Effect of surface-active agent on morphology and properties of electrospun PVA nanofibres

After the addition of a surface-active agent, sodium dodecyl benzene sulfonate (SDBS), electrospun polyvinyl alcohol (PVA) nanofibres showed a significant enhancement in the mechanical properties, such as improved tensile strength and elongation at break. The improved crystallinity and strong intermolecular hydrogen bonds between the molecules of SDBS and PVA were the two main factors that improved the mechanical properties. In addition, a sharp decrease in surface tension of PVA solution with the addition of SDBS was observed, and the protruding droplet at the tip of needle diminished in the electrospinning process.     

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 PHBV/ZnO membranes: Structure and properties

Polyhydroxy butyrate-co-valerate (PHBV) ?? Zinc oxide (ZnO) nano composite fibers were prepared using electrospinning. The structural and optical properties were studied using Fourier transform infrared spectroscopy (FT-IR), Xray diffraction (XRD) and photoluminescence study (PL). The morphology observed with scanning electron microscope (SEM) revealed no significant changes in the nano composite fibers as compared to bare polymer. The low concentration of ZnO nanoparticles resulted in an increase in overall crystallinity of the polymer matrix which was confirmed from FT-IR and XRD results. The photoluminescence (PL) study indicated the quenching of visible emission in the composite fibers. The ratio of UV to visible emission (I_uv/I_vis) intensity was found to be 12.8 times enhanced in the composite fibers compared to bare ZnO nanoparticles. The nanofibrous mats are self supported and hence offer potential applications in optoelectronic devices and the biomedical imaging.     

Medical Waste Treatment via Waste Electrospinning of PS

Body fluid medical wastes are infectious clinical wastes (blood, saliva, urine) due to their high pathogenic content. Incineration is the most commonly used method in waste management that possess high water content along with molecularly dissolved species such as proteins. The process is costly; so that the removal of solid content dissolved in aqueous part by preliminary filtration can reduce the volume of the waste material. In this study, fibrous mats were prepared by electrospinning of PS wastes from DMF and THF solutions. Then they are employed in the removal of protein-based solid contents of body fluid medical wastes before their disposal. Two sources of PS waste (CD cover and Styrofoam) were employed along with virgin PS for comparison. The adsorption capacity of as-prepared electrospun fibers was examined for three model proteins: Bovine Serum Albumin (BSA), Myoglobin (MYO), and Trypsin (TRY). The fibers obtained from PS CD wastes have remarkably larger protein sorption capacities (particularly BSA) than the fibers obtained from virgin PS. XPS reveals the presence of CaCO₃ domains in CD covers added into PS during their production steps probably to increase mechanical properties. There may be an electrostatic interaction between Ca²⁺ and the negatively charged groups of the protein. In this way, PS wastes could be converted to a beneficial secondary product by electrospinning and also resulting materials promises for the disposal of body fluid medical wastes. This may be one of the frontiers study on the removal of medical wastes by adsorbents produced via electrospinning of waste polymers.     

Fabrication and Characterization of Graphene Enriched Polysulfon Amide Nanocomposites by Electrospinning System

In this paper, we report on the fabrication and characterization of poly(sulfone amide)/graphene (PSA/G) nonwoven based nanocomposite mat assembled via electrospinning technique. Different types of nanocomposite mats were electrospun by varying the weight percentage of graphene in the polymer solution. The surface morphologies, chemical structural, thermal, and electrical properties of the nanocomposites were evaluated systematically. The morphology of the PSA/G nanocomposites exhibited that mesh-like ultrafine nanofibers were densely aligned. Thermal stability and electrical properties of the PSA/G composites could be improved obviously with the addition of graphene. And the thickness uniformity of the nanocomposite mat was improved by using an electrospinning system. Our experimental results suggested that the PSA/G nanocomposites have potential to serve in many different applications, especially in the area of electronic components.     

