The effect of sequential polymer addition on wet- and dry-web mechanical characteristics: Laboratory, semi-pilot, and pilot studies

Fibre properties can be modified by treatment of the fibre surface with oppositely charged polyelectrolytes. Sequential addition of oppositely charged polyelectrolytes forms macromolecular layered structure of polyelectrolytes. The use of polyelectrolyte multilayers increases dry-paper strength with only minor changes in density, in light-scattering, or in the formation of the sheet. However, there is little information on multilayers' effects on wet-web mechanical properties, especially on dynamic tensile and relaxation behaviour. Tests on laboratory scale showed that the sequential addition of polymers can significantly improve the strength of the wet and dry paper web. Wet-paper tensile strength was improved 45% when cationic starch was added to pulp (1%) and A-PAM by spraying (0.3 g/m²) onto wet handsheets. Furthermore, semi-pilot and pilot trials confirmed the laboratory findings, and similar effects on wet-paper tensile strength were observed. Overall, modifying the interactions between fibres in wet state seems to be very beneficial for wet web runnability. However, the generation of polymer multilayers or even a bi-layer on the paper machine by spraying may be challenging, although its huge benefits seem to make it an interesting option.