Summaries of July 2004 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] visit www.tappi.org.

TESTING

USING PEEL AS A MEASURE OF PAPER SURFACE STRENGTH

APPLICATION: Paper surface strength--an important property influencing coating, printing, and converting--can be reliably measured by this simple procedure based on peeling tapes from paper surfaces.

The force required to initiate delamination of paper when peeling a strip of adhesive tape can serve as a measure of paper surface strength. We obtained measurements which were insensitive to tape properties, peeling direction, and peeling velocity by using a 180[degrees] peeling geometry in which only the test tape was allowed to bend. We compared measurements of peel surface strengths to IGT surface strength velocities for 15 uncoated papers, including machine-made fine papers, newsprint, and filter paper. The newsprint and fine papers surface peel strengths were linearly correlated with the IGT results, whereas the filter paper data were poorly correlated. We believe the IGT test was compromised by excessive liquid pickup in the very porous filter paper. The peeling measurements offer the advantages that a force is directly measured, measurements from vastly different paper types can be directly compared, and, the procedure does not require operator assessment of the onset of paper failure. View this paper online at http://www.tappi.org/index.asp?pid=29717

Boxin Zhao and Robert Pelton are with McMaster Centre for Pulp and Paper Research, Department of Chemical Engineering, McMaster University, Hamilton, Ontario, Canada L8S 4L7 Email Zhao at [e-mail] or Pelton at [e-mail].

SIZING

SIZING PERFORMANCE AND HYDROLYSIS RESISTANCE OF ALKYL OLEATE SUCCINIC ANHYDRIDES

APPLICATION: With a long useful life in the emulsion form, ethyl oleate succinic anhydride could become one of the preferred sizing chemicals in papermaking.

Alkenylsuccinic anhydride (ASA) is one of the alkaline sizing chemicals commonly used in papermaking. ASA has the advantage of efficient sizing performance, but it has two shortcomings: (a) instability in aqueous emulsions and (b) sticky behavior of the hydrolyzed ASA formed during white water circulation.

New sizing compounds have now been synthesized to overcome these problems. The new compounds are alkyl oleates linked to succinic anhydride, or AOSA. The researchers studied these compounds and compared them to conventional ASA in terms of sizing performance and stability. The characteristic difference between AOSA and ASA is that for AOSA compounds the succinic anhydride groups are always linked to the center of the alkenyl chains. For the AOSA compounds synthesized, ethyl oleate succinic anhydride (EOSA) showed sizing efficiency similar to that of ASA for handsheets prepared with 20% PCC filler.

When the EOSA emulsion was stored for one day, the degree of sizing was almost the same as that obtained with fresh EOSA, whereas for ASA, there was almost no sizing after one day of storage. Moreover, the degree of stickiness of the calcium salt of hydrolyzed EOSA in water was lower than that of hydrolyzed ASA. With these improvements, EOSA may find use as an efficient, stable size for both internal and surface sizing in papermaking.. View this paper online at http://www.tappi.org/index.asp?pid=29718

Akira Isogai and Shin Morimoto 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. E-mail Isogai at [e-mail].

CORROSION

CORROSIVITY OF LIQUORS IN CONTINUOUS DIGESTERS

APPLICATION: This review shows the importance of analyzing black liquor before and after corrosion testing and highlights factors that can affect those results.

This paper summarizes some of the most comprehensive studies on corrosion of cooking liquors, but with only brief mention of the caustic stress corrosion cracking of carbon steel digesters.

Any straightforward correlation between the corrosion rate of carbon steel and only one inorganic/organic component of the cooking liquor is probably misleading. The interaction of several components may be an important factor in overall corrosivity of cooking liquors. The existence of some organic compounds has been explained to be a reason for non-corrosion of some digesters, while other seemingly identical vessels were severely corroded. However, there are no systematic studies on organic compounds acting as general corrosion inhibitors in digesters.

This review also shows the importance of analyzing the cooking liquors used in corrosion tests. The composition of black liquors changes during corrosion tests through the degradation of black liquors at higher temperatures. Especially when the alkalinity of the test liquor is modified by adding sodium hydroxide, the test liquor should be analyzed before and after the corrosion tests. View this paper online at http://www.tappi.org/index.asp?pid=29719

Anja Klarin-Henricson is senior consultant in operations management with Electrowatt-Ekono, a part of Jaakko Poyry Group, Tekniikantie 4 A, P.O. Box 93, FIN-02150 Espoo, Finland, email [e-mail]

COATING

EXPERIMENTAL AND STATISTICAL INVESTIGATION OF DRYING EFFECTS ON COATED OFFSET PAPER QUALITY

APPLICATION: This study shows that mottle tendency and roughness of wood-containing papers can be controlled by optimizing the drying of coating and by proper selection of the most influential coating raw materials.

This study used a simulation program to statistically analyze the effect of drying on coating properties. A series of tests, in which papers were coated and dried under different conditions, was carried out on pilot coaters. The samples obtained were printed under controlled conditions to evaluate the print quality. We used the test and simulation results to determine the migration of water in the coating, the evaporation rate, and the water absorption rate into the base paper at different points of the drying section. A statistical determination was made about the effects of drying conditions on the final product properties.

Increasing the web temperature at the beginning of the drying section resulted in increased paper roughness and decreased paper gloss. Four coating colors at two coat weights all behaved in a similar way. Conventional high-low-high drying theory to avoid mottle was valid with lightweight coated (LWC) coat drying when the speed was 1000 m/min and the delay times for convective drying were relatively long. With starch-containing coating color, the back-trap mottle tendency correlated well with the evaporation rate when coating was at 77% solids content. The delay time for air drying was 345 ms in these trials. Further, a short delay time before drying evened out the effects of drying on mottle. With a short delay (190 ms) before the air dryers, the differences between trial points were clearly smaller than with longer delays. View this paper online at http://www.tappi.org/index.asp?pid=29720

Pasi Rajala is with Metso Paper, Air Systems, Pansiontie 56, Fin-20240, Turku, Finland. Email Rajala at [e-mail]. Timo M. Koskinen is with UPM-Kymmene, R & D, P.O. Box 51, 37601 Valkeakoski, Finland. Email Koskinen at [e-mail].

