The effect of waterborne polyurethane coating on the mechanical properties of epoxy-based composite containing recycled carbon fibres

The current study focuses on the influence of waterborne polyurethane surface-modified recycled carbon fibre (rCF) on tensile, flexural, and low-velocity impact properties of the epoxy-based composite. The recycled carbon fibres were coated by five different concentrations of waterborne polyurethane (WBPU) bonded with 3-aminopropyltriethoxysilane. The chemical bonding between the fibres and the coating and their morphological structures are demonstrated by Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), respectively. Furthermore, the single fibre tensile tests showed the enhancement of tensile strength and Young's modulus results after the coating. The thermal stability of the coated fibres was changed significantly compared to the uncoated fibres and the contact angle of their surface was reduced dramatically. The measured contact angles between the single fibres and the resin decreased from 70° to 40°. The epoxy-based composites were manufactured by the vacuum infusion method at room temperature. Significant improvements were attained in the tensile and flexural properties of the composites reinforced by coated fibres. The tensile and flexural strength of the mentioned composites were enhanced by up to 107% and 68%, respectively. Fractography confirmed the strong adhesion between the coated fibres and the matrix. Eventually, the impact resistivity of the fabricated composites was improved by approximately 49%.