CATHODIC DISBONDING OF INDUSTRIAL CHLORINATED RUBBER-BASED PRIMER USED IN RUBBER/METAL COMPOSITES: AN ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY ANALYSIS

Abstract

ABSTRACT Chemlok 205 primer is a common bonding agent used together with a top coat in rubber/metal–bonded composites. Recent studies indicated that a stand-alone Chemlok 205 primer failed when its metal substrate underwent corrosion. The failure was suspected to be caused by coating degradation, followed by cathodic disbonding, induced from the corrosion reaction. Therefore, in this work, the effect of cathodic polarization on the coating delamination was further investigated. The work intends to focus on understanding the adhesion failure processes involved. Thus, electrochemical impedance spectroscopy (EIS) was employed on a stand-alone industrial coating Chemlok 205 primer on mild steel substrate subjected to cathodic polarization potential of −0.8 V versus Ag/AgCl reference electrode in 0.5 M NaCl. The coating barrier properties were interpreted through Nyquist and Bode plots of the EIS plots for a selected time interval. The data obtained were modeled against three distinguished electrical equivalent circuits representing the stages of coating degradation against time. Analysis through Nyquist and Bode plots indicated that the stand-alone Chemlok 205 primer coating experienced a significant drop in coating impedance before experiencing adhesion loss. The changes in the coating capacitance and coating resistance indicated that the coating underwent degradation first before adhesion failure.