ABSTRACT:The search for a better use of wood in the pulp industry has fuelled interest in a more rational use of its components, particularly xylans. The impact of xylans removal and of xylans redeposition on pulp properties for tissue and P&W paper grades are discussed in this paper. Kraft pulp (15.6% xylans) treatment with 10-70 g . L -1 NaOH resulted in pulps of 14.5-5.9% xylans. The treatments decreased pulp lignin and HexA contents and caused significant positive impact on subsequent oxygen delignification and ECF bleaching. Xylan removal decreased pulp beatability, water retention value and tensile index but increased drainability, water absorption capacity, capillarity Klemm and bulk. Overall, xylan depleted pulps showed almost ideal properties for tissue paper grade pulps. In a second step of the research, xylans extracted from unbleached (BXL) and bleached eucalyptus pulps (WXL) by cold caustic extraction (CCE) were added to a commercial brown pulp in the oxygen delignification (O-stage) and further bleached. Xylans deposition occurred at variable degree (up to 7% on pulp weight) depending upon the O-stage reaction pH. Pulp bleachability was not impaired by WXL xylan deposition but slightly negatively affected by BXL xylans. Pulp beatability was improved by xylan deposition. The deposited xylans were quite stable across bleaching and beating, with the WXL xylans being more stable than the BXL ones. At low energy consumption, the deposited xylans improved pulp physical and mechanical properties. Xylans extraction by CCE with subsequent deposition onto pulp in the O-stage proved attractive for manufacturing high xylan P&W paper grades. EFEITOS DA XILANA NA PRODUÇÃO DE CELULOSE DE EUCALIPTORESUMO: A busca por uma melhor utilização da madeira na indústria de celulose tem alimentado o interesse em uma utilização mais racional dos seus componentes, em particular as xilanas. O impacto da remoção das xilanas e de sua redeposição nas propriedades da polpa solúvel e tipos de papel de imprimir e escrever (P&W), são discutidos neste trabalho.

a b s t r a c tWood utilization for pulp and paper and biorefinery applications requires some kind of mechanical and/or physical-chemical pretreatment. Among the chemical treatments the alkaline ones are the most used worldwide, although acid and solvent treatments have also being used. This paper deals with eucalypt wood deconstruction with alkaline processes including soda-AQ, soda-AQ-O 2 , soda-O 2 , and kraft. The kraft process is largely used by the pulp industry and is evaluated here only to serve as a reference. The behavior of the four eucalypt clones selected in chapter 2 were investigated when submitted to the aforementioned processes regarding their screened yield, chemical demands and pulp quality at different kappa number levels (15, 35, 50, and 70). The two most promising processes (kraft and soda-AQ) were chosen for producing pulps (kappa 15 and 20) which were studied in depth (content of carbohydrates, uronic acid, hexenuronic acid, polysaccharide molecular weight, residual lignin structure, etc.), as well as their respective black liquors (heating value, solid content, elemental analysis, and lignin structure). The main findings of this work were: (1) the wood of the four different hybrid eucalypt clones behave similarly in the various alkaline deconstruction treatments; (2) the soda-AQ and Kraft were considered the most suitable processes for producing pulp on the basis of yield, chemical demands and pulp fiber integrity;(3) the soda-AQ process can potentially replace the kraft for a high degree of wood delignification (kappa number 15); (4) the alkaline processes using oxygen (soda-AQ-O 2 and soda-O 2 ) are more suitable for wood deconstruction aimed at biofuels; and (5) the soda-AQ process resulted black liquor of more suitable burning characteristics than the kraft.

