A comparative study of polyelectrolyte multilayers and other chemical dosage strategies: Effect on properties of paper sheets produced in laboratory scale using tap and mill process waters

In this study, the addition of up to four layers of PEM was studied and compared with the use of single-additions or dual-additions of the same chemicals with respect to their effect on strength and bulk properties of paper sheets produced in the laboratory. First, this was made under clean conditions, i.e. in tap water, to set a baseline for the performance. The systems studied were cationic/anionic polyacrylamide (CPAM/APAM), polyvinylamine/carboxymethyl cellulose (PVAm/CMC) and cationic starch/anionic polyacrylamide (CS/APAM).One of the main findings of the study was that with single-additions with increasing dosage levels of PVAm, CPAM or CS, the tensile strength index of the produced sheets increased at first, but the effect seemed to level off at higher dosages. By comparing the effect from single-addition of each cationic component to the effect of a polyelectrolyte multilayer (1-4 layers) of the same component together with an anionic component, it was found that significantly higher tensile strength could be reached with the PEM strategy for the combinations PVAm/CMC and CS/APAM. For CPAM/APAM, however, very little advantage of using a multilayering approach was seen.All measured variations in sheet density were small, although with some indications that the density was lower for sheets with PEM, medium for sheets made with a single-dosage strategy and highest for sheets made with the dual-addition strategies.The later part of this activity also addressed the influence from dissolved and colloidal substances (DCS) to investigate the possibilities of implementing the polyelectrolyte multilayering technique in practice by repeating some of the trial points of the CS/APAM system in mill process water. Firstly, this part of the study showed that PEMs can be successfully built in mill process waters. Further, it was found that although the adsorbed amounts might differ compared to in the cleaner system, the trends for the dosage strategies and their strengthening effects remained.