Summaries of July 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.

ENVIRONMENTAL CONTROL

COMPARATIVE ANNUAL COST EFFICIENCY BETWEEN THERMAL AND CHEMICAL OXIDATION OF TRS IN KRAFT MILLS

APPLICATION: Engineers can apply these guidelines to estimate and analyze the annual operating costs for destroying TRS by chemical oxidation as opposed to traditional incineration.

The customary way to destroy total reduced sulfur (TRS) is to incinerate the high-volume, low-concentration noncondensable gases (HVLC NCG) in a lime kiln, power boiler, recover boiler, or dedicated incinerator. An alternative approach is to oxidize contaminants chemically. Sodium hypochlorite and chlorine dioxide are the main oxiders used and are readily at hand at any plant that has a bleaching process. A number of these chemical scrubbers have been developed and implemented in mills.

What about the costs? Estimates of annual operating costs are presented for the main options in the thermal and chemical approaches. These estimates are used to evaluate the most cost-efficient option for a plant with a bleaching process. As a rule, thermal incineration is the more cost efficient approach when the HVLC flow is lower than 10,000 N*[m.sup.3]/h and TRS loads are higher than 6.8 kg/h. Chemical oxidation is the better alternative when the situation is reversed. In general, the greater the gas flow and the more NCG is diluted, the more attractive chemical oxidation becomes.

What are other mills doing? For low-volume, high-concentration gases, the lime kiln is commonly the primary incineration point, with the power boiler as backup. For HVLC, the most commonly preferred option is the power boiler. A dedicated thermal oxidizer is appropriate for HVLC when a waste fuel source is available and is the cheapest alternative in terms of capital cost if the mill cannot use power or recovery boilers. Chemical oxidation is becoming more popular, especially in Canada. View this paper online at http://www.tappi.org/index.asp?pid=32716&ch=1

Andre Normandin is with Mesar/Environair Inc., 410, Charest Est., Bureau 550, Quebec, QC Canada G1K 8G3. Email him at [e-mail].

COATING

PRINT QUALITY AND THE DISTRIBUTION OF OFFSET INK CONSTITUENTS IN PAPER COATINGS

APPLICATION: Mills, converters, and printers can use the results from this study in optimizing the coating formulations for desired print quality, and in understanding how different coating chemistry changes the printing result.

Little is known about the distribution of offset ink components in coated paper, although this is likely to be critical to print quality. This work focused on two fundamental processes that cause differences in distribution of ink constituents into a coating structure during printing. In the first, adsorptive chromatographic fractionation, chemical components of an ink mixture separate on contact with the paper coating due to their different adsorption characters. These differences arise from coating pigment chemistry, surface area, and morphology variables. In the second, latex-oil diffusion, molecular movement due to a concentration gradient takes place as oil molecules penetrate into the polymer latex matrix.

Our results indicated that adsorptive chromatographic fractionation, and the resulting distribution of ink constituents in a coating structure after printing, affected print quality parameters such as print gloss and density. Latex-oil diffusion and its constituents' distribution affected ink setting dynamics during printing, but did not influence print gloss or density. The inference is that adsorption onto the paper coating material surfaces delays permeation (sorption into the coating paper) of the slightly polar ink oils, hence delaying the concentration of solved ink resins on the ink-coating interface. Absorption through diffusion of ink oils by the paper coating latex internal matrix usually takes longer. In volumetric terms, it occurs away from the initial critical concentrating region of ink setting and cohesive ink tack build-up. Superimposed on these effects is the capillarity arising from the packing of pigments and binders. View this paper online at http://www.tappi.org/index.asp?pid=32717&ch=1

Sanna Rousu is technical customer services manager, Stora Enso UK, Orpington, UK; Patrick Gane is head of research and development, Omya Development AG, Oftringen, Switzerland; Dan Eklund is emeritus professor, Abo Akademi University, Finland. Email Rousu at [e-mail]

BLEACHING

EFFECT OF COOKING CONDITIONS ON ECF BLEACHING AND BRIGHTNESS REVERSION OF BIRCH KRAFT PULPS

APPLICATION: The concentrations of hydroxide ion and hydrogen sulfide ion in a birch kraft cook have an impact on the results of ECF bleaching.

