Origin Of DCS In Aspen APMP And Influence Of Uronic Acid On Retention/Drainage Aids

A large amount of dissolved and colloidal substances (DCS) was released into theprocess water during the alkali treatment and hydrogen peroxide bleaching processes.The main components in DCS were lignin, dissolved hemicellulose and pecticsubstances. The accumulation of DCS due to the cycle of white-water process can leadto many problems such as the decrease in drainage rates and many paper defects. Theeffects of DCS on papermaking were studied by many researchers. However, the maincomponent in DCS such as uronic acid was less reported. It is important to studysystematically the structure and behavior of uronic acid in the aspen alkaline peroxidemechanical pulp (APMP) for optimizing the pulping and papermaking conditions.In this paper, the compositions and characteristics of DCS in the aspen APMPduring the alkali treatment and alkaline peroxide bleaching processes were studied.Firstly, the components and content of carbohydrates were analized by GC-MS. Theexisting form of carbohydrate was also discussed. Secondly, the affect of beating on therelease rules of DCS were studied. The macropore adsorbent resins, cellulose pad andanion exchange resin were used to separate and purify the uronic acid, removing thelignin, GGMs and neutral sugar setp by setp. Finally, the galacturonic acid was used asuronic acid model and its effects on the retention/drainage properties were discussed.The results showed that both the alkali treatment and hydrogen peroxide bleachingcould promote the release of DCS, such as lignin, carbohydrate and MTBE extractives.The carbohydrates in DCS existed in the form of polymers rather than monomers.The water retention value of pulp increased to be saturated with the growth ofbeating degree. The lignins generated in beating process were mostly colloidalsubstance. The refining of pulp could promote the release of carbohydrates. Thecarbohydrate content in DCS in beating process was lower than that in bleachingprocess. The XAD-8macroporous adsorption resin was effective in removing lignin andthe removal efficiency of lignin reached over99%. However, the IRA-93anionexchange resin was not effective in separating the acid sugar and neutral sugar. Thepolygalacturonic acid and poly4-O-methyl-glucuronic acid xylose could not beeffectively separated by the IRA-93due to its low polarization degree and smallhydrated radius. The addition of polygalacturonic acid could decrease the efficiency ofsingle-component (CPAM) and two-component (PDADMAC/CPAM) retention/drainage aid system. Filtration rate and fines retention rate could be decreased byaddition of polygalacturonic acid. Nevertheles, the addion of galacturonic acidmonomer had little effect on the obove retention/drainage aid system.