Gloss, hydrophobicity and surface texture of papers with organic nanoparticle coatings

We present an eco-friendly and sustainable alternative for common waxes and fluoropolymer coatings to control the hydrophobicity of paper surfaces, in parallel with improved gloss. Organic nanoparticles were synthesized and deposited from an aqueous dispersion. Due to the high glass transition temperature of the nanoparticles, the evaporation of water during curing leads to the formation of a roughness profile with microdomains (> 1 mu m roughness) that are internally nanostructured (<30 nm roughness). The hydrophobicity and gloss of this coating is controlled by a multilevel roughness profile in combination with fibrous substrates. As such, water contact angles of above 150 degrees can be obtained while maintaining high gloss. Further analysis of the surface morphology for uncoated and nanoparticle coated papers is made by non-contact optical profilometry and AFM measurements. The overall scale-length of roughness measurements can be covered by calculating the correlation length from each surface profile. As such, the gloss values relate to a surface texture parameter determined by the ratio of root-mean-square roughness and correlation length on the microscale. The anisotropy in gloss corresponds to different roughness values in parallel and perpendicular directions. The water contact angles relate to the surface texture parameter on the nanoscale.