A superhydrophilic bilayer structure of a nylon 6 nanofiber/cellulose membrane and its characterization as potential water filtration media.

A bilayer structure of a nylon 6 nanofibrous membrane on a cellulose membrane has been successfully developed for water filter application. The nylon 6 nanofibrous membrane was deposited on the cellulose membrane via the electrospinning technique. The bilayer membrane properties, including mechanical strength, wettability, porosity, and microfiltration performance (flux and rejection), were thoroughly investigated. The membrane properties were studied using nylon 6 nanofibrous membranes having various fiber diameters and membrane thicknesses, which were obtained by adjusting the solution concentration and spinning time. The measurement of solution parameters, i.e., viscosity, conductivity, and surface tension, showed a strong relationship between the solution concentration and these parameters, which later changed the fabricated fiber sizes. The FTIR spectra depicted complete solvent evaporation after the electrospinning process. Smaller nanofiber diameters could improve the mechanical strength of the membranes. The porosity test showed a strong relationship between the nanofiber diameter and the pore size and pore distribution of the membranes. The water contact angle measurement showed the significant influence of the cellulose membrane on increasing the hydrophilicity of the bilayer structure, which then improved the membrane flux. The particle rejection test, using PSL sizes of 308 and 450 nm, showed high rejection (above 98%) for all sample thickness variations. Overall, the bilayer structure of the nylon 6 nanofibers/cellulose membranes showed excellent and promising performance as water filter media.

Electrospun nanofiber from various source of expanded polystyrene (EPS) waste and their characterization as potential air filter media.

This paper reported on the fabrication of nanofibrous membranes from various sources of expanded polystyrene (EPS) waste using electrospinning technique and their application as air filter media. The filter membranes were made from four EPS waste sources, i.e. food packaging, EPS craft, instant noodle cup, and electronic packaging. The properties of the membranes fabricated from those sources were compared to obtain the best EPS waste source for air filter application. To make the precursor solutions, those samples were dissolved in d-limonene:DMF with the concentration of 15, 20, and 25 wt%. The solid EPS density, solution viscosity, and surface tension were measured. The fiber diameter and morphology of nanofibers were characterized by scanning electron microscopy (SEM) for each EPS variation. The fabricated membrane properties (crystallinity, wettability, and mechanical strength) and filtration properties (pressure drop, PM2.5 filtration efficiency, and quality factor) were fully characterized and analyzed. Homogeneous fiber diameter with various morphologies (beaded, wrinkled, and smooth fiber) were obtained from all samples with hydrophobic to super-hydrophobic surface (water contact angle ranging from 106 to 153°). Also, the EPS solid density affected the solution viscosity with the expression of η = 0.132 ρ0.29, which then affected the fabricated membrane packing density, porosity, and mechanical properties. Overall, the experimental results showed that all EPS nanofiber filters had great potential as an air filter media. The EPS filter made from food packaging waste with the solution concentration of 15 wt% exhibited the highest efficiency and quality factor of 99.99% and 0.15 Pa-1, respectively.

Controlled morphology of electrospun nanofibers from waste expanded polystyrene for aerosol filtration.

This paper reports on the recycling of expanded polystyrene (EPS) waste to be repurposed as EPS nanofibrous mats for air filtration applications. The EPS nanofibrous mats were prepared via electrospinning technique. The EPS solutions for producing the mats were made by dissolving the EPS waste in dimethylformamide (DMF) and d-limonene solvents. The mixing ratio of DMF and d-limonene solvents were varied to obtain EPS solutions with different surface tension and viscosity. As a result, different fiber morphology (smooth fiber, wrinkled fiber, and beaded fiber) and diameter ranging from 314 nm to 3506 nm were obtained. The synthesized EPS nanofibrous mats were characterized by scanning electron microscope, Fourier-transform infrared spectroscopy, x-ray diffraction spectroscopy, differential scanning calorimetry, mechanical strength, porosity, and water contact angle measurement apparatus. The mechanical strength measurement exhibited that the beaded fiber had the highest tensile strength and the lowest elasticity compared to wrinkled and smooth fiber. The water contact angle measurement showed that the EPS nanofibrous mats were classified as ultra-hydrophobic, which was a good criterion for air filter media. Some filtration parameters of the EPS nanofibrous mats were measured, including particle collecting efficiency, pressured drop, and quality factor. The particle collecting efficiency of each EPS nanofibrous mats was measured using monodisperse polystyrene latex (PSL) particles and PM2.5 from burning incense as the test particles. The EPS nanofibrous mats had a high collecting efficiency (up to 99.99%) and had a low pressure drop (below 70 Pa) for the face velocity of 5.4 cm s-1. The quality factor of the EPS nanofibrous mats reached 0.10 for PSL filtration and 0.16 for PM2.5 filtration. Overall, the EPS nanofibrous mats with controlled morphology were suitable to be used as air filtration media with high mechanical strength, ultra-hydrophobic surface, and high quality factor.

