Caracterização tecnológica da madeira de Eucalyptus benthamii para produção de celulose kraft.

O objetivo deste trabalho foi avaliar a qualidade tecnológica da madeira de Eucalyptus benthamii para produção de celulose kraft. Suas características foram comparadas com as de um híbrido de Eucalyptus grandis x Eucalyptus urophylla que é, provavelmente, o clone mais plantado no Brasil e, portanto, de grande importância no setor nacional de celulose e papel. Determinaram-se a densidade básica, composição química e características dimensionais das fibras das duas espécies. A madeira do Eucalyptus benthamii apresentou estrutura anatômica bastante semelhante às outras espécies do gênero e, ainda, densidade básica e dimensões das fibras dentro dos parâmetros dos clones de Eucalyptus utilizados atualmente pela indústria nacional de celulose e papel. Do ponto de vista de constituição química, o Eucalyptus benthamii demonstrou possuir qualidade tecnológica inferior à do híbrido urograndis, pois apresentou maiores teores de extrativos e de lignina, menor teor de glucanas, maior teor de galactanas e menor relação S/G (Siringila/Guaiacila), características que contribuem para um menor rendimento em polpa. Estudos deverão ser realizados para avaliar o desempenho da espécie na polpação kraft, no branqueamento e as propriedades de resistências da polpa celulósica

Bioethics in brazilian dentistry undergraduate courses: Bioética nos cursos de graduação em odontologia brasileiros

A literature review was conducted with the objective of evaluating the insertion and teaching of bioethics in Brazilian dentistry undergraduate courses, after the publication of the National Curriculum Guidelines of 2002. Twelve articles were selected from the Pubmed, Scielo and Lilacs databases, published between 2002 and 2020. The results showed that many colleges had not yet inserted the discipline of bioethics in their syllabus, in some of those they had inserted, teaching was predominantly theoretical and disjointed from the other disciplines. It was also evidenced that, in institutions where active methodologies were associated with the teaching of bioethics, the results were more positive. It is concluded that the insertion of bioethics can contribute to the ethical and humanistic formation of the students, and more recent studies on the subject are necessary

Reaction Rates of Lignin and Hexenuronic Acids with Chlorine Dioxide, Ozone, and Sulfuric Acid

The reaction rates of lignin and hexenuronic acids (HexA) with chlorine dioxide, ozone, and sulfuric acid were investigated. In unbleached and oxygen-delignified eucalyptus kraft pulps containing both lignin and HexA, only HexA, or only lignin reacted with chlorine dioxide, ozone, and sulfuric acid under typical bleaching conditions. The maximum reaction rates of chlorine dioxide with lignin and HexA were 57.2 and 26 mmol/kg/min, respectively, for unbleached pulp, and 26.7 and 13 mmol/kg/min, respectively, for oxygen-delignified pulp. The maximum reaction rates of ozone with lignin and HexA were 58.6 and 132 mmol/kg/min, respectively, for unbleached pulp, and 56.8 and 134 mmol/kg/min, respectively, for oxygen-delignified pulp. The maximum reaction rates of sulfuric acid with lignin, and HexA were 1.11 and 0.93 mmol/kg/min, respectively, for unbleached pulp, and 1.95 and 0.80 mmol/kg/min, respectively, for oxygen-delignified pulp. Chlorine dioxide reacts faster with HexA in the presence of the residual lignin. The kinetic results suggest that pulp treatment with ozone, when justifiable, should follow but not precede chlorine dioxide oxidation. Unbleached pulp residual lignin and HexA react twice as fast with chlorine dioxide than the lignin and HexA present in oxygen-delignified pulp, while the pulp type has no significant effect on lignin and HexA reactivity toward ozone. HexA reactions with sulfuric acid and ozone can be described by two-phase pseudo first-order reaction rates

Influência do branqueamento com ozônio e peróxido de hidrogênio no rendimento e qualidade de fibras secundárias.