Electrospinning and mechanical properties of polymeric fibers using a novel gap-spinning collector

Tissue engineering is an interdisciplinary field which combines the basic principles of life sciences and engineering. One promising idea is the combination of scaffolds and living cells in order to produce new functional tissue. The scaffolds play the role of a microenvironment that guides the cells towards tissue formation and regeneration. One of the most frequently used techniques to produce scaffolds is electrospinning. Tissue engineered constructs have to exhibit physiological and mechanical properties comparable to the native tissue they are intended to replace. To create polymeric fibers with controlled orientation, a cylindrical collector that rotates at a certain speed could be used, creating fibers that run longitudinally. The process of gap-spinning enables the production of specifically aligned fibers. Aim of this study was to develop a novel setup capable of producing multilayered structures with controlled fiber angle. The structural, morphological and mechanical characteristics of the fibers were accessed using scanning electron microscopy and uniaxial tensile tests. Longer pre-stretching led to thinner (in the sub-micron scale), more brittle and less elastic fibers. In a nutshell, the results indicated that fiber mats of desired orientation, fiber diameter and mechanical properties could be produced by controlled gap-spinning with a translational collector.     

Encapsulation of Phytoncide in Nanofibers by Emulsion Electrospinning and their Antimicrobial Assessment

Phytoncides are volatile organic compounds released from trees and plants and are well known for their natural antibacterial activity. In this study, emulsion electrospinning was used to encapsulate phytoncide in the core of nanofibers, with the aim of developing environmentally friendly, functional nanofibers with a sustained release of the encapsulated component. Core/sheath structured phytoncide/poly(vinyl alcohol) nanofibers were successfully prepared by emulsion electrospinning using an ordinary single-nozzle electrospinning setup. An oil-in-water emulsion of an aqueous solution of poly(vinyl alcohol) (as the aqueous phase) and phytoncide (as the oil phase) was used to prepare the core/sheath structured nanofibers. Nanocomposite fibers were electrospun under various spinning conditions and emulsion formulations to find the suitable processing conditions for fabricating nanofibers with core/sheath structures. The resulting nanofibers exhibited a well-aligned core/sheath structure with fiber diameters of 250-350 nm. The release profile of phytoncide from the core of nanofibers over a 21 day period showed that phytoncide was released in a sustained manner over 14 days. The core/sheath structured phytoncide/poly(vinyl alcohol) nanofibers exhibited 99.9 % bacterial reduction against both Staphylococcus aureus and Escherichia coli, indicating that the encapsulated phytoncide in the fiber provided strong antimicrobial effects.     

Electrospinning of cellulose nanofibers mat for laminated epoxy composite production

In this study, a new approach consisting of chemical treatment steps followed by electrospinning process was applied to produce cellulose nanofibers from wheat straws. Wheat straws were initially pretreated by NaOH solution to open the complex structure of raw materials and remove non-cellulosic materials. Then, acid and alkali hydrolysis was separately performed to eliminate hemicellulose and soluble lignin. Also, bleaching processes were implemented to remove the insoluble lignin. Cellulose nanofibers were produced by electrospinning of various concentrations of cellulose in different solvents including sodium hydroxide/urea/thiourea, pure trifluoroacetic acid (TFA), and TFA/methylene chloride. Images obtained by Scanning Electron Microscope (SEM) showed long and uniform nanofibers produced from electrospinning of cellulose/TFA/methylene chloride solution. An epoxy based laminated composite was prepared by a lamina of cellulose microfiber and electrospun nanofiber mat using hand lay-up composite manufacturing method. The fracture surface of the epoxy nanocomposite was analyzed by SEM images. In addition, the mechanical properties of laminated epoxy composites were compared with pure epoxy by conducting tensile and impact tests. Tensile test results showed that the ultimate tensile strength, elongation, and modulus of laminated epoxy nanocomposites were significantly increased. Moreover, it was found that by adding a nanofiber lamina in the epoxy composite, the impact resistance was significantly improved as a result of crack growth prevention.     

