Electrospun meta-aramid/cellulose acetate and meta-aramid/cellulose composite nanofibers

Meta-aramid/cellulose acetate and meta-aramid/cellulose composite nanofibers were successfully prepared in this paper. There were some new interactions formed among composite ingredients and the beads of nanofibers decreased with increasing the weight proportion of ingredients and concentration of composite solution. The meta-aramid/cellulose acetate composite solution was more favorable for electrospinning because of its lower viscosity and surface tension than meta-aramid/cellulose composite solution, and the uniform nanofibers were obtained when the weight proportion of meta-aramid/cellulose acetate was larger than 1:2, however, it was feasible for meta-aramid/cellulose composite solution when the weight proportion of composite solution exceeded 4:1. The thermal property and mechanical property of composite nanofibers were improved after blending meta-aramid with cellulose acetate or cellulose.     

Laser induced surface modification of clay-PAN composite nanofibers

In this study a newly laser treatment method for surface modification of nanofibers is introduced. The new method is based on different infrared absorption of materials. Surface modification of Clay-PAN composite nanofibers was performed using selective laser etching approach with CO₂ pulsed laser in order to increase surface area of nanofibers. The surface structure of resulted nanofibers is characterized using field emission scanning electron microscope and the results show characteristic modification of the surface topography of laser treated nanofibers. The modified surface structure of nanofibers was studied and analyzed for different laser pulse numbers and laser fluence. The results show that nanofiber surface modification strongly depends on the number of CO₂ laser pulses and frequency of modified sites on the surface of nanofibers increasing with increasing the pulse fluence. This new technique is highly selective and can also compete with conventional techniques for nanofibers surface modification.     

Fabrication and characterization of electrospun nanofibers of high DP natural cotton lines cellulose

Nanofibers of natural cotton lines cellulose, with a degree of polymerization above 10000, were prepared by electrospinning. The effects of cellulose concentration, flow rate and electric field strength on the morphologies of the fibers were systematically investigated. Furthermore, two effective improvements on the electrospinning apparatus were made: heating the pathway between the tip of the needle and the collector instead of the needle or the collector, and covering the drum with activated cellulose flake. High quality cellulose nanofibers were obtained under the optimized spinning conditions combined with the apparatus improvements. Moreover, oriented cotton nanofibers were acquired by elevating the rotation speed of the drum collector. The wettability of the nonwoven was greatly improved compared with the original activated cellulose. The obtained nonwoven or nanofibers of the natural cotton cellulose could be potentially applied in tissue scaffolds, protective clothing and high efficient water absorbing materials etc.     

Three-layer composite filter media containing electrospun polyimide nanofibers for the removal of fine particles

Polyimide (P84) nanofibers of 200-500 nm were deposited uniformly on needle punched aramid felt with basis weight of 260-350 g/m² by optimized electrospinning. High temperature adhesive was then electro-sprayed on the nanofiber side deliberately to bind a thin protective layer made of temperature-resistant non-wovens. The three layer structure was afterwards enforced by hot pressing to form composite filter media. The application of the adhesive was tailored not to affect the permeability of the substrate felt while exerting adhesion strength of over 1000 kPa for the media to be suitable for flue gas dust treatment under 240 ºC. When 0.3-10 μm NaCl aerosols were used as the simulated dusts, it was found that even a small amount of P84 nanofibers could obviously elevate the filtration efficiency. The composite showed 100 % removal efficiency of particles equal and greater than 2.0 μm, and 99.5 % for particles 1.0-2.0 μm in diameter.     

Facile fabrication of carbon nanotubes/polystyrene composite nanofibers for high-performance electromagnetic interference shielding

Polystyrene (PS) composites with nanofibrous structure consisting of multi-walled carbon nanotubes (MWCNTs) with 0-10 wt.% of nanofiller have been fabricated via electrospinning technique. The surface morphology and thermal properties of the composites were evaluated by scanning electron microscopy (SEM) and thermo-gravimetric analysis (TGA). The SEM analysis of the composite nanofibers samples revealed that the average diameter of the nanofibers increases with increasing MWCNTs content. The resultant MWCNTs/PS composite nanofibers diameters were in the range of 391±63 to 586±132 nm. The thermal stability of composites was increased after addition of MWCNTs to PS matrix. The electrical conductivity of the composites with different weight percentage of MWCNTs was investigated at room temperature. Electrical conductivity of MWCNTs/PS composite nanofiber followed percolation theory having a percolation threshold V _c= 0.45 vol% (~0.75 wt. %) and critical exponent q=1.21. The electrical conductivity and thermal properties confirmed the presence of good dispersion and alignment MWCNTs encapsulated within the electrospun nanofibers. The electromagnetic interference (EMI) shielding effectiveness of the MWCNTs/PS composites was examined in the measurement frequency range of 8.2-12.4 GHz (X-band). The total EMI shielding efficiency of MWCNTs/PS composite nanofibers increased up to 32 dB. The EMI shielding results for MWCNTs/PS composite nanofibers showed that absorption loss was the major shielding mechanism and reflection was the secondary mechanism. The present study has shown the possibility of utilizing MWCNTs/PS composite nanofibers as EMI shielding/absorption materials.     