The synthesis of nanofiber membranes from acrylonitrile butadiene styrene (ABS) waste using electrospinning for use as air filtration media.

Acrylonitrile butadiene styrene (ABS) waste has been successfully recycled into nanofiber membranes by an electrospinning method for air filter applications. The ABS precursor solutions were made by dissolving the ABS waste in three different solvents, DMAc, DMF, and THF, with various concentrations of 10, 20, and 30 wt%. The solvent and solution concentrations affected the fiber properties (size and morphology) and membrane properties (wettability, crystallinity, and mechanical). Accordingly, we tested the fabricated membranes using SEM, FTIR, XRD, water contact angle, and tensile strength test measurements. The SEM images depicted three different morphologies, i.e. beads, beaded fibers, and pure fibers. The FTIR spectra showed that the solvents completely evaporated during the electrospinning process. The water contact angle test exhibited the hydrophobic properties of all the membrane samples. The XRD spectra showed the amorphous structures of all the membranes. The tensile strength test showed that the membranes fabricated using DMF and DMAc solvents had the best mechanical properties. Considering the fiber size, wettability, and mechanical properties, the membranes fabricated using DMAc and DMF solvents had the best criteria as air filter media. Filtration tests on the membranes fabricated using DMAc and DMF solvents with various solution concentrations depicted that the beads affected the membrane pressure drop and efficiency. The beads gave more space among the fibers, which facilitated the air flow through the membrane. The beads greatly reduced the pressure drop without an overly reduced membrane filtration efficiency. This led to a high-quality factor of the membranes that demonstrated their applicability as potential air filter media.

Polyvinylpyrrolidone/cellulose acetate electrospun composite nanofibres loaded by glycerine and garlic extract with in vitro antibacterial activity and release behaviour test.

The antibacterial activity of garlic (Allium sativum) is believed to be due to its organosulfur compounds, which can supposedly be used further in biomedical applications. This paper reported the use of electrospinning to encapsulate a garlic extract and glycerine in nanofibrous mats. Polyvinylpyrrolidone (PVP) and cellulose acetate (CA) were the building blocks of the composite fibres that served as the hydrophilic matrix to encapsulate the garlic extract with glycerine added mainly to improve the mechanical characteristics of the composite fibres. The combinations of the fibres were PVP/CA, PVP/CA/garlic, PVP/CA/glycerine, and PVP/CA/glycerine/garlic. The characterizations included the morphology, chemical interaction, swelling degree, weight loss, acidity level, wettability, in vitro antibacterial test, and release behaviour test. The composite nanofibrous mats were uniform, bead-free with a size ranging from 350 nm to 900 nm. The Fourier-transform infrared spectra proved the presence of the garlic extract and glycerine in the fibres. The swelling degree test showed that the fibrous mats generally did have maximum swelling degrees above 100% except for the PVP/CA fibrous mat, whose maximum value was not achieved within 48 hours. The fibrous mat with glycerine showed generally larger weight loss compared to the fibrous mats without glycerine. The result of the contact angle measurement proved that the composite fibres are all hydrophilic with the PVP/CA/glycerine/garlic fibres being the least hydrophilic. The pH level of the fibre mats was from 3.7 to 4.0 due to the use of acetic acid. The Young's modulus and ultimate tensile strength of the mats were significantly reduced due to the presence of glycerine. The encapsulation of the garlic extract in the fibres did not eliminate the antibacterial activity of the garlic extract, as proven in the in vitro antibacterial test. The release of the garlic extract from the composite PVP/CA/glycerine/garlic fibres was found to be the largest due to the large diameter of the fibres, while the blend of PVP with CA successfully reduced the rate of release due to the insolubility of CA. We successfully encapsulated the garlic extract and glycerine in the PVP/CA nanofibrous mats with antibacterial activity.

Mangosteen pericarp extract embedded in electrospun PVP nanofiber mats: physicochemical properties and release mechanism of α-mangostin.