An Investigation into Scalability Production of Ultra-Fine Nanofiber Using Electrospinning Systems

An integrated experimental and modeling approach was utilized to study scalable production of nanofibers via electrospinning. Two concepts have been investigated to study the fabrication of PAN nanofibers, which are needle-based and orifice-guided electrospinning to utilize the optimum setup. Moreover, it was observed that the natural flow rate of electrospinning does not scale linearly with number of needles (unlike polymer processing methods such as dry spinning), which was explained based on the partial pressure of the solvent vapor, peculiar to multi-needle setup, and the stress relaxation in the solution. In addition, it was demonstrated that the minimum voltage required to continuously electrospun fibers increases as the distance between needles is reduced, which was explained by the shielding effect of neighboring needles and elucidated by the Finite Element Analysis (FEA) models. Nano-fibers with diameters less than 100 nm were produced in this investigation.     

Electrospinning and microwave absorption of polyaniline/polyacrylonitrile/multiwalled carbon nanotubes nanocomposite fibers

Electrical conductive nanocomposite fibers were prepared with polyaniline (PANI), polyacrylonitrile (PAN) and multi-walled carbon nanotubes (MWCNTs) via electrospinning. The morphology and electrical conductivity of the PANI/PAN/MWCNTs nanocomposite fibers were characterized by scanning electron microscope (SEM) and Van De Pauw method. Electrical conductivity of nanocomposite fibers increased from 1.79 S·m^?1 to 7.97 S·m^?1 with increasing the MWCNTs content from 3.0 wt% to 7.0 wt%. Compared with PANI/PAN membranes, the mechanical property of PANI/PAN/MWCNTs nanocomposites fiber membranes decreased. The microwave absorption performance of composite films was analyzed using waveguide tube, which indicated that with the thickness increasing the value of R_L reduced from ?4.6 to ?5.9 dB.     

Preparation of Cu-BTC/PVA Fibers with Antibacterial Applications

In this study, a metal-organic framework (MOF)/polymer electrospun fiber was prepared. The MOF, copper-1,3,5- benzenetricarboxylate (Cu-BTC), was synthesized using a sonochemical method at 25 °C, with a 1:1:1 mixture of dimethylformamide, ethanol, and deionized water as solvent. The sonication time was shown to have a pronounced effect on the morphology and structure of the Cu-BTC. A square pyramid shape with sides of 100 nm was obtained after 2 h of sonication. Extending the sonication time provided a lower amount of unknown phase and produced a uniform Cu-BTC framework. The Cu-BTC-modified PVA fibers were then fabricated by electrospinning. The effect of the Cu-BTC and PVA concentration was investigated at 25 kV, a flow rate of 10 μl/min, and a working distance of 150 mm. FTIR spectra and FESEM images showed good dispersion of the Cu-BTC on the PVA fiber. The as-prepared Cu-BTC-modified PVA fibers exhibited excellent antibacterial effectiveness against S. aureus.     

Investigation of Parameters for Preparing Nanofiber Yarn via a Stepped Airflow-assisted Electrospinning

Electrospinning is a simple and cost-effective method to prepare fiber with nanometer scale. More importantly, 3D flexible nanofiber yarns that fabricated by electrospinning have shown excellent application prospects in smart textiles, wearable sensors, energy storage devices, tissue engineering, and so on. However, current methods for preparing electrospinning nanofiber yarns had some limitations, including low yarn yield and poor yarn structure. In this paper, a stepped airflow-assisted electrospinning method was designed to prepare continuously twisted nanofiber yarn through introducing stepped airflow into traditional electrospinning system. The stepped airflow could not only help to improve nanofiber yield, but also good for controlling the formed nanofibers to be deposited in a small area. In addition, the experimental methods of single factor variables were used to study the effects of stepped airflow pressure, applied voltage, spinning distance, solution flow rate, air pumping volume and friction roller speed on nanofiber yarn yield, nanofiber diameter, yarn twist and mechanical property. The results showed that prepared nanofiber yarns exhibited perfect morphologies and the yield of nanofiber yarn could reach to a maximum of 4.207 g/h. The breaking strength and elongation at break of the prepared yarn could reach to 23.52 MPa and 30.61 %, respectively.     

