Enhancing coated paper mechanical properties via doping kaolin with ammonium molybdate

Abstract

Mechanical properties of paper coating layers are very important in converting and printing operations. Kaolin is commonly used in paper coating as cheap pigment in addition to its superior properties. In this study, a new approach for improving coated paper mechanical properties using doped kaolin with ammonium molybdate was presented. Kaolin and modified kaolin were characterized using several analyses tools (e.g., XRD, SEM, and EDX), and then they were applied in paper coating mixture. The results revealed that the dopant was found in the kaolin as MoOx; this oxide form with its needle shapes led to change in the kaolin crystals, and its presence in high concentrations led to exfoliation of kaolin. Also, at high concentration it was found that MoOx reacted with γ-alumina that is found in kaolin after its heating at 300°C to form aluminum molybdate. It can be observed that modified kaolin increased the coated paper porosity and consequently the opacity; also bulk and thickness were increased. Significant improvement in coated paper tensile strength, bursting strength, tensile energy absorption, and bending stiffness was also noticed. Thermal study also showed that increasing the concentration of ammonium molybdate increased the heat stability of the coated paper.