Evaluation of bi-functionalized alumina-epoxy nanocomposite coatings for improved barrier and mechanical properties

Abstract

The effect of embedding bi-functionalised alumina nanoparticle in epoxy resin and its electrochemical and mechanical properties has been extensively investigated. An amino (−NH2) and thio (-SH) functionalized nano alumina particles were synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Thermogravimetric analysis (TGA), and SEM/EDX technique. The colloidal behaviour of alumina-epoxy nanocomposite was influenced effectively by the presence of 3-amino-1, 2, 4-triazole-5-thiol (3ATT) as bi-functional group. The physical, thermal, mechanical and electrical properties of the nanocomposite exhibited strong dependence on the nature of functionalization. The pure epoxy resin and bi-functionalized alumina-epoxy nanocomposite were coated on the mild steel and their protective properties against corrosion were analysed by electrochemical techniques. The current measured at the scratch by scanning electrochemical microscopy (SECM) was much lower (2.5 nA) for the bi-functionalized alumina-epoxy nanocomposite coated steel than pure epoxy coated steel (10.0 nA) at 40 d immersion in seawater. Enhancement of the coating resistance was observed by electrochemical impedance spectroscopy (EIS) for the bi-functionalized alumina-epoxy nanocomposite coated steel (Rc = 2598.35 kΩ.cm2) compared with pure epoxy coated steel (Rc = 9.45 kΩ cm2) at 40 d immersion in seawater. Addition of 3 wt% of bi-functionalized alumina nanoparticle in the epoxy matrix significantly improved its inhibitive and protective properties against corrosion. Surface morphological studies were done by FE-SEM/EDX technique. Mechanical properties have been greatly improved by the reinforcement of bi-functionalized alumina in the epoxy resin. It is reported for the first time that the barrier and mechanical properties of nanocomposite consisting of epoxy-bi-functionalized/alumina nanoparticles with -NH2 and thiol (-SH) are improved significantly. A possible mechanism has also been proposed for the investigated coatings.