Abstract
This paper investigated the modification of the advanced active screen plasma (ASP) technology on PAN-derived carbon fibres (CFs) with gas mixtures of N2-H2 and N2-H2-Ar, separately. A more-than-30% improvement was found in the interfacial shear strength (IFSS) between the modified CFs and the epoxy substrate in the resulting composites, as disclosed by single fibre push-out tests. Based on the study of surface morphology, surface chemistry and water-sorption behaviour, the interfacial adhesion enhancement mechanisms were attributed to (1) the increased chemical bonding between the introduced functional groups on the fibre surface and the matrix; (2) the improved surface hydrophilicity of CFs; and (3) the enhanced van der Waals bonding due to the removal of surface contaminations.
Highlights
Owing to the excellent properties of carbon fibres (CFs), such as outstanding mechanical properties, high strength-to-weight ratio, high thermal stability and corrosion resistance, they have become the materials of choice for the reinforcements of high-performance composites [1]
I, pyrrolic N and oxidised N groups were found on both ASPN and ASPAr-treated fibre surfaces with the binding energies at around 400.1 and 401.8–402.8 eV. This is because, during the active screen plasma (ASP) treatments, the CF surfaces were exposed to the energetic plasma species, whose interactions contributed to creating active sites for the attachment of nitrogen species to form functional groups
The physisorption decreased for both the freshly ASP-treated CFs and the aged ASPtreated CFs. This is believed to be associated with the sizing layers on the pristine CFs and the change in surface morphology caused by the mild chemical etching of hydrogen (Figure 5)
Summary
Owing to the excellent properties of carbon fibres (CFs), such as outstanding mechanical properties, high strength-to-weight ratio, high thermal stability and corrosion resistance, they have become the materials of choice for the reinforcements of high-performance composites [1] Their chemical inertness and low surface free energy, which is attributed to the high density of graphitic planes on the surface, limit the interfacial adhesion of CFs to the matrix [2]. Notwithstanding the fact that improved mechanical properties of composites and CF/matrix interfacial adhesion by CF surface modification have been reported, the extent of the improvement spans a wide range This could be attributed partially to the effect of different surface treatments on the strength of CFs and partially to the various evaluation methods with different stress states used. Systematic surface characterisation was carried out using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and dynamic vapour sorption (DVS)
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