Co-authors​ :

 Kyungil KONG (UNITED KINGDOM), Lourens BLOK , Ian HAMERTON (UNITED KINGDOM) 

In the field of fibre-reinforced polymer (FRP) composites, recycling and reuse have emerged as vital strategies to reduce environmental impact. The primary obstacle in recycling FRP composites is the extraction of fibres from the composite matrix and the reclamation of their inherently strong entanglement. Therefore, a hydrodynamically stable suspension of recycled fibres is proposed for the remanufacturing of aligned FRP composites, emphasizing sustainability. This study presents an eco-friendly and cost-effective approach for the surface treatment of recycled carbon fibres to optimize their suspension, focusing on key factors necessary for a uniform and stable suspension. The research emphasizes the importance of surface characteristics and chemical composition in preventing the clumping of recycled fibres in water. We discovered that treating the surface of virgin and discontinuous recycled carbon fibres alters the C-H and O-H bonds, as observed by Fourier transform infrared spectroscopy. This alteration notably increases the concentration of hydroxyl groups on the fibres, enhancing their affinity for water molecules due to their polar-hydrophilic traits, thus significantly improving water suspension compared to commercial and proprietary water-soluble carbon fibres that are coated with water-soluble sizing. The treatment also fortifies the mechanical strength of these fibres, evidenced by the increase in both their ultimate tensile strength and axial Young’s modulus following the proposed surface treatment. Interestingly, longer in size and more toughened fibres formed more substantial clumps in suspension. However, our experimental results indicated a hydrodynamic stable suspension of the surface-treated carbon fibres because they yielded polar-hydrophilic characteristics. Additionally, as the crowding factor (index as the level of how densely packed the fibres are in the fluid), the surface treatment of the fibres lessens the likelihood of fibre-to-fibre contacts and boosts their interaction with water molecules, thereby enhancing suspension. Among different physical suspension techniques, high shear mixing emerged as more effective, attributed to its superior hydrodynamic turbulence and shear force. The use of a baffled vessel further augmented the stability of the fibre suspension, as the baffles interrupted turbulent currents and facilitated a more stable suspension flow. This study highlights the critical impact of surface treatment on the physical and chemical attributes of recycled carbon fibres, significantly influencing their behaviour and distribution in the fluid.