Rubens Chaves de Oliveira

Seed storage hemicelluloses as wet-end additives in papermaking☆

Xyloglucans and galactomannans are examples of hemicelluloses that can be accumulated in seeds of many plants, being extensively studied and used for industrial applications. Guar gum and starch are polysaccharides currently used as wet-end additives in papermaking, whereas xyloglucans have never been reported to improve paper quality. In this work we show that different types of xyloglucans improved the mechanical properties of paper sheets without affecting the optical ones. Addition of 1% (w/w) of hemicelluloses to cellulosic pulp was able to increase by about 30% the mechanical properties such as burst and tear indexes. Seeds of several species could be used as source for the production of wet-end additives, since the results did not vary with the source of polysaccharides. Even if the utilisation of these hemicelluloses will not cost less than starch or guar gum, it might represent an important strategy for sustainable use of rainforest species.

Caracterização tecnológica, para produção de celulose, da nova geração de clones de Eucalyptus do Brasil

Last generation of Eucalyptus clones pulped by the main Brazilian kraft pulp mills were used for this study. Detailed chemical analysis of the woods were carried out to establish the wood quality. Laboratory simulation of a modern continuous digester technique was used for pulp production. Results demonstrated the high quality of Eucalyptus clones wood that are being planted in Brazil for kraft pulp production.

Influência da densidade básica da madeira na qualidade da polpa kraft de clones hibrídos de Eucalyptus grandis W. Hill ex Maiden X Eucalyptus urophylla S. T. Blake

Foram estudados dois clones de Eucalyptus com densidades basicas de 447 e 552 kg/m³. O processo kraft foi utilizado para a producao de celulose, tendo sido aplicadas diferentes cargas de alcali para se obterem polpas com numero kappa 18 ± 0,5. As polpas foram branqueadas pela sequencia ODEopDD, a alvuras de 90 ± 1% ISO, e refinadas, sendo suas propriedades fisico-mecânicas e opticas analisadas. A madeira de baixa densidade mostrou-se mais recomendavel para a producao de celulose, por ter apresentado maior rendimento depurado, viscosidade da polpa mais elevada, ter requerido menor carga de alcali no cozimento, ter proporcionado menor teor de solidos no licor residual e menor consumo de reagentes quimicos no branqueamento. As propriedades mecânicas e estruturais das polpas nao foram afetadas significativamente pela densidade basica das madeiras.

Propriedades mecânicas de meniscos frescos de coelhos e preservados em glicerina 98

The present study evaluated the compressive strength of medial menisci of New Zealand rabbits, through mechanical compression test. Thirty menisci were distributed in three groups: group MF, composed by ten fresh menisci; MG group, composed by ten menisci preserved in 98% glycerin for 30 days; and, group MR, ten menisci preserved in 98% glycerin for 30 days and rehydrated in NaCl 0.9% for 12 hours. The menisci in each group were submitted to compression test in the perpendicular direction to the anatomical plane and had the elasticity limit, the elastic deformity, the rupture stress point and the stiffness index evaluated. The menisci from the preserved groups MG and MR had the elastic limit similar to the fresh menisci group (MF). The group of menisci preserved in glycerin (MG) presented lower elastic deformity capacity (P<0.05) if compared to the other groups, MF and MR, and a higher tension capacity at elastic limit. The menisci from group (MG) presented higher stiffness (P<0.05) than the ones in the MF and MR groups. It can be concluded that the group menisci preserved in glycerin 98% followed by rehydration in Nacl 0,9% (MR), did not showed any significant alterations in the capacity of the menisci elastic limit.

EFFECTS OF XYLAN IN EUCALYPTUS PULP PRODUCTION

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.

Effect of Acid Leaching of Eucalyptus Wood on Kraft Pulping and Pulp Bleachability

Abstract This work evaluated the impact of chip acid leaching prior to kraft cooking on pulp yield bleachability and strength properties. Optimal leaching time, temperature, and pH (3 h, 70°C, and pH 2.0) were used to leach wood chips prior to kraft cooking, followed by oxygen delignification, ECF, and light-ECF bleaching with the sequences AZDP (0.19% ClO2), AZDP (0.76% ClO2), and A/Z/EDP (1.06% ClO2). Acid leaching significantly reduced the metals content of the wood chips. Time and pH greatly influenced the metals removal rate, whereas temperature did not. Acid treatment had no effect on cooking yield but improved delignification rate. The pulp from acid leached chips showed improved performance during oxygen delignification and bleaching over the reference pulp. For light-ECF bleaching, chip leaching resulted in H2O2 and NaOH savings of 18 and 14.5 kg/t pulp, respectively. No significant differences in strength properties between the reference and leached pulps were observed.

