Spray Deposited Surface Treatment for Enhanced Mechanical Properties of Recycled Carbon Fiber Reinforced Composites

ABSTRACT Chemical surface modification of recycled carbon fibers (rCF) offers a promising yet relatively underexplored pathway to enhance their fiber‐matrix adhesion, vital in enabling product stewardship of carbon fiber reinforced polymer composites (CFRPs). Herein, the development of an easily translatable spray coating approach to improve the mechanical properties of milled CF (mCF) reinforced composites is investigated. This work reports a thermally activated surface modification of mCF (~100 μm), mediated by the generation of a carbene intermediate from bisdiazomethanes upon thermal activation. A solution of bisdiazomethane in acetone (0.5 g/L) was prepared and applied to mCF via spray coating, followed by gentle heating (120°C) to facilitate covalent surface modification of the fibers. Successful surface modification was confirmed via XPS. Addition of these fibers to an epoxy polymer at wt% of 0.5, 1, 2, and 5 wt% revealed statistically significant improvements in mechanical properties. The highest improvements were recorded at 15.37% (2 wt%), 10.21% (5 wt%), 14.63% (5 wt%), and 17.36% (1 wt%) for tensile strength, tensile modulus, flexural strength, and flexural modulus, respectively. SEM images of the fractured surfaces revealed good adhesion of the modified fibers with the surrounding epoxy matrix, consistent with enhanced interfacial adhesion.