Plybond chemistry for multiply board
Jaana Laine · Aaltodoc (Aalto University) · 2018
The consumption of multiply packaging boards has vastly increased. To save environment and materials, the consumption of recycled fibers has grown at the same time. However, recycled fibers are poor in quality. Especially Z-directional tensile between plies is difficult to improve and lower quality fibers address more challenges. The aim of the thesis was to establish reliable way to make multiply sheets in laboratory environment, using the latest z-directional strength improving techniques. Both folding boxboard (FBB) and testliner sheets were formed with dynamic sheet former (DSF). At the same time, the best performing plybond chemistry was under study. A nonionic spray starch was introduced between top/middle and middle /bottom plies of FBB. Anionic, amphoteric and cationic strength chemicals were tested in the spray starch. Z-strength was tested, and the retention of starch granules was observed microscopically. The study showed, that multiply sheets including special layers were possible to form, but the time-consuming forming of several layers needs some alteration. Results revealed, that the spray starch alone promotes strength. The strength of FBB was improved by 23 % with combination of spray starch, low amount of cationic starch and amphoteric polymer carrying relatively low anionic charge. Starch granules were detected between layers. Also, anionic chemical was found to improve strength when sufficient amount of cationic starch was added into the pulp. An aqualayer consisting of refined pulp, cationic starch and cationic, anionic or amphoteric strength chemical was introduced between testliner plies. Testliner was tested for burst, short span compression SCT and Z-strength. It was seen that refined pulp had strength improving tendency. Anionic strength chemistry was found to improve the z-strength of testliner even further. The burst strength and SCT of test liner were also improved. In this study charge of the strength chemical was not dictating property.