Effects of poly (vinyl alcohol) (PVA) content on preparation of novel thiol-functionalized mesoporous PVA/SiO2 composite nanofiber membranes and their application for adsorption of heavy metal ions from aqueous solution

Thiol-functionalized mesoporous poly (vinyl alcohol)/SiO₂ composite nanofiber membranes and pure PVA nanofiber membranes were synthesized by electrospinning. The results of Fourier transform infrared (FTIR) indicated that the PVA/SiO₂ composite nanofibers were functionalized by mercapto groups via the hydrolysis polycondensation. The surface areas of the PVA/SiO₂ composite nanofiber membranes were >290 m²/g. The surface areas, pore diameters and pore volumes of PVA/SiO₂ composite nanofibers decreased as the PVA content increased. The adsorption capacities of the thiol-functionalized mesoporous PVA/SiO₂ composite nanofiber membranes were greater than the pure PVA nanofiber membranes. The largest adsorption capacity was 489.12 mg/g at 303 K. The mesoporous PVA/SiO₂ composite nanofiber membranes exhibited higher Cu²⁺ ion adsorption capacity than other reported nanofiber membranes. Furthermore, the adsorption capacity of the PVA/SiO₂ composite nanofiber membranes was maintained through six recycling processes. Consequently, these membranes can be promising materials for removing, and recovering, heavy metal ions in water.     

Electrospun nanofibrous alginate sulfate scaffolds promote mesenchymal stem cells differentiation to chondrocytes

Cartilage tissue engineering is one of the interesting approaches used for repairing cartilage injuries. This study reports the fabrication of polyvinyl alcohol/alginate sulfate (PVA/ALG-S) nanofibrous mats as a functional support for chondrogenic differentiation of human bone marrow mesenchymal stem cells (hBM-MSCs). The PVA/ALG-S nanofibers were obtained through electrospinning of PVA solutions containing 10, 20, and 30 wt% of ALG-S. The appearance of a band at 833 cm⁻¹ assigned to the symmetrical C O S vibration associated to a C O SO₃ group confirmed the presence of ALG-S in nanofibrous mat. The SEM images illustrated the bead-free and smooth morphology of PVA/ALG-S nanofibers with a mean diameter of 185 ± 0.06 nm. The MTT assay of the hBM-MSCs seeded on scaffolds indicated the appropriate cytocompatibility of nanofibrous PVA/ALG-S scaffolds. Furthermore, the appropriate attachment and spreading of the hBM-MSCs based on SEM images, and their differentiation to the chondrocyte-like cells accompanied by a decrease in cell growth on MTT analysis and more color absorption in alician blue staining indicated the effective role of alginate sulfate on cell differentiation. Finally, the expression of Type II collagen by RT-PCR and immunocytochemistry analyses revealed the chondrogenic differentiation of hBM-MSCs on alginate sulfate nanofibers.     

Electrospinning preparation and microstructure characterization of homogeneous diphasic mullite ceramic nanofibers

In this work, diphasic mullite (3Al₂O₃·2SiO₂) nanofibers with good homogeneity were prepared by electrospinning method. Aluminum nitrate (AN) and aluminum isopropoxide (AIP) were used as alumina sources, commercial colloidal silica as silica source, and polyvinyl alcohol (PVA) as polymer additive. Precursor nanofibers with continuous and uniform structures were acquired at mass ratio of PVA to precursor sol from 0.06 to 0.09. γ-Al₂O₃ phase was obtained at 878 ^°C and mullite phase formed at 1322 ^°C upon heating of the precursor under air atmosphere. Calcined samples suggested mullite as dominant phase at 1300 ^°C and amorphous SiO₂ could even exist at 1400 ^°C. As-prepared nanofibers possessed continuous structures with subequal average diameters at 900–1200 °C. However, such morphological characteristics were lost at temperatures above 1300 ^°C due to rapid growth of crystal grains. Al and Si elements were uniformly distributed in fibers and mixed at nanoscale, confirming homogeneity and diphasic features of nanofibers.     

Preparation of atactic poly(vinyl alcohol)/silver composite nanofibers by electrospinning and their characterization

Poly(vinyl alcohol) (PVA)/silver composite nanofibers were successfully prepared by the electrospinning method. Water‐based colloidal silver in a PVA solution was directly mixed without any chemical or structural modifications into PVA polymer fibers to form organic–inorganic composite nanofibers. The ratio of silver colloidal solution to PVA played an important role in the formation of the PVA/silver composite nanofibers. We prepared two different atactic PVA/silver nanocomposites with number‐average degrees of polymerization of 1700 and 4000 through electrospinning with various processing parameters, such as initial polymer concentration, amount of silver colloidal solution, applied voltage, and tip‐to‐collector distance. The PVA/silver composite nanofibers were characterized by field emission scanning electron microscopy and transmission electron microscopy (TEM). TEM images showed that silver nanoparticles with an average diameter of 30–50 nm were obtained and were well distributed in the PVA nanofibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and characterization of poly(vinyl alcohol) nanofiber mats crosslinked with blocked isocyanate prepolymer

Poly(vinyl alcohol) (PVA) nanofibers crosslinked with blocked isocyanate prepolymer (BIP) were successfully prepared using the electrospinning process and subsequent thermal treatment. Fourier transform infrared spectroscopy and solid‐state ¹³C NMR spectroscopy demonstrated that chemical crosslinks between the hydroxyl group of PVA and the isocyanate group of BIP were formed. Thermogravimetric analysis and differential scanning calorimetry results indicated that when the BIP content was increased, the thermal stability of PVA/BIP nanofibers increased, and the crystallinity of PVA decreased. Field emission scanning electron microscopy was used to measure the average diameter (200–300 nm) of the electrospun PVA/BIP nanofibers. The water contact angles were 10.2° and 113° for the pristine PVA nanofibers and PVA nanofibers crosslinked with 8 wt% BIP, respectively. The tensile strength of the crosslinked PVA nanofibers was 53.7 MPa, which was seven times higher than that of pristine PVA. The improved tensile strength and water resistance of the crosslinked PVA/BIP nanofibers were due to a combination of increased crosslinking density and decrease in the number of hydroxyl groups on the surface of the PVA/BIP nanofibers. Copyright © 2010 Society of Chemical Industry     

