Effect of cotton nanocrystals on corrosion resistance and properties of electrodeposited Cu-Sn coatings

Cu-Sn electrodeposited coatings are widely used for decorative, corrosion-resistant, and wear-resistant purposes, especially in electronics, automotive, and aerospace industries. This study investigated the effect of cellulose nanocrystals (CNC), extracted from cotton by acid hydrolysis, as an additive at concentrations from 0%v/v to 7.5%v/v in a Cu-Sn electrolyte bath. The morphology, composition, and structure of the coatings were analyzed using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), and roughness measurements. Wettability was evaluated through contact angle measurements. CNC incorporation led to more compact coatings with reduced roughness. Current efficiency increased with 1%v/v and 2.5%v/v CNC, indicating reduced energy consumption during electrodeposition. Contact angles rose from 95° to 106° and 126° with 1%v/v and 2.5%v/v CNC, showing enhanced hydrophobicity. Corrosion resistance was assessed in 3.5 wt.% NaCl solution using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), with the best performance and highest tin content observed at 1%v/v CNC. Microhardness also increased with CNC addition, reaching its highest value at 7.5%v/v. These findings highlight CNC as a low-cost and sustainable additive to enhance the properties of Cu-Sn coatings.