In this study, Total Chlorine Free (TCF) bleaching processes were evaluated for bleaching a secondary fiber of different origens. The samples were bleached to a target brightness of 78 % ISO. The results were interpreted on the basis of chemical cost to reach the target brightness, bleaching yield and bleached pulp quality as measured by viscosity, fluorescence and b* color coordinate. The ozone stage was responsible for improve TCF bleaching performance. The pulp bleached by sequences contained a ozone stage followed by chelation, without interstage washing (ZQ), and a final hydrogen peroxide stage unpressurized (P) or pressurized with oxygen (PO), designed as (ZQ)(PO) showed good results. These sequences decreased pulp b* coordinate significantly and fluorescence slightly. For  all three bleaching processes, it was determined that process yield is negatively affected by hot alkaline stages such as oxygen, O, peroxide, P, and peroxide pressurized with oxygen, (PO) and also for the origin of the pulps of secondary fibers.Nesse estudo, foram avaliadas seqüências "Total Chlorine Free" (TCF) para o branqueamento de fibras secundárias provenientes de três fontes diferentes. As polpas foram branqueadas a um nível mínimo de alvura de 78% ISO, sendo que a quantidade necessária de reagentes e as suas principais propriedades foram avaliadas. A utilização do ozônio mostrou-se eficiente no branqueamento TCF, pois permitiu alcançar a alvura objetivo nos três tipos de polpas, por meio das seqüências (ZQ)P e (ZQ)(PO). As letras apresentadas nas seqüências de branqueamento possuem os seguintes significados: os estágios de ozônio, Z, seguido de uma quelação, Q, e um simples estágio de peróxido, P, ou um estágio de peróxido pressurizado com oxigênio (PO). E também reduziu significativamente a coordenada de cor b* e ligeiramente a fluorescência das polpas. Os resultados de rendimento para os processos avaliados nesse estudo foram afetados negativamente por estágios alcalinos, como oxigênio, O, P e (PO), em altas temperaturas e também pela origem das polpas de fibras secundárias

Reaction Rates of Lignin and Hexenuronic Acids with Chlorine Dioxide, Ozone, and Sulfuric Acid

The reaction rates of lignin and hexenuronic acids (HexA) with chlorine dioxide, ozone, and sulfuric acid were investigated. In unbleached and oxygen-delignified eucalyptus kraft pulps containing both lignin and HexA, only HexA, or only lignin reacted with chlorine dioxide, ozone, and sulfuric acid under typical bleaching conditions. The maximum reaction rates of chlorine dioxide with lignin and HexA were 57.2 and 26 mmol/kg/min, respectively, for unbleached pulp, and 26.7 and 13 mmol/kg/min, respectively, for oxygen-delignified pulp. The maximum reaction rates of ozone with lignin and HexA were 58.6 and 132 mmol/kg/min, respectively, for unbleached pulp, and 56.8 and 134 mmol/kg/min, respectively, for oxygen-delignified pulp. The maximum reaction rates of sulfuric acid with lignin, and HexA were 1.11 and 0.93 mmol/kg/min, respectively, for unbleached pulp, and 1.95 and 0.80 mmol/kg/min, respectively, for oxygen-delignified pulp. Chlorine dioxide reacts faster with HexA in the presence of the residual lignin. The kinetic results suggest that pulp treatment with ozone, when justifiable, should follow but not precede chlorine dioxide oxidation. Unbleached pulp residual lignin and HexA react twice as fast with chlorine dioxide than the lignin and HexA present in oxygen-delignified pulp, while the pulp type has no significant effect on lignin and HexA reactivity toward ozone. HexA reactions with sulfuric acid and ozone can be described by two-phase pseudo first-order reaction rates

MOLYBDENUM CATALYZED ACID PEROXIDE BLEACHING OF EUCALYPTUS KRAFT PULP

Molybdenum catalyzed peroxide bleaching (PMo Stage) consists of pulp treatment with hydrogen peroxide under acidic conditions in the presence of a molybdenum catalyst. Molybdenum is applied in catalytic doses (50-200 mg/kg pulp) and may originate from various sources, including (NH4)6Mo7O24.4H2O, Na2MoO4.2H2O, siliconmolybdate, etc. This work is aimed at optimizing the PMo stage and evaluating its industrial application in the OAZDP sequence. Optimum PMo stage conditions for bleaching eucalyptus pulp were 90 ºC, pH 3.5, 2 h, 0.1 kg/adt Mo and 5 kg/adt H2O2. The PMo stage was more efficient to remove pulp hexenuronic acids than lignin. Its efficiency decreased with increasing pH in the range of 1.5-5.5, while it increased with increasing temperature and peroxide and molybdenum doses. The application of the PMo stage as replacement for the A-stage of the AZDP sequence significantly decreased chlorine dioxide demand. The PMo stage caused a decrease of 20-30% in the generation of organically bound chlorine. The quality parameters of the pulp produced during the PMo stage mill trial were comparable to those obtained with the reference A-stage

