Abstract
The paper presents results of investigations concerning influence of climatic factors and environmental pollution on chemical and physical destruction of polyurethane top coat. In order to increase the operational life of polyurethane coating, its composition was modified by nanoparticles addition of aluminium dioxide (of grain size d=20 nm) or silica (of grain size d=16 nm), which mass share was 3%. Three-year ageing on climatic station of coating systems samples with such modified top coat as well as with unmodified top coat caused its chemical destruction as FTIR (Fourier-transform infrared spectroscopy) examinations documented relevant increase of carbonyl groups (C=0) content. This fact testified oxidation degree rise of superficial layers which indicated their oxidation resistance decrease. Also oxidation initial temperature decrease of polyurethane coating was revealed using DSC (Differential Scanning Calorymetry). Influence of climatic factors and environmental pollution contributed also to the physical destruction of the coating which caused an increase of its surface roughness and generated craters, etchings and cracks (including the silver cracks). Destruction degree of climatically aged polyurethane coating influenced erosive wear intensity of three-layer polyurethane-epoxy coating system. The lowest chemical and physical destruction under the influence of operational factors as well as the highest hardness revealed the coating systems with polyurethane top coat modified with aluminium dioxide what was the reason that they showed also the lowest erosive wear intensity. On the other hand, aged analogously coating systems with polyurethane top coat modified with silica were marked by comparably bigger destruction than the coating systems modified with aluminium dioxide which was the reason of their erosive wear intensity increase.
Highlights
Polymer coatings are commonly used in order to protect technical objects surface against destructive action of climatic and environmental factors as well as to improve their visual appearance
Modification of polyurethane coatings with silica nanoparticles worsened resistance of the coatings to ageing which was documented by FTIR (Figs 4-6) and (Figs 7-12) differential scanning calorimetry (DSC) examinations
FTIR examinations of coating systems with polyurethane top coat, which were aged at the climatic station for 3 years, documented changes in chemical structure of the top coat layer
Summary
Polymer coatings are commonly used in order to protect technical objects surface against destructive action of climatic and environmental factors as well as to improve their visual appearance. Properties of polymer coatings depend strongly on paint mixing way, influencing dispersion degree of nanoparticles, which was documented by Xiong M. and co-authors in the work [43] They applied the high shear mixing technique obtaining in this way good dispersing of silica nanoparticles in polymer composition which resulted in increase of coatings tensile strength as well as glass transition temperature (Tg) of acrylic material. Through the optimal choice of a nanofiller kind and its volume share as well as its grains shape and size one can increase coatings resistance to the influence of such factors like climatic (moisture, solar radiation) and environmental (aggressive media, erosive particles, microorganisms). The aim of polyurethane coatings modification with addition of nanofillers is their tightness enhancement which transfers to their protective efficiency increase as a result of their resistance to mechanical and corrosive loads growth [5, 6, 27, 29, 39, 46]
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