A physical approach to define a class A surface in polymer thermosetting composite materials

In polymeric composite material, a class A surface is a high‐quality surface according to its visual appearance. Bulk molding compound polymeric composites behave as a dielectric material with high bulk light scattering, low specular reflection, and low surface scattering. Gloss, related to specular reflection, is then low and cannot be a sufficient criterion to qualify a composite surface. For this purpose, we propose using either haze or roughness and power spectrum density (PSD) measured by AFM. An alternative solution to qualify a surface sample is to cover the sample by a metallic film. The sample then behaves as a metallic material with a main specular reflection and light scattering exclusively because of the surface. Measurements of gloss, haze, PSD, or roughness over a given spatial frequency range can qualify a sample surface and could especially define a surface in the class A family.