Summaries of August 2004 peer-reviewed papers.
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BIOCHEMICAL PULPING OF WHEAT STRAW
APPLICATION: Fungal pretreatment of wheat straw yields better quality pulp, reduces cooking chemicals and cooking time, and diminishes the environmental impact.
Biopulping is the treatment of wood chips with lignin-degrading fungi prior to pulping. An environmentally friendly technology, biopulping reduces electrical energy consumption by as much as 30%-40% and improves the strength properties of mechanical pulp.
This study was about the biochemical pulping of wheat straw. The lignin-degrading fungi Ceriporiopsis subvermispora and Phlebia sp. preferentially attack the lignin content of wood. Treatment of wheat straw with C. subvermispora reduced the lignin by 16.5% and the extractives content by 44.3%. During chemical pulping, the kappa number was reduced by 22%-27% at the same alkali charge, or the alkali charge was reduced by 30 kg/ton of raw material, or the cooking time was reduced by up to 30%.
Compared to the control pulp, the biopulp was of better quality, with higher brightness, higher whiteness, and lower yellowness. The COD load in biopulp effluents was lower than in the control pulp effluents. Biopulping benefits with Phlebia subserialis and Phlebia brevispora were not as favorable as those obtained with C. subvermispora. View this paper online at http://www.tappi.org/index.asp?pid=29984
Pratima Bajpai, Shree Prakash Mishra. Om Prakash Mishra, Sanjay Kumar, and Pramod K. Bajpai are with the Thapar Centre for Industrial Research & Development, Bhadson Road, Patiala--147 004, India. Sarju Singh is with Indian Agro Paper Mills Association, 12/22, 1st Floor, East Patel Nagar, New Delhi--110 008, India. Email P. Bajpai at email@example.com.
FORMATION OF AOX AND OCL IN ECF BLEACHING OF BIRCH PULP
APPLICATION: Although a hot acid stage reduced the AOX analyzed in the subsequent chlorine dioxide stage, it was not effective in reducing the total stable AOX in the bleaching sequence.
How does the hexenuronic acid (HexA) in birch kraft pulp influence the formation of chlorinated organic substances in the effluent (AOX) and in the pulp (OCI)? To answer this question, these researchers determined the AOX and OCI content and the filtrate from the first D stage was also stored for 10 days, and the AOX levels were determined again. The pulps they used consisted of birch chips cooked to two different kappa numbers. These pulps were oxygen delignified, treated in a hot acid stage, or not pretreated at all before D(EP)D bleaching.
The amount of HexA removed in the first D stage correlated with the unstable part of the AOX formed in this stage, where the unstable part is the AOX eliminated during 10 days of storage. This linear relationship shows that the unstable AOX originates from HexA. The levels of OCI and stable AOX correlated with the Klason lignin content of the pulp. Although a hot acid stage reduced the AOX analyzed in the subsequent chlorine dioxide stage, it was not effective in reducing the total stable AOX in the bleaching sequence. The stability of the AOX should be carefully considered when AOX analyzes are carried out and when different means of AOX reduction are evaluated.
The same factors influenced the AOX formation in the case of birch and spruce, but the birch pulps gave higher levels of both total AOX and stable AOX for a given charge of chlorine dioxide. This difference could not be explained only in terms of the different HexA and lignin levels. View this paper online at http://www.tappi.org/index.asp?pid=29985
Magnus Bjorklund is at Karlstad University. Ulf Germgard is at Karlstad University, SE-65188 Karlstad. Sweden. Jiri Basta is with Eka Chemicals AB, SE-44580 Bohus, Sweden. Email Bjorklund at firstname.lastname@example.org.
SUBSTITUTION OF ASPEN HIGH-YIELD PULP FOR HARDWOOD KRAFT PULP IN FINE PAPERS AND ITS EFFECT ON AKD SIZING
APPLICATION: High-yield aspen pulp can be used as a substitute for part of the hardwood kraft pulp without any loss of sizing efficiency.
High-yield pulp has been gaining ground in many paper grades, including coated and uncoated papers, but some papermakers have concerns about its high charge demand and its impact on sizing efficiency. Consequently, these researchers determined the charge characteristics of an aspen high-yield pulp. They found that the pulp has a high charge demand (about 100 [micro]eq/g), about 50% of which cannot be removed even after excessive washing with water.
What is the effect on alkyl ketene dimer (AKD) sizing when aspen high-yield pulp is substituted for hardwood kraft pulp? The degree of sizing was found to be higher for sheets made with the high-yield pulp than for sheets made without it. In other words, substituting the high-yield pulp improved the chemistry of the paper, making it possible to increase the degree of AKD sizing.
Papermakers can further improve the degree of AKD sizing for sheets made with aspen high-yield pulp by adding polyethyleneimine (PEI) before adding AKD. There are two approaches for adding PEI. PEI can be added to the high-yield pulp alone, or it can be added to the mixed furnish of high-yield pulp and kraft pulp. The researchers observed that adding PEI to the mixed furnish is more effective in increasing the sizing degree than adding it to the high-yield pulp alone. These differences were attributed to two distinct functions of PEI: neutralization of anionic trash in the high-yield pulp and sizing promotion for AKD.
Precipitated calcium carbonate (PCC) was used as a filler to study its effect on AKD sizing of sheets containing high-yield pulp. PCC was shown to have an adverse effect on sizing, similar to that observed for sheets made without high-yield pulp. View this paper online at http://www.tappi.org/index.asp?pid=29986
Kaitang Hu is with Tianjin University of Science and Technology, Tianjin, P.R. China. Email Hu at email@example.com. Yonghao Ni is with the Limerick Pulp and Paper Research and Education Centre, University of New Brunswick, Fredericton, NB, Canada. Email Ni at firstname.lastname@example.org. Xuejun Zou is with Paprican, Pointe Claire, Quebec, Canada. Email Zou at email@example.com.