BACKGROUND: α-Mangostin is a major active compound of mangosteen (Garcinia mangostana L.) pericarp extract (MPE) that has potent antioxidant activity. Unfortunately, its poor aqueous solubility limits its therapeutic application. Purpose: This paper reports a promising approach to improve the clinical use of this substance through electrospinning technique. METHODS: Polyvinylpyrrolidone (PVP) was explored as a hydrophilic matrix to carry α-mangostin in MPE. Physicochemical properties of MPE:PVP nanofibers with various extract-to-polymer ratios were studied, including morphology, size, crystallinity, chemical interaction, and thermal behavior. Antioxidant activity and the release of α-mangostin, as the chemical marker of MPE, from the resulting fibers were investigated. RESULTS: It was obtained that the MPE:PVP nanofiber mats were flat, bead-free, and in a size range of 387-586 nm. Peak shifts in Fourier-transform infrared spectra of PVP in the presence of MPE suggested hydrogen bond formation between MPE and PVP. The differential scanning calorimetric study revealed a noticeable endothermic event at 119°C in MPE:PVP nanofibers, indicating vaporization of moisture residue. This confirmed hygroscopic property of PVP. The absence of crystalline peaks of MPE at 2θ of 5.99°, 11.62°, and 13.01° in the X-ray diffraction patterns of electrospun MPE:PVP nanofibers showed amorphization of MPE by PVP after being electrospun. The radical scavenging activity of MPE:PVP nanofibers exhibited lower IC50 value (55-67 µg/mL) in comparison with pure MPE (69 µg/mL). The PVP:MPE nanofibers tremendously increased the antioxidant activity of α-mangostin as well as its release rate. Applying high voltage in electrospinning process did not destroy the chemical structure of α-mangostin as indicated by retained in vitro antioxidant activity. The release rate of α-mangostin significantly increased from 35% to over 90% in 60 minutes. The release of α-mangostin from MPE:PVP nanofibers was dependent on α-mangostin concentration and particle size, as confirmed by the first-order kinetic model as well as the Hixson-Crowell kinetic model. CONCLUSION: We successfully synthesized MPE:PVP nanofiber mats with enhanced antioxidant activity and release rate, which can potentially improve the therapeutic effects offered by MPE.

Intermolecular Interactions and the Release Pattern of Electrospun Curcumin-Polyvinyl(pyrrolidone) Fiber.

An electrospun fiber of polyvinyl(pyrrolidone) (PVP)-Tween 20 (T20) with curcumin as the encapsulated drug has been developed. A study of intermolecular interactions was performed using Raman spectroscopy, Fourier transform infrared (FT-IR), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). The Raman and FT-IR studies showed that curcumin preferrably interacted with T20 and altered PVP chain packing, as supported by XRD and physical stability data. The hydroxyl stretching band in PVP shifted to a lower wavenumber with higher intenstity in the presence of curcumin and PVP, indicating that hydrogen bond formation is more intense in a curcumin or curcumin-T20 containing fiber. The thermal pattern of the fiber did not indicate phase separation. The conversion of curcumin into an amorphous state was confirmed by XRD analysis. An in vitro release study in phosphate buffer pH 6.8 showed that intermolecular interactions between each material influenced the drug release rate. However, low porosity was found to limit the hydrogen bond-mediated release.

Self-assembly of colloidal nanoparticles inside charged droplets during spray-drying in the fabrication of nanostructured particles.

Studies on self-assembly of colloidal nanoparticles during formation of nanostructured particles by spray-drying methods have attracted a large amount of attention. Understanding the self-assembly phenomenon allows the creation of creative materials with unique structures that may offer performance improvements in a variety of applications. However, current research on the self-assembly of colloidal nanoparticles have been conducted only on uncharged droplet systems. In this report, we first investigated the self-assembly processes of charged colloidal nanoparticles in charged droplets during spray-drying. Silica nanoparticles and polystyrene spheres are used as a model system. To induce a positive or a negative charge on the droplets, we used an electrospray method. Repulsive and attractive interactions between charged colloidal nanoparticles and droplet surface are found to control the self-assembly of colloidal nanoparticles inside the charged droplet. Interestingly, self-assembly of colloidal nanoparticles inside charged droplets under various processing parameters (i.e., droplet charge, droplet diameter, and surface charge, size, and composition of colloidal nanoparticles) allows the formation of unique nanostructured particles, including porous and hollow particles with control over the internal structure, external shape, number of hollow cavities, and shell thickness, in which this level of control cannot be achieved using conventional spray-drying method.

Experimental evaluation of the pressure and temperature dependence of ion-induced nucleation.

