The use of stagnation point adsorption reflectometry to study molecular interactions relevant to papermaking chemistry

In the present report the following systems have been studied with the stagnation point adsorption reflectometer (SPAR). (a) Kinetics of the adsorption of cationic polyacrylamide (C-PAM) on silica and comparison with batch experiments of the same types of C-PAM and cellulosic fibres. (b) Deposition of silica particles onto C-PAM pre-covered silica surfaces in order to study the mechanism behind microparticle based flocculants and to evaluate possible ways to optimise these systems. The results show that: (a) the adsorption kinetics of C-PAM on silica and cellulosic fibres show large similarities. It is hence possible to study adsorption of C-PAM on these silica surfaces in order to evaluate how changes in polymer composition will alter the adsorption onto cellulosic fibres provided the molecular mass is high enough to prevent the influence of polymer migration into the pores of the fibres. This would endanger the comparison between adsorption onto silica and onto cellulosic fibres. (b) It was possible to, in detail, study the interaction between silica particles and polyelectrolytes preadsorbed to the silica wafer. In this way it was possible to find the mechanism describing how different particles are bound to the preadsorbed polymer. By comparison to fibre flocculation studies it was also found that the molecular interpretation from this macroscopic investigation turned out to be wrong but by combining the macroscopic evaluation with the SPAR evaluation it was possible to suggest an optimum microparticle composition. The combination of SPAR measurements with fibre flocculation measurements for the optimisation of the composition of new retention aids seems very promising. (C) 1999 Elsevier Science B.V. All rights reserved.