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

Abstract

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 H 12MDI, 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.