Correlating filler transparency with inorganic/polymer composite transparency

The transparency of metal oxide containing polymeric composites was correlated to its filler transparency using a new method based on light microscopy analysis. Filler particles were pressed into filler tablets from which fragments were submerged in different refractive index liquids. Transparencies of different particulate materials with diameters from 0.007 to 1.5 μm were investigated. The transparencies depended on light absorption of the solid, filler particle size and refractive index mismatch of filler and liquid. A correlation between filler transparency and the transparency of filler containing polymers (composites) was established. The method allows to predict the composite transparency for any filler particle size and any filler particle/polymer refractive index mismatch. Manufacturing-caused, batch-wise quality differences in transparency of the same filler material showed similar transparency trends for filler/liquid and filler/polymer transparencies when no quantitative difference was found by nitrogen adsorption, XRD, DRUV–Vis, DRIFTS and SEM analysis.