COMPARISON BETWEEN ANALYTICAL PYROLYSIS AND NITROBENZENE OXIDATION FOR DETERMINATION OF SYRINGYL/GUAIACYL RATIO IN Eucalyptus spp. LIGNIN

Pyrolysis-gas chromatography/mass spectrometry (Py-GC-MS) was applied to measure the lignin syringyl/guaiacyl (S/G) ratio in E. dunni, E. grandis, E. nitens, E. urograndis, and E. urophylla woods. A total of 41 compounds were identified, of which 11 were derived from carbo-hydrates and 30 from lignins. The S/G ratio was calculated on the basis of the areas of peaks recorded in the pyrograms and compared with the results obtained by alkaline nitrobenzene oxidation. The values of S/G found by pyrolysis were similar for all the species using the compounds guaiacol, 4-methylguaiacol, 4-vinylguaiacol, vanillin, 4-ethylsyringol, 4-vinylsyringol, homosyringaldehyde, acetosyringone, and syringylacetone, as lignin markers. The selected markers were efficient for the deter-mination of S/G ratio in eucalyptus wood by Py-GC-MS. The Py-GC-MS technique produced results that are comparable to the nitrobenzene oxidation method, with the advantage of requiring small wood samples and a short analysis time

Efeito dos sólidos dissolvidos da madeira na branqueabilidade e nas propriedades físico-mecânicas e ópticas de polpa kraft branqueada de eucalipto

Muitos estudos demonstram que o rendimento da polpação kraft pode ser melhorado pela readsorção de xilanas à polpa durante o cozimento, e o licor negro kraft contém fração significativa das xilanas da madeira, sendo uma importante fonte dessas macromoléculas. Porém, o efeito dessa técnica nas propriedades físico-mecânicas e ópticas de polpa branqueada de eucalipto, ainda não está bem esclarecido. Neste estudo foram produzidas polpas de eucalipto provenientes de cozimento kraft convencional, com diferentes adições de licor negro (0, 25, 50, 75 e 100 % v/v). Os cozimentos foram conduzidos até número kappa 17-18 e as polpas resultantes foram deslignificadas com oxigênio em condições fixas. O branqueamento foi realizado utilizando uma sequência DHT(EP)DP até alvura final 92 % ISO. Em seguida as polpas foram refinadas num moinho PFI a diferentes níveis de revoluções (0, 500, 1.500, 3.000 e 6.000) e realizados testes de resistência ao rasgo, ao arrebentamento e à passagem de ar, alongamento, opacidade, densidade, volume específico aparente, capilaridade Klemm e índice de retenção de água (WRV). A eficiência e o ganho de alvura da pré-deslignificação com oxigênio foram ligeiramente prejudicados pela adição de licor negro ao cozimento kraft. A adição de 50 % de licor negro aos cozimentos resultou em polpas de pior branqueabilidade, sendo a demanda de cloro ativo aumentada em 5,3 kg/t celulose seca para obtenção de alvura 92 % ISO. As propriedades físico-mecânicas e ópticas das polpas kraft branqueadas não foram influenciadas, significativamente, pelo uso de licor negro no cozimento.Many studies have shown that the yield of kraft pulping can be improved by xylan reabsorption to the pulp during the cooking, and kraft black liquor contains significant fraction of xylan from wood, an important source of these macromolecules. However, the effect of this technique in the physical-mechanical and optical properties of bleached eucalyptus pulp is not very clear. This study produced pulp from eucalyptus kraft conventional cooking with different additions of black liquor (0, 25, 50, 75 and 100% v/v). The cooking was conducted to kappa number 17-18 and the resulting pulps were delignified with oxygen in fixed conditions. Bleaching was performed using a sequence DHT (EP) DP to end whiteness 92% ISO. Next pulps were refined in a PFI mill at different levels of revolutions (0, 500, 1,500, 3,000 and 6,000) and tests of tear resistance, bursting and the air flow, elongation, opacity, density, apparent specific volume, Klemm capillary and water retention value (WRV). The efficiency and brightness gain of the pre-delignification were slightly affected by the addition of black liquor in kraft pulping. The addition of 50% of black liquor to cooking resulted in a worse pulp ability for bleaching, and the chlorine demand increased by 5.3 kg/t pulp oven dry to obtain 92% ISO brightness. The physical-mechanical and optical properties bleached kraft pulps were not influenced significantly by the use of black liquor in cooking