To what extent do the kappa number of the pulp and the concentrations of hydroxide ion and hydrosulfide ion in the cooking liquor influence

ECF bleaching during birch kraft pulping?

To study this question, we carried out cooks with high and low levels of hydroxide ions and hydrosulfide ions. The pulps were cooked to two different kappa number levels and were bleached in both OD(EOP)DnD and OD(EOP)DP bleaching sequences. The parameters studied were kappa number, brightness, HexA content, and brightness reversion in both humid and dry atmospheres.

A higher hydroxide ion level during kraft cooking gave a brighter unbleached pulp and a somewhat higher final brightness in both the OD(EOP)DnD and OD(EOP)DP sequences. A higher level of hydrosulfide ion during kraft cooking did not give a higher unbleached brightness, but it led to better brightness development during the ECF bleaching sequences.

The kappa number reduction during bleaching was not influenced by the cooking variables studied, and the final kappa number was not critical for the final bleached brightness. A cooking kappa number increase from 16 to 22 gave a 17% increase in chlorine dioxide consumption in the OD(EOP)DnD sequence.

The humid brightness reversion correlated with the HexA content after bleaching, but the dry brightness reversion did not correlate with any of the studied parameters. For the humid atmosphere, a final D stage gave less brightness reversion than a final P stage, but the reverse was true for the dry atmosphere. View this paper online at http://www.tappi.org/index.asp?pid=32718&ch=1

At the time of this work Magnus Bjorklund was at Karlstad University. Currently he and Jiri Basta are with Eka Chemicals AB, SE-44580 Bohus, Sweden. Ulf Germgard is at Karlstad University, SE-65188, Karlstad, Sweden. Email Bjorklund at [e-mail]

ADDITIVES AND FILLERS

CALCIUM CARBONATE COMPOSITE FILLERS

APPLICATION: Increasing the percentage of calcium carbonate in paper could reduce production costs and improve the performance of paper.

Composites of precipitated calcium carbonate (PCC) and pulp were produced by co-precipitating calcium carbonate on top of nonwood and wood pulps. These composites were added to a base pulp, from which handsheets were produced. The handsheets were compared with two types of reference handsheets, one made by adding commercial PCC to the base pulp and one made by adding a blend of PCC and pulp to the base pulp.

The results showed that increasing the amounts of composite filler in handsheets decreases the bulk of paper. Tensile strength was similar for composite and PCC reference handsheets. The Scott bond strength for samples with composite filler added was higher than for the PCC reference samples. Internal bond strength was highest for bagasse composite sheets. Light scattering and opacity were higher for the composite papers than for the reference handsheets. Lower strength and higher optical properties were obtained for handsheets with composite fillers added than for handsheets prepared from the blend reference.

Scanning electron microscopy pictures of the samples showed that the PCC is spaced along the length of the fibrils in the composite filler. Hence, the highly refined pulp fibers and PCC form a porous network. The adhesion of PCC to the fiber surfaces prevents the cellulose fibrils from completely collapsing and bonding. Thus, in composite sheets, a higher fraction of the cellulose surface area is available for light scattering, which increases the optical performance. View this paper online at http://www.tappi.org/index.asp?pid=32719&ch=1

Ramjee Subramanian is a research associate, Laboratory of Paper Technology, HUT, Finland, Thad Maloney is with KCL, Espoo, Finland. Hannu Paulapuro is a professor, Laboratory of Paper Technology, HUT, Finland. Email Subramanian at [e-mail].

CORROSION

PERFORMANCE OF STEELS AGAINST CORROSION IN PERACID BLEACH MEDIA

Long-term immersion and electrochemical corrosion tests help in identifying appropriate material of construction for handling peracid bleach media of lower pH.