EMISSIONS MONITORING

EFFECTS OF CNCG BURNING ON LIME COMPOSITION AND S[O.sub.2] EMISSIONS FROM A LIME KILN

APPLICATION: Burning CNCG has little or no effect on kiln performance, but it can lead to high S[O.sub.2] emissions.

Malodorous noncondensable gases (NCG) produced in kraft pulp mills contain large amounts of reduced sulfur compounds that must be treated before being vented to the atmosphere. NCG can be burned in lime kilns, recovery boilers, bark boilers, or in dedicated incinerators, depending on volume and concentration. Of these, the unit most commonly used for burning concentrated NCG is the lime kiln.

Because of its high sulfur content, the burning of concentrated NCG (CNCG) is thought to have an effect on TRS and S[O.sub.2] emissions as well as on the composition and quality of product lime. A systematic study was conducted to examine such effects at Votorantim Celulose e Papel (VCP), Luiz Antonio, Sao Paulo, Brazil. The CNCG delivery system at this mill is unique. The gas stream is normally burned in the recovery boiler, but it can also be burned in the lime kiln if the boiler is not available.

While the burning of CNCG had no significant effect on kiln performance, it resulted in high S[O.sub.2] emissions from the kiln stack. Sulfur entered the kiln mainly with CNCG and methanol and exited the kiln mainly with lime. Although lime can effectively remove S[O.sub.2], the removal efficiency decreased from 98% of the total sulfur input when CNCG was not burned to 89% when CNCG was burned in the kiln. For this kiln, the critical sulfur input level, above which excessive S[O.sub.2] emissions occur, was about 40 kg/h. View this paper online at http://www.tappi.org/index.asp?pid=29721

Honghi Tran and Xiasong Mao are with the Pulp and Paper Centre, University of Toronto, Toronto, Ontario, Canada. Roberto Villarroel and Thiago Alexandre Gazoni are with Votorantim Celulose e Papel--Unidade, Luiz Antonio, Sao Paulo, Brazil. Email Tran at [e-mail].

ONLINE EXCLUSIVE RETENTION

EFFECTS OF SYSTEM CLOSURE ON RETENTION AIDS FOR SC-GRADE MANUFACTURE

APPLICATION: The study shows the trends that might be expected in retention aid performance, for various retention aid systems, with increasing system closure.

As the degree of mill system closure increases, how well will currently available retention and drainage aid systems function in mechanical printing grade mills? In previous reports, we investigated the effects of system closure on retention aid performance in hydrosulfite-brightened thermomechanical pulp (TMP) for newsprint. In this report, we examine the use of a series of retention aids for applicability to system closure when using peroxide-brightened TMP pulp.

We measured the performances of 12 different types of retention and drainage aid systems in the laboratory at three simulated levels of system closure. In this work, we have defined the degree of system closure in terms of fresh process water make-up to the mill. The levels of system closure were 55, 20, and 3 [m.sup.3]/metric ton. The results also confirmed that, with increased system closure, the increase in dissolved substances concentration tends to result in a poorer performance of cationic polyacrylamide (CPAM) polymers and polyethylene oxide (PEO) enhancers. We found that the best performing CPAMs were those with high molecular weight and high charge density. View this paper online at http://www.tappi.org/index.asp?pid=29722

Marco Polverari, Bruce B. Sithole, and Lawrence H. Allen preformed these studies while with Paprican, Pointe-Claire, Quebec, Canada. Polverari is now with E.QU.I.P. International, Inc., 19400 Clark Graham, Baie d'Urfe, Quebec, Canada. Email Allen at [e-mail].

ONLINE EXCLUSIVE PAPERMAKING ADDITIVES

ROSIN SIZING UNDER NEUTRAL-ALKALINE PAPERMAKING CONDITIONS

APPLICATION: This study may help in developing new technologies for using rosin size or anionic polymer size under neutral-alkaline papermaking systems.

This study explores technologies for rosin use in neutral alkaline papermaking conditions, and the development of new anionic resin to be used in neutral-alkaline papermaking. We critically examined the technologies for rosin sizes used in neutral to alkaline papermaking systems, noting physical differences, such as addition points, and differences between polyaluminium compounds and polyamine, metal ions/polyamine, and polyamine-epichlorohydrin resin.

The results showed that premixing sizing is a good method that mills can easily adopt. Modified polyamine-epichlorohydrin resin is the best prospective chemical agent to greatly improve the sizing of rosin sizing at neutral-alkaline conditions, if better sizing levels than that of alum-rosin at acidic condition can be achieved.

However, to develop highly efficient technologies for rosin sizes used in neutral-alkaline papermaking systems will require much work. We need to completely understand the physical and chemical mechanisms that can greatly increase the sizing level of rosin sizes at neutral-alkaline conditions. We also need to find the best polyamine-epichlorohydrin chemical for rosin sizing at neutral-alkaline, based on efficiency and economics, View this paper online at http://www.tappi.org/index.asp?pid=29723

Yong Zou, Jeffery S. Hsieh are with Pulp and Paper Engineering, School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, as was Tim S. Wang; Wang, Eric Mehnert, and John Kokoszka are with EvCo Research, LLC, Atlanta, GA 30318. Email Hsieh at [e-mail].