Study On The Stickies Deposition And Its Enzymatic Control In Secondary Fibers Recycling

The waste paper has been one of the most important resources for pulp and paper industry in China. During the recycling of waster paper, the stickies deposit was formed and it was harmful to the running of paper machine and the product quality. Based on the previous researches, a pressure-sensitive adhesive (PSA) was used as the model substance of secondary stickies to study the stability and the depositability of the secondary stickies. The effect of pectinase treatment of DCS on stickies deposit was evaluated.The results showed that, the stickies deposit formed at the presence of calcium ions, which would result in destability of the stickies. With the increase of calcium ions concentration, the stability of the stickies decreased and stickies deposit increased. It was proposed that the ionic strength of the colloidal suspension was promoted by the addition of calcium ions and the double electrical layers were compressed, which led to destabilization of secondary stickies and stickies deposit.The addition of cationic polymers such as cationic polyacrylamide (CPAM) and polyethylene imine (PEI) led to the destabilization of the secondary stickies and the stickies deposit in fiber suspensions. The amounts of the stickes deposit increased at a low cationic polymers dosage, and then decreased when the addition of the cationic polymers was increased. In other words, low amounts of cationic polymers induced the destabilization of secondary stickies and stickies deposit, but the stickies deposit would decrease when the flocculated stickies were absorbed onto the surfaces of the fibers at the high level of the cationic polymers.At the presence of calcium ions, the low amounts of cationic polymers such as CPAM and PEI would lead to more deposits. When the concentration of the cationic polymers increased, it was beneficial to the decrease of stickies deposit.The results showed that the fillers such as talc and calcium carbonate were one of the important components of stickies deposits. The stickies particles could be adsorbed onto the fillers such as talc and precipitated calcium carbonate (PCC), which caused the destabilization of the stickies particles. The destabilization of secondary stickies was intensified in the presence of cationic polyacrylamide (CPAM). Compared to talc, PCC could adsorb more stickies particles, and it could adsorb the destabilized stickies particles caused by CPAM and then adsorbed more secondary stickies as a nucleus, which enhanced the flocculation of CPAM to secondary stickies. The flocculated stickies particles could be adsorbed on the fibers in the presence of effective cationic polymers, and the stickies deposit would decrease.There was no obvious effect of the single surfactant on the stability and deposit of the secongdary stickies. The addition of the fillers caused the decrease of the stickies deposit in the presence of the surfactant. At the same level of the surfactant, the high filler and the high deposit was introduced.The anionic trash in dissolved and colloidal substances (DCS) negatively affected the efficiency of cationic polymers and aggravated the stickies deposit, and polygalacturonic acid was believed as the main source of anionic trash in DCS. A pressure sensitive adhesive (PSA) was used as the model substance of microstickies in bleached deinking pulp (BDIP). The effect of DCS from bleached chemi-thermo-mechanical pulp (BCTMP) and polygalacturonic acid (PGA) and their pectinase treatment on the efficiency of cationic polymers and stickies deposit were discussed.The results showed that the DCS from the BCTMP lowered the efficiency of cationic retention aids and deteriorated the stickies deposition. Pectinase treatment of DCS was beneficial to the stickies control, because polygalacturonic acid which was the main source of anionic trash was degraded. The cationic demand of DCS decreased after pectinase treatment, and the efficiency of cationic polymers was improved, so more stickies particles were adsorbed to the fibers, which cause the decrease of stickies deposition.