Progress in Organic Coatings 79 (2015) 53–61 Contents lists available at ScienceDirect Progress in Organic Coatings j o ur na l ho me pa ge: www.elsevier.com/locate/porgcoat Thermal curing study of bisphenol A benzoxazine for barrier coating applications on 1050 aluminum alloy Julien Escobar a , Marc Poorteman a , Ludovic Dumas a,b , Leïla Bonnaud b , Philippe Dubois b , Marie-Georges Olivier a,∗ a Department of Materials Science, Materials Engineering Research Center (CRIM), University of Mons, Place du Parc 20, B-7000 Mons, Belgium b Laboratory of Polymeric and Composite Materials, Center of Innovation and Research in Materials and Polymers (CIRMAP), Materia Nova Research Center & University of Mons, Place du Parc 20, B-7000 Mons, Belgium a r t i c l e i n f o Article history: Received 9 May 2014 Received in revised form 9 October 2014 Accepted 5 November 2014 Keywords: Benzoxazine coating Aluminum substrate Thermal curing Barrier properties a b s t r a c t Polybenzoxazine coatings were elaborated by dip coating of a solution, prepared from a commercial bisphenol A benzoxazine (BA-a), on a 1050 aluminum alloy. The monomer was dissolved in acetone and the influence of the different application parameters (withdrawal speed and viscosity of the solu- tion) on the wet coating thickness was evaluated. A heat treatment was then performed on the coating to polymerize the benzoxazine monomer by a ring opening mechanism attested for by Fourier Trans- form Infrared spectroscopy (FT-IR) and followed by Differential Scanning Calorimetry (DSC). Dielectric Analysis (DEA) and Thermogravimetric Analysis (TGA) showed a particular behavior related to a partial decomposition taking place at 180 ◦ C and associated with the creation of intermediary ionic and volatile species. Finally, the barrier protection was evaluated by Electrochemical Impedance Spectroscopy (EIS) for 30 days in sodium chloride solution (0.1 M). The results showed an improvement of the impedance modulus from 10 4  cm 2 for an uncoated aluminum to a value as high as 10 9  cm 2 with a 10-m thick polybenzoxazine coating. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Aluminum alloys are widely used in aircraft industry because of their numerous advantages such as high strength/stiffness to weight ratio, good formability and recycling potential. Neverthe- less, these alloys are susceptible to localized corrosion [1–3] and, therefore, need to be protected. Several coatings are commonly used at an industrial level in order to improve their corrosion resis- tance such as anodizing layer [4], conversion coating [5] and organic coatings [6]. In most cases, these coatings are chromate-containing layers [4–6], showing excellent anti-corrosive performance. Due to the high chromate toxicity for human beings and environment, the use of these compounds will be banished in 2017 in the aircraft sector. Many studies concern the development of new technolo- gies and alternatives aiming at avoiding the use of chromate: sol–gel coatings [7–11], new anodizing layers [12–15] and elabora- tion of organic-, inorganic- or hybrid coatings [16–19]. Epoxy resin coatings are generally used as organic coatings to prevent corrosion ∗ Corresponding author. Tel.: +32 65374431; fax: +32 65374416. E-mail address: marjorie.olivier@umons.ac.be (M.-G. Olivier). of aeronautic structures due to their good mechanical properties, strong adhesion, high crosslinking density and excellent chemical resistance [20,21]. However, this protective coating is known to be less efficient in aqueous environment. Water can migrate at the interface between the organic coating and the substrate and be at the origin of corrosion, blistering and delamination processes [20,21]. Furthermore, the release of by-products or the use of acid and base as catalyst are unattractive. Recently, polybenzoxazines have gained an increasing interest due to their potential of com- bining the excellent properties of traditional epoxy- or phenolic resins. This class of polymers offers highly attractive properties such as high glass transition temperatures, low absorption of water, near zero shrinkage [22] and good dielectric properties [23]. More- over, no catalyst is required for their polymerization. Benzoxazine monomers are typically elaborated from a phenol, an amine and formaldehyde. By changing the different groups of the components, several types of benzoxazines can be elaborated with a large panel of different properties [24–26]. Only few studies can be found in the literature about the use of this new polymer family as an alternative to epoxy coatings and their potential performance as barrier pro- tective coatings. Zhou et al. [27,28] prepared a 5-m thick hybrid polybenzoxazine cured epoxy on a steel substrate. A benzoxazine precursor (B-TMOS) mixed with an epoxy resin was applied by dip http://dx.doi.org/10.1016/j.porgcoat.2014.11.004 0300-9440/© 2014 Elsevier B.V. All rights reserved.