Surface properties of an associative alkali soluble polymer (Acrysol TT-935)

Abstract

Acrysol TT-935 R&H is an associative alkali soluble polymer with applications to the paper and coating industry. For hydrophobic modified polymers there is a lack of fundamental understanding on their surface properties in aqueous solutions. The aim of this work is to report surface properties of the Acrysol TT-935 obtained from the equilibrium surface tension (EST) (by the du Noüy ring method) within the pH range 5–11 at room temperature and the dynamic surface tension (DST) (by the maximum bubble pressure technique) and the titration curves. From equilibrium surface tension a wide variation in surface activity of the polymer occurred when the pH changed within the range 5–6.5, and it was a function of pH and polymer concentration. This was explained in function of the ionization degree of the methacrylic acid group in the polymer. Also it was shown that critical aggregation concentration and saturation area (cac and Γ s) of the polymer solutions remained constant at different pH within the studied range. The surface properties were obtained using Volmer surface equation of state. Dynamic surface tension experiments were carried out at constant time (1 s) and concentrations beyond the cac in the pH range from 6.5 to 11. From this data, the polymer species were determined as function of pH and changes in the adsorption process were confirmed. The adsorption kinetics at the interface were analysed using a theoretical diffusion model. The polymer solutions showed a pronounced minimum level at pH 6.5 at bulk concentrations greater than 0.60%. This minimum in surface tension occurs at the p K a of the polymer and could be correlated with the change in the activity of the various polymer species in bulk solution and with the fast and strong adsorption and interaction of these species at the interface. The surface properties of the polymer showed how the adsorption process occurred, and the DST gave information about the aggregation mechanism at different pH’s. Characteristics surface tension values over shorter times are also relevant to many industrial applications.