Solvent-Free Polyaniline Coating for Corrosion Prevention of Metal

Chapter 16 Solvent-Free Polyaniline Coating for Corrosion Prevention of Metal

Xianhong Wang, Jinlong Lu, Ji Li, Xiabin Jing, and Fosong Wang Polymer Material Engineering Laboratory and Open Laboratory of Polymer Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, Peoples Republic of China

Solvent free emeraldine base/epoxy resin coating was prepared employing liquid aliphatic polyamine as the "solvent" for emeraldine base(EB) as well as the "hardener" for epoxy resin(EPR). EB/EPR Coatings with EB loading of 1-2wt% showed good corrosion prevention on mild steel either in 0.1 M HCl solution or in 3.5wt% NaCl solution. Electrochemical impedance spectra analysis found new elements in the equivalent circuits due to the introduction of EB into the coating. Quasi-periodic change in the oxidation degree of EB was found when EB reacted with iron powder. This was a sound evidence that EB acted as the "catalyst" for the iron to form a dense iron oxide layer. Therefore, it was reasonable that even the EB/EPR coating with very low EB loading exhibited long term corrosion prevention effect on mild steel.

254 © 2003 American Chemical Society

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In Electroactive Polymers for Corrosion Control; Zarras, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2003. 255 Introduction

Recently, intrinsically conducting polymers like polyaniline have been demonstrated to be promising corrosion prevention materials for mild steel(7,2,3). Both EB and emeraldine salt(ES) exhibit corrosion prevention properties in lab studies, but they are difficult to process in the solvents widely acceptable in the coating industry. This is more serious with EB. Since only very strong oxidative acid like concentrated sulfuric acid, or very strong polar solvent like N-methylpyrrolidone(NMP) or dimethylacetamide, could be used to dissolve or disperse EB(4). These solvents are difficult to remove since they have high boiling point, and therefore, they are not welcome to the coating industry. Even though sometimes aniline oligomer was used for the same purpose in place of EB, the solvent was still NMP(5j. Recently, Wei et al successfully employed amine capped aniline oligomer as anti-corrosion agent where the oligomer itself was the hardener of epoxy resin, however, this idea was only suitable for aniline oligomer(<5). Recently, a solvent free method was developed in this lab, where liquid aliphatic polyamine-tetraethylene pentaamine was used as the "solvent" for EB as well as the hardener for epoxy resin(EPR). Corrosion prevention coating free of organic solvent was therefore prepared(7,impedance spectra technique, UV-vis spectra and surface morphology studies were used to clarify why this coating displayed good corrosion prevention on mild steel, even with very low EB loading.

Experimental EB was prepared according to a patent technique developed by this group(9). Ammonium persulfate in IN HC1 solution was dropped into aniline/water/acetone/IN HC1 solution to initiate the polymerization, the resultant precipitate was compensated by ammonia and dried under vacuum to obtain EB. Liquid organic polyamine like tetraethylene pentaamine(TEPA) was used as

Downloaded by HAINAN UNIV on October 20, 2015 | http://pubs.acs.org Publication Date: February 28, 2003 | doi: 10.1021/bk-2003-0843.ch016

In Electroactive Polymers for Corrosion Control; Zarras, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2003.