect on PESU/GNPs epoxy nanocomposite. Interestingly, these two tougheners also dominates the toughening mechanism in PESU/GNPs/CNTs epoxy nanocomposites. Meanwhile, the influence of CNTs on fracture toughness was not clearly demonstrated on hybrid nanocomposite system.