We report on the combination of cellulose nanofibrils (CNFs) and condensed tannins from Acacia mearnsii for the development of hybrid, functional films. The tannins are fractionated and concentrated in polyphenolics that are used for functional components in the hybrid materials. Cogrinding of wood fibers with the tannins in aqueous media allows simultaneous fiber deconstruction and in situ binding of tannins on the freshly exposed cellulosic surfaces. Hence, a tightly bound bicomponent system is produced, which is otherwise not possible if typical adsorption protocols are followed, mainly due to the extensive hydration typical of CNFs. A nonionic surfactant is used to tailor the cellulose–tannin interactions. The proposed strategy not only enables the incorporation of tannins with CNFs but also endows a high and prolonged antioxidant effect of films formed by filtration. Compared to tannin-free films, those carrying tannins are considerably more hydrophobic. In addition, they show selective absorption of ultraviolet light while maintaining optical transparency in the visible range. The proposed simple protocol for incorporating tannins and surfactants with CNFs is suitable to produce functional materials. This is possible by understanding associated interfacial phenomena in the context of sustainable materials within the concept of the circular bioeconomy.
físico-químicas (viscosidade, ácidos hexenurônicos, etc.) e anatômicas (comprimento, largura, etc.)
Thermal treatments arise as an alternative to increase the physical and biological properties of wood, though they usually cause a reduction in mechanical strength. Therefore, the aim of the study was to determine the brittleness of Eucalyptus wood submitted to freezing and heat treatments. Freezing occurred with green condition specimens and the heat treatment with samples in equilibrium moisture content (20°C and 65% RH). The static bending test was carried out on an EMIC® universal testing machine. The freezing showed slight changes in the mechanical properties of Eucalyptus wood, not differing from natural wood. The treatments with high temperatures caused significant losses in mechanical strength, evidenced by decreases in maximum load and increases in brittleness. In the combined treatments, there was no sum of effects. Therefore, heat treatments modify the mechanical properties of wood, increasing its brittleness and following the tendency that, as the temperature increases, the mechanical resistance decreases.
RESUMO O escasso conhecimento tecnológico sobre as madeiras nativas do Brasil, aliado à dificuldade de exploração, motivaram a pesquisa das características da madeira de Maclura tinctoria (L) D. Don ex Steud, popularmente conhecida por Tajuva. O estudo teve como objetivo a caracterização química e a determinação das densidades básica e ponderada da madeira de Maclura tinctoria. Utilizou-se as normas da Americam Society for Testing and Materials-ASTM (1997) para determinação da densidade e da Technical Association of the Pulp and Paper industry-TAPPI (1995), para as análises químicas da madeira: Cinzas, lignina insolúvel em ácido, carboidratos e extrativos totais. A densidade apresentou decréscimo de valores em relação à posição axial da planta, tendo como valores médios 0,54 g.cm-³ e 0,55 g.cm-³ para densidade básica e densidade ponderada, respectivamente. Com relação aos constituintes químicos, os resultados obtidos foram em média: 1,21% de cinzas, 17,56% para lignina insolúvel, 71,02% de holocelulose e, 12,62% para extrativos totais. Considerando os atributos químicos, a espécie não é indicada para a produção de polpa celulósica. No entanto, posteriores estudos sobre a durabilidade e a qualidade da madeira poderão indicar a melhor utilização e a destinação final para a madeira da Tajuva.
O crescente interesse mundial na polpa celulósica produzida a partir da madeira de Acacia mearnsii incentiva estudos que comprovem sua propensão e eficiência para esse fim. Dessa forma, o objetivo deste estudo foi avaliar as propriedades físico-químicas da madeira de Acacia mearnsii, bem como avaliar seu desempenho na produção de celulose kraft, sob diferentes condições de cozimento. Amostras de madeiras das áreas de produção de sementes (APS) e clones foram avaliados. A polpação kraft foi realizada com fator H constante (1363) e álcali ativo variando de 14% a 24%. A densidade básica das madeiras de clone e APS não diferiram estatisticamente (0,544 g/cm³). A análise química revelou que o conteúdo médio (clone e APS) de extrativos, lignina e carboidratos foi de 4,67%, 16,66% e 77,02%, respectivamente. A condição de polpação mais eficiente foi obtida com álcali ativo de 14%, número kappa 16 e rendimento depurado de 57%. De acordo com os resultados, a madeira de Acacia mearnsii apresentou grande potencial para ser utilizada como fonte de fibra curta na obtenção de polpa celulósica pelo processo kraft.