EFEITO DOS S 3LIDOS DISSOLVIDOS DA MADEIRA NA BRANQUEABILIDADE E NAS PROPRIEDADES F\ucdSICO-MEC\uc2NICAS E 3PTICAS DE POLPA kraft BRANQUEADA DE EUCALIPTO

Muitos estudos demonstram que o rendimento da polpa\ue7\ue3o kraft pode ser melhorado pela readsor\ue7\ue3o de xilanas \ue0 polpa durante o cozimento, e o licor negro kraft cont\ue9m fra\ue7\ue3o significativa das xilanas da madeira, sendo uma importante fonte dessas macromol\ue9culas. Por\ue9m, o efeito dessa t\ue9cnica nas propriedades f\uedsicomec\ue2nicas e \uf3pticas de polpa branqueada de eucalipto, ainda n\ue3o est\ue1 bem esclarecido. Neste estudo foram produzidas polpas de eucalipto provenientes de cozimento kraft convencional, com diferentes adi\ue7\uf5es de licor negro (0, 25, 50, 75 e 100 % v/v). Os cozimentos foram conduzidos at\ue9 n\ufamero kappa 17-18 e as polpas resultantes foram deslignificadas com oxig\ueanio em condi\ue7\uf5es fixas. O branqueamento foi realizado utilizando uma sequ\ueancia DHT(EP)DP at\ue9 alvura final 92 % ISO. Em seguida as polpas foram refinadas num moinho PFI a diferentes n\uedveis de revolu\ue7\uf5es (0, 500, 1.500, 3.000 e 6.000) e realizados testes de resist\ueancia ao rasgo, ao arrebentamento e \ue0 passagem de ar, alongamento, opacidade, densidade, volume espec\uedfico aparente, capilaridade Klemm e \uedndice de reten\ue7\ue3o de \ue1gua (WRV). A efici\ueancia e o ganho de alvura da pr\ue9-deslignifica\ue7\ue3o com oxig\ueanio foram ligeiramente prejudicados pela adi\ue7\ue3o de licor negro ao cozimento kraft. A adi\ue7\ue3o de 50 % de licor negro aos cozimentos resultou em polpas de pior branqueabilidade, sendo a demanda de cloro ativo aumentada em 5,3 kg/t celulose seca para obten\ue7\ue3o de alvura 92 % ISO. As propriedades f\uedsico-mec\ue2nicas e \uf3pticas das polpas kraft branqueadas n\ue3o foram influenciadas, significativamente, pelo uso de licor negro no cozimento.Many studies have shown that the yield of kraft pulping can be improved by xylan reabsorption to the pulp during the cooking, and kraft black liquor contains significant fraction of xylan from wood, an important source of these macromolecules. However, the effect of this technique in the physical-mechanical and optical properties of bleached eucalyptus pulp is not very clear. This study produced pulp from eucalyptus kraft conventional cooking with different additions of black liquor (0, 25, 50, 75 and 100% v/v). The cooking was conducted to kappa number 17-18 and the resulting pulps were delignified with oxygen in fixed conditions. Bleaching was performed using a sequence DHT (EP) DP to end whiteness 92% ISO. Next pulps were refined in a PFI mill at different levels of revolutions (0, 500, 1,500, 3,000 and 6,000) and tests of tear resistance, bursting and the air flow, elongation, opacity, density, apparent specific volume, Klemm capillary and water retention value (WRV). The efficiency and brightness gain of the pre-delignification were slightly affected by the addition of black liquor in kraft pulping. The addition of 50% of black liquor to cooking resulted in a worse pulp ability for bleaching, and the chlorine demand increased by 5.3 kg/t pulp oven dry to obtain 92% ISO brightness. The physical-mechanical and optical properties bleached kraft pulps were not influenced significantly by the use of black liquor in cooking