Emulsification of Alkyl Ketene Dimer (AKD) -characterization of dispersions and emulsifiers

Doktorsavhandling, 2005

Alkyl Ketene Dimer (AKD) is a commonly used hydrophobizing agent in the paper industry, introducing capillary absorption barriers for polar liquids, which makes the paper more resistant to liquid penetration. Since AKD is a so-called internal sizing agent it is usually added in the form of a water-borne dispersion. The objective of this thesis was to investigate the emulsification of the AKD and to characterize and facilitate the formulation of an emulsion with good stability using both normal and degradable surfactants. The AKD was characterized by means of viscosity as a function of temperature, oil number (NOIL) and HLB number. Since the normal way of dispersing AKD goes via high shear emulsification, a low energy emulsification system was developed in order to simplify the emulsification process. It was found that the addition of a fatty alcohol to the formulation was crucial for the emulsification result, giving smaller droplet size and improved emulsion stability. The presence of a lamellar liquid crystalline phase seemed to be of major importance for the long-term stability. Also the order of addition of the components was of importance; adding water to the oil-surfactant mixture resulted in emulsions with a smaller droplet size than mixing the other way around. The surfactants used for emulsification of AKD are only needed in the emulsification process. At a later stage they may cause problems like foaming and uncontrolled wetting of the paper surface. It was demonstrated that cleavable surfactants could successfully be used as emulsifiers for AKD. Both so-called ester-quats and normal ester surfactants were used, showing a potential use of these surfactants that are susceptible to alkaline hydrolysis. A model system based on the polar oil squalane was also emulsified using surface active ortho esters. This relatively new class of acid-labile surfactants showed promising results both in absence and in presence of a stabilizing polymer. Depending on the constituents of the trifunctional ortho ester surfactants, the degradation was shown to proceed at different rates.