Analysis And Control Of Dissolved And Colloidal Substances In Wrapping Tissue Paper Production

The consumption of wrapping tissue paper grows rapidly with the growth in thepeople living standard. The main raw material for wrapping tissue paper production iswood pulp, but the amount of domestic bleached wood pulp can not meets thedemand of papermaking industry. It is necessary to develop the technology ofapplying second fiber to the wrapping tissue paper production. However, thedissolved and colloidal substances (DCS) will enrich gradually with the improvedlevel of white water closed cycle during the production of wrapping tissue paper, andthis exposes adverse effect on the paper machine runnability and paper quality. So it istheoretical significance and practical application value for promoting the applicationof deinked pulp and the improvement of paper quality in the wrapping tissue paperproduction to study the characteristic of DCS, their effect on the papermaking andchemical control of DCS.In this paper, the characteristics of DCS present in pulps of different operationunits were firstly studied using different analytical methods. The effect of simulatedwhitewater cycle on the characteristics of DCS and the properties of papermakingunder laboratory conditions were also studied. Finally, three kinds of cationic fixingagents were used to control the DCS from pulp and whitewater in order to explore areasonable and feasible method for the control of DCS.The characteristics of DCS present in pulps of different operation units werestudied using some analytical methods.The results showed that all the performanceindicators of DCS present in the bleach tower were the highest during the productionof deinked pulp and that in the headbox were the highest during the production ofpaper. The content of DCS in rare whitewater and cloudy water is1.337g/Land1.508g/L respectively, and the chemical oxygen demand is524mg/L and788mg/L. TheDCS content of unbleached pulp is27.55mg/g (o.d. pulp). The DCS content of pulpexisting in the bleaching tower is43.85mg/g (o.d. pulp). The DCS content ofpostbleached pulp is20.90mg/g (o.d. pulp). The DCS content of pulp without aids is12.00mg/g (o.d. pulp) and that of pulp with aids is13.60mg/g (o.d. pulp). The DCScontent of headbox is201.18mg/g (o.d. pulp). The results of gas charomatographycoupled with mass spectrum analysis indicated that the carbohydrates of DCS aremainly composed with xylose, glucose, mannose, glucuronic acids and pectic acids;and the main components of MTBE extractives are some fatty acids, resin acids and glyceride.The effect of whitewater cycle on the properties of DCS, pulp and paper werediscussed through simulating the whitewater cycle under laboratory conditions. Theresults showed that, with the increase of whitewater cycle times, all the performanceindicators of DCS and beating degree of pulp increased, but the physical strength andbrightness of paper decreased. When the number of whitewater cycle times reachednine, the content of DCS, the cationic demand, the chemical oxygen demand and theturbidity increased respectively by62.3%,123.0%312.5%and103.8%. Meanwhile,the beating degree of pulp increased by6°SR. However, the tensile strength, thebursting strength, the tearing strength and the folding strength decreased by28.4%,25.3%,20.5%and41.5%, respectively.Poly(dimethyl-diallylammonium chloride)(PDADMAC), polyamine (PA) andpolyethyleneimine (PEI) were used to control the DCS present in the deinked pulpand the whitewater. The results indicated that the appropriate dosage of PDADMAC,PA and PEI was respectively0.148%,0.19%and0.204%, and the appropriate treatingtime was5min,6min and5min when the deinked pulp was treated. While when thewhitewater was treated, the appropriate dosage of PDADMAC, PA and PEI was0.0292g/L,0.0228g/L and0.0269g/L, respectively. The appropriate time was thesame as5min. The PDADMAC was chosed as the most appropriate fixtive when thedeinked pulp was treated, and the tensile strength, tearing strength and burstingstrength of handsheets was increased respectively by6.1%,18.3%and10.7%.Nevertheless the most appropriate fixing agent was PEI when the whitewater wastreated. The tensile strength, tearing strength and bursting strength of handsheets wasincreased by18.8%,20.6%and22.6%, respectively.