Abstract
Polymer coatings have been used for the corrosion protection of metal surfaces acting as a physical barrier against several corroding media. In spite of the good efficiency of these coatings their resistance is limited due to the presence of localized defects which give place to localized corrosion. Aiming to improve the barrier properties of these coatings this work has proposed the use of nanocomposites as powder coatings based on a standard formulation of a commercial powder varnish. Nanocomposites with 2 and 4 wt% contents of organophilic montmorillonite (OMMT) were obtained in the molten state through of a co-rotating twin-screw extruder. The application of the nanocomposite coatings was performed by electrostatic pulverization on mild steel panels. The coatings were characterized to determine their structure using X-ray diffraction (XRD). The morphologies of the coatings were assessed using transmission electron microscopy (TEM). Gloss and adhesion measurements and the flexibility and impact resistance of the coatings were included in the physical assessment of the coatings. The corrosion performance was evaluated by the salt spray test and by electrochemical impedance spectroscopy (EIS). The coatings with clays presented predominantly exfoliated structures, with good dispersion of OMMT in the epoxy matrix. The addition of OMMT reduced the impact resistance, flexibility and gloss but increased the barrier properties of the coatings. The best corrosion performance in NaCl solution was achieved for 4 wt% OMMT.
Highlights
IntroductionBecause of the improved physical and chemical properties provided by ceramic materials to polymers, lamellar silicate polymer nanocomposites have attracted the attention of both industry and the scientific community[1,2]
Because of the improved physical and chemical properties provided by ceramic materials to polymers, lamellar silicate polymer nanocomposites have attracted the attention of both industry and the scientific community[1,2].Several polymer matrices have been used in the production of nanocomposites, among which the epoxy resins are highlighted in view of their wide application in engineering[3,4].Recently, lamellar silicate nanocomposites have been used as anticorrosion reinforcement in liquid coatings, in special to those based on an epoxy matrix
The data provided by the X-ray diffraction analysis performed on the cured epoxy resin-based powder coatings are shown in the diffractograms of Figure 1
Summary
Because of the improved physical and chemical properties provided by ceramic materials to polymers, lamellar silicate polymer nanocomposites have attracted the attention of both industry and the scientific community[1,2]. The improved barrier properties of the coatings are based on the concept of the tortuous path caused by the exfoliation of clay, which reduces the diffusion of gas and/or liquid molecules throughout the coating Such reduced diffusion highlights the huge potential of the manufacturing of nanocomposites applied to powder coatings via intercalation in the molten state[5,6]. A fair anticorrosive performance of a powder coating was observed by Piazza et al.[9] by incorporating 2 and 4 wt% of montmorillonite to the formulation of a polyester-based powder coating They concluded that the coatings barrier properties are directly associated to the clay lamellar structure and to the electrostatic forces existing between matrix and filler, resulting in coatings with better resistance to the permeability of gases and/or liquid molecules. To evaluate the influence of the filler addition, the morphology, physical properties, anticorrosive performance and barrier properties of the nanocomposite coatings were characterized
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