Proceedings of Progress in Paper Physics Seminar 2004, Norway, Trondheim, 21 a 24 de Junho, p. 50-52 Influence of hemicelluloses content on the paper quality produced with Eucalyptus globulus fibres. Ofélia Anjos 1 , António Santos 2 , and Rogério Simões 2 1 Escola Superior de Agrária – 6001-909 Castelo Branco, Portugal, ofelia@esa.ipcb.pt 2 Universidade da Beira Interior, 6201-001 Covilhã, Portugal, rsimoes@ubistb.ubi.pt Abstract The raw-material composition and the cooking conditions determine the pulp composition and this affect the behaviour of the pulp in the beating process and the papermaking potential. However, at industrial scale the variability of the pulp composition, for a given raw material and a given process, is relatively low and usually it is difficult to quantify the impacts of pulp composition on beating and papermaking. In the present study E. globulus bleached pulps were produced under different cooking conditions by the kraft process in order to obtain pulps with significant different hemicelluloses content (19% versus 14.5%). The behaviour of the pulps in beating and the papermaking potential were investigated under two beating intensities in the PFI mill and at four beating times. The pulp suspensions were characterised in terms of drainability, fibre morphology, wet fibre flexibility and relative bonded area. The paper produced was evaluated in terms of structural, superficial, mechanical and optical properties. The results showed the clear effect of the hemicelluloses content on the beating rate as well as on the paper properties. Key words: Hemicelluloses content; Eucalyptus globulus; paper quality; fibres Introduction The behaviour of the fibres in the refining process depends on their physical and chemical characteristics. Lot of work has been done on the softwood fibres and some hardwood fibres 1,2 , but E. globulus has received comparatively little attention. The data regarding the influence of refining intensity on the fibre performance are scarce 2 . On the other hand, the increased use of modified kraft cooking processes and the wood variability makes available in the market bleached kraft E. globulus pulps with different responses in refining. The different behaviours in refining are usually associated with the different hemicelluloses content. The objective of this paper is to investigate the behaviour of E. globulus pulps with very different hemicelluloses content in refining and evaluate their papermaking potential. Materials and Methods Eucalyptus globulus industrial wood chips (basic density=0.536 kg/L) were cooked at laboratory scale by the kraft process under markedly different reaction conditions in order to obtain two pulps with very different hemicelluloses content. One of the pulps was produced under conventional (CV) conditions while the other was produced by a modified kraft process (MOD) with 8/1 liquor/wood ratio and liquor replacement at the middle of the cooking cycle. The kappa number of both pulps was close to 15. The two pulps were bleached using a D 0 E 1 D 1 E 2 D 2 sequence. The hemicelluloses content of the pulps was determined by HPLC analysis of the neutral sugars after hydrolysis of the pulps with trifluoroacetic acid according to an optimised procedure adapted from the literature 3 . The papermaking potential of the pulps was evaluated in the PFI mill, using two refining intensities, 2N/mm and 5N/mm, and different refining revolutions. These were selected in order to obtain similar net specific energy consumption in refining for the two series. 30 g (o.d.) of air dry bleached pulp was refined at 10% consistency for each refining point. After beating, laboratory isotropic paper sheets were produced according to the Scan standards, using demineralised water. The biometrics characteristics of the fibre elements in the suspension were evaluated by the Morfi® and the wet fibre flexibility (WFF) index determined according to the procedure of Steadman and Luner 4 , using a Cyberflex® equipment. The fine content of the suspension was determined in the Bauer- 1