Carbon-fibre-reinforced polymer (CFRP) composites are promising materials for non-metallic pipe applications in the oil and gas industry owing to their high corrosion resistance, specific strength and stiffness. However, CFRP has poor gas barrier performance meaning that a liner has to be inserted. Graphene-based nanomaterials have been demonstrated to improve gas barrier properties in thermoplastic polymers, and thus, a CFRP–graphene hybrid composite could provide an alternative to lined pipes. In this work, a method combining spray coating with vacuum-assisted resin infusion was developed to fabricate CFRP hybrid composites with preferred in-plane aligned graphene nanoplatelets. Tensile and flexural properties, as well as CO₂ gas permeability, were evaluated. It was illustrated that both tensile and flexural properties performed better under relatively low GNP loadings (< 0.2 vol%), while gas barrier property was significantly improved with the increasing GNP loadings which fits the Nielsen model with an effective GNP aspect ratio of 350. Graphical abstract

The needs for sustainable development and energy efficient manufacturing are crucial in the development of future composite materials. Out-of-oven (OoO) curing of fiber-reinforced composites based on smart conductive polymers reduces energy consumption and self-regulates the heating temperature with enhanced safety in manufacturing, presenting an excellent example of such energy efficient approaches. However, achieving the desired curing processes, especially for high-performance systems where two-stage curing is often required, remains a great challenge. In this study, a ternary system consisting of graphene nanoplatelets/HDPE/PVDF was developed, with a double positive temperature coefficient (PTC) effect achieved to fulfill stable self-regulating heating at two temperatures (120 and 150 °C). Systematic studies on both single and double PTC effects were performed, with morphological analysis to understand their pyroresistive behaviors. Compared to the oven curing process, up to 97% reduction in the energy consumption was achieved by the ternary system, while comparable thermal and mechanical properties were obtained in the carbon fiber/epoxy laminates. This work presents a new route to achieve OoO curing with two-stage self-regulating heating, which can be utilized in many high-performance composite applications.