Enzymatic Deinking Of Waste Newsprint Study

With the recycling of secondary fibers becoming popular nowadays, the conventional chemical deinking is challenged excessively in various aspects. Enzymatic deinking, as a proven effective and economical replacement, somewhat solves problems.of environmental pollution, decreased paper quality and machine runnability based on biochemical reactions with the help of some chemicals.In this study the rarely reported enzymatic deinkings with lipase, cellulase/ xylanase (C/X) mixture and lipase/ (cellulase/ xylanase) (L/(C/X)) mixture were applied to old newsprint in order to explore new deinking forms for the future use. Investigations were carried out in turn regarding the process condition optimization for enzymatic deinkings, the mixing ratio determination for C/X and L/(C/X) combinations and the comparison between enzymatic and chemical deinkings; Deinking mechanisms concerned were probed as well.Principal results are like the following:1. Deinking process conditions for lipase, xylanase and cellulase were optimized as: pH5.0, temperature 50℃ (47℃ for lipase deinking), reaction time 50min, pulp consistency 10%, flotation time 10min, lipase dosage 0.5~lIU/g, xylanase dosage 3IU/g and cellulase dosage 0.2~0.5IU/g.2. When C/X was fixed in a ratio of 50/50 and L/(C/X) in 40/60, the combined enzymatic deinkings achieved slightly higher pulp brightness, but much better fiber strength than that of cellulase and C/X forms, plus the saved enzyme dosages for each.3. Comparative experiments showed the three enzymatic deinkings resulted in parallel pulp brightness but all better than chemical deinkings. Except cellulase the fiber strengths of the rest were improved too, and the drainage comparison in similar situation as well (but lipase deinking got a modest level). Pulp yield was in a sequence of lipase > xylanase > cellulase > chemical deinkings which was closely associated with the degree of fiber degradation.4. A research about how the cellulase system affected the deinking results was done on ONP by varying F/C ratios of certain constituent cellulases. It was found to raise the F/C ratio, i.e. to get the cellulase system to contain more exo-glucanase and cellobiohydrolase, would decompose cellulose structures in a heavier way and produce more reduced sugar, thereby increase the pulp brightness but decrease the fiber strength adversely.5. With analysis of reduced sugar, crystal rate, infrared spectrum and SEM pictures it was learnt that chemical deinkings remained bigger ink particles and destroyed the cellulose crystal to the most, both reductive to the final fiber strength; lipase3reacted with ink carriers with the least damage to the pulp; xylanase and cellulase were effective in ink removal and fibrillation on fibers so brightness and strength enhanced partially, but the severe degradation of cellulase caused loss to its pulp yield.