RCAAP Repository

Bubbfil spinning is to use polymers' or melts' bubbles or membranes for fabrication of nanomaterials including smooth nanofibers and discontinuous nanofibers by using electrostatic force, blowing air or mechanical force to overcome the surface tension, it mainly includes the bubble-electrospinning, blown bubble spinning and membrane spinning. The initial ejecting velocity of the Bubbfil spinning process is as high as 100 meters per second. A history of the development of Bubbfil spinning is briefly elucidated, its main properties are emphasized, some effective modifications are discussed for different applications including single bubble electrospinning, blown bubble spinning, air-jet assisted bubble electrospinning, electrostatic-field-assisted blown bubble spinning, and vibration bubble electrospinning which is suitable for melts or high-concentration solutions. Morphology properties are also discussed for different applications.

This paper studies the effect of airflow direction on morphology of the nanofibers obtained by the blown bubble-spinning, a kind of Bubbfil spinning processes. Regenerated silk fibroin is used in the experiment, and the results indicate that nanofibers with random array structure can be obtained when the blowing air direction is perpendicular to the direction of bubble ejection. While uniform oriented fiber bundles composed of superfine fibers are obverse when the blowing air directs to the bubble ejection. The paper reveals that blowing air direction can be used to control morphology and structure of fibers during the spinning process.

This paper presents a study of the amidoxime/Europium (ІІІ)-chelated complex (AECC) fibers which can be used as functional fibers for technical textiles such as decorations, protections and medical textiles etc. First, the EuCl3solution were prepared and reacted with amidoxime fibers using optimized process conditions at 50 °C, 5 hours. Subsequently, the morphology, element analysis, fluorescence and mechanical properties of the AECC fibers were systematically investigated. Finally, the effects of different pH values and temperature on the content of Eu (III) complexes fiber were studied, respectively. The results showed that the AECC fibers possess enhanced fluorescence intensity and good mechanical properties. The results also illustrated that coordination reaction was identified between Eu (III) ions and amidoxime fiber and the electronic energy of C1s, O1s, N1s and Eu (III) ions in amidoxime fibers has significant changes compared to original fibers. The fluorescence emission bands of the AECC fibers were observed when the excitation wavelength λ equal to 380 nm. In conclusion, this study provided a theoretical basis for the preparation and practical application of fluorescent fibers.

In this paper, a novel method called blown bubble-spinning was employed to produce nanofibers. Compared with the traditional technologies, such as melt blowing and electrospinning, hot airflow is used in blown bubble-electrospinning to overcome the surface tension of the polymer bubbles and to pull multiple jets from the broken bubble into nano scale ones which are solidified to nanofibers after solvent evaporation, the technology requires no electrostatic force. The effect of Nylon6/66 polymer concentration on the morphology of nanofibers is investigated. The results indicate that nanofibers without beads were successfully fabricated under this one-step process and spontaneously aggregated to form superfine fiber assemblies. Besides, average diameters of both fiber assemblies and inner nanofibers increased with polymer concentrations, ranging from 6 micrometers to 34 micrometers and 180nm to 524nm, respectively. This study provides a promising approach to directly generate fiber assemblies composed of nanofibers, which may show great potential in the future applications.

Electrospinning is a simple method for producing ultrafine fibers, and has attracted much recent interest. The classical approach was either polymer solutions or polymer melts. Bubbfil spinning (e.g. bubble-electrospinning) is a facile method to fabricate nanofibers with high surface area to volume ratio and high porosity. Polyether sulfone (PES) dissolved in N,N-Dimethylacetamide (DMAC) was used in this study to compare fiber morphologies of two technologies at the same spinning conditions. Effects of solution concentration, applied voltage and tip-to-collector distance on the morphology of the fibers were experimentally studied. It revealed that the Bubbfil spinning process is a better candidate for mass-production of nanofiber with controllable morphology.

