Effect of color on scratch and mar visibility of polymers

Polymer scratch mechanics has been widely studied. However, the physics behind scratch visibility is still not well understood. Scratch deformation mechanisms certainly affect visibility but also other material properties, such as roughness, color or gloss. This work relates to methods to quantitatively evaluate the effect of sample color on polymer scratch and mar induced visibility, aiming at linking scratch behavior with the underlying physics. A custom-built black box was utilized for the analysis of samples possessing different colors and surface finishing. Automatic image analysis was performed through a commercial software to quantify the onset of visibility in terms of a critical load above which the scratch becomes visible. Trained surveyors visually quantified said critical load. White color was shown to delay the onset of visibility by reducing the contrast between the damaged and undamaged area. For instance, the critical load for the onset of visibility for a white polycarbonate copolymer was nearly twice the value reported for its black variant. Consistent results were obtained for all tested samples. Similar findings were reported for the mar phenomenon, highlighting how white color can also mask a different type of damage. The usefulness of the present work and some future perspectives are discussed.