Buckling analysis of laminated composite plates submitted to compression after impact

The aim of this work is the experimental evaluation of the residual strength of composite laminates under compression after low velocity impact. Different kinds of delaminations, partial, embedded and through-the-width, were studied. Carbon-fibre reinforced epoxy composite was used and the experimental tests were performed on [0]₁₆, [0, 90, 0, 90]_2S and [0_i, 90_i]_s with i=2, 3, 4, 5, using a drop-weight-testing machine. The impacted plates were inspected by the ultrasonic C-Scan to evaluate the size and the shape of the delamination. Results show that the presence of delamination decreases the compressive strength. The stacking sequence and laminate thickness were verified to have a remarkable influence on the value of the residual compressive strength, and play an important role on the observed buckling failure modes.     

Preparation and characterization of nylon-6/gelatin composite nanofibers via electrospinning for biomedical applications

Easy fabrication, porosity, good mechanical properties, and composition controllable of the electrospun nanofiber mat make this material a promising candidate for wound dressing applications. In the present study, nylon6/gelatin electrospun nanofiber mats are introduced as novel wound dressing materials. The introduced mats were synthesized by electrospinning of nylon6 and gelatin mixtures, three mats containing different gelatin content were prepared; 10, 20 and 30 wt%. Interestingly, addition of the gelatin did not affect the mechanical properties of the nylon 6, moreover the mat containing 10 wt% gelatin revealed higher mechanical properties due to formation of spider-net like structure from very thin nanofibers (～10 nm diameter) bonding the main nanofibers. Biologically study indicates that gelatin incorporation strongly enhances the bioactivity performance as increasing the gelatin content linearly increases the MC3T3-E1 cell attachment. Overall, the obtained results recommend exploiting the introduced mats as wound dressing material.     

Electrospinning of silk nanofibers. I. An investigation of nanofiber morphology and process optimization using response surface methodology

Ultra fine fibers were electrospun from regenerated silk fibroin/formic acid solution. Effect of some process parameters on the morphology, diameter and variation in fiber diameter of electrospun fibers were experimentally investigated. Scanning electron microscope was used for the measurement of fiber diameter. Fibers with diameter ranging from 80 to 210 nm were collected depending on the solution concentration and the applied voltages. Response surface methodology (RSM) was used to obtain a quantitative relationship between selected electrospinning parameters and the average fiber diameters and its distribution. It was shown that concentration of silk fibroin solution had a significant effect on the fiber diameter and the standard deviation of the fiber diameter. Applied voltage had no significant effect on the fiber diameter and its standard deviation.     

Electrospinning of polycaprolatone nanofibers with DMF additive: The effect of solution proprieties on jet perturbation and fiber morphologies

Electrospinning is a straightforward method to produce sub-micrometer or nanoscale fiber. Polycaprolactone (PCL), an important polymer in biomedical applications, has been electrospun in several solvent systems. N,Ndimethylformamide (DMF) is often used as an additive in the solvent system to prepare PCL nanofibers. The adding of the DMF changes the physical properties of the solution. To trace and understand the influence of these changes on the jet formation as well as the resultant fibers morphologies, a model of jet perturbation based on the Plateau-Rayleigh Instability theory was established to explicate the formation of the particles/fibers and some experiments for testing the solution properties and fibers morphologies were carried out. With the adding of DMF in dichloromethane (DCM)/DMF mixed solvents, the solution surface tensions increase while solution viscosities decrease, which triggers the change of electrospinning to electrospraying in general. However, according to the obtained results, the addition of the DMF makes it easier to induce the transformation of particles electrospraying to fibers electrospinning with smaller diameter. This is attributed to the higher dielectric constant, lower vapor pressure, and higher electric conductivity of DMF. The theoretical model and experimental results strengthen the relations of solution properties, jet moving behaviors, and the resultant fiber morphologies.     

