Quantifying Surface Mechanical Properties of Filled Coatings Exposed to Accelerated Weathering Conditions

摘要

Photodegradation of polymeric coatings creates irreversible changes in material properties that lead to coating failures such as gloss loss, cracking, or chalking. The underlying causes for failure are related to the chemical and physical changes that occur in the binder matrix or at the matrix-pigment filler interface during weathering. Depth sensing indentation is used in conjunction with thermal and spectroscopic techniques to track coating changes as a function of weathering. In this paper, the elastic modulus of an epoxy and acrylic urethane coating are measured as a function of elevated ultraviolet light exposure. Three different types of TiO2 pigments are used to investigate the effect of pigment size, pigment volume concentration, and photoreactivity on surface mechanical properties. Particle dispersion and size were found to control the increase in surface modulus. The filled epoxy degrades much slower than the unfilled epoxy, but there is no discernable difference within filler types or concentrati ons. The acrylic urethane degrades much slower than the epoxy and differences between the particle photoreactivity are evident. Particles with the highest photoreactivity increased the degradation rate compared to the less reactive, surface treated particles.