Spreading and adhesion of ASA on hydrophilic and hydrophobic SiO2

The spreading kinetics and adhesion of liquid alkenyl succinic anhydride (ASA) on hydrophilic and hydrophobic SiO2 surfaces was studied. Contact angles were measured both in air and in aqueous environment. ASA spread fairly well on both surfaces in air, but when immersed in aqueous solution it spread only on the hydrophobic surface. The contact angle in water on the hydrophilic surface was ≈170°. The work of adhesion of ASA to both surfaces in air was about 60 mJ/m2. When immersed in water the work of adhesion of ASA on the hydrophobic surface was 22 mJ/m2, and less than 1 mJ/m2 on the hydrophilic surface. In the pH range used in papermaking there was no significance of pH on spreading of ASA, but at high pH effects on the surface tensions due to hydrolysis of ASA were observed. Ca2+-ions had no effect on the spreading of ASA on the hydrophilic surface but strongly influenced spreading on the hydrophobic surface. ASA is extensively used as a hydrophobing agent and tends to form detrimental deposits on equipment used for manufacture of paper. From the results it can be concluded that best way to prevent fouling on paper machines by hydrophobic substances is to maintain the process surfaces wetted by water and to choose surface materials that stay hydrophilic as consistently as possible.