Progress in Organic Coatings 49 (2004) 130–136 Evaluation of corrosion performance of a UV-cured polyurethane coating in the presence of organic phosphorous compounds Trinh Anh Truc a,b , Nadine Pébère a,∗ , To Thi Xuan Hang b , Yves Hervaud c , Bernard Boutevin c a Centre Inter Universitaire de Recherche et d’Ingénierie des Matériaux (CIRIMAT), Laboratoire Interfaces et Matériaux, UMR CNRS 5085, ENSIACET 118, Route de Narbonne, 31077 Toulouse Cedex 04, France b Laboratory of Protective Coatings, Institute for Tropical Technology, Nghia Do, Cau Giay, Hanoi, Viet Nam c Laboratoire de Chimie Macromoléculaire, UMR CNRS 5076, ENSCM, 8 Rue de l’Ecole Normale, 34296 Montpellier Cedex 5, France Received 25 March 2003; accepted 30 August 2003 Abstract This study is focussed on the use of organic phosphorous compounds for the improvement of the corrosion protection of a carbon steel by a UV-cured polyurethane coating. Two compounds were employed: one with a long hydrocarbon chain: tridecylphosphate (TDP) and the second one with an unsaturated hydrocarbon chain: methacryloxyethylphosphate (MOP). The compounds were used either for surface treatments before the application of the organic coating or added directly to the coating. Corrosion resistance of the coated steel was evaluated by electrochemical impedance spectroscopy. For the surface treatment, the treatment time was optimised for the mixture 5% TDP + 1.5% MOP. A treatment time of 60min led to the best protection. By incorporating the phosphorous compounds into the polyurethane coating, it was shown that TDP alone significantly improved the protective properties. © 2003 Elsevier B.V. All rights reserved. Keywords: Carbon steel; Surface treatment; UV-curing; Polyurethane coating; Electrochemical impedance spectroscopy 1. Introduction Anticorrosive pre-treatments before painting have been the subject of numerous investigations, particularly on car- bon steels and galvanised steels. Due to the problems of high toxicity associated with chromate treatment, differ- ent studies have been carried out to develop an environ- mentally more acceptable treatment. Organic phosphorous compounds are commonly used to inhibit the corrosion of carbon steel [1–4] and zinc [5] in aqueous solutions. Their use is relatively risk-free due to their low toxicity. In a previous work [6], surface treatments were carried out on a carbon steel in a solution containing a mixture of phosphorous compounds: tridecylphosphate (TDP) and methacryloxyethylphosphate (MOP). It was found that the presence of MOP in the TDP solution creates a synergistic effect for the formation of a film on the steel surface. For a solution containing 5% TDP, the optimum concentration of MOP giving the best protection is 1.5%. The film was porous and essentially identified as a Fe(TDP) n complex ∗ Corresponding author. Fax: +33-5-62-88-56-63. E-mail address: nadine.pebere@ensiacet.fr (N. P´ eb` ere). with n = 1 or 2. The synergistic effect was explained by a competitive action of the two compounds on the carbon steel surface. At the beginning of immersion, the role of MOP is predominant and its aggressiveness generates the formation of ferrous ions which react with TDP to form the Fe(TDP) n complex. Then, the competition mechanism allows the growth of the film on the steel surface. However, the protective properties of the surface treatment were not durable and the treated carbon steel surface was degraded after twenty hours of immersion in a 0.1 M sodium chloride solution. In this study, two ways were chosen to improve the corro- sion resistance of the carbon steel treated with these organic phosphorous compounds: (i) by covering the pre-treated carbon steel by a UV-curable polyurethane aliphatic diacry- late coating (PU) or (ii) by incorporating the compounds in the PU coating. In the latter case, the compounds could play the role of corrosion inhibitors. The UV-curable resin was applied without solvent. This point is particularly in- teresting because it avoids the emission of volatile organic compounds during coating application. To evaluate the protective properties of the different systems, electrochemical impedance measurements were 0300-9440/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.porgcoat.2003.08.022