Nanocellulose reinforced PVA composite films: Effects of acid treatment and filler loading

Nanocellulose was prepared by acid hydrolysis of microcrystalline cellulose (MCC) at different hydrobromic acid (HBr) concentrations. Polyvinyl alcohol (PVA) composite films were prepared by the reinforcement of nanocellulose into a PVA matrix at different filler loading levels and subsequent film casting. Chemical characterization of nanocelluloses was performed for the analysis of crystallinity (X_c), degree of polymerization (DP), and molecular weight (M_w). The mechanical and thermal properties of the nanocellulose reinforced PVA films were also measured for tensile strength and thermogravimetric analysis (TGA). The acid hydrolysis decreased steadily the DP and M_w of MCC. The crystallinity of MCC with 1.5 M and 2.5 M HBr showed a significant increase due to the degradation of amorphous domains in cellulose. Higher crystalline cellulose showed the higher thermal stability than MCC. From X-ray diffraction (XRD) analysis, nanocellulose samples showed the higher peak intensity than MCC cases. Reduction of MCC particle by acid hydrolysis was clearly observed from scanning electron microscope (SEM) images. The tensile and thermal properties of PVA composite films were significantly improved with the increase of the nanocellulose loading.     

Preparation and characterization of PVA/PU blend nanofiber mats by dual-jet electrospinning

A series of blend nanofiber mats comprising poly(vinyl alcohol) (PVA) and polyurethane (PU) were prepared by dual-jet electrospinning in various parameters. Orthogonal experimental design was used to investigate how those parameters affected on fiber diameters and fiber diameter distribution. Altogether three parameters having three levels each were chosen for this study. The chosen parameters were tip-to-collector distance (TCD), voltage and tip-to-tip distance (TTD). Fiber diameters, thermal properties, mechanical properties and hydrophilicity of the blend nanofiber mats were examined by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), tensile test, contact angle and water absorption test, respectively. The results showed that the optimum conditions for PVA/PU blend nanofiber mats fabricated by dual-jet electrospinning were TCD of 20 cm, voltage of 18 kV and TTD of 4 cm. Besides, the thermal stability of PVA/PU blend nanofiber mats had been improved compared with pure nanofibers. Furthermore, the elongation and tensile strength of the blend nanofiber mats were significantly increased compared with pure PVA and pure PU, respectively. And the blend nanofiber mats exhibited well hydrophilicity.     

A Novel Needleless Electrospinning System Using a Moving Conventional Yarn as the Spinneret

A novel electrospinning system for the mass production of nanofibers using a moving conventional yarn as the spinneret was designed. In the process of electrospinning, a large number of jets were ejected from the surface of the polymer liquid carried by the yarn. The effects of conductivity, surface structure and fineness of the yarn on the morphology and productivity of the obtained nanofibers were discussed in the research. Results indicate that the productivity of nanofibers can be increased up to 1.17 g/h with our method, which is a more than fourfold enhancement compared to less than 0.3 g/h with the method of single-needle electrospinning. Both issues of needle clogging in needle electrospinning and intense solvent evaporation due to the open solution surface in most needleless electrospinning techniques can be avoided.     

A Study of Combining Elastin in the Chitosan Electrospinning to Increase the Mechanical Strength and Bioactivity