An experimental system for the study of ion-induced nucleation in a SO(2)/H(2)O/N(2) gas mixture was developed, employing a soft x-ray at different pressure and temperature levels. The difficulties associated with these experiments included the changes in physical properties of the gas mixture when temperature and pressure were varied. Changes in the relative humidity (RH) as a function of pressure and temperature also had a significant effect on the different behaviors of the mobility distributions of particles. In order to accomplish reliable measurement and minimize uncertainties, an integrated on-line control system was utilized. As the pressure decreased in a range of 500-980 hPa, the peak concentration of both ions and nanometer-sized particles decreased, which suggests that higher pressure tended to enhance the growth of particles nucleated by ion-induced nucleation. Moreover, the modal diameters of the measured particle size distributions showed a systematic shift to larger sizes with increasing pressure. However, in the temperature range of 5-20 °C, temperature increases had no significant effects on the mobility distribution of particles. The effects of residence time, RH (7%-70%), and SO(2) concentration (0.08-6.7 ppm) on ion-induced nucleation were also systematically investigated. The results show that the nucleation and growth were significantly dependent on the residence time, RH, and SO(2) concentration, which is in agreement with both a previous model and previous observations. This research will be inevitable for a better understanding of the role of ions in an atmospheric nucleation mechanism.

High performance electrospinning system for fabricating highly uniform polymer nanofibers.

A high performance electrospinning system has been successfully developed for production of highly uniform polymer nanofibers. The electrospinning system employed a proportional integral-derivative control action to maintain a constant current during the production of polyvinyl acetate (PVAc) nanofibers from a precursor solution prepared by dissolution of the PVAc powder in dimethyl formamide so that high uniformity of the nanofibers was achieved. It was found that the cone jet length observed at the end of the needle during the injection of the precursor solution and the average diameter of the nanofibers decreased with decreasing Q/I, where Q is the flow rate of the precursor solution of the nanofibers and I is the current flowing through the electro spinning system. A power law obtained from the relation between the average diameter and Q/I is in accordance with the theoretical model.

A constant-current electrospinning system for production of high quality nanofibers.

A constant-current electrospinning system has been successfully developed to produce high quality nanofibers. In order to keep at a certain value of the electric current, a proportional integral-derivative (PID) control action was employed, in which the PID parameters were manually tuned. The desired value of electric current was quickly achieved and no overshoot was observed in the system output. The restoration of the electric current due to a disturbance occurred rapidly.Poly(vinyl pyrrolidone) PVP nanofibers have been produced from a precursor solution prepared by dissolution of the PVP powder in a mixture of dimethyl formamide and ethanol using the constant-current electrospinning system. The cone jet shape observed at the end of the needle during the injection of the precursor solution became shorter with increasing electric current. The diameter of the PVP nanofibers was very uniform and reduced with increasing electric current, which is consistent with the model.

Optical and electrical properties of indium tin oxide nanofibers prepared by electrospinning.

Indium tin oxide (ITO) nanofibers were successfully prepared via an electrospinning method, followed by annealing at 400 °C. Mixed solutions of ITO nanoparticle sol and polyethylene oxide (PEO) were used as precursors of the nanofibers. The PEO decomposed during annealing to yield ITO fibers. The fibers were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), thermo-gravimetric/differential thermal analysis (TG/DTA), UV-vis spectrophotometry and four-probe resistivity measurements. The diameter of the prepared fibers was controlled by adjusting the flow rate and the applied electric current. In(2)O(3) crystallized in the ITO nanofibers with a crystallite size of 27 nm. The optical transmittance in the visible region approached 90% in films deposited for 5 min, confirming that the nanofiber film is still transparent in the optical region. The sheet resistance of the nanofiber film was linearly dependent on the inverse of the deposition time and on the PEO/ITO ratio.

Patterned indium tin oxide nanofiber films and their electrical and optical performance.

We report on the preparation and characterization of indium tin oxide (ITO) nanofiber films with a patterned architecture that are transparent and conductive with a uniform fiber size. ITO nanofiber films with a crisscross pattern were prepared by the electrospinning of a precursor solution containing ethanol, dimethyl formamide (DMF), indium chloride tetrahydrate, tin chloride pentahydrate and poly(vinyl pyrrolidone) (PVP K90) onto a metal mesh template, followed by calcinations after transfer to a glass substrate. The resulting ITO nanofibers had diameters of the order of 100 nm and were composed of single-crystalline nanoparticles that were pure in chemical composition. The morphology, crystallinity and performance of the resulting nanofibers could be controlled mainly by calcination. Optical and electrical investigations demonstrated that these nanofiber films are transparent conductors with an optical transmittance as high as 92%. The resulting patterned ITO nanofiber films would be suitable for applications such as solar cells, sensors and electromagnetic field filters.