Peracids are among the nonchlorine bleach chemicals that have been studied for use in papermaking. Considering the fact that change of chemicals affects the corrosivity of the bleach media, we investigated the corrosivity of peracid solutions and the corrosion performance of various steels in them.

We subjected austenitic stainless steels (304L, 316L, 317L) and a duplex stainless steel (2205) to electrochemical polarization and weight loss tests at room temperature and at 50[degrees]C. The tests show peracetic acid ([P.sub.a]) to be most corrosive, followed by a mixture of peracetic acid and Caro's acid ([P.sub.xa]), and Caro's acid ([P.sub.x]). Comparison of the corrosivity of peracid solutions with those of other prevailing bleach chemicals show it to be less corrosive than peroxide and chlorine dioxide up to 1000 ppm chlorine. The test materials can be put in following order of increasing corrosion resistance: 304L < 316L < 317L < 2205. A suggestion on appropriate material for handling these liquors has been listed below:

Solutions     [P.sub.x]1  [P.sub.x]2  [P.sub.xa]1  [P.sub.xa]2

Room Temp.    304L        2205        304L         304L
50[degrees]C  304L        2205        304L         2205

Solutions     [P.sub.a]1  [P.sub.a]2  [P.sub.a]0

Room Temp.    2205        2205        304L
50[degrees]C  2205        2205        304L

([P.sub.a]=peracetic acid, [P.sub.x]=Caro's acid, [P.sub.xa]=mixture of
[P.sub.x] and [P.sub.a])

Thus, peracetic and Caro's bleaching solutions at pH 5 could be handled in the acid stages of existing bleach plants with equipment built for previous CEDED-type bleaching sequences or today's chlorine dioxide/peroxide sequences. View this paper online at http://www.tappi.org/index.asp?pid=32720&ch=1

Gayaan Singh and Ajay Kumar Singh are with the Department of Paper Technology, Indian Institute of Technology, Roorkee, Saharanpur Campus, P.B. 83, Saharanpur-247001, India.

ONLINE EXCLUSIVE ENVIRONMENTAL

USE OF KRAFT RECOVERY CYCLE RESIDUALS IN MINERALIZATION OF FORESTS--CONTROLLING LEACHING RATES OF LIMITED SOLUBLE SPECIES

APPLICATION: Many inorganic solid residuals from the kraft pulp industry can be recycled back to the forest. This paper describes methods for modifying and evaluating the leaching behavior of lime mud and green liquor dregs. The information will be useful to companies reusing these materials in the forest.

We sought to find a method to recycle inorganic solid residuals from the kraft recovery cycle as vitalizing agents, especially in acidified forests. One such method is pelletization, followed by thermal treatment, which sinters the material into a more stable and dense matrix with a low dissolution rate due to the small available surface area. Predicting the leaching rate from pelletized residuals in natural environments requires an understanding of both the hydrodynamic mass transport properties of the acidic solution-pellet system and the heterogeneous reaction kinetics on the pellet surface. This study examines the leaching rates of limited soluble species, such as calcium, from single pellets of treated lime mud and green liquor dregs under well-controlled laboratory leaching tests. Results indicate a significant effect of the physical structure of the pellets on leaching properties of calcium. We developed models that describe the leaching rates. We found that a combined mass transfer and surface reaction describes the leaching rate of limited soluble species at a pH level of 5.5. The mass transfer of hydrogen ions to the surface is determined as the rate-determining step at a pH level of 4.6. We concluded that by using a combination of well-controlled experiments and mathematical modeling, it is possible to understand the different phenomena that control the leaching mechanism of limited soluble species. View this paper online at http://www.tappi.org/index.asp?pid=32721&ch=1

Maryam Mahmoudkhani, Tobias Richards, and Hans Theliander are with the Department of chemical and Biological Engineering, Chalmers University of Technology, Gothenburg, Sweden. Email Theliander at [e-mail].