Study On Characteristics And Control Of Sticky Contaminants In Papermaking Process Of Newsprint

Recycle of waste papers can save forest, energy and minimize impacts to environment. Stickies remain one of the major obstacles in the manufacture of quality newsprints from recycled fibers. Problems caused by sticky contaminants affect severely on processes of producing newsprints with recycled fibers, especially under the current situations of increasingly using recycled fibers for producing more and more paper grades, as well as for the high-speed modern paper machines. Components in recycled pulps are complicated due to they contain not only fibers, fines and filler but also lots of sticky contaminants. It is important to optimize the operation conditions in deinking and flotation and screening processes to remove effectively the sticky contaminants. However, thoese operations can not remove all the sticky contaminants, and stickies still remain the most troublesome obstacle in the papermaking system with recycled fibers.Sources of stickies may include adhesives, hot melts, coating binders, ink residues, de-inking chemicals, rosin, and wet strength resins. In practice, the contaminants remained in the pulp furnish can build up within paper machine headbox, forming wire, press section, and dryer section, causing operation barrier and suffering product quality. Therefore, control of sticky contaminants efficiently is crucial for newsprint mills using waste paper as their fiber resources. In this paper, sticky contaminants were qualitatively and quantitatively studied, and an approach through absorption them onto pulp fibers were examined.Macrostickies samples were acquired by screening deinked pulps with a PulpMac Master Screen, then they were image-analyzed by using a software of Verity Master Screen. Status of macrostickies and their removal from the major operating units were further discussed. The results showed that most stickies were in the range of 0.01-0.1 mm2. More than 90% stickies generated during repulping can be removed from the system, e.g. about 45% and 31% of macrostickies were removed from the coarse screening and low-consistency cleaning, and the fine screening, respectively. The heat dispersing showed the beneficial to reduce the dimension of stickies remained in the pulp.Analyzed by FTIR, Py-GC-MS and SEM-EDAX, it is showed that the organic compounds in sticky substances were mainly polyvinyl acetates and styrene-acrylic ester copolymers. The major elements in extractives included C, O, Al, Si, Ca, and trace of Na and Mg.White water sampled from units of the water circulation system was analyzed. Characteristics of the dissolved and colloidal substances including DCS, DS, CS, SS and TS were examined, furthermore, their distribution and changes were discussed based on each operation units. Conductivity, cationic demand, turbidity of the water samples and their changes with pH values were also examined. Results showed that a higher content of DCS existed in the first loop of the system than that in the second loop and the paper machine loop. The DCS/TS in the white water from the dumping tower and 2# DAF were respectively accounted for about 88%, meanwhile, the DS in DCS were found for over 90%, for example, DS/DCS was 98.2% in the white water from the press section of the PM. The DCS were mainly consisted of the DS, but with only a limited amount of CS. DCS accumulated gradually with running time of the PM. SS can be effectively removed in a DAF, up to 80% or even higher, which accompanied with the removal of CS.The MTBE extractives of DCS were analysed by GC-MS. Results showed that resin acids and some aliphatic acids in samples, including dehydroabietic acid, abietic acid, pimaric acid, isodextropimaric acid, oleic acid, glutaric acid and octanedioic acid. Ddehydroabietic acid was major component and accounted for 28.2%, and abietic acid 12.7%. Degraded components of carbohydrate were confirmed in the DCS, including xylose, arabinose, galactose and glucose, as well as glucuronic acid and galacturonic acid. The xylose accounted for about 30.9%, and glucuronic acid, arabinose and glucose followed.The cationic talc was applied to the deinked pulp to control the sticky contaminants. The effects of cationic talc on stickies and dissolved and colloid substances were investigated, compared with that of the conventional talc. Characteristics of wet-end chemistry were examined for the pulps with both talcs, furthermore, influences on paper properties were also discussed. The results showed that the cationic talc can effectively reduce the amount of stickies and DCS, and decrease the cationic demand of the pulp as well as the turbidity of the filtrate. Deposition of stikies can be reduced by 63.1% as adding 2.0% of cationic talc in the pulp, and the DCS reduced from 1989 mg/L to 1927 mg/L. Addition of cationic talc increased significantly the ash content of the paper, meanwhile, influenced negatively the paper strength properties.