The addition of graphene and novel fibre nanotubes to carbon fibre composites : effects on mechanical properties

Abstract

The incorporation of multifunctional carbon nanomaterials, graphene nanoplatelets (GNP) and cup-stacked carbon nanotubes (CSCNT) into the polymer matrix of conventional carbon fibre reinforced composites as fillers, offers the potential for mechanical multifunctional improvements, for instance strength, stiffness and toughness without disrupting the original in plane mechanical properties. In this research, the GNP, the CSCNT and a novel combination of them (hybrid GNP-CSCNT nanofillers) were dispersed within a thermosetting resin matrix via mechanical dispersion techniques, such as ultra-sonication and ball milling/mixing to achieve uniform dispersion and full exfoliation of carbon nanomaterials in the matrix. The principal purpose of the combination of GNP and novel CSCNT into the matrix was to promote the strength and toughness properties of the polymer matrix as well as the conventional CFRP by availing the synergetic influence between these carbon nanomaterials. Three types of polymer nanocomposites (NP) were prepared successfully by the combination of these two dispersion techniques with the following formulations: GNP/epoxy nanocomposites, CSCNT/epoxy nanocomposites and hybrid GNP-CSCNT/epoxy nanocomposites. The greatest improvements of the HNP were achieved in flexural strength and flexural modulus after the combination of 2 wt.% of GNP and 2 wt.% of CSCNT by approximately 40% and 61%, respectively. In addition to significant improvement in fracture toughness by 85% at the same weight content, substantial improvements in the mechanical properties of novel HCFRP (hybrid GNP-CSCNT/CF/epoxy nanocomposites) were also gained after using the same optimum proportional weight content of these combined carbon nanomaterials. The flexural strength and flexural modulus improved by approximately 18% and 28% respectively, while the shear strength improved by 37%. Additionally, the energy propagation of Mode I and Mode II interlaminar fracture toughness increased by approximately 73% and 132% respectively. Most of the aforementioned properties of HCFRP showed superior improvement when 6 wt.% of CSCNT were individually incorporated, for instance the shear property of CSCNT/CF/epoxy nanocomposites improved by 38%, flexural strength by 25% and interlaminar fracture toughness Mode I and Mode II by 104% and 151% respectively. The GNP produces less improvements at optimum weight concentration 5 wt.% in comparison to CSCNT/CF/epoxy nanocomposites. For instance shear strength of GNP/CF/epoxy nanocomposites improved by 31%, flexural strength 20% and interlaminar fracture toughness Mode I and Mode II by 15% and 84% respectively. The fracture mechanisms for these enhancements were investigated by extensive fratographyical analysis to show the synergetic associated mechanisms of hybrids composites. Multiple fracture mechanisms systems were generated into the fracture surface of the HCFRP after the addition of combined carbon nanomaterials into the fibre network. In conclusion, the addition of novel CSCNT is better than GNP in reinforcing the mechanical properties of thermoset resin (i.e. epoxy) and conventional CFRP. Additionally, the inclusion of the combined nanomaterials; GNP and CSCNT is useful in promoting the mechanical properties over the parent hybrid composites. Moreover, it is expected to be harmless to the original mechanical properties of epoxy composites and conventional carbon fibre composites.