Surface Treatment by Hydrophobic Particles: Influence of Starch and Ionic Strength

This paper deals with the colloidal behavior of mixtures of cationic polymer particles and anionic starch. Such mixtures are commonly used for the hydrophobization of paper. The effect of the concentration of anionic starch and of the presence of different electrolytes was assessed. In a previous study, oxidized starch had been found to induce aggregation of cationic hydrophobic nanoparticles, and in the study reported here it is demonstrated that this aggregated state is beneficial for the performance, enabling a substantial reduction of the amount of polymer nanoparticles needed to reduce the water uptake. It was found that when the particles were in a highly aggregated state, the water uptake by the paper surface was very small. The effect of mono- and divalent ions on the colloidal stability was also investigated. In general, it was found that an increased ionic strength gave a less hydrophobic paper surface. Na2SO4 was more detrimental than NaCl and CaCl2, which is explained by the valence of the anion. This implies that the hydrophobization can be tuned by controlling the aggregation of the polymer particles