Scratch resistance of self-healing paints on wood

Paints and varnishes are used to protect or to color bare materials. Their protective or decorative function can, however, be reduced by external mechanical loading. Newly formulated self-healing paints have superior scratch resistance and self-heal even smaller defects. Here we show how to compare scratch resistance of such paints.

Paints and varnishes can be found on almost every object in daily life: home appliances, wood, electronics, toys, cars, buildings, etc. Their goal is to protect the base material against corrosion and to color the object. Paints are usually deposited in water-based liquid form on a solid substrate where they solidify. The protective function of paints and varnishes can be severely reduced when they are damaged and the bare material is exposed to the environment. This can lead to accelerated corrosion. Similarly, external mechanical damage can lead to superficial damage of the paint and loss of gloss or appearance of scratches and wear. Renewing paint is a relatively costly process and therefore new paints that better resist external damage have been developed. This new generation of paints is called self-healing because they are able to repair themselves without external intervention or with increased temperature or light. Autonomous healing is usually based on defect-filling mechanism where microcapsules in the damaged (scratched) area react with the surrounding material and fill the defect by polymerized material. The external-driven healing mechanisms are based on either temperature or light which activates defect closing by decomposing bonds thus causing polymer flow to the defect.
Characterization of scratch resistance of paints by scratch testing has been well documented and the same method should therefore be applicable to self-healing paints. Scratch test of paints is usually used for determination of scratch resistance and the prescan and postscan features (surface scanning at very low load with the same tip before and after the scratch) are extremely useful to quantify the level of recovery.
In this application report we show a comparison of scratch tests on two traditional and one self-healing paint on wood. The ability to self-repair will be demonstrated using the postscan feature which measures the residual scratch depth. The scratch test results will be completed with microindentation measurements of elastic modulus.

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