THE BUILDUP OF DISSOLVED SOLIDS IN CLOSED WHITE WATER SYSTEMS
APPLICATION: A mathematical model can predict the buildup of dissolved solids in closed white water system.
Reducing the use of fresh water in paper machines remains an important concern to papermakers. This research work pertains to the buildup of dissolved solids in closed white water systems. Mathematical models were established to predict the buildup of substantive and nonsubstantive materials in white water.
According to the model, the final equilibrium concentration of any dissolved solids in a closed water system will increase sharply when the degree of closure is higher than 80%. However, the concentration of dissolved solids is less than or equal to the flow-proportional average concentration of that species in all outside water sources entering the system even for a fully closed mill.
The solids coming into the system in dissolved form will not precipitate out from the water as a result of only the increase in the concentration, no matter how high the number of recycle times climbs and no matter how high the degree of closure is. The precipitation of dissolved materials can only happen if the environmental conditions, such as pH, temperature, charge density, and chemical reactions are changed in a closed mill. Laboratory experiments were also conducted to verify the models by simulating the closure of a paper machine. View this paper online at http://www.tappi.org/index.asp?pid=29987
At the time of this study, Yufeng Xu and Yulin Deng were with the School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, 500 10th Street NW, Atlanta, GA 30332-0620. Xu is currently with the Cincinnati Technology Center, International Paper, 6285 Tri-Ridge Blvd., Loveland, OH 45140. Contact Deng at firstname.lastname@example.org, or by phone at +1 404 894-5700
MILL SCALE APPLICATION OF PEROXYBOOST
APPLICATION: For pulp bleaching, the use of in-situ peracetic acid generated from TAED and peroxide provides a useful option for debottlenecking mills that have limited chlorine dioxide capacity. It may also reduce bleaching costs via chlorine dioxide replacement.
Mill trials with Potlatch Corporation, Lewiston, Idaho, USA, evaluated the industrial application of peracetic acid generated by reacting tetra acetyl ethylene diamine (TAED) and peroxide. The aim of the trials was to assess the potential for reducing total chlorine dioxide consumption in the bleaching sequence.
The mill trials used in-situ peracetic acid (Pa) under alkaline conditions in an O-Pa-[D.sub.1](EOP)-[D.sub.2] bleaching sequence. The peracetic acid was continuously fed to the post oxygen stage high-density storage chest using specifically designed dosing equipment. The result was a significant reduction in total chlorine dioxide usage-up to 7.90 lb/air-dried short ton of pulp. Further trials are planned to optimize the TAED addition and chlorine dioxide savings. View this paper online at http://www.tappi.org/index.asp?pid=29988
Neil Turner and Jane Mathews are with Warwick International Limited, Mostyn, Holywell, Flintshire, UK; Gopal C. Goyal (now with International Paper) was with Potlatch Corporation, Cloquet, Minnesota, USA; and Rocky W. Smith is with Weyerhaeuser Company, 100 Clinchfield St., Kingsport, TN. Email Goyal at email@example.com.
COATING TALC DOES NOT HAVE TO HAVE POOR RHEOLOGY!
APPLICATION: The appropriate ore body and pigment processing techniques can minimize equipment and chemical requirements for optimum pigment dispersion, while improving slurry and coating color performance. The combination of improved performance and lower production costs gives papermakers more flexibility and control over coating pigment applications.
Lamellar pigments can enhance coating coverage and printability in lightweight coated (LWC) rotogravure applications. However, pigments with high aspect ratios and narrow particle size distributions (PSD) can contribute to increased high-shear viscosity and undesirable shear-thickening rheology in slurries and coating colors. Such behavior can hamper pigment slurry screenability and the screenability and runnability of LWC rotogravure formulations, which use high proportions of high-aspect-ratio pigments and are extremely dependent upon high-shear viscosity.
This work describes how an experimental coating talc that made down easier and provided improved slurry screenability and rheology at higher solids and lower chemical dosages in comparison to traditional coating talc without compromising performance. Pilot coater trial results indicated that an abundance of platy fines associated with the experimental coating talc improved LWC rotogravure coating color water retention and coater runnability. Although differences in coating structure related to the two products were apparent at low talc contents, experimental and traditional coating talc provided similar LWC rotogravure paper properties at higher dosages. View this paper online at http://www.tappi.org/index.asp?pid=29989
David B. Willoughby is senior paper technical engineer and Shripal Sharma is senior industry manager, Paper Luzenac America, Inc., Centennial, CO 80112 USA. Email Willoughby at firstname.lastname@example.org or Sharma at email@example.com.
COMING NEXT MONTH IN TAPPI JOURNAL:
Coating Measurement: Raman microscopy in lateral mapping of chemical and physical composition of paper coating by Jouko Vyorykka, Kari Juvonen, Douglas Bousfield, and Tapani Vuorinen
Environmental Control: The application of photocatalysis on Ti[O.sub.2] for degrading COD in paper mill wastewaters by Leah Kanzic Boyd and Catherine Bothe Almquist
Nonwood Fibers: Recycling potential of bagasse and wheat straw pulps By Mayank Garg and Surendra Pal Singh
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|Title Annotation:||TAPPI Journal Summaries|
|Publication:||Solutions - for People, Processes and Paper|
|Date:||Aug 1, 2004|
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