Surface mechanical properties of polymeric coatings under accelerated weathering

The surface of coatings and plastics is the first target in any degradation process initiated by ultraviolet (UV) radiation or mechanical stress (via scratch and abrasion). Surface damage can lead to changes in optical, morphological, and mechanical properties and can result in pathways for ingress of moisture and corrosive agents. Current test methods for monitoring performance of protective coatings focus on chemical properties and optical properties, such as colour and gloss measurements, or invasive tests such as abrasion and cross-cut adhesion.

Evaluation of scratch resistance

In a new study, a macroscopically nondestructive performance protocol using nanoindentation metrology via a well-controlled scratch test was applied to evaluate the scratch resistance and monitor the surface mechanical property changes in a protective coating under accelerated weathering.Polyurethane (PU) coatings with different polyol compositions were chosen for the study. Coating specimens were exposed to high-intensity UV radiation at 55°C and 75% RH conditions.

Influence of polyol type and UV radiation dose

Exposed specimens were removed at specified UV exposure times for surface modulus/hardness and scratch resistance characterisation via nanoindentation and scratch test.The effect of polyol type and UV radiation dose on the scratch damage (scratch morphology) was investigated and correlated with the surface hardness and modulus of the materials.

The study is published in: Journal of Coatings Technology and Research  September 2018, Volume 15, Issue 5, pp 913–922.