Mechanical characterisation of a long discontinuous fibre reinforced composite to evaluate the recycling potential of carbon fibre in structures

Abstract : Carbon fibre composites have been extensively used in the past decades in high-tech industries for the design of structures such as aircraft parts and wind turbine [1]. Many of these composites are reaching the end of their life, and there is a need to address their recycling. For this reason, the recycling process of thermoset materials have been widely investigated in the literature [2], from the most known and named mechanical recycling to the more complex solvolysis and thermolysis. Even though many recycling processes exists it is still difficult nowadays to find recycled fibres with a length of more than 1 or 2 centimetres. In consequence this study focusses on a discontinuous nonwoven unidirectional CF with a fibre length distribution between 20mm and 200mm that can simulate the behaviour of a fabric made of recycled carbon fibre. The first operation was to get rid of the sizing and the binder by a thermal treatment. It appeared that a temperature between 400 and 500°C in an oxygen atmosphere was the most suitable. The treated and untreated CF were tested by single fibre tensile test to ensure that the CF properties (modulus and tensile strength) were intact after the thermal treatment. Once the conservation of the fibre properties was observed the unidirectional nonwoven fabric has been used in a vacuum infusion system to produce a composite material made of 60% CF in weight. This composite material has been compared in term of tensile strength and InterLaminar Shear Strength (ILSS) to the same material made of continuous and untreated fibres. According to the tests, a loss of the tensile strength of about 20-30% was observed for discontinuous CF fibres after treatment but the Young modulus remained constant. The ILSS measurement demonstrated a small increase in the adhesion between the thermoset matrix and the fibres for treated and discontinuous CF. [1] V. P. McConnell, “Launching the carbon fibre recycling industry,” Reinf. Plast., vol. 54, no. 2, pp. 33–37, 2010. [2] G. Oliveux, L. O. Dandy, and G. A. Leeke, “Current status of recycling of fibre reinforced polymers: Review of technologies, reuse and resulting properties,” Prog. Mater. Sci., vol. 72, pp. 61– 99, Jul. 2015.