Efeitos da sequência de branqueamento na ação de alvejantes óticos em celulose kraft de eucalipto

Durante o processo de branqueamento a celulose e tratada com reagentes quimicos que, ao se tornarem residuos na polpa, podem interferir na acao dos alvejantes oticos. Diferentes sequencias de branqueamento podem produzir polpas com o mesmo grau de alvura, mas com potenciais diferentes para incremento da brancura por meio da aplicacao de alvejantes oticos. Neste trabalho, objetivou-se avaliar a influencia da sequencia de branqueamento da celulose na eficiencia de alvejantes oticos dos tipos dissulfonados e tetrassulfonados. Foram utilizadas polpas kraft de eucalipto branqueadas por quatros sequencias de branqueamento em tres niveis de alvura. Para cada sequencia de branqueamento foi gerado um modelo matematico predizendo a brancura final da polpa em funcao da alvura inicial e carga (quantidade de reagente) de alvejante aplicada. Foi constatado que a presenca de residuos organoclorados na celulose reduz a eficiencia dos alvejantes. Sequencias que utilizam menor carga de dioxido de cloro possibilitam maiores ganhos na brancura com a aplicacao de alvejantes oticos. A substituicao de um estagio final de branqueamento com dioxido de cloro por um estagio com peroxido de hidrogenio aumentou a eficiencia dos alvejantes.

Enzymatic bleaching of eucalyptus kraft pulp: effects on the prebleaching filtrate, pulp quality and paper properties

Abstract Enzymatic bleaching appears to be a promising approach for clean bleaching processes and the reduction of bleaching chemical consumption. In this work, the quality of the filtrates and the pulps has been characterized after enzymatic prebleaching stages of eucalyptus kraft pulp. Four different conditions with xylanase were investigated. Following each prebleaching stage, the properties of the pulp [kappa number, brightness, content of hexenuronic acid (HexA), xylan removal, and pulp yield lost], and of the resulting effluents (chemical oxygen demand (COD), biochemical oxygen demand (BOD), color, and conductivity) were determined. In addition, a complete bleaching sequence was performed to characterize the pulp quality at the end of the sequence. Finally, the pulp was refined in a PFI mill, and the mechanical and physical properties of the resulting paper were determined. The best pulp quality was achieved at pH 7, at which a lower kappa number, higher pulp brightness, and smaller amount of HexA were observed. Under this condition, however, a larger yield loss and a higher effluent COD load had to be accepted. After the complete bleaching sequence, the enzymatic treatments yielded pulps with higher brightness and viscosity as well as with a lower kappa number. The enzymatic treatments resulted in small changes in the mechanical and physical properties of the paper handsheets produced.

Combination of enzymatic, mechanical and ultrasonic treatments for improvement of the properties of secondary pulps

This study evaluated the property recovery capability of handsheets formed from secondary fibers by combining different techniques. To attain that, pulps derived from post-consumer cardboard scrap were subjected to various refining intensities respectively in a PFI mill (0, 400, 800 and 1200revolutions) and ultrasound (0, 10, 20 and 30minutes), followed by enzymatic treatments with enzymes Cellulase, Hemicellulase, Mixture 1 and Mixture 2 (both mixtures composed of cellulase and hemicellulase). The papermaking potential of the pulps was evaluated by means of physical and mechanical tests on the resulting paper after the relevant treatments. It was found that both the combination of PFI mill refining with enzymatic treatments and the combination of ultrasound with enzymatic treatments were effective in improving paper properties. It was also found that interfiber bonding properties such as tensile index and ring crush strength had greater increases, in relation to the initial pulp, in pulps derived from the combined PFI mill refining with enzymatic treatments. As for intrinsic fiber strength properties, such as tear resistance, had greater increases in pulps derived from the combined ultrasound with enzymatic treatments.

Melhoramento das propriedades de papéis reciclados através da ultrassonificação das fibras e adição de xilanas

RESUMO – Nesse estudo foi avaliado o potencial de utilizacao de vibracoes ultrassonicas e adicao de xilanas para melhorar a qualidade do papel reciclado. Inicialmente, foi realizado um estudo de otimizacao do tratamento ultrassonico. Foram avaliadas as influencias do pH, da consistencia da massa e do tempo de tratamento. A consistencia da massa nao afetou significativamente os resultados. Entretanto, elevados tempos de tratamento e valores de pH intensificaram os efeitos da ultrassonificacao. O tratamento ultrassonico melhorou as propriedades mecânicas do papel de forma semelhante ao refino em PFI, embora com menor intensidade. As ondas ultrassonicas atuam, principalmente, promovendo o desfibrilamento externo das fibras. Tambem foram investigados os impactos da adicao de xilanas na polpa. Os resultados indicaram que, mesmo com pequenas dosagens de xilanas (10 g/kg), foi possivel aumentar significativamente a resistencia mecânica do papel. Dosagens acima de 50 g/kg nao sao justificaveis. As tecnologias de ultrassonificacao e adicao de xilanas evidenciaram grande potencial tecnico para melhorar a qualidade do papel reciclado. Palavras-chave: Fibras secundarias, Ultrassom e Xilanas.