Native cellulose can be disintegrated into substructures with nano-size dimension through electronspinning. Typically, the most common source material available for cellulose nano-fiber production is wood. More attempts are employed to find new suitable resources to produce nano-cellulose at present. Bamboo boasts the abundant resource in China and possesses fast-growing, anti-bacterial, anti-UV, aroma absorbance properties as well as superior physical and mechanical characters. Cellulose is the main constituent in bamboo, which shows great potential to be the ideal source for producing cellulose nano-fiber. Traditional method for bamboo cellulose extraction needs the use of high concentrated alkaline. Such process causes severe environment problems. Therefore, study on alternative green technologies is inevitable. In this work, self-produced xylanase was applied to hydrolyze bamboo noncellulosic substances. Results indicated that such xylanase from Streptomyces sp. FA1 isolated from bamboo retting system showed broad pH range for xylan hydrolysis, which presented activity of 180 U/mL and 270 U/mL under preferred pH5.5 and pH7, respectively. Three pretreatment methods (including high temperature, ultrasonic generator and supersonic cleaner) were employed to enhance the bamboo processing, among which, xylanase hydrolysis on high temperature pretreated (120°C, 60 min) bamboo showed the most obvious effect. Thermogravimetric test represented that the weight loss of xylanase hydrolysis on high-temperature pretreated sample was higher than that of original sample, which might be attributed to the decomposition of hemi-cellulose and part of cellulose. This study establishes a base for future studies to develop enzymatic hydrolysis of bamboo noncellulosic materials, making them suitable for cellulose nano-fiber producing.

Melt blowing is commonly used to convert polymer resin directly into nonwoven fabrics of superfine fibers. Further decrease of the fiber diameter will improve the filtration and adsorption properties remarkably and thus has been appealing to the researchers. Besides the dual slot die, the annular die is utilized to manufacture superfine fibers in the melt blowing process as well. In the dual slot die, the high velocity air flow from both sides of the polymer melt. However, the air encircles the polymer melt entirely in the annular die, which is in favor of the polymer drawing and thus manufacture of nanofibers. In this paper, the air flow field model of the annular die is established and solved numerically. The polymer drawing with the melt blowing annular die is modeled and simulated by introducing the simulation results of the air flow field. The predicted fiber diameters coincide with the experimental data. Effects of the polymer flow rate and initial air velocity on the fiber diameter are also explored. The results show good perspective of using melt blowing technology to manufacture nanofibers materials because melt blowing has a higher output than electrospinning.

Keratin, as one of the most abundant proteins, has been widely used for bio-related applications due to its biocompatibility and biodegradability. In this study, keratin was extracted from human hair by sulphitolysis extraction method and then blended with poly (ethylene oxide) (PEO) at different proportions. The keratin/PEO mixture was dissolved in distilled water, and finally electrospun into composite nanofibers. The viscosity of keratin/PEO solution reduced with the increase of keratin mixture ratio. The viscosities of the solutions at mixture ratios of 30/70 and 40/60 keratin/PEO showed flow curves comparable with that of 6 and 4wt% pure PEO solutions, respectively. The morphology, structure, and thermal property of the composite nanofibers were evaluated by Scanning Electron Microscope (SEM), Fourier Transform infrared spectroscopy (FTIR), and Differential Scanning Calorimetry (DSC), respectively. SEM analysis revealed that the morphologies of nanofibers were determined by the keratin content of keratin/PEO blend. Bead-free nanofibers could be found when the mixture ratio of keratin was below 70 wt% in the blend. FTIR analysis indicated that electrospinning process induced structural modifications in both the crystalline microstructure of pure PEO and keratin chains with a planar conformation with respect to the helical conformation. Thermal behavior of the keratin/PEO composite nanofibers showed that a high draw occurred in the electrospinning process causing the protein chains a less complex super-molecular reorganization that denatured at lower temperatures. The keratin/PEO composite nanofibers has potential for biomaterials such as cell culture substrate.

This paper studies the two-dimensional micro-scale molecular simulations of the jet flow using Lagrange discrete systems and adopting Andresen flexible constraint mechanism. At the effects of different excitation conditions and boundary conditions, the low Mach number flow field and sound field are obtained, and characteristic results are given. At the jet flow and pipe flow regions, particles velocities distribution is consistent with traditional method. There are many small groups which have a bigger velocity value, and form the disturbance sources. The stronger interaction with the tube wall produces greater sound pressure, thus random collisions method at the tube wall is effective to deal with sound propagation problem. Therefore, this paper offers preliminary and calculated basis for the molecular and macroscopic quantum aerodynamic problems.

