IMPROVING EUCALYPTUS PULP REFINING THROUGH THE CONTROL OF PULP CONSISTENCY AND STOCK pH: Comparisons at given bulk and given tensile strength Celso Foelkel Irineu Dalmolin University of Santa Maria Santa Maria, RS, 97119-900 Brazil ABSTRACT Eucalyptus pulps have short and numerous fibers. They are well-suited to the manufacture of printing & writing and tissue papers. Refining is a vital step in preparing the pulp to papermaking. Refining optimization may improve the eucalyptus pulp performance oriented to the end product. Papermakers are willing to achieve sheet specifications, such as bulk, tensile, tear, porosity, etc. When optimum refining is searched, the comparisons among treatments may be performed at given bulk or tensile index, instead of given freeness or given net energy. This is a more realistic situation regarding the end product quality. In this paper, the properties of handsheets were compared at given bulks and given tensile. When the purpose is to improve fiber bonding, mainly to the printing & writing papers, the pH and consistency are suggested to be higher (pH around 9, consistency around 5). Tissue papers require loosen sheet structure. In this case, it is advised to run beating at lower pH’s (5-7) and lower consistencies (3-4%). INTRODUCTION Stock preparation is a vital step in the way to develop the desirable paper properties. Eucalyptus fibers are popular raw material to the manufacture of printing & writing and tissue papers. The pulp has numerous and short fibers. They impart special properties to the papers because some unique characteristics. Tissue papers require softness, bulk, fluffiness, tactility and absorption. Printing and writing papers demand formation, opacity, bulk, strength, porosity, smoothness, printability and dimensional stability. All these properties can be upgraded and optimized via an appropriate refining. Refining is a key operation in the stock preparation. One of the issues to be controlled is the specific consumption of energy to develop the required properties. Paper properties and refining energy are related to operational parameters, such as pulp consistency and stock pH. This paper is intended to show the influence of pH and consistency on the refining performance of eucalyptus fibers. A commercial bleached kraft eucalyptus pulp was submitted to the tests. Three levels of consistency (3%, 4%, 5%) and three of pH (5, 7, 9) were evaluated in a factorial type experiment, with one replication. The trials were performed using a commercially sized double disk refiner with 20 “ disks, with duo-flow feed. The equipment was a DD 4000 Beloit refiner driven through a variable speed coupling by a 400 kW induction motor. Power measurements were made with a strain gauge torque sensor and appropriate signal conditioners. The refiner was outfitted with bar width = 3mm; groove width = 3mm; groove depth = 10mm; refining angle = 5º. Operating speed was kept constant at 1200 rpm during the trial. The refining strategy was single pass, straight-through refining. Speed and motor power were kept constant during all the trial, calculated to guarantee 0.6 Ws/m refining intensity, according to the specific edge load theory. Different levels of net specific energy applied to the pulp were achieved by varying the refiner throughput. This was obtained thanks to a variable speed feeding pump.