Abstract
PEEK appears as an excellent candidate to substitute epoxy resins in carbon fibre laminates for high-performance aeronautical applications. The optimization of the properties and, in particular, of the transition region between the fibres and the matrix appear as a major issue prior to serial production. Graphene, modified with two compatibilizers, has been incorporated in the polymer layer with the purpose of imparting additional functionalities and enhancing the matrix-fibre interaction. It is found that both carbon fibres and modified graphene significantly influence the crystallization behaviour and smaller, and/or more imperfect crystals appear while the degree of crystallinity decreases. Despite this, nanoindentation studies show that the PEEK layer exhibits significant modulus improvements (≈30%) for 5 wt.% of graphene. Most importantly, the study of the local mechanical properties by nanoindentation mapping allows the identification of remarkably high modulus values close to the carbon fibre front. Such a relevant mechanical enhancement can be associated with the accumulation of graphene platelets at the polymer–fibre boundary, as revealed by electron microscopy studies. The results offer a feasible route for interlaminar mechanical improvement based on the higher density of graphene platelets at the fibre front that should promote interfacial interactions. Concerning electrical conductivity, a large anisotropy was found for all laminates, and values in the range ~10−4 S/cm were found for the through-thickness arrangement as a consequence of the good consolidation of the laminates.
Highlights
Introduction published maps and institutional affilAdvanced polymer-based composites have progressively substituted metals for lightweight applications in the aerospace and aeronautical industry [1,2]
To neat poly(ether ether ketone) (PEEK), the first was related to the scission of the polymeric chains, and the second was attributed to the oxidation of the carbonaceous char formed in the first stage [44]
The results revealed that graphene reinforced the PEEK matrix and suggested that local variations of the quantity and orientation of graphene layers produce a broadening of the mechanical properties at the sub-micrometre scale
Summary
Advanced polymer-based composites have progressively substituted metals for lightweight applications in the aerospace and aeronautical industry [1,2]. In the case of highperformance structures, epoxy carbon fibre (CF) laminates have traditionally overstocked the market. The fibres bear the in-plane stresses, while the polymer matrix dominates the through-thickness properties. Epoxies are brittle and prone to cracking, and the laminates exhibit low-energy absorbance [2]. Over the past few decades, the incorporation of nanofillers to create multiscale composites appeared as a successful strategy to overcome the brittle nature of epoxies and enhance the out-of-plane properties [1,2,3,4,5]. Epoxies demand time-consuming autoclave procedures to allow chemical reactions during moulding, and the weldability, moisture resistance, and recyclability are quite limited
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