Conductive polymer coatings towards inhibition of microbial-induced corrosion of low carbon steel

Abstract

Microbial-induced corrosion (MIC) is an electrochemical form of corrosion that is initiated, facilitated, or accelerated by bacteria and biofilms on the metal substrate. Coating methods have been widely used to inhibit MIC because of their effectiveness, ease of application and low cost. Conventional coatings for MIC inhibition are based on heavy metals such as tin, copper, and zinc; however, these coatings are toxic to the environment. Recently, environmentally friendly coatings were developed to overcome MIC problems. Among these new coatings, studies have focused on conductive polymers, which have both antibacterial and anticorrosive properties. The biocidal and anticorrosive properties of conductive polymers make them appropriate coatings for MIC inhibition. This research project is aimed to study and compare the behaviour towards MIC of four types of conductive polymer coatings namely, polyaniline nanofibres, polyaniline-silver nanocomposite, polyaniline-carbon nanotube, and polyaniline-graphene nanocomposite. These polymers were synthesized and produced through in situ chemical polymerization from various chemicals. This was followed by coating the synthesized polymer coatings onto mild steel substrates by solvent casting method. The behaviour of the polymer coated substrates towards MIC was investigated through immersion test in Pseudomonas aeruginosa inoculated nutrient-rich simulated seawater (NRSS) medium for one to eight weeks. The corrosion rates and corrosion resistance of the coated mild steel were determined by electrochemical test and electrochemical impedance spectroscopy (EIS) in 3.5% sodium chloride solution respectively. Materials characterisation and analysis were carried using field emission electron microscope (FESEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Adhesion and conductivity test were performed on the polymer-coated mild steels using pull off and four point probe instruments respectively. The overall results show that nanocomposite coatings displayed better MIC inhibition behavior in comparison with pure polyaniline coating and PANI-graphene act as the best MIC inhibition coating. This is due to the good antibacterial and anticorrosive properties of the coating which effectively inhibit MIC. In addition, electrically conductive polymer coatings could inhibit biofilm formation and impart good anticorrosive properties. This research project concluded that these conductive polymer coatings are suitable candidates for MIC inhibition applications.