The measurement and significance of fines - Pulp and Paper Canada

MEASUREMENTFIG. 3. Cross-sections of dry sheets showing improvedsheet consolidation with increasing amount of fines. Thesheets were made at 35 kPa wet-pressing pressure. Theirapparent density values were: A – 0.439 g/cm 3 , B – 0.469g/cm 3 , C – 0.521 g/cm 3 . The procedure for obtaining crosssectionsis described elsewhere [22].FIG. 4. Scattering coefficient against sheet density for thepulps of Table I. The arrows in this and subsequent Figures5 to 9 indicate results obtained at 414 kPa wet-pressingpressure. The scattering coefficient was measured at 681nm.FIG. 5. Finite- and zero-span tensile strengths against sheetdensity for the pulps of Table I.FIG. 6. Elastic modulus vs. sheet density for the pulps ofTable I.FIG. 7. MIT double folds vs. sheet density for the pulps ofTable I.FIG. 8. Scott internal bond strength vs. sheet density forthe pulps of Table I.freeness (Table I), and the air permeabilityof the sheet (Fig. 9). The addition of8.2% fines to pulp A dropped its air permeabilityto one-thirtieth.To achieve an equivalent drop in thesetwo properties, the original pulp wouldhave to be beaten to about 6,000 revolutions(see Table II). In other words, as faras pulp freeness and sheet porosity arePulp & Paper Canada T 49 104:2 (2003) ❘❘❘ 43

MEASUREMENTFIG. 9. Air permeability as a function of sheet density forthe pulps of Table I. Permeability was calculated as thereciprocal of the Gurley air resistance.FIG. A1. Comparison of fines contents of mechanical pulpsas measured by the Kajaani FS-200 fibre length analyzerand the Bauer-McNett fibre length classifier. The pulpswere made from both softwoods and hardwoods.concerned, the pulp behaved as if highlybeaten. These observations accord withearlier work by Tasman [13].In conclusion, the addition of fines toa chemical pulp improves sheet consolidationand many dry-sheet strength properties,and the improvements can be significant2 . However, fines drasticallydecrease pulp freeness and sheet porosity;the pulp behaves as if highly beaten. Freenessdrop results in poor dewatering. Reducedporosity retards moisture escapeand slows the drying rate. Both factorscontribute to decreased pulp or papermachine productivity. Fines accumulationin the furnish will cause such conditions.ACKNOWLEDGEMENTSI thank Wayne Bichard, Susan Madey, PhilAllen, and Mel Pitz (Alberta-Pacific ForestIndustries Inc.) for contributing data toFigures 1 and A1, James Drummond forproviding sheet cross-sections in Figure 3,and Gunar Laivins and Martin MacLeodfor their valuable comments.LITERATURE1. TAPPI Test Method T 233 cm-95. Fiber length ofpulp by classification.2. TAPPI Test Method T 261 cm-94. Fines fraction ofpaper stock by wet screening.3. TAPPI Test Method T 269 cm-92. Comprehensiveretention evaluation for paper machines.4. SETH, R.S. Beating and refining response of somereinforcement pulps. Tappi J. 82(3): 147(1999). [Errata:Tappi J. 82(4): 16 (1999). Tappi J. 82(12): 11(1999)].5. PIIRAINEN, R. Optical method provides quick andaccurate analysis of fiber length. Pulp and Paper59(11): 69 (1985).6. OLSON, J.A., ROBERTSON, A.G., FINNIGAN,T.D., TURNER, R.R.H. An analyzer for fibre shapeand length. JPPS 21(11): J367 (1995).7. Pulp and Paper Testing. Papermaking Science andTechnology. Book 17. Helsinki: FAPET, 98 (1999).8. BICHARD, W., SCUDAMORE, P. An evaluation ofthe comparative performance of the Kajaani FS-100and FS-200 fiber length analyzers. Tappi J. 71(12): 149(1988).9. JORDAN, B.D., O’NEILL, M.A. The birefringenceof softwood mechanical pulp fines. JPPS 20(6): J 172(1994).10. SETH, R.S., JANG, H.F., CHAN, B.K., WU, C.B.Transverse dimensions of wood pulp fibres and theirimplications for end use. In Trans., 11th