RESUMOA eficiência da deslignificação com oxigênio (pré-O 2 ) é muito baixa para polpas de baixo número kappa e que contêm altas concentrações de ácidos hexenurônicos, pois o oxigênio não reage com esses ácidos, sendo mínima a eliminação destes durante a deslignificação com oxigênio em simples ou duplo estágio. Neste estudo, investigaram-se as propriedades físico-mecânicas de polpas produzidas por cozimentos cineticamente modificados até número kappa 17 e 14 e branqueadas pelas técnicas AD(EO)D, para polpa de kappa 17 e D HT (EPO)DP, para polpa de kappa 14. O objetivo principal do estudo foi o de avaliar as propriedades físico-mecânicas das polpas submetidas a sequências de branqueamento sem o oxigênio, no início da sequência. Como referências, foram produzidas polpas de número kappa 17 e 14 as quais foram posteriormente deslignificadas com oxigênio e branqueadas com sequências convencionais: A/D(EO)D, para polpa de número kappa 17 e D HT (EPO)DP, para polpa de kappa 14. O branqueamento alternativo, sem a pré-O 2 , resultou em polpas branqueadas de maior integridade que as da referência, o que foi comprovado pelos valores significativamente mais altos de VEA (bulk), índice de rasgo, opacidade e resistência à passagem de ar (RPA) da polpa fracamente refinada (polpa para produzir papel tissue). Por outro lado, a alta integridade das fibras oriundas das polpas branqueadas por processos alternativos diminuiu suas conformabilidades e colapsabilidades, com consequente diminuição do índice de tração da polpa fracamente refinada. Porém, mediante um refino mais intenso (polpa para produzir papel de imprimir e escrever -P&W) o índice de tração foi recuperado. A alta integridade das polpas branqueadas sem a pré-O 2 dificulta o seu refino. Para alcançar o grau de drenagem de 35 o SR com as polpas provenientes dos processos alternativos de branqueamento, foi necessário aplicar cerca de 30% a mais de energia em relação à referência. Palavras-chave:propriedades físico-mecânicas; cozimento modificado; branqueamento; ácidos hexenurônicos; celulose; eucalipto. ABSTRACTThe efficiency of oxygen delignification is very low for pulps of low number kappa and with high concentrations of hexenuronic acids, therefore the oxygen does not react with these acids, so being minimum the elimination of these during the oxygen delignification (pre-O 2 ) in simple or double stage. In this study, the physicalmechanical properties of pulp of kappa number 17 and 14, produced with modified cooks and with the application of AD(EO)D techniques for pulp of kappa 17 and D HT (EPO)DP for pulp of kappa 14 for the bleaching up to 90% ISO, had been investigated. The main objective of this study was to evaluate the physicalmechanical properties in pulps submitted to the bleaching sequences without oxygen in the beginning of the sequence. As references, cooks had been carried until numbers kappa 17 and 14, oxygen delignification and conventional bleaching for sequences A/D(EO)D for pulp of kappa 17 and D HT (EPO)DP for pulp of kappa 14. The alternative bleachi...

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The chemical composition and morphology of pulp fibers have a significant impact on the properties of fiber products. Pulp samples from a novel unique Eucalyptus triple hybrid [Eucalyptus grandis × (Eucalyptus urophylla × Eucalyptus globulus)] were obtained by various pulping processes -kraft, soda-anthraquinone (NaOH-AQ), and thermomechanical pulping (TMP). The chemical composition of the fiber surfaces was evaluated by X-ray photoelectron spectroscopy (XPS). The surface lignin content of NaOH-AQ pulp fibers was lower than that of the kraft counterpart. However, kraft pulp handsheets showed better physical and mechanical properties. XPS data strongly suggests that together with the pulp bulk chemical composition the xylan is more abundant on the surface of kraft fibers, which is reflected on their better mechanical properties. Moreover, the relatively low surface lignin content in TMP pulp compared to wood suggests that defibration takes place in the secondary wall, where lignin is less concentrated.

A novel alternative was investigated for elevating the xylan content of eucalyptus pulp through xylan deposition in the course of the oxygen delignification stage. The pH in the range of 10–13 was the only variable evaluated, while the other variables were kept constant in a range similar to industrial practice. Xylans were obtained from unbleached and bleached eucalyptus pulps by cold caustic extraction (CCE), giving rise to brown xylan liquor (BXL) and white xylan liquor (WXL), respectively. The liquors were added to a commercial brown pulp during oxygen delignification. The xylan-enriched pulps were subsequently bleached to 90% ISO with the D(EP)D sequence, beaten in a PFI mill and evaluated for their physical and mechanical properties. Xylan deposition occurred at variable degrees depending upon the pH. Pulp bleachability was not impaired by WXL xylan deposition but was slightly negatively affected by BXL xylan. Pulp beatability was improved by both WXL and BXL xylan deposition. The deposited xylan was more stable across bleaching and beating with the WXL xylan than the BXL xylan deposits. At low energy consumption, the deposited xylan improved pulp physical and mechanical properties. Xylan extraction by CCE with subsequent deposition in the oxygen delignification is an interesting technique to manufacture eucalypt pulps of high xylan content. The potential for industrial application is high as no significant modification of current pulp mill installations is needed.

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Eucalyptus wood is among the most important biomass resource in the world. Wood mechanical defibration and fibrillation are energy-intensive processes utilized not only to produce pulp for papermaking, but also to produce reinforcement fibers for biocomposites, nanocellulose, or pretreat lignocellulosic material for biofuels production. The structural features of different Eucalyptus hybrids affecting the refining energy consumption and produced fiber furnish properties were evaluated. The defibration and fiber development were performed using an alkaline peroxide mechanical pulping (APMP) process, which included chelation followed by an alkaline peroxide treatment prior to wood chip defibration. Despite the similar wood densities and chemical compositions of different Eucalyptus hybrids, there was a clear difference in the extent of defibration and fibrillation among the hybrids. The high energy consumption was related to a high amount of guaiacyl lignin. This observation is of major importance when considering the optimal wood hybrids for mechanical wood defibration and for understanding the fundamental phenomena taking place in chemi-mechanical defibration of wood.