Fabrication of superhydrophobic cellulose/chitosan composite aerogel for oil/water separation

Superhydrophobic cellulose and chitosan composite aerogel (SCECS) is fabricated through a novel and simple approach for the first time. During the preparation of cellulose and chitosan composite aerogel (CECS), chitosan is selfassemble into number micron-diameter particles on the surface of aerogel, which is similar to the micromorphology of a lotus leaf. Based on the rough surface, CECS is modified by sodium stearate through electrostatic interaction and ion exchange. Water contact angles of 156° are obtained for superhydrophobic aerogel. SCECS can remove various oils from water and with absorption capacities of 10 g/g for oil. Furthermore, the special structure of a non-porous of surface and porous layer of internal is benefit to separate surfactant-stabilized water-in-oil emulsions under gravity.     

The formation and UV-blocking property of flower-like ZnO nanorod on electrospun natural cotton cellulose nanofibers

We report a simple and effective route to fabricate branched hierarchical flower-like nanostructures of ZnO on natural cotton cellulose fiber by combining electrospinning and the low-temperature hydrothermal growth technique. First, natural cotton cellulose nanofibers were prepared by electrospinning cotton cellulose /LiCl/DMAc solution. The electrospun cotton cellulose nanofibers served as flexible substrate, on which the branched, highly uniform, and dense flower-like ZnO were hydrothermally grown. The as-prepared cotton cellulose/ZnO nanocomposite fibers were characterized by SEM, HRTEM, EDS, TG, and UV-vis spectrophotometry. The modified cotton cellulose nanocomposite fibers were not only exhibiting dispersed uniformly, but also rendered excellent protection against UV radiation because of the incorporation of flower-like ZnO nanostructures. Therefore, the as-prepared nanocomposite fibers demonstrate a significant performance in ultraviolet protection and provide a potential application for ultraviolet detection.     

Process optimization for ethanol production from photoperiod-sensitive sorghum: Focus on cellulose conversion

Photoperiod-sensitive sorghum, as a competitive biomass for ethanol production, was investigated to develop an integrated process for improving ethanol yield. Response surface methodology was employed to study the relationship between pretreatment variables (including temperature, sulfuric acid concentration, and reaction time) and cellulose recovery, as well as efficiency of enzymatic hydrolysis (EEH) in the solid part. Recovery yield decreased and EEH increased as the pretreatment temperature, acidic concentration, and reaction time increased. A model was successfully developed to predict total glucose yield with a maximum value of 82.2%. Conditions of co-fermentation were also optimized, and the optimal ethanol yield was obtained with constant-temperature simultaneous saccharification and fermentation at 38 °C. Acetate buffer at a concentration of 50 mM was found helpful for increasing efficiency of enzymatic hydrolysis, as well as ethanol yield. The maximum ethanol yield was 0.21 g ethanol per dry mass at the conditions of 38 °C, 0.05 g yeast/L, and 50 mM acetate buffer. A complete cellulose balance was provided for the whole process.     

Study of nano-fiber cellulose production by Glucanacetobacter xylinum ATCC 10245

Bacterial Celluloses (BC) are gaining importance in research and commerce due to numerous factors affecting the bacterial cellulose characteristics and application in different industries. The aim of the present study was to produce bacterial cellulose in different media using different cultivation vessels. Bacterial cellulose was produced by static cultivation of Glucanacetobacter xylinum ATCC 10245 in different culture media such as Brain Heart Agar, Luria Bertani Agar /Broth, Brain Heart Infusion, Hestrin-Schramm and medium no. 125. Cultivation of bacterium was conducted in various culture vessels with different surface area. The cellulose membrane was treated and purified with a 0.1 M NaOH solution at 90 degreesC for 30 min and dried by a freeze- drier at -40 degreesC to obtain BC. The prepared bacterial cellulose was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and X-ray diffraction (XRD). The amount of produced BC was related directly to the surface area of culture vessels.     

纤维素酶在速溶茶中的应用研究

通过对纤维素酶的应用研究，探讨出在速溶茶加工过程中，纤维素酶应用较合适的温度、时间及浓度。结果表明浸提温度为45℃、浸提时间为60min、添加量为0.15u/ml是本实验中纤维素酶发挥作用的较佳条件。     

Enhancement of thermal and physical properties of epoxy composite reinforced with basalt fiber

The basalt chopped fiber reinforced epoxy composites using different curing systems were prepared in order to investigate the thermal characteristics of the composites. 2 different curing systems for bisphenol F type epoxy resin — an epoxy-amine curing system and an epoxy-anhydride curing system — were selected and used to investigate the interaction between matrix resin and basalt fiber in the means of thermal properties and physical properties. Through the evaluation of T _g and thermal degradation behavior of both systems, it was deduced that the type of curing system as well as basalt fiber reinforcement have a great role in determining thermal properties of the composites. Also, the tensile and flexural properties of the composites were systematically evaluated in order to further understand the effect of curing agents on the interaction with basalt fiber.     