Fund. Res.Symp., Cambridge, Pira International, Leatherhead,UK, 473-503 (Sept. 1997).11. HTUN, M., DE RUVO, A. The implications of theRésumé: L’ajout de fines à une pâte chimique permet d’améliorer considérablement la consolidationde la feuille et un bon nombre de caractéristiques de résistance de la feuille sèche.Toutefois, les fines réduisent radicalement l’égouttage de la pâte et la porosité de la feuille; la pâtese comporte comme si elle était très raffinée. La baisse de l’égouttage entraîne un mauvais essorage.Une faible porosité retient l’humidité dans la feuille et ralentit la vitesse de séchage. Ces deuxfacteurs contribuent à réduire la productivité de la pâte ou de la machine à papier. Une accumulationde fines dans la composition de fabrication entraînera de telles situations. Les fibres sontimportantes dans la fabrication du papier et elles doivent être mesurées avec précision. Les analyseursoptiques de la longueur des fibres actuels peuvent ne pas indiquer la teneur en finesappropriée.Reference: SETH, R.S. The measurement and significance of fines. Pulp & Paper Canada104(2): T47-T50 (February 2003). Paper presented at the 88th Annual Meeting in Montreal, QC,on January 28 to 31, 2002. Not to be reproduced without permission of PAPTAC. Manuscriptreceived September 7, 2001. Revised manuscript approved for publication by the Review Panel July10, 2002.Keywords: CHEMICAL PULPS, FINES, MEASUREMENT, PULP PROPERTIES, PRODUC-TIVITY.fines fraction for the properties of bleached kraftsheet. Svensk Papperstidn. 81 (16): 507 (1978).12. LAIVINS, G.V., SCALLAN, A.M. The influence ofdrying and beating on the swelling of fines. JPPS 22(5): J178 (1996).13. TASMAN, J.E. The mechanical modification ofpapermaking fibres. Pulp and Paper Magazine of Canada67(12): T553 (December 1966).14. LOBBEN, T.H. Effect of fines on the strengthproperties of chemical pulps. Norsk Skogindustri 31(4):93(1977).15. LOBBEN, T.H. On the influence of the pulp componentson the shrinkage and elongation of paper.Norsk Skogindustri 32(4): 80(1978).16. MOLINA MANCEBO, R., KRKOSKA, P., BLAZEJ,A. The concept, properties and papermaking role offines. Papir a Celuloza 36 (11): V75 (1981).17. Carton Board — Profitable use of pulps and processes.Stockholm: Swedish Forest Products ResearchLaboratory, 77 (1983).18. PRZYBYSZ, K., CZECHOWSKI, J. The effect ofpulp fines on the drying process and paper strengthproperties. Cellulose Chemistry and Technology 19 (2):197 (1985).19. PAAVILAINEN, L. Importance of particle size —fibre length and fines — for the characterization ofsoftwood kraft pulp. Paperi ja Puu 72(5): 516 (1990).20. RETULAINEN, E., MOSS, P., NIEMINEN, K.Effect of fines on the properties of fibre networks. InTrans. 10th Fund. Res. Symp., Oxford, Pira International,Leatherhead, UK, 727-769 (Sept. 1993).21. FERREIRA, P.J., MARTINS, A.A., FIGUEIREDO,M.M. Primary and secondary fines from Eucalyptusglobulus kraft pulps. Characterization and influence.Paperi ja Puu 82 (6): 403 (2000).22. WILLIAMS, G.J., DRUMMOND, J.G. Preparationof large sections for the microscopical study of paperstructure. JPPS 26(5): J188 (2000).23. CHANG, H., SINKEY, J.D., YAN, J.F. Chemicalanalysis of refiner pulps. Tappi J. 62(9): 103 (1979).24. SETH, R.S. Zero-span tensile strength of papermakingfibres. Paperi ja Puu 83(8): 597 (2001).END NOTES1. Mechanical pulp fines, however, behavedifferently. Being lignin-rich [23], theyare relatively much stiffer. They do notbond that well to fibres, and do not losetheir free surface as much. Therefore,they contribute greatly to light scattering.2. The changes in strength properties withfines addition can be relatively small if thepulp is already beaten for high sheet consolidation[13-15].44 ❘❘❘ 104:2 (2003) T 50 Pulp & Paper Canada