While electrospun chitosan membranes modified to retain nanofibrous morphology have shown promise for use in guided bone regeneration applications in in vitro and in vivo studies, their mechanical tear strengths are lower than commercial collagen membranes. Elastin, a natural component of the extracellular matrix, is a protein with extensive elastic property. This work examined the incorporation of elastin into electrospun chitosan membranes to improve their mechanical tear strengths and to further mimic the native extracellular composition for guided bone regeneration (GBR) applications. In this work, hydrolyzed elastin (ES12, Elastin Products Company, USA) was added to a chitosan spinning solution from 0 to 4 wt% of chitosan. The chitosan–elastin (CE) membranes were examined for fiber morphology using SEM, hydrophobicity using water contact angle measurements, the mechanical tear strength under simulated surgical tacking, and compositions using Fourier-transform infrared spectroscopy (FTIR) and post-spinning protein extraction. In vitro experiments were conducted to evaluate the degradation in a lysozyme solution based on the mass loss and growth of fibroblastic cells. Chitosan membranes with elastin showed significantly thicker fiber diameters, lower water contact angles, up to 33% faster degradation rates, and up to seven times higher mechanical strengths than the chitosan membrane. The FTIR spectra showed stronger amide peaks at 1535 cm⁻¹ and 1655 cm⁻¹ in membranes with higher concentrated elastin, indicating the incorporation of elastin into electrospun fibers. The bicinchoninic acid (BCA) assay demonstrated an increase in protein concentration in proportion to the amount of elastin added to the CE membranes. In addition, all the CE membranes showed in vitro biocompatibility with the fibroblasts.     

Electrospun Sericin/PVA/Clay nanofibrous mats for antimicrobial air filtration mask

In this study, Sericin/Poly Vinyl Alcohol (PVA)/Clay (Cloisite 30B) nanofibrous mats are prepared by electrospinning technique for antimicrobial air filtration mask. The process parameters of electro-spinning machine such as acceleration voltage, nozzle flow rate and nozzle & collector distance are optimised on the basis of morphology of fibre observed through scanning electron microscopy (SEM). The optimum conditions for producing nanofibrous mat without bead are acceleration voltage 27.5 kV, nozzle collector distance 8 cm and flow rate 0.8 ml/hr using 10 % (w/v) solution of Sericin/PVA (1:1 wt/wt). The process parameters of electro-spinning machine for the processing of Sericin/PVA/Clay nanofibrous mats with varied clay concentrations ranging from 0.1-0.75 % are also optimized. The spun fibre diameter varied from 300-400 nm at different specified conditions. These nanofibrous mats are characterized for its structural, mechanical and antimicrobial properties. Respirable Suspended Particulate Matter (RSPM) test was conducted to check the particulate matter (PM 2.5) absorption capacity of nanofibrous mats. Results shows that sericin/PVA/clay nanofibrous mat would be a promising material for making protecting clothing based air filtration mask.     

Genetic analyses of grain-filling rate and duration in maize

Grain-filling rate and duration influence grain yield in maize (Zea mays L.), but very little information on their inheritance exists. To devise effective breeding strategies, the genetic nature of these traits must be understood. The objectives of this study were to (1) examine general combining ability (GCA) and specific combining ability (SCA) for grain-filling rate, grain-filling duration, and related agronomic traits via North Carolina Design II, (2) determine the inter-relationships among these traits and their influence on yield via correlation and path coefficient analyses, and (3) identify an indirect selection criterion for yield. Design II crosses among four inbred lines used as males and a set of four inbred lines as female parents were grown in 1996. Combining ability analyses indicated that both GCA (V_g) and SCA mean squares (V_s) were significant for grain-filling rate (on a kernel or an ear basis) and effective filling duration. General combining ability was more important than SCA for both kernel-filling rate and effective filling duration, whereas SCA effect was more important for ear-filling rate. The ratio 2V_g/(2V_g + V_s) was 0.85, 0.88, and 0.45 for kernel-filling rate, effective filling duration, and ear-filling rate, respectively. Kernel-filling rate had a positive phenotypic correlation with kernel weight and was negatively correlated with midsilk date and effective filling duration. Kernel number per ear was more important than kernel-filling rate in influencing grain yield. These relationships were confirmed by results from a 1997 experiment using nine commercial hybrids. Chlorophyll readings taken with SPAD chlorophyll meter at a late developmental stage gave a positive genetic correlation with single-plant yield (r = 0.73). A path coefficient analysis revealed that chlorophyll concentration had a small direct effect on grain yield, whereas it had a large indirect effect on grain yield via kernel number per ear and grain-filling duration. Kernel weight and midsilk date could serve as indirect selection criteria for effective grain-filling duration and kernel-filling rate. Chlorophyll concentration at a late developmental stage could also be an indirect selection criterion for final grain yield.     

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.