Synthesis and Characterization of Zinc/Polypyrrole Nanotube as a Protective Pigment in Organic Coatings MOHAMMAD REZA MAHMOUDIAN, YATIMAH ALIAS, WAN JEFREY BASIRUN, and RAMIN YOUSEFI This study deals with the synthesis and characterization of zinc/polypyrrole nanotube (Zn/PPy) as a protective pigment in organic coatings. The PPy nanotube is synthesized by chemical oxidative polymerization, and zinc nanoparticles are deposited onto the surface of the synthe- sized PPy nanotube in the presence of sodium dodecyl sulfate. Field emission scanning electron microscopy, transmission electron microscopy, and X-ray diffraction results confirm the exis- tence of the nanotube morphology and the zinc nanoparticles. Electrochemical impedance spectroscopy and potentiodynamic polarization are performed on steel plates coated with polyvinyl butyral incorporated with the Zn/PPy nanotube. The results show that the existence of zinc can improve the protective properties of the pigment. The existence of zinc leads to a cathodic protection and the main product of zinc corrosion is the stale zinc hydroxide which can block the pores in the coating. In addition, the zinc nanoparticles can increase conductivity of the PPy nanotube leading to increasing nanotube’s ability to form protective layers of metal oxides on the steel surface. DOI: 10.1007/s11661-013-1686-y Ó The Minerals, Metals & Materials Society and ASM International 2013 I. INTRODUCTION ELECTROACTIVE polymers such as polypyrrole (PPy) and Polyaniline (PAn) have been studied inten- sively during the last decade because of their high electrical conductivity and good environmental stability. These compounds are organic materials that generally possess an extended conjugated p-electron system along a polymer backbone. Among the electroactive polymers, PPy can be easily synthesized from a range of aqueous and nonaqueous solvents. [1,2] Over the past few decades, PPy is considered as one of the bright prospects for corrosion control. It is well known that PPy provides beneficial protection to various kinds of metals in a corrosive environment. [3,4] On the other hand, the nanoscale of PPy shows further improvement in the protective properties against corrosion because of the increase of the surface area. The majority of researchers reported a greater ability of PPy to interact with the corrosive species with the increasing surface area. [5,6] Recent research shows that the template-directed method is a good technique for the synthesis of conducting polymer tubes with uniform dimensions. While the use of hard-template materials usually requires their removal using strong acids/bases or an organic medium, [7] the use of soft templates such as organic acids does not require removal after the polymerization process. [8] Recent reports demonstrate that polymer/Zn systems can be considered as powerful anticorrosive coat- ings. [9,10] In this system, the zinc acts as sacrificial anode against the corrosion of mild steel and organic layer acts as a physical barrier. [11] Recently, ZnO nanoparticles have been used to increase the protective properties of electroactive polymers coatings. [12] It has been shown that the formation of voluminous zinc corrosion prod- ucts within the pores of electroactive polymers can improve their barrier property. [13] Owing to the excellent properties of zinc which can increase the efficiency of electroactive coatings for corrosion control, the poly- mer/Zn coating systems are becoming increasingly important in many modern technologies such as the automotive industry. A review of recent reports shows that researchers have focused on methods that can be used for preparation of electroactive polymer/Zn systems, such as using the mixture of PAn and zinc particles (dust) (or zinc nano- particles) [14] and modification PPy or PAn coating by deposition of zinc particles from aqueous zinc sulfate solution. [15] On the other hand, the results of new investigations confirmed the effect of electroactive poly- mer morphology on their protective properties. [16–18] The ability of Zn and nanoscale electroactive polymers for corrosion control can create a good motivation for synthesizing composites of Zn/electroactive polymers with a new morphology as a pigment in organic coatings. MOHAMMAD REZA MAHMOUDIAN, Postdoctoral, is with the Department of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia, and also Lecturer with the Department of Chemistry, Shahid Sherafat, University of Farhangian, 15916 Tehran, Iran. Contact e-mail: M_R_mahmoudian@yahoo.com YATIMAH ALIAS, Professor, is with the Department of Chemistry, University of Malaya. WAN JEFREY BASIRUN, Professor, is with the Depart- ment of Chemistry, University of Malaya, and also Nanotechnology & Catalysis Research Centre, Institute of Postgraduate Studies, Uni- versity of Malaya. RAMIN YOUSEFI, Professor, is with the Department of Physics, Masjed-Soleiman Branch, Islamic Azad University (I.A.U.), Masjed-Soleiman, Iran. Manuscript submitted April 10, 2012. METALLURGICAL AND MATERIALS TRANSACTIONS A