Elemental and chemical depth profiling of high-build single-component (1K) polyester-polyurethane coil coatings

Abstract

The interior structure and chemistry of single-component (1K) polyester-polyurethane (PU) coil coatings, which find preferred application in the construction industry, was comprehensively investigated by energy-dispersive X-ray spectroscopy (EDX), Fourier-transform infrared (FTIR) spectroscopy and X-ray electron spectroscopy (XPS). Fabrication of extended tapers in the millimetre-range through a double-layered coating system with a total dry film thickness of 50 μm was achieved by cryo-ultra-low-angle microtomy (cryo-ULAM). The linearity and surface topography of shallow angle ULAM cuts created at different preparation conditions were examined at mesoscopic and microscopic scale by coherence scanning interferometry, atomic force microscopy (AFM) and scanning electron microscopy (SEM). EDX mappings recorded on the exposed sections enabled to determine the elemental structure and the distribution of embedded fillers at plane-view. Focal plane array (FPA) FTIR spectroscopy in attenuated total reflection (ATR) mode was used to acquire high-resolution chemical data from the fabricated taper, revealing the clustering of nitrogen-containing groups. Compositional depth profiling of the investigated high-build PU coating system was achieved by performing XPS line scans on the exposed sections. Depth analysis at a chemical level was obtained by means of evaluating the high-resolution carbon C1s spectra, which showed an enhancement of nitrogen and oxygen containing functionalities near the primer/substrate interface. All methods of this correlative work of analysis consistently indicate the presence of chemical gradients related to the cross-linking agent.