Flame-resistant materials are key components in buildings and several other engineering applications. In this study, flame retardancy and thermal stability were conferred to a highly flammable technical thermoplastic—polypropylene (PP)—upon compositing with a carbonaceous tannin-based particulate (CTP). Herein, we report on a straightforward, facile, and green approach to prepare self-extinguishing thermoplastic composites by thermoblending highly recalcitrant particulate. The thermal stability and mechanical properties of the composites are tethered to the CTP content. We demonstrate that the addition of up to 65 wt% of CTP improved the viscoelastic properties and hydrophobicity of the PP, whereas having marginal effects on bulk water interactions. Most importantly, compositing with CTP remarkably improved the thermal stability of the composites, especially over 300 °C, which is an important threshold associated with the combustion of volatiles. PP-CTP composites demonstrated great capacity to limit and stop fire propagation. Therefore, we offer an innovative route towards thermally resistant and self-extinguishing PP composites, which is enabled by sustainable tannin-based flame retardants capable of further broadening the technical range of commodity polyolefins to high temperature scenarios.
<p>O objetivo deste estudo foi avaliar as propriedades de polpas kraft marrons de madeiras de<bold> Eucalyptus grandis</bold>e<bold> Eucalyptus urograndis</bold>de composição química distinta, principalmente em relação aos seus conteúdos de xilanas, para fabricação de papéis. As polpas marrons de número kappa 17-18 e conteúdos de xilanas variando de 6 a 21% foram produzidas sob diferentes protocolos de cozimento: 1) kraft convencional; 2) pré-hidrólise kraft; 3) kraft de alta alcalinidade; e 4) kraft de alto rendimento. As polpas marrons foram refinadas em moinho PFI e seus respectivos papéis produzidos foram avaliados quanto às suas propriedades físico-mecânicas e ópticas. De modo geral, as propriedades de resistência dos papéis foram beneficiadas pelo conteúdo de xilanas. Para níveis muito altos de refino, ocorreram quedas bruscas de resistência ao rasgo para os papéis e o consumo de energia de refino foi influenciado pelo conteúdo de xilanas nas polpas marrons. Os mais altos valores de volume específico aparente foram obtidos para os papéis com baixo conteúdo de xilanas, o que os torna interessantes, se branqueados, no segmento de papéis tissue. Os papéis com elevado conteúdo de xilanas apresentaram-se economicamente atrativos e com características de resistências adequadas para o segmento de papéis de imprimir e escrever.</p>
Aerogels are 3-D nanostructures of non-fluid colloidal interconnected porous networks consisting of loosely packed bonded particles that are expanded throughout their volume by gas and exhibit ultra-low density and high specific surface area. Cellulose-based aerogels can be obtained from hydrogels through a drying process, replacing the solvent (water) with air and keeping the pristine three-dimensional arrangement. In this work, hybrid cellulose-based aerogels were produced and their potential for use as dressings was assessed. Nanofibrilated cellulose (NFC) hydrogels were produced by a co-grinding process in a stone micronizer using a kraft cellulosic pulp and a phenolic extract from Maclura tinctoria (Tajuva) heartwood. NFC-based aerogels were produced by freeze followed by lyophilization, in a way that the Tajuva extract acted as a functionalizing agent. The obtained aerogels showed high porosity (ranging from 97% to 99%) and low density (ranging from 0.025 to 0.040 g·cm−3), as well a typical network and sheet-like structure with 100 to 300 μm pores, which yielded compressive strengths ranging from 60 to 340 kPa. The reached antibacterial and antioxidant activities, percentage of inhibitions and water uptakes suggest that the aerogels can be used as fluid absorbers. Additionally, the immobilization of the Tajuva extract indicates the potential for dentistry applications.
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