Interaction Forces Involved in Deinking Processes with Fatty Alcohol Ethoxylates - Fundamental Considerations, 2000 Pulping / Process & Product Quality Conference Proceedings

M. A.  Azevedo, J. D. Miller, J. K. Borchardt, J. Nalaskowski, J. Drelich--Fatty alcohol ethoxylate surfactant formulations have gained acceptance as deinking chemicals in the paper recycling industry due to their efficiency in the removal of toner particles during wastepaper deinking. Therefore, the interaction of toner particles in the presence of these nonionic surfactants is of interest with regard to both fundamental and practical aspects of the process. The interfacial activity of C12En (n=2 to 7) fatty alcohol ethoxylate surfactants was studied using atomic force microscopy, contact angle measurements, and particle-particle agglomeration/sedimentation tests. It has been established by atomic force microscopy measurements using the colloidal probe technique that the interaction force between toner surfaces in the 1´10 -4 M aqueous solutions of ethoxylates is significantly influenced by the pH of the solution, despite the fact that ethoxylates are not sensitive to pH. This dependence is related to the composition of the polymeric toner. For alkaline conditions, repulsive surface forces were measured, for all alcohol ethoxylates. However this repulsive interaction does not appear to be related to the ethoxylates but is more related to the surface structure of the toner, particularly to the polymethyl-methacrylate segments and their extension. Under acidic conditions (pH 4), when the toner’s polymethyl-methacrylate segments are coiled and retracted, attractive forces are observed. However this attractive force in the acidic region is reduced in the presence of C12E2 and C12E4 ethoxylates and is eliminated for ethoxylates having more than 4 ethoxylate groups per molecule. Under these circumstances only repulsive forces were measured between toner surfaces.

The significance of these measurements is revealed from deinking pilot plant studies, which show that pulping of office waste with commercial methoxylates similar in composition to C12E2 results in agglomeration of toner ink particles that are sufficiently large and thick enough to be removed by fine screening. From the other hand, ethoxylates having a larger number of ethoxy groups stabilize the repulsive forces between toner particles.