Scielo RSS <![CDATA[Matéria (Rio de Janeiro)]]> vol. 19 num. 4 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[When nanotechnology meets filteration: From nanofiber fabrication to biomimetic design]]> Nanotechnology for the scientific and economical revival is of indispensable importance, and the so-called nano-age or nano-industrialization is coming. The paper reveals the very frontier of nanotechnology in mass-production of nanofibers, and the bubble-electrospinning is introduced, and its application to filteration is emphasized. By mimicking the structure of silkworm cocoon, the filteration efficiency reaches its maximum, while the pressure drop through the filter is minimal, and small water cluster is obtained after nanofiber membrane for water purification. <![CDATA[Mini-review on Bubbfil spinning process for mass-production of nanofibers]]> 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. <![CDATA[On air blowing direction in the blown bubble-spinning]]> 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. <![CDATA[Development and characterization of the amidoxime/Europium (ІІІ)-chelated complex fibers]]> 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 EuCl3 solution 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. <![CDATA[Effect of solution concentrations on the morphology of nylon6/66 nanofibrous yarns by blown bubble-spinning]]> 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. <![CDATA[Comparison between electrospun and Bubbfil-spun Polyether sulfone fibers]]> 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. <![CDATA[Characterization of xylanase from Streptomyces sp. FA1 and its application for bamboo hydrolysis]]> 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. <![CDATA[Modeling the nanofiber fabrication with the melt blowing annular die]]> 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. <![CDATA[Preparation and characterization of electrospun human hair keratin / poly (ethylene oxide) composite nanofibers]]> 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. <![CDATA[Molecular dynamic study of the jet noise about the micro-scale tube]]> 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. <![CDATA[Contrastive research on the waterproof and dustproof mechanism of wild silkworm silk and domestic silkworm silk]]> 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. <![CDATA[A conservation law for self-hydrolysis process of aqueous sodium borohydride]]> 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.