Biblioteca Digital

Layer-by-layer (LBL) assembly was used to combine crystalline rod-like nanoparticles obtained from a vegetable source, cellulose nanowhiskers (CNWs), with collagen, the main component of skin and connective tissue found exclusively in animals. The film growth of the multilayered collagen/CNW was monitored by UV-Vis spectroscopy and ellipsometry measurements, whereas the film morphology and surface roughness were characterized by SEM and AFM. UV-Vis spectra showed the deposition of the same amount of collagen, 5 mg m(-2), in each dipping cycle. Ellipsometry data showed an increment in thickness with the number of layers, and the average thickness of each bilayer was found to be 8.6 nm. The multilayered bio-based nanocomposites were formed by single layers of densely packed CNWs adsorbed on top of each thin collagen layer where the hydrogen bonding between collagen amide groups and OH groups of the CNWs plays a mandatory role in the build-up of the thin films. The approach used in this work represents a potential strategy to mimic the characteristics of natural extracellular matrix (ECM) which can be used for applications in the biomedical field.; CNPq; CAPES[04/2008]; FAPEMIG[021/2008]; FAPEMIG[PPM III 0207/09]; FAPEMIG[PRONEX EDT 479/07]; Pro-reitoria de Pesquisa-UFMG

In this work cassava bagasse, a by-product of cassava starch industrialization was investigated as a new raw material to extract cellulose whiskers. This by-product is basically constituted of cellulose fibers (17.5 wt%) and residual starch (82 wt%). Therefore, this residue contains both natural fibers and a considerable quantity of starch and this composition suggests the possibility of using cassava bagasse to prepare both starch nanocrystals and cellulose whiskers. In this way, the preparation of cellulose whiskers was investigated employing conditions of sulfuric acid hydrolysis treatment found in the literature. The ensuing materials were characterized by transmission electron microscopy (TEM) and X-ray diffraction experiments. The results showed that high aspect ratio cellulose whiskers were successfully obtained. The reinforcing capability of cellulose whiskers extracted from cassava bagasse was investigated using natural rubber as matrix. High mechanical properties were observed from dynamic mechanical analysis. (C) 2010 Elsevier B.V. All rights reserved.; FAPESP; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); CAPES-COFECUB; COFECUB; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); CNPq

Cellulose cassava bagasse nanofibrils (CBN) were directly extracted from a by-product of the cassava starch (CS) industry, viz. the cassava bagasse (CB), The morphological structure of the ensuing nanoparticles was investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), presence of other components such as sugars by high performance liquid chromatography (HPLC), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) experiments. The resulting nanofibrils display a relatively low crystallinity and were found to be around 2-11 nm thick and 360-1700 nm long. These nanofibrils were used as reinforcing nanoparticles in a thermoplastic cassava starch matrix plasticized using either glycerol or a mixture of glycerol/sorbitol (1:1) as plasticizer. Nanocomposite films were prepared by a melting process. The reinforcing effect of the filler evaluated by dynamical mechanical tests (DMA) and tensile tests was found to depend on the nature of the plasticizer employed. Thus, for the glycerol-plasticized matrix-based composites, it was limited especially due to additional plasticization by sugars originating from starch hydrolysis during the acid extraction. This effect was evidenced by the reduction of glass vitreous temperature of starch after the incorporation of nanofibrils in TPSG and by the increase of elongation at break in tensile test. On the other hand...

The surface of ramie cellulose whiskers has been chemically modified by grafting organic acid chlorides presenting different lengths of the aliphatic chain by an esterification reaction. The occurrence of the chemical modification was evaluated by FTIR and X-ray photoelectron spectroscopies, elemental analysis and contact angle measurements. The crystallinity of the particles was not altered by the chain grafting, but it was shown that covalently grafted chains were able to crystallize at the cellulose surface when using C18. Both unmodified and functionalized nanoparticles were extruded with low density polyethylene to prepare nanocomposite materials. The homogeneity of the ensuing nanocomposites was found to increase with the length of the grafted chains. The thermomechanical properties of processed nanocomposites were studied by differential scanning calorimetry (DSC), dynamical mechanical analysis (DMA) and tensile tests. A significant improvement in terms of elongation at break was observed when sufficiently long chains were grafted on the surface of the nanoparticles. It was ascribed to improved dispersion of the nanoparticles within the LDPE matrix. (C) 2009 Elsevier Ltd. All rights reserved.; CAPES (Brazil); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Fruit purees, combined or not with polysaccharides, have been used in some studies to elaborate edible films. The present study was conducted to evaluate tensile properties and water vapor barrier of alginate-acerola puree films plasticized with corn syrup, and to study the influence of cellulose whiskers from different origins (cotton fiber or coconut husk fiber, the latter submitted to one- or multi-stage bleaching) on the film properties. The whiskers improved the overall tensile properties (except by elongation) and the water vapor barrier of the films. The films with coconut whiskers, even those submitted only to a one-stage bleaching, presented similar properties to those of films with cotton whiskers, despite the low compatibility between the matrix and the remaining lignin in coconut whiskers. This was probably ascribed to a counterbalancing effect of the higher aspect ratios of the coconut whiskers. (C) 2011 Elsevier Ltd. All rights reserved.; CNPq; CNPq; Embrapa; Embrapa

