Summaries of March 2005 peer-reviewed papers.

TAPPI JOURNAL is a monthly publication that includes full-text, peer reviewed research papers exploring every aspect of pulp and papermaking. Each issue presents technically sound, applications-based research; special insights from the authors; and more. TAPPI Membership includes access to all TAPPI JOURNAL content online at www.tappi.org. In addition, convenient print and electronic subscription options are available; TAPPI members receive substantial subscription discounts.

For more information about joining TAPPI, or to subscribe to TAPPI JOURNAL, contact the TAPPI Member Connection Center: Phone: [phone] (USA), 1 800 446-9431 (Canada), [phone], by email at [e-mail], or visit www.tappi.org.

PAPERMAKING

A NOVEL METHOD TO IMPROVE WET STRENGTH OF PAPER

APPLICATION: The combination of TEMPO-mediated oxidation of bleached kraft pulp under suitable conditions and alum addition in papermaking can give sufficient wet strength to paper without adding conventional wet strength agents.

Papermakers need new, efficient, and environmentally sound techniques to improve the wet tensile strength of paper. Commercial polyamideamine-epichlorohydrin (PAE) resin solutions have been the most used--and efficient--wet strength additives for many years. However, PAEs contain toxic, low-molecular-weight organic chlorine compounds originating from epichlorohydrin.

As a potential alternative, we investigated catalytic oxidation using TEMPO (2,2,6,6-tetramethylpiperidine-1-oxy radical), sodium bromide, and sodium hypochlorite (NaClO). We applied these at room temperature to aqueous kraft pulp slurries at pH 10.5 under various conditions for chemical modifications of pulp fiber surfaces. When optimum oxidation conditions were adopted for the TEMPO-mediated oxidation of bleached kraft pulp the wet tensile strength of test handsheets clearly improved, to about three times that of the original pulp.

Because aldehyde groups are efficiently introduced into the TEMPO-oxidized pulps, the wet tensile strength improvement of the handsheets must be brought about by inter-fiber covalent bond formation. This occurs through hemiacetal linkages between hydroxyl groups of cellulose/hemicellulose and aldehyde groups formed at C6 primary hydroxyl groups of cellulose by the TEMPO-mediated oxidation. Moreover, we found that wet tensile strength further improved when the TEMPO-oxidized pulps were combined with alum addition in the handsheet-making process, while dry tensile strength decreased to some extent. The formation of aluminum carboxylate linkages between pulp fibers in the dried handsheets probably has an additive effect on the wet tensile strength improvement. Therefore, the combination of the TEMPO-mediated oxidation of bleached kraft pulp under suitable conditions and aluminum sulfate addition in papermaking can efficiently improve wet tensile strength of paper without any conventional wet strength additives. View this paper online at http://www.tappi.org/index.asp?pid=31877&ch=1

Tsuguyuki Saito and Akira Isogai are with the Dept. of Biomaterial Sciences, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan. Email Isogai at [e-mail].

REFINING

CHARACTERIZING REFINING ACTION IN PFI MILLS

APPLICATION: This study compares the PFI mill to industrial refiners in terms of specific energy and refining intensity and identifies some of the key reasons for the differences. Mills can benefit from this work in knowing the true magnitude of the difference between the PFI mill and their industrial refiners.

The PFI mill continues to be the most commonly used laboratory refining device despite much evidence that its refining effect differs from disc and conical refiners. The origin of this difference is evident in its unique geometry, high consistency, and mode of operation. But how do these translate into refining action?

This paper examines the features of the PFI mill which affect its refining action and compares these to commercial refiners in terms of refining energy, refining intensity, and other factors governing action on pulp. Some comparisons are given of pulp property changes at equivalent values of energy and refining intensity in the PFI mill and conical refiners. The PFI mill is shown to be a high energy, low intensity device and the available evidence suggests that it imposes a greater proportion of compressive to shear forces than do industrial refiners. Comparisons to theoretical values of refining intensity and energy are consistent with cyclic compression and internal fibrillation View this paper online at http://www.tappi.org/index.asp?pid-31879&ch=1

Richard J. Kerekes is director, Pulp and Paper Centre, The University of British Columbia, Vancouver, British Columbia. Email Kerekes at [e-mail].

STEAM

ENERGY REDUCTION AT A KRAFT MILL: EXAMINING THE EFFECTS OF PROCESS INTEGRATION, BENCHMARKING, AND WATER REDUCTION

APPLICATION: Before implementing strategies to reduce energy costs by reducing water use, process engineers should analyze the demand for energy in different process areas, the costs of available fuel and generated power, and the effects of seasonal variations on water use.