Scaling up the production rate of nanofibers by needleless electrospinning from multiple ring

Mass production of nanofibers is crucial in both laboratory research and industry application of nanofibers. In this study, multiple ring spinnerets have been used to generate needleless electrospinning. Multiple polymer jets were produced from the top of each ring in the spinning process, resulting in thin and uniform nanofibers. Production rate of nanofibers increased gradually with the increase of the number of rings in the spinneret. Spinning performance of multiple ring electrospinning, namely the quality and production rate of the as-spun nanofibers, was dependent on experimental parameters like applied voltage and polymer concentration. Electric field analysis of multiple ring showed that high concentrated electric field was formed on the surface of each ring. Fiber diameter together with production rate of needleless electrospinning was dependent on the strength and distribution of the electric field of the spinneret. Needleless electrospinning from multiple ring can be further applied in both laboratory research and industry where large amount of nanofibers must be employed simultaneously.     

Antimicrobial and cellular activity of poly(L-lactide)/chitosan/Imipenem antibiotic composite nanofibers

Synthesis of biocompatible polymer nanofibers is valuable, due to their use as a cover for burns and as a replacement for bandage because of their antimicrobial properties. In this study, electrospinning of chitosan(Ch) and nanofibers synthesis with antibacterial properties was investigated. Nanofibers with antibacterial properties were synthesized by electrospun of Ch/poly(L-lactide)(PLA)/Imipenem(Imi) polymer solution. The results showed that the optimized ratio of Ch/PLA polymer solution was ratio of 50:50 and Ch 2 wt% and PLA 10 wt% polymer solution was the best weight percentage for nanofiber preparation. Also, the average diameter of Ch/PLA/Imi nanofibers was 143 nm and measured with ImageJ software. Afterwards, the antibacterial properties of Imi as additives (with different percentages) was studied in the polymer solution. The scanning electron microscopy (SEM) images and antibacterial tests were showed that the electrospun of Ch/PLA/Imi polymeric nanofibers were effective against Gram negative bacteria Escherichia coli (E. coli) and inhibited growth of E. coli. The growth and viability percentage of fibroblast cells with nanofibers in αMEM culture are at desirable levels after 6 days.     

The removal of heavy metals in aqueous solution by hydroxyapatite/cellulose composite

Hydroxyapatite has an excellent ion-exchangeability and is expected to be used as an agent for the removal of heavy metal ions in wastewater. However, the pure hydroxyapatite is very difficult to use because it exists in the form of white powder. Thus, the pure hydroxyapatite was mixed with cellulose to utilize its ion-exchangeability. In this research, a method for dispersion of hydroxyapatite in cellulose matrix is described and its dispersion is observed with scanning electron microscopy. The removal ratios of some heavy metal ions with hydroxyapatite composite are examined with regard to reaction time and amount of hydroxyapatite composite. The ion-exchangeability of hydroxyapatite composite did not seem to be interfered by cellulose matrix during removing heavy metal ions.     

Fabrication of nanofibers with ultrahigh production by a facile high pressure air-jet atomized electrospinning

A novel method named as high pressure air-jet atomized electrospinning was proposed to prepare nanofibers with ultrahigh production. The spinning solution with lower concentration and viscosity was cutted into micron-sized droplets by a 700 mesh filter in the front of nozzle and then was crushed and atomized into massive smaller droplets, which were drawn into nanofibers directly under the electric force and airflow force. Flow field under different air pressure was simulated to study its effect on the formation of nanofibers. The airflow showed the minimum pressure and maximum velocity at a location 2 cm away from the spray nozzle, where small droplets cutted were crushed and atomized into massive smaller droplets by the converging airflow. The velocity and distribution region of the airflow increased with increasing air pressure. It showed a smaller diameter of 150 nm and ultrahigh production of 75.6 g/h for nanofibers prepared based on this novel method at the air pressure of 0.8 MPa. The production of nanofibers almost reached thousands of times of that from conventional needle electrospinning.     

Thermal stability and physical properties of epoxy composite reinforced with silane treated basalt fiber

This study evaluates the influence of different silane coupling agents on the thermal and physical properties of epoxy-anhydride composite reinforced with basalt fiber. The silane coupling agents were selected by their functional groups so that they could have different chemical interactions with the epoxy and anhydride curing agents. The thermal and degradation behavior of the composites with different fiber contents were evaluated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Through the evaluation of T _g and thermal degradation behavior of both systems, it was deduced that the silane coupling agents have a great influence on the thermal properties of the composites as well as interfacial improvement. Also, the tensile properties of the composites were systematically evaluated in order to further understand the effect of silane coupling agents on the interaction with basalt fiber and epoxy matrix.