There is growing interest in cellulose nanofibres from renewable sources for several industrial applications. However, there is a lack of information about one of the most abundant cellulose pulps: bleached Eucalyptus kraft pulp. The objective of the present work was to obtain Eucalyptus cellulose micro/nanofibres by three different processes, namely: refining, sonication and acid hydrolysis of the cellulose pulp. The refining was limited by the low efficiency of isolated nanofibrils, while sonication was more effective for this purpose. However, the latter process occurred at the expense of considerable damage to the cellulose structure. The whiskers obtained by acid hydrolysis resulted in nanostructures with lower diameter and length, and high crystallinity. Increasing hydrolysis reaction time led to narrower and shorter whiskers, but increased the crystallinity index. The present work contributes to the different widespread methods used for the production of micro/nanofibres for different applications. (C) 2012 Elsevier Ltd. All rights reserved.; Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP); Fundacao de Amparo a Pesquisa do Estado de Sao Paulo - FAPESP [2009/10734-6, 2007/50863-4]; Fundacao de Amparo a Pesquisa do Estado de Minas Gerais (FAPEMIG); Fundacao de Amparo a Pesquisa do Estado de Minas Gerais - FAPEMIG; Financiadora de Estudos e Projetos/Ministerio da Ciencia e Tecnologia FINEP/MCT; Financiadora de Estudos e Projetos/Ministerio da Ciencia e Tecnologia - FINEP/MCT; Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior - CAPES; Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES); EMBRAPA (Empresa Brasileira de Pesquisa Agropecuaria); Empresa Brasileira de Pesquisa Agropecuaria - EMBRAPA; Conselho Nacional de Desenvolvimento Cientifico e Tecnologico - CNPq; Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)

Este trabalho contemplou o estudo do desenvolvimento de amidos termoplásticos (TPS) obtidos a partir da raiz de mandioca bruta e de seus derivados (amido e resíduo). A técnica de preparação deu-se por mistura física dos componentes, via estado fundido, empregando-se o plasticizante glicerol em proporções variadas. Contemplou ainda a busca de alternativas que viessem a melhorar o desempenho mecânico e a resistência à absorção de umidade dos TPS. Foi realizado um estudo inicial de caracterização dos materiais originais e constatou-se que a presença de açúcares na raiz e de fibras no resíduo é o principal diferencial com relação à composição do amido industrial. Os TPS preparados a partir de amido industrial e de raiz apresentaram fraco desempenho mecânico. Por outro lado, as fibras presentes no resíduo foram capazes de gerar TPS com melhores propriedades mecânicas. Os açúcares naturalmente presentes na raiz ocasionaram um efeito adicional de plasticização ao TPS influenciando principalmente nas propriedades de alongamento na ruptura. Os TPS preparados apresentaram comportamentos semelhantes frente à absorção de água. As estratégias empregadas na tentativa de melhorar o desempenho do TPS preparado a partir de amido de mandioca industrial foram: desenvolvimento de blendas de TPS com poli (álcool vinílico) (PVA); adição de látex de borracha natural às blendas TPS/PVA; uso de partículas minerais (alumina e carbeto de silício) aos TPS e uso de nanofibras de celulose (whiskers) como reforço aos TPS. Estas nanofibras foram extraídas a partir das fibras contidas no resíduo da industrialização do amido de mandioca. Em todos os casos foram realizados estudos da morfologia e do desempenho dos materiais resultantes. Os resultados revelaram que as blendas TPS/PVA e TPS/PVA/látex foram...

Recentemente, a busca por novos materiais tem se caracterizado pelo desenvolvimento de processos mais limpos, com utilização de matérias-primas renováveis, e produção de derivados não agressivos ao meio ambiente, sem perda de qualidade ou desempenho. O isolamento de nanocelulose a partir de fibras vegetais e resíduos agroindustriais, para utilização em matrizes poliméricas, é um exemplo dessa nova visão da ciência dos materiais em busca da sustentabilidade. Nesse sentido, as técnicas de extração da nanocelulose têm sido bastante investigadas. No presente trabalho foram feitas adaptações de trabalhos descritos na literatura, visando tornar o processo ecologicamente correto. As fontes de nanocelulose utilizadas foram a casca de arroz e a testa de soja. Os materiais, após moagem, foram submetidos à extração com hexano, álcool etílico e água, nesta ordem. Por tratamento alcalino em autoclave foi removida a maior parte da lignina e da hemicelulose. A polpa obtida foi branqueada utilizando um processo totalmente livre de cloro, levando àcelulose purificada. A hidrólise ácida parcial, feita com ácido sulfúrico, permitiu o isolamento dos nanocristais de celulose, também chamados de whiskers de celulose. Foram feitas análises termogravimétricas e por espectroscopia no infravermelho ao final de cada processo...

Bacterial cellulose (BC), excreted by Gluconacetobacter xylinus, is a unique nanofibrilar biopolymer with a wide range of applications in human and veterinary medicine, odonthology, pharmaceutical industry, biotechnological, food and paper industry. The major research activities of our research group include the following headlines: - Surface-modification of BC matrices and BC whiskers for the design of novel functional BC nanocomposite systems. This domain includes the surface-activation of BC with CBMs (Carbohydrate Binding Modules) conjugated with bioactive peptides for biomedical applications.[1] CEB-UM has already shown that the adsorption of CBM-RGD (the minimal essential cell adhesion recognition motifs) onto BC improves its ability to adsorb fibroblasts.[2] Also, research on the use of BC tubes as new guides for neuronal growth (CAPES, 3989/05-4) and, for the first time, on assessing the in vivo cytotoxicity of BC nanofibers (SFRH/BD/18418/2004), is on course. - Design of novel BC structures with tailored microporosity, for biomedical applications (SFRH/BD/48759/2008). - Engineering of electro-conductive and electro-active BC scaffolds with potential applications in neuronal growth. The embedded polymeric directionally of the BC nanofibers is expected to exhibit shear piezoelectricity which...

Solid lithium-conducting nanocomposite polymer electrolytes based on poly(oxyethylene) (POE) were prepared from high aspect ratio cellulosic whiskers and lithium imide salt, LiTFSI. The cellulosic whiskers were extracted from tunicate -a sea animal- and consisted of slender parallelepiped rods that have an average length around 1 µm and a width close to 15 nm. High performance nanocomposite electrolytes were obtained. The filler provided a high reinforcing effect while a high level of ionic conductivity was retained with respect to unfilled polymer electrolytes. Cross-linking and plasticizing of the matrix as well as preparation of the composites from an organic medium were also investigated.

This paper present the most relevant advances in the fields of: i) cellulose fibres surface modification; ii) cellulose fibres-based composite materials; and iii) nanocomposites based on cellulose whiskers or starch platelet-like nanoparticles. The real breakthroughs achieved in the first topic concern the use of solvent-free grafting process (plasma) and the grafting of the matrix at the surface of cellulose fibres through isocyanate-mediated grafting or thanks to "click chemistry". Concerning the second topic, it is worth to mention that for some cellulose/matrix combination and in the presence of adequate aids or specific surface treatment, high performance composite materials could be obtained. Finally, nanocomposites allow using the semi-crystalline nature and hierarchical structure of lignocellulosic fibres and starch granules to more deeply achieve this goal profitably exploited by Mother Nature

A new series of biomimetic stimuli-responsive nanocomposites, which change their mechanical properties upon exposure to physiological conditions, was prepared and investigated. The materials were produced by introducing percolating networks of cellulose nanofibers or “whiskers” derived from tunicates into poly(vinyl acetate) (PVAc), poly(butyl methacrylate) (PBMA), and blends of these polymers, with the objective of determining how the hydrophobicity and glass-transition temperature (Tg) of the polymer matrix affect the water-induced mechanically dynamic behavior. Below the Tg (~60–70 °C), the incorporation of whiskers (15.1 – 16.5% v/v) modestly increased the tensile storage moduli (E′) of the neat polymers from 0.6 to 3.8 GPa (PBMA) and from 2 to 5.2 GPa (PVAc). The reinforcement was much more dramatic above Tg, where E′ increased from 1.2 to 690 MPa (PVAc) and ~1 to 1.1 GPa (PBMA). Upon exposure to physiological conditions (immersion in artificial cerebrospinal fluid, ACSF, at 37 °C) all materials displayed a decrease of E′. The most significant contrast was seen in PVAc; for example the E′ of a 16.5% v/v PVAc/whisker nanocomposite decreased from 5.2 GPa to 12.7 MPa. Only a modest modulus decrease was measured for PBMA/whisker nanocomposite; here the E′ of a 15.1% v/v PBMA/whisker nanocomposite decreased from 3.8 to 1.2 GPa. A systematic investigation revealed that the magnitude of the mechanical contrast was related to the degree of swelling with ACSF...

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This work focuses on analysis and comparison of accelerated weathering of samples of polylactic acid reinforced with cellulose whiskers (PLA-CW), conducted in QUV chamber-Panel, and their subsequent exposure to biotic soil environment. The cellulose whiskers (microfibrils) were obtained from banana rachis and pseudostem Musa cavendish. Changes in thermal, structural and mechanical properties, due to degradation processes of PLA-CW, were studied using DSC, IR Spectroscopy, XRD, NMR, GPC and Mechanical test. The results show that the percentage of biodegradability in soil, based on CO2 release, is higher for samples of PLA-CW that have been previously exposed to UV-photodegradation, which induces hydrolysis that stimulates the biodegradability of PLA-CW. The results indicate that PLA-CW has short half-life after biodegradation in soil and it is suitable for land disposal.