This Paprican study focused on identifying opportunities for reducing energy costs related to water use at a particular Canadian kraft mill. A computer model of the mill was constructed and validated with measured data to ensure that it represented the mass and energy balances of the mill process areas. Simulations for proposed projects were run on this model to predict the outcome.

In the first phase, opportunities for reducing energy were identified through the methods of pinch analysis and benchmarking. Pinch analysis determines the absolute minimum energy consumption of a given process. Benchmarking was based on data derived from similar operations in other mills. Implementing the projects of Phase 1 in the simulation resulted in total predicted steam savings of 50,500 kg/h in summer and 51,800 kg/h in winter. However, the projects of Phase 1 did not significantly address water use.

In the second phase, additional opportunities were considered for saving energy by reducing the use of water. The Phase 2 modifications resulted in additional predicted steam savings of 38,000 kg/h in summer and 58,700 kg/h in winter. Water reduction should be considered with process integration techniques because each method can identify independent opportunities for steam savings.

To achieve meaningful reductions, a mill must reduce the water use in the heat recovery system and in the process areas simultaneously. Mill engineers should also consider the seasonal variations in water use and should bear in mind the limits of economically viable steam savings. View this paper online at http://www.tappi.org/index.asp?pid=31880&ch=1

Michael Towers is a research engineerwith the Pulp and Paper Research Institute of Canada, P.O. Box 21018, Prince George, BC, Canada, V2M 7A5. Email Towers at [e-mail].

NONWOOD FIBERS

BIOPULPING OF WHOLE JUTE PLANT IN SODA-ANTHRAQUINONE (AQ) AND KRAFT PROCESSES

APPLICATION: Pretreatment of jute plant with fungal strains before soda-AQ or kraft pulping reduces cooking time, kappa number, and chemical requirements, and improves the physical properties of the resulting pulp.

This study evaluated the effectiveness of nine fungal strains (Ceriporiopsis subvermispora [1-3], Phanerochaete chrysosporium [1,3,4,5], Fomes lignosus, and ST-2) as pretreatment for jute biopulping.

Dried, whole jute plants were cut into small pieces. Sample amounts were mixed in polyethylene bags with water containing various salts. Separate bags were then inoculated with 10 plugs of fresh culture of nine fungal strains, and 14 g of glucose was added. The bags were incubated at 30[degrees]C for 14 days. Control experiments were performed without fungus using the same conditions.

All pulps were tested according to TAPPI Test Methods for kappa number, density, burst, tear, and tensile strength. Out of the nine fungal strains tested, P. chrysosporium-1, P. chrysosporium-3, C. subvermispora-2, and F. lignosus were more effective in reducing the pulp kappa number. The kappa number of biotreated pulp in the soda-anthraquinone (AQ) process can be reduced by 20%. The desired kappa number can also be obtained by reducing alkali charge (9%)

Physical properties (burst, tear, and tensile index) of biochemical pulps processes improved significantly (20%-40%).

In both soda AQ and kraft processes, cooking time can be reduced (from 120 min to 60 min in the kraft process and from 90 min to 60 min in the soda-AQ process). View this paper online at http://www.tappi.org/index.asp?pid=31881&ch=1

At the time of this study, Ghulam Mohiuddin, Mamunur Rashid, and Sk Abul Hasib were with the International Jute Study Group (IJSG), Dhaka, Bangladesh; Mizanur Rahman and Abdur Razzaque were with Karnaphuli Paper Mills Limited (KPM) of Bangladesh Chemical Industries Corporation (BCIC). Email Mohiuddin at [e-mail].

CHEMICAL RECOVERY

PREDICTION OF DUST COMPOSITION AND AMOUNT IN KRAFT RECOVERY BOILERS

APPLICATION: This mathematical model can help engineers predict what the effects will be when a mill upgrades a recovery boiler.

A comprehensive mathematical model is a useful tool for predicting the effects of recovery boiler upgrades. Dust properties and the extent of carryover and fume geneneration vary from boiler to boiler. An existing modular model for recovery boilers has now been modified to accurately predict the compositions and amounts of recovery boiler dust. The revised model provides a tool for predicting the fireside effects of upgrading combustion air systems. View this paper online at http://www.tappi.org/index.asp?pid=31883&ch=1

Barry Malmberg and Lou Edwards are with the Dept. of Chemical Engineering, University of Idaho, P.O. Box 441021, Moscow, Idaho, 83844-1021. Sten Lundborg, Mikael Ahlroth, and Bjorn Warnqvist are with AF-Celpap, Fleminggatan 7, Delivery: Box 8309, SE-104 20 Stockholm, Sweden. Email Malmberg at [e-mail].