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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.

In integrated factories of pulp and paper, the bleaching control is made by kappa number and/or brightness. However, the product paper is evaluated and valued for its whiteness. The level of final brightness of pulp certainly affects the demand for optical brighteners in paper manufacturing, nevertheless, there is not a direct correlation between consumption of optical brightener and final brightness, being the method of bleaching pulp, especially from the final stage of bleaching, also important in relation to this demand. Therefore, this study aimed to evaluate the potential of using the parameter whiteness as a tool to control bleaching pulp, instead of the traditional brightness and evaluate the impacts of different methods of bleaching and the pulp final brightness level in action of optical brighteners, to improve their performance. It was observed that the whiteness and brightness of the pulp are highly correlated and that the control of the bleaching plant can be done by any one of these two parameters. It was also concluded that, considering current prices of bleaching reagents and of optical brighteners, it is better to bleach the pulp up to lower brightness values (e.g. 88% ISO) and use larger amounts of optical brighteners to brighten the mass until the whiteness of 130 CIE. This conclusion is valid for whiteness measured before the size press. Further studies are needed to validate this conclusion considering the finished product.

Elephant grass (Pennisetum purpureum) (EG) is a fast-growing plant with high biomass productivity in the range of 30-45 bone dry t/ha/yr. This high productivity qualifies EG as a potential raw material for bleached pulp production. This study evaluated elephant grass as a raw material for paper pulp production. This was accomplished through determining its full chemical and morphological characterization, pulpability at kappa numbers 15 and 20 via the kraft and soda-AQ processes, and its pulp bleachability to 90% ISO brightness. The results were compared with those of a commercial hybrid eucalyptus wood clone (Eucalyptus urophylla x Eucalyptus grandis) (EUCA) that is widely planted in Brazil. Concerning its chemical composition, the elephant grass presented a high ash (60,100 mg/kg) and total extractives content (14.8%). However, the elephant grass showed good potential for pulp production. The kraft process was the ideal cooking process at kappa number 20, producing the highest screened yield (47.9%), bleachability (0.163 Δkappa/TAC), and good viscosity (812 dm 3 /kg). For EUCA, the ideal cooking process was the kraft process at kappa number 20, resulting in a screened yield of 52%, bleachability of 0.217 Δkappa/TAC, and final viscosity of 886 dm 3 /kg. This high productivity qualifies EG as a potential raw material for bleached pulp production.

The Klason method is adequate for quantifying lignin in softwood (SWD) but is less so for hardwood (HWD). The latter contains a fraction of acid-soluble lignin (ASL) that is not measurable under the conditions prevailing in the Klason method and that must be quantified by other means. This study aimed at investigating the composition of ASL obtained from eucalypt and pine woods by using pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). About 2.7% and 0.9% ASL by dry wood weight were measured in the acid filtrate of eucalypt and pine, respectively, by the Technical Association of the Pulp and Paper Industry (TAPPI) UM 250 method. The acid filtrate was lyophilized and processed by Py-GC-MS, allowing identification of 26 primary pyrolysis products, with 2% and 52% relative molar abundance coming from lignin and carbohydrates, respectively, for eucalypt and 24 primary pyrolysis products, with 1% and 54% relative molar abundance from lignin and carbohydrates, respectively, for pine. The main products derived from lignin were phenol, 4-methylphenol, guaiacol, 4-methylcatechol, syringol, acetosyringone and vanillin. It was concluded that measurements of ASL remain a requirement for accurate eucalypt and pine wood lignin quantification because lignin derivatives remain in the acid filtrate from the Klason lignin quantification method. Corrections for carbohydrate-derived compounds are not necessary, despite their predominance in the filtrate, because these derivatives do not interfere with ultraviolet (UV) absorption.

RESUMO:Durante o processo de branqueamento a celulose é tratada com reagentes químicos que, ao se tornarem resíduos na polpa, podem interferir na ação dos alvejantes óticos. Diferentes sequências de branqueamento podem produzir polpas com o mesmo grau de alvura, mas com potenciais diferentes para incremento da brancura por meio da aplicação de alvejantes óticos. Neste trabalho, objetivou-se avaliar a influência da sequência de branqueamento da celulose na eficiência de alvejantes óticos dos tipos dissulfonados e tetrassulfonados. Foram utilizadas polpas kraft de eucalipto branqueadas por quatros sequências de branqueamento em três níveis de alvura. Para cada sequência de branqueamento foi gerado um modelo matemático predizendo a brancura final da polpa em função da alvura inicial e carga (quantidade de reagente) de alvejante aplicada. Foi constatado que a presença de resíduos organoclorados na celulose reduz a eficiência dos alvejantes. Sequências que utilizam menor carga de dióxido de cloro possibilitam maiores ganhos na brancura com a aplicação de alvejantes óticos. A substituição de um estágio final de branqueamento com dióxido de cloro por um estágio com peróxido de hidrogênio aumentou a eficiência dos alvejantes.Palavras-chave: alvejante ótico, branqueamento, celulose de eucalipto. EFFECTS OF THE BLEACHING SEQUENCE ON THE OPTICAL BRIGHTENERS ACTION IN EUCALYPTUS KRAFT PULP INTRODUÇÃOAlvura e brancura são propriedades da celulose que expressam o quanto branco a celulose se apresenta. A alvura é calculada baseada na refletância apenas de radiação nos comprimentos de onda próximos à 457nm (faixa do azul), enquanto que a brancura considera a refletância em toda a região do visível, que vai de 400nm à 700nm (JORDAN, 1996).A alvura é muito utilizada pelas indústrias de celulose. Por se tratar de um material amarelado, a celulose absorve radiação violeta e azul-violeta (LEONARDI, 1990). Ao remover os compostos que conferem a coloração amarelada, o processo de branqueamento aumenta a reflexão de radiação na faixa do azul, o que torna a análise de alvura eficiente para o controle do processo de branqueamento (DENCE;REEVE, 1996).As indústrias de papel necessitam de um controle mais rigoroso das características óticas do seu produto. Portanto, utilizam a análise de brancura, que ao avaliar a reflectância em toda a região do visível, expressa um valor para o branco mais coerente com a percepção do olho humano.Para atingir elevado grau de brancura, a celulose pode ser tratada com alvejante ótico. Segundo Pelissari et al. (2003), dependendo da composição da polpa, os alvejantes óticos são responsáveis por 25 a 35 % da brancura final do papel. O branqueamento ótico é considerado como o

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AbstractCorn fibers are a significant residue of agriculture due to the huge amounts, which has fueled interest in a more rational use of its components, particularly regarding hemicelluloses. The impact of hemicellulose redeposition on printer and writing (P&W) paper grade pulp properties are discussed in this paper. Xylans extracted from corn fibers (16.9 % xylans) by cold caustic extraction (CCE) were added to commercial brown pulps (eucalypt and pine) in the oxygen delignification (O-stage) and further bleached to 90 % ISO brightness. Hemicelluloses deposition occurred at variable degree (up to 7 % on pulp weight). Pulp bleachability was not impaired by xylan deposition for eucalypt and pine pulps. Xylan deposition onto fibers was more efficient in eucalypt pulp than pine. Pulp beatability and strength properties were improved by xylan deposition for P&W paper grades.