Preparation, characterization and electrochemical corrosion studies on environmentally friendly waterborne polyurethane/Na+-MMT clay nanocomposite coatings

In this study, we present the first practical evaluation for the corrosion protection effect of waterborne polyurethane (WPU)/Na+-montmorillonite (Na+-MMT) clay nanocomposite coating. Typically, a series of waterborne polyurethane (WPU)/Na+-montmorillonite (Na+-MMT) clay nanocomposite materials have been successfully prepared by effectively dispersing the inorganic nanolayers of commercially purified Na+-MMT clay in WPU matrix through direct aqueous solution dispersion technique. First of all, WPU was prepared by polymerizing PCL, DMPA and H12MDI, followed by characterized by nuclear magnetic resonance (1H NMR), Fourier transform infrared (FTIR) and gel permeation chromatography (GPC). Subsequently, the as-prepared PU/Na+-MMT clay nanocomposite (Na+-PCN) materials were subsequently characterized by FTIR, X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM). PCN materials in the form of coating at low Na+-MMT clay loading up to 3 wt% coated on the cold-rolled steel (CRS) coupons were found to exhibit superior corrosion protection effect over those of neat WPU based on a series of electrochemical measurements of corrosion potential, polarization resistance, corrosion current and impedance in 5 wt% aqueous NaCl electrolyte. Effects of the material composition on the gas permeability, thermal stability and optical clarity of neat WPU along with a series of Na+-PCN materials, in the form of coating and free-standing film, were also studies by gas permeability analyzer (GPA), thermogravimetric (TGA), differential scanning calorimetry (DSC) and ultraviolet UV–visible transmission spectroscopy, respectively. As control experiments, a series of PU/organo-MMT nanocomposite (denoted by organo-PCN) materials were also prepared for comparative studies.