Antibacterial electrospun chitosan/poly(vinyl alcohol) nanofibers containing silver nitrate and titanium dioxide

Chitosan/poly(vinyl alcohol) (PVA) nanofibers with antibacterial activity were prepared by the electrospinning of a chitosan/PVA solution with a small amount of silver nitrate (AgNO₃) and titanium dioxide (TiO₂). Nanofibers with diameters of 270–360 nm were obtained. The yield of low‐viscosity chitosan (LCS)/PVA nanofibers was higher than that of high‐viscosity chitosan (HCS)/PVA, and the water content of the HCS/PVA nanofibers and the LCS/PVA nanofibers were 430 and 390%, respectively. The nanofibers developed in this study exhibited antibacterial activities of 99 and 98% against Staphylococcus aureus and Escherichia coli, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The optical properties of PVA/TiO2 composite nanofibers

The electrospun nanofibers emerge several advantages because of extremely high specific surface area and small pore size. This work studies the effect of PVA nanofibers diameter and nano‐sized TiO₂ on optical properties as reflectivity of light and color of a nanostructure assembly consisting polyvinyl alcohol and titanium dioxide (PVA/TiO₂) composite nanofibers prepared by electrospinning technique. The PVA/TiO₂ composite spinning solution was prepared through incorporation of TiO₂ nanoparticles as inorganic optical filler in polyvinyl alcohol (PVA) solution as an organic substrate using the ultrasonication method. The morphological and optical properties of collected composites nanofibers were highlighted using scanning electron microscopy (SEM) and reflective spectrophotometer (RS). The reflectance spectra indicated the less reflectance and lightness of composite with higher nanofiber diameter. Also, the reflectance and lightness of nanofibers decreased with increasing nano‐TiO₂ concentration. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Efficient preparation of polymer nanofibers by needle roller electrospinning with low threshold voltage

A novel electrospinning system with needle roller as spinneret for efficient preparation of nanofibers was proposed. The results of finite element simulation indicate that the electric field is more concentrated at the tip of needle piece compared with that for disc and coil spinnerets, which can effectively reduce the threshold voltage of electrospinning. Using polyvinyl alcohol (PVA) as model polymer, the effects of spacing between needle pieces and concentration of spinning solution on fiber diameter and productivity of nanofibers were investigated. The results indicate that the average diameter decreases and the uniformity of diameter increases when increasing the spacing between needle pieces. When the spacing between the needle pieces is 14 mm, the average and standard deviation (SD) of fiber diameter is as small as 190 and 72 nm, respectively. The productivity of nanofibers slightly increases with the concentration of spinning solution, and it is as high as 12.8 g/h when the PVA concentration was 11 wt% for a needle piece spacing of 10 mm, which is much higher than the productivities of reported electrospinning systems. The proposed system has the potential for the preparation of uniform nanofibers with increased throughput and reduced cost. POLYM. ENG. SCI., 59:745–751, 2019. © 2018 Society of Plastics Engineers     

Effects of the tacticities of poly(vinyl alcohol) on the structure and morphology of poly(vinyl alcohol) nanowebs prepared by electrospinning

The effects of tacticities on the characteristics of poly(vinyl alcohol) (PVA) nanowebs prepared by an electrospinning technique were investigated. PVA webs composed of uniform nanofibers with syndiotactic dyad (s‐dyad) contents of 53.5 and 57.3% were successfully obtained with electrospinning. By changing processing parameters such as the initial polymer concentration, applied voltage, and tip‐to‐collector distance, we found suitable conditions for forming PVA webs with uniform nanofibers. PVAs of higher s‐dyad contents were prepared at a lower solution concentration and at a higher applied voltage because of the easy formation of syndiotactic PVA chain entanglements at a very low polymer concentration. The average diameter of the nanofibers in a PVA web with the higher s‐dyad content of 57.3% (ca. 240 nm) was thinner than that of the nanofibers in a PVA web with the lowers‐dyad content of 53.5% (ca. 270 nm). In addition, the crystallinity and thermal stability were greatly increased with an increase in the s‐dyad content. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Splashing needleless electrospinning of nanofibers

This article proposes a new needleless electrospinning apparatus applying the method of splashing polymer solution onto the surface of a metal roller spinneret. When a high voltage is applied, many spinning jets form on the free surface of polymer solutions. Multiple electrified jets undergo strong stretching and bending instability, solvent evaporates, and solidified nanofibers deposit on the collector, as in an ordinary single‐needle electrospinning process. The production of nanofibers is enhanced by 24–45 times comparing with a single‐needle system. And the productivity is easy to scale up. The effects of processing parameters, including solution concentration, applied voltage, distance between spinneret to collector, and rotational speed of the roller spinneret on the morphology of nanofibers are investigated in this article. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

A starch‐based biodegradable film modified by nano silicon dioxide

The purpose of this work was to improve the properties of the starch/poly(vinyl alcohol) (PVA) films with nano silicon dioxide (nano SiO₂). Starch/PVA/nano‐SiO₂ biodegradable blend films were prepared by a solution casting method. The characteristics of the films were assessed by Fourier Transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X‐ray photoelectron spectroscopy (XPS). The results obtained in this study indicated that the nano