Optimization of ASA emulsification in internal sizing of paper and board (2009)

In paper- and boardmaking, internal sizing is used for making the end product more resistant to liquid penetration. Rosin, Alkyl Ketene Dimer (AKD) and Alkenyl Succinic Anhydride (ASA) internal sizing agents exist for this purpose. ASA is added to the papermaking process in the form of an emulsion. The dispersion of ASA oil, water, and a stabilizing agent (stabilizer) are mixed under shear forces to create the emulsion. \n\nIn this master's thesis, different emulsions, emulsification techniques and stabilizers in the process industry were studied. Emulsions in food, medical, petroleum and papermaking processes had potential stabilizers to be used for hydrophobation of paper and board with ASA. The comparison between rosin, AKD and ASA internal sizing agents was also done. The goal was to find optimal emulsification methods and emulsion stabilizers for ASA emulsification. \n\nThe effect of different ASA compounds, one pure ASA and the other, easy emulsifying (EE-ASA), with surface active agents (surfactants) added, were examined with various emulsion stabilizers. Emulsification process of ASA was studied by choosing thirty four stabilizers based on earlier experiments and literature over various fields of emulsification. The chosen stabilizers were reference cationic potato starch, different charge densities and molecular weights having cationic and anionic polyacrylamides (C- and A-PAM's), caboxymethyl celluloses (cmc's) and amphoteric polymers, among other stabilizers which gave steric or electrostatic stabilization effect on emulsion droplets. For the nano- and microparticle stabilization effect, betonies and colloidal silica were utilized. Particle size, pH and visual determinations were carried out and twenty stabilizers were selected for turbidity and zeta potential testing. A good ASA emulsion particle size was in between 0.5 µm - 5 µm in d(0.5) values. The most stable emulsions had no phase inversion, only little creaming and foaming during the 4 hour study. \n\nEleven stabilizers were selected for sheet tests with ASA dosages of 1 kg/t and 2 kg/t. Water absorption tests showed the highest hydrophobation with medium molecular weight and medium charge density having 6.C-PAM and pure ASA and with polyvinyl alcohol, PVA 3-96, with both ASA's. Generally, pure ASA produced higher hydrophobation with only little difference to EE-ASA. The best Cobb hydrophobation values were around 21-23 g/m2 of absorbed water. The best dry tensile index, around 90 Nm/g, were seen with cationic starch and EE-ASA, and the best wet tensile index of 65 Nm/g with medium molecular weight, medium cationic polyamidoamine-epichlorohydrin (PAAE) and EE-ASA. \n\nFinally, six stabilizers were selected for deposition tests where ASA emulsions were exposed to precipitated calcium carbonate (PCC), CaCO3, which is known to forms sticky deposits with ASA's hydrolysis products in paper or board machines water circulation. ASA emulsions stabilized with reference cationic starch showed the lowest deposit amounts, 1.3 and 1.2 g/m2, with pure ASA and with EE-ASA. With EE-ASA, medium molecular weight and medium charge density having 6.C-PAM gained value 5.4 g/m2 but caused serious deposition problems with pure ASA. The deposit nature on sample steel plates varied. PAAE emulsion was easy to remove from the metal surface, whereas starch emulsion would have needed chemical treatment to be removed. PAAE with pure ASA, indicated below average deposition amounts, 11.5 g/m2. Generally neither of the two ASA's was superior compared to the other, when considering fouling. Reference starch and PVA indicated smallest ASA amounts on the deposition test sample plates based on thermal gravimetric analysis. \n\nCost savings could be realized with 6.C-PAM and with PAAE stabilizers with both ASA's. For reference starch, there was practically no difference between the two ASA's and for the 6.C-PAM, EE-ASA was better, whereas for PAAE, pure ASA showed best total results. The PAAE positive effects to wet strength made the chemical commercially interesting.