Submitted by Nathália Faria da Silva (nathaliafsilva.ufv@gmail.com) on 2017-06-29T19:14:50Z No. of bitstreams: 1 texto completo.pdf: 607964 bytes, checksum: fdb46a7a071b2f719d74013d21e07ea6 (MD5) / Made available in DSpace on 2017-06-29T19:14:50Z (GMT). No. of bitstreams: 1 texto completo.pdf: 607964 bytes, checksum: fdb46a7a071b2f719d74013d21e07ea6 (MD5) Previous issue date: 2000-08-15 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / O objetivo deste trabalho foi avaliar, para um mesmo grau de deslignificação, o rendimento, a viscosidade, as propriedades físico- mecânicas e a branqueabilidade de polpas produzidas pelo processo RDH. Para se ter o mesmo grau de deslignificação foi feita a otimização do perfil de temperatura (150, 160 e 170°C) em relação ao tempo de cozimento, mantendo-se as demais condições do processo constantes. Com a elevação da temperatura de cozimento, houve redução no rendimento depurado e na viscosidade e acréscimo no teor de rejeitos. A variação da temperatura de cozimento não afetou a branqueabilidade das polpas, para um teto de alvura de 90% ISO. A carga poluente do filtrado do branqueamento também não variou. A grande diferença entre as viscosidades das polpas marrons quase desapareceu após o branqueamento, sendo a deslignificação com oxigênio a principal responsável por esse fato. As análises de carboidratos e de pentosanas revelaram que a polpa produzida em baixa temperatura (150°C) apresentou maior teor de xilanas que as polpas produzidas em temperaturas mais elevadas (160 e 170°C). A polpa produzida a 150°C apresentou relação índice de rasgo/índice de tração menor que as polpas produzidas a 160 e 170°C, e as duas últimas apresentaram-se estatisticamente iguais. O consumo de energia para refino foi maior para a polpa produzida a 170°C, tendo as demais polpas apresentado o mesmo consumo. As propriedades de arrebentamento, volume específico aparente, drenabilidade e energia absorvida durante tração (TEA) não variaram entre as polpas. / The objective of this study was to evaluate, at a same delignification level, the yield, viscosity, physical-mechanical properties and bleachability of RDH pulps produced at different cooking temperatures (150, 160 and 170°C). Higher temperature resulted in lower screened yield, lower viscosity and higher rejects. Modification of cooking temperature did not affect pulp bleachability or pollution load in the bleaching filtrate. The large differences of viscosity among unbleached pulps produced at different cooking temperatures almost disappeared after bleaching. Oxygen delignification was considered to be the main cause for this viscosity equalization. Carbohydrates analysis indicated that pulp produced at lower cooking temperature (150°C) presented higher xylan content than pulps produced at higher temperatures (160 and 170°C). The pulp produced at 150°C showed smaller tear to tensile index ratio than pulps produced at 160 and 170°C. Pulps produced at 160 and 170°C presented statistically identical physical-mechanical properties. Refining energy consumption was higher for pulp produced at 170°C while pulps produced at 150 and 160°C presented the same energy consumption. Pulp properties such as bursts, apparent specific volume, drainability and tensile energy absorption (TEA) were not affected by cooking temperature.

Cette étude avait pour objectifs principaux d'étudier le fonctionnement minéral d'une plantation d'eucalyptus et d'évaluer les effets du reboisement sur un sol de savane du littoral congolais. Une amélioration des systèmes de culture était également recherchée, afin d'assurer une production soutenue et durable de bois d'eucalyptus dans ces sols. <br />Les cycles biogéochimiques ont été étudiés dans une plantation clonale d'eucalyptus âgée de 6 à 9 ans (fin de la rotation) et dans une savane représentative de l'écosystème originel. Les stocks d'éléments biodisponibles dans les sols des 2 écosystèmes ont été quantifiés et les principaux flux d'éléments minéraux sous forme dissoute ont été mesurés pendant 3 années : apports atmosphériques, pluviolessivats, écoulements de troncs, ruissellements superficiels, transferts sous la litière et à la base des différents horizons pédologiques (jusqu'à 6 m de profondeur). Lors du brûlis de la savane, les restitutions au sol sous forme de cendres ainsi que les transferts dans l'atmosphère ont été quantifiés. La localisation spatiale des racines a également été étudiée dans la plantation ainsi que la dynamique d'incorporation des éléments dans la savane entre 2 brûlis annuels. L'étude de chronoséquences de peuplements couvrant l'ensemble de la rotation de futaie a permis d'aborder les dynamiques (i) d'incorporation d'éléments minéraux dans la biomasse, (ii) de retours au sol avec les litières, ainsi que (iii) de transferts internes dans les arbres. <br />Les résultats montrent que les cycles biogéochimiques dans l'écosystème de savane ont été profondément modifiés par la plantation d'eucalyptus. Le cycle de l'azote a été le plus affecté en raison de l'arrêt des brûlis et de la fixation symbiotique, qui représentent des flux importants en savane. Ce clone d'eucalyptus s'est révélé très bien adapté malgré la pauvreté des sols, en raison en particulier d'un recyclage intense d'éléments nutritifs. Les transferts internes de N, P, K dans la biomasse et les restitutions importantes de N, Ca et Mg avec les litières permettent de limiter la dépendance des arbres vis à vis des réserves du sol en fin de rotation. Les bilans entrées-sorties indiquent néanmoins que les fortes productions de biomasse des eucalyptus ont lieu aux dépens du capital d'azote hérité de la savane et qu'une augmentation importante des apports par fertilisation sera indispensable pour maintenir la production. Des recommandations sylvicoles ont été proposées afin de limiter au maximum les exportations minérales et orienter les futures expérimentations.

This case study investigated profitability of a small stand of fast-grown Eucalyptus nitens in Canterbury for sawn timber production. This stand was pruned and thinned and then harvested at 15 years old. An estimate of per-hectare log yields and diameters was made from the stand. Sample logs were sawn, dried and profiled, then products quantified. Log prices were estimated using the residual value method. Prices were summed for sawn products from each log, from which processing expenses and sawmill profit were deducted for an estimate of log value. In the absence of market prices for sawn E. nitens products empirical estimates of price were derived from market survey data. Predictive models were produced from estimated stand log yields along with predicted product revenues and processing costs from sample logs. These were used for estimating per-hectare log residual values from the case study stand trees. Financial returns to the grower were then calculated as discounted cash flows from the estimated log residual values per hectare, taking into account grower costs along with harvesting and transport costs. Best-practice processing methods were identified from the literature and applied as a productivity benchmark. Methods were developed with the view to standardising data across research efforts that seek to improve grade recoveries for E. nitens. A range of factors were investigated that potentially influenced E. nitens log residual value in this case study, including log diameter and log position. Outcomes included a reasonably favourable return on investment for the grower. However, this depended on a number of factors such as land price, distance from processor, product prices, grading methods, drying methods and level of sawmill profit. The application of contemporary best practice small-scale processing methods indicates that E. nitens has potential as a profitable plantation species for solid timber production.