Mechanical, wear, thermal conductivity and hydrophobicity behavior of Kevlar fiber-epoxy structural composites reinforced with onion peel carbon quantum dot and commercial carbon nanotubes: a comparative study

The primary objective of this investigation is to conduct a thorough analysis of carbon quantum dots (CQDs) particles derived from onion peel, comparing them with carbon nanotubes (CNTs) particles. The synthesis of CQDs involves the meticulous application of the hand layup method, a methodology replicated in the fabrication of CNT composites. Both filler composites undergo additional reinforcement with Kevlar fibers. Test specimens are precisely sectioned from the composite plates utilizing an abrasive cutting machine. Subsequent characterization is performed in strict adherence to the American Society of Testing and Materials (ASTM) standards, encompassing mechanical, wear, thermal conductivity, and water contact angle properties. In the realm of mechanical properties, the composite designation EKCQ3, comprising 2 vol.% of CQDs with 35 vol.% of Kevlar, exhibits remarkable mechanical strength. In comparison to EKCN3 (designation with 2 vol.% of CNTs), EKCQ3 demonstrates an 8.75% improvement in tensile strength, a 12.1% enhancement in flexural strength, a 27.2% boost in compression strength, and a 13.5% increase in impact resistance. Similarly, in wear properties, the CQD composite designation showcases superior wear resistance. EKCQ3 exhibits high wear resistance with a specific wear rate of 0.07 mm³/Nm and a coefficient of friction (COF) of 0.22. The reduced particle size of CQDs contributes to uniform dispersion, enhancing bonding and adhesion with Kevlar fibers in the matrix, thereby leading to improved mechanical and wear properties. In thermal conductivity, the CNTs composite designation demonstrates a high thermal conductivity of 0.47 W/mK. However, CQDs also deliver very close thermal conductivity values of 0.45 W/mK, highlighting their comparable performance in this aspect. Regarding water contact angle, the overall composite designation exhibits hydrophobic behavior, showcasing water contact angles ranging between 90 and 95°. In summary, CQDs outperform CNTs in mechanical and wear properties. In terms of thermal conductivity, CQDs demonstrate slightly superior performance, with only a marginal difference observed between CQDs and CNTs. Carbon quantum dots (CQDs) emerge as the preferred material for applications requiring optimal mechanical strength, wear resistance, and thermal conductivity, coupled with inherent hydrophobic characteristics.