Effect of the hemicellulose in the properties of nanopaper.

The foldable, low thermal expansion, and optically transparent are main properties of paper produced with cellulose nanofibers (nanopaper), being able to be used ifl the development of flexible circuit technologies. In this context, this work evaluates the importance of hemicellulose in the properties of nanofiber paper (NFP). The hemicellulose extraction from Pinus sp bleached cellulose pulp was performed with NaOH 17.5% for 1.5 h. Thereafter, the pulp was washed with 8.3% NaOH, then was add 10% acetic acid until neutralization, and washed with water. The nanofibrils were obtained by mechanical defibrillation in a Super Masscoloider Masuko Sangyo mill. The NFP with the grammage of 40 and 50 g/m2 were produced by filtration and drying under pressure. The extraction process reduced 80% of xylose, 40% of mannose and 40% of galactose compared of the bleached cellulosic pulp. The NFPs with around 15% of hemicellulose are homogeneous and transparent, the interstices between the fibers, observed by scanning electron microscopy, are small enough to avoid light scattering, making the cellulosic material transparent. The NFP of 40 and 50 g/m2 had a thickness of 45 J..Im,water absorption of 63 and 34 g/m2, respectively. They did not present air permeability. NFP of 40 and 50 g/m2 without hemicellulose had a thickness of 76 and 87 um, water absorption of 128 g/m2 and air permeability of 202 and 384 s/100 em", respectively. The spaces created by the coalescence of the cellulose nanofibrils after the extraction of the hemicellulose result in the dispersion of the light and consequently in the opacity of the NFP. Extraction of hemicellulose reduced the tensile and bursting strength by 80%. Therefore, hemicellulose acts as an inhibitor of the coalescence of microfibrils, providing adhesion and increase of the mechanical properties

Connecting Regional Development to Environmental Education

<p>In this study we investigate how environmental education can be connected with the regional sustainable development We perceive that the dialogues surrounding Environmental Education in formal education have been dividing opinions over the last two decades. This does not happen only in relation to the conceptual precepts, but mainly in relation to the field of activity. Our theoretical support comes from authors engaged with the Critical Environmental Education, signaling for the construction of what we call Reference Framework. Our research is developed from a qualitative perspective, having as a strategy the exploratory case study. For the analysis of the documents we make reference to the methodology of content analysis proposed by Bardin (2011) and reflective application of the Reference Framework. We argue that so far in Brazil, environmental education is divided into two major theoretical trends that reflect the practices of environmental educators. On the one hand, supporting a behaviorist / liberal / conservative tendency of Environmental Education (CARVALHO, 2001; GUIMARÃES, 2000; LOUREIRO, 2008), understand environmental practices from its immediate resolution dimension, focusing actions that situate environmental practices through changes in social behaviors, mostly promoted by environmental activism. On the other hand, we have the opposite, that is, the popular / critical / emancipatory tendency which situates its argumentative and practical content situates in the significant assumption of a new societal posture in relation to the economic models adopted. It establishes the connection between environmental education and local / regional development, delineating a perception of reality, forming a dimension of creating other ways of relating human and non-human, including the emergence of a rationality that impresses ethical socio-environmental values, other forms of understanding of the world and the concept of environmental rationality.</p&gt

Síntese de nanopartículas de prata em filmes de nanocelulose.

O setor de embalagens busca materiais que protejam e conservem os alimentos visando manter sua qualidade. Sendo a celulose o polímero natural mais abundante na Terra, com regeneração via fotossíntese, uma alternativa promissora. O uso da nanocelulose ainda agrega características de alta e resistência e translucidez ao material. Estudos mostram que as nanopartículas de prata (NPs Ag) agem contra mais de 650 agentes patogênicos sem desenvolver resistência. A síntese de nanopartículas de prata (NPs Ag) em filmes de nanocelulose combinam as propriedades de resistência e biodegradabilidade da nanocelulose com a ação antibacteriana da NPs Ag. Para isso foram sintetizadas NPs Ag pelo método de reagente de Tollen na superfície de filmes de nanocelulose de pinus sp em duas concentrações. As NPs Ag foram caracterizadas por difração de raios-X e microscopia eletrônica de varredura. Os filmes obtidos apresentaram concentração de 32 e 89 mg de NPs Ag por kg de nanocelulose. A síntese da NPs Ag foi um processo eficiente sendo necessário testes in vitro para avaliar a ação antibacteriana do material

Foraging at the Edge of Chaos: Internal Clock versus External Forcing

Activity rhythms in animal groups arise both from external changes in the environment, as well as from internal group dynamics. These cycles are reminiscent of physical and chemical systems with quasiperiodic and even chaotic behavior resulting from “autocatalytic” mechanisms. We use nonlinear differential equations to model how the coupling between the self-excitatory interactions of individuals and external forcing can produce four different types of activity rhythms: quasiperiodic, chaotic, phase locked, and displaying over or under shooting. At the transition between quasiperiodic and chaotic regimes, activity cycles are asymmetrical, with rapid activity increases and slower decreases and a phase shift between external forcing and activity. We find similar activity patterns in ant colonies in response to varying temperature during the day. Thus foraging ants operate in a region of quasiperiodicity close to a cascade of transitions leading to chaos. The model suggests that a wide range of temporal structures and irregularities seen in the activity of animal and human groups might be accounted for by the coupling between collectively generated internal clocks and external forcings

Dynamic instabilities in resonant tunneling induced by a magnetic field

We show that the addition of a magnetic field parallel to the current induces self sustained intrinsic current oscillations in an asymmetric double barrier structure. The oscillations are attributed to the nonlinear dynamic coupling of the current to the charge trapped in the well, and the effect of the external field over the local density of states across the system. Our results show that the system bifurcates as the field is increased, and may transit to chaos at large enough fields.Comment: 4 pages, 3 figures, accepted in Phys. Rev. Letter

Elaboração de compósitos utilizando resíduo gerado na hidrólise enzimática de lodo da indústria de papel.

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Oxidação de filme de celulose nanofibrilada visando a fixação da enzima lacase.

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Influência da hemicelulose na formação de nanofibrilas.

É crescente o interesse na utilização da celulose nanofibrilada devido as suas propriedades físicas como alta resistência, baixa densidade e translucidez, além dos benefícios ecológicos. A polpa celulósica obtida pelo processo Kraft frequentemente utilizada no processo de obtenção da nanofibrilas apresenta cerca de 15% em massa de hemicelulose, sendo importante avaliar a influência da hemicelulose na formação das nanofibras. Para tal, foram produzidas suspensões de nanocelulose uma com hemicelulose e outra na qual a hemicelulose foi extraída, obtidas pelo método mecânico de desfibrilação da celulose. As técnicas empregadas para a caracterização foram difração de raios x, microscopia eletrônica de transmissão e reologia. O comportamento reológico mostrou que a extração da hemicelulose exclui a necessidade de uma tensão inicial para escoamento, ocorrendo também a redução da cristalinidade da celulose e a aglomeração das nanofibrilas