Wild silk has properties of waterproof and dustproof, but its domestic partner has neither. Scanning electron microscopy (SEM) was used to observe and compare their morphology difference so that the possible mechanism can be elucidated. By the contrastive research, this paper concludes that the mechanism of waterproof and dustproof of wild silk is due to selective repulsion, each hierarchical cascade of nanoparticles can repel either water molecules or fine particles in air. The SEM study reveals that the different nanoparticles with hierarchical structure on the silk surface are main factors of the highly selective repulsion. This theory can also explain the waterproof property of lotus leaf. A better understanding of the repulsion mechanism of wild silk could help the further design of bio-mimetic waterproof/dustproof artificial materials.

A conservation law is obtained for self-hydrolysis process of aqueous sodium borohydride, which gives an explicit relationship between the concentrations of NaBH4 and hydrogen ions during the global reaction.

The aim of this study is to evaluate cytotoxicity between polyurethane and non-latex orthodontic elastomeric ligatures. Seven elastomeric ligatures of black-coloured from different manufactures (3 non-latex, 3 polyurethane and 1 latex) were divided into 7 groups of 10 elastics each: Group UK (nonlatex, 3M Unitek), Group TP (nonlatex, TP Orthodontics), Group AO (nonlatex, American Orthodontics), Group O (Polyurethane, OrthoSource), Group M (Polyurethane, Morelli), Group TD (Polyurethane, Tecnident) and Group TC (latex - Control, TP Orthodontics). The cytotoxicity essay was performed using cell cultures (L-929 line cells, mouse fibroblast) that were submitted to the cell viability test with neutral red ("dye-uptake") at 1, 2, 3, 7 and 28 days. Analysis of variance (ANOVA) with 1-way analysis followed by the Tukey post hoc test were employed (p<.05). The results showed no statistically significant differences between Groups UK, TP and AO in all experimental times (p>.05). There was a statistically differences (p<.05) between the viability cell of Groups UK, TP and AO with the Groups O, M, TD and TC at 1, 2, 3 and 7 days. There was no statistically differences (p>.05) between the groups O, M and TD at in all experimental times. It can be concluded that the nonlatex elastomeric ligatures of Unitek, TP Orthodontics, and American Orthodontics showed higher cell viability compared to others ligatures.

Este estudio propone una alternativa para la recuperación de las orugas de tractores Bulldozer desgastadas por el efecto abrasivo del suelo. Para este fin, se aborda un análisis comparativo entre la resistencia al desgaste de una oruga original con dos orugas semejantes, recuperadas por procesos distintos. El primer proceso de recuperación utiliza la aplicación de un postizo en la región de desgaste y el segundo consiste de la recuperación de la región afectada mediante deposición por soldadura de un revestimiento duro. Las probetas fueron sometidas a ensayos de desgaste tipo rueda de caucho y chorro de arena seca (ASTM G 65-04); el análisis microestructural fue realizado por medio de la utilización de las técnicas de análisis de microscopia óptica (MO) y microscopia electrónica de barrido (SEM). Se obtiene como micromecanismo de desgaste predominante en la soldadura el microcorte, en tanto que para los demás materiales (ambos aceros) se observa deformación plástica y presencia de microsurcos. Fue posible observar que el proceso de recuperación de orugas utilizando el revestimiento con electrodo E-83.58 mostro ser una alternativa para este tipo de recuperación.

Corpos de prova de aço inoxidável ISO 5832-1 foram tratados por dois diferentes processos, nitretação por plasma em baixa temperatura e SHTPN, com objetivo de obter camada superficial rica em nitrogênio (fase S ou γN) e livre de precipitados. O tempo de nitretação para ambos os processos foi o mesmo (3 h), de modo a possibilitar um comparativo dos resultados obtidos. Utilizaram-se as seguintes técnicas de análise: microscopia eletrônica de varredura (MEV), microscopia ótica (MO), microdureza, difração de raios-X (DRX) e espectroscopia por dispersão de comprimento de onda. Os resultados indicaram que a nitretação em baixa temperatura possibilita a formação de camada de fase S com concentrações da ordem de 0,90 % N (peso) com espessuras de pouco mais de 2 µm, enquanto o SHTPN gera camadas com 0,45 % N (peso) e espessuras de até 200 µm.

A retração na madeira pode ser analisada sob o ponto de vista de sua influência em tensões, deformações e deslocamentos, presentes nas estruturas. Essa retração pode ser computada como parcela nas relações tensão-deformação, considerando-se nessa análise uma peça de madeira em forma de tronco cilíndrico sem forças externas, num sistema de coordenadas cilíndricas. Devido à simetria radial o campo de deslocamentos é função do raio e o deslocamento na direção angular é nulo. Considerando-se também que a deformação longitudinal seja constante, as deformações são escritas em função dos coeficientes de deformação reduzida e de um coeficiente associado denominado de k, apresentados por Lekhnitskii, os quais dependem das propriedades de elasticidade do material. Com isso a equação diferencial que rege esse problema é função dos coeficientes de deformação e consequentemente da retração. Para exemplificar o uso da equação regente do problema e consequente determinação de tensões nas direções radial e tangencial e deslocamentos radiais foram utilizados os coeficientes de elasticidade da espécie de madeira Pinus caribaeaobtidos em procedimento experimental auxiliar. De um modo geral, os resultados mostraram a importância de se verificar a influência da retração no estado de tensão radial e tangencial e nos deslocamentos radiais em peças de madeira.

A liga Al-6%Cu foi solidificada direcionalmente sob condições transitórias de extração de calor e microestruturas dendríticas, variáveis térmicas de solidificação, ou seja, velocidade de deslocamento da isoterma líquidus (VL), taxa de resfriamento (TR) e gradiente de temperatura à frente da isoterma liquidus (GL) foram caracterizadas, determinadas experimentalmente e correlacionadas com os espaçamentos dentríticos terciários (λ3). Para tanto, foi projetado, construído e aferido um dispositivo de solidificação direcional horizontal. Os resultados encontrados mostram que leis de potência -1,1 e -0,55 caracterizam a variação dos espaçamentos terciários com a velocidade de deslocamento da isoterma liquidus (VL) e a taxa de resfriamento (TR), respectivamente. Finalmente, é realizado um estudo comparativo entre os resultados obtidos neste trabalho e aqueles publicados na literatura para ligas Al-Cu solidificadas direcionalmente sob condições transientes de fluxo de calor nos sistemas verticais ascendente e descendente.

Vinyl ester resins are widely used in sandwich composite structures. Because of their good resistance to chemicals, flexibility and easy processing, these sandwich are extensively applied in the marine sector. These composites are typically manufactured by liquid molding processes, especially infusion. In this study, RTM light was used to inject the polymeric resin into the mold cavity, flowing in the space between the impermeable core and the mold walls, where the fibrous medium was. In this process, viscosity, gel time and curing time of the resin are very important parameters. This work addressed the curing and post-curing characteristics of a vinyl ester resin, and also the characteristics of neat and reinforced vinyl ester using dynamic mechanical analysis (DMA). The increase in shear rate did not significantly influence resin viscosity within the studied range. Differential scanning calorimetry showed the efficiency of the post-curing stage, with the decrease in residual enthalpy. With DMA, it was possible to determine gel time and gel temperature, which yielded similar values to those found by the SPI (Society of the Plastics Industry) method, indicating that the simpler SPI method can be reliably used for that.

As intensidades de emissão das espécies N2+, H, C, NH, N2, Ar e CN do plasma de carbonitretação (usando os gases Ar+N2+CH4) foram medidas por espectroscopia de emissão óptica (OES) em pressão e temperatura constantes (2mbar e 500 °C) variando o fluxo de CH4. Em seguida, amostras de Ti comercialmente puro (Ti CP) foram carbonitretadas em plasma nas mesmas condições do estudo por OES. O objetivo desse trabalho é avaliar a influência das espécies presentes no plasma, detectadas por seus padrões de emissão, na composição de fases superficiais, nas características topográficas e no perfil de microdureza do revestimento de TiCN. Foi observado que o aumento da concentração de CH4 no plasma gerou as espécies H (dissociado do CH4) N2+, C, NH e CN. A evolução contínua de CN e uma queda progressiva na espécie N2+ influenciaram a composição da superfície e as propriedades aqui avaliadas. A análise de difração de raios X em ângulo rasante revelou a presença de nitreto e carbonitreto de titânio na superfície com composição química correlacionada com as alterações das intensidades de emissão das espécies CN e N2+. As topografias das amostras, avaliadas por microscopia de força atômica, apresentaram aumento nos parâmetros de rugosidade comparados com a amostra padrão. A rugosidade Ra aumentou com o aumento da intensidade de emissão óptica de CN e redução de N2+. Com auxílio da espectroscopia micro-Raman foi encontrado carbono não reagido com o titânio na forma de um filme que se desenvolveu com o aumento da intensidade da linha de emissão do CN. Este filme pode, hipoteticamente, ter sido o responsável pela queda progressiva da dureza superficial do revestimento.

O objetivo principal deste artigo é avaliar o comportamento à compressão dos concretos utilizando métodos combinados de testes não destrutivos, como a velocidade de ultrassom e o índice esclerômétrico. Para tanto, foram confeccionados corpos de prova cilíndricos e cúbicos de concretos, com diferentes tipos de brita de acordo com o diâmetro máximo (brita 0,1 e 2) e relações água/cimento. Para a previsão da resistência à compressão dos concretos, os resultados experimentais foram comparados com os resultados teóricos propostos por Rilem [4], Gasparik [5] e Di Leo e Pascale [6]. Como conclusão, pode afirmar-se que existiu uma maior variabilidade nos resultados de velocidade de ultrassom para resistências de concretos acima de 30 MPa, diferentemente do encontrado nos resultados dos índices esclerométricos. As funções potenciais que relacionavam a resistência do cilindro e a velocidade de ultrassom apresentaram comportamentos semelhantes para os concretos com brita 1 e 2, sendo significativamente diferentes aos concretos de brita 0. Já para as medidas dos índices esclerométricos, não se pode verificar diferenças quanto ao tipo de brita nos resultados experimentais. A combinação dos resultados de resistências experimentais e teóricas dos métodos combinados de testes não destrutivos ficou abaixo da reta de representação unitária (experimental/teórico), o que permite concluir que os modelos propostos não foram confiáveis para a previsão da resistência do concreto a partir da velocidade de ultrassom e do índice esclerométrico.

Os precursores mais empregados para obtenção da fibra de carbono são a poliacrilonitrila, o piche e o rayon. Com o aumento da demanda de materiais compósitos leves e de alta resistência, a produção da fibra de carbono tem aumentado exponencialmente e novos precursores têm sido requisitados. A lignina, um material orgânico natural, tem sido estudada como possível candidata para a produção das fibras. Além de ser rejeito industrial e de biorrefinarias, as fibras de carbono obtidas com a lignina podem ter um custo mais vantajoso quando comparado com os demais precursores comerciais. Em decorrência da biodiversidade de vegetais na natureza, a lignina pode apresentar diferentes estruturas. O método de recuperação também é parâmetro que influencia diretamente na sua composição. Como as propriedades térmicas para extrusão são fortemente dependentes dessas e de muitas outras variáveis, muitas pesquisas têm sido reportadas utilizando lignina pura de diversas fontes, lignina modificada e com adição de plastificantes. As etapas de pré-tratamento, termoestabilização e carbonização/grafitização também têm sido avaliadas para conferir melhores propriedades mecânicas ao produto final. Não obstante serem muitas as condições para a produção da fibra de carbono a partir da lignina, resultados bastante promissores têm sido alcançados. As aplicações em diversas áreas estão diretamente relacionadas com o conjunto de propriedades mecânicas inerentes a ela. A fibra de carbono proveniente da lignina vem contribuir com inúmeros empregos no mercado, de maneira a baratear sua produção, minimizar a dependência de materiais fósseis e tornar sua manufatura ecologicamente sustentável.