Research Of Anionic Trash Control In Furnish Containing High-Yield Pulp

High yield pulp (HYP) has advantages with its stiff fibers, high bulk and opacity and good dimensionalstability. The HYP have wide adaptability and the production process of HYP is e envionmently friendly and relatively low manufacturing cost. In recent years, HYP has been widely used in uncoated printing and writing paper, coated printing paper and paperboard and other paper species. Although the high yield pulp has many advantages as mentioned above, the high yield pulp contains a high content of anionic trash. The anionic trash would weaken effects of cationic wet-end additives and affect the normal operation of the paper machine and product quality. To reduce or eliminate the negative effects which caused by anionic trash, the anionic trash catchers (ATCs) are usually added into the paper stock.In this study, several different kinds of anionic trash catchers were used, PAC (polyaluminum chloride), PEI (polyethyleneimine), and a new DADMAC-based polymer. The characteristics and effects of the several anionic trash catchers were investigated. The factors include anionic trash catchers dosages, high yield pulp content, retention and drainage systems and anionic trash catchers adding methods. The aim is to seek the appropriate conditions for the three ATCs respectively and providing solutions to controll anionic trash in high yield pulp. In this study, Zeta potential of the slurry, turbidity and cationic demand of white water, and the retention of fines and filler were determined to characterize effects of anionic trash catchers, and the focused beam reflectance measurement was used to study the flocculation mechanism of anionic trash catchers.The study results showed, the Zeta potential decreased linearly with the increased high yield pulp content; the cationic demand of slurry filtrate increased with the increased high yield pulp content; the first pass retention and ash content negatively affected by HYP content increasing, and the filtrate turbidity increased with the HYP content improvement. For example, the Zeta potential decreased from-23.0/mv to-27.6/mv as HYP content increased from0%to50%. When the high-yield pulp content was10%and40%, ATC D and PEI had obviously positive effects on the Zeta potential and cationic demand; PAC need more amount of dosage to meet the better performance of anionic trash catcher. In the maximum amount of0.6%, PAC had good effect on the retention; PEI and D have very significant effects on retention under the maximum amounts.The first pass retention and ash content of three retention systems had little difference in slurry containing high yield pulp without ATCs adding, and the FPR (First Pass Retention) all stayed between83%-84%. In the presence of anionic trash catchers adding, PEI with PAC both could have better synergy with dual and triple retention systems with the higher retention rate in these two systems. The retention rate in three retention systems had small difference of D and dual and triple retention systems showed slight advantages.Through the flocculation experiments verifying, the flocculation mechanism of PAC is based on charge neutralization and the average chord length of the flocculated particles does not change too much in comparing with blank one. PEI’s flocculation mechanism is patches and its fixation effect of anionic trash is better than that of PAC. The flocculation occurs more slowly with adding D. The time that flocs reach to the maximum size is longer than that of PEI or PAC. D is a anionic trash catchers with three-dimensional structure and the flocculated time is longer because part of the charge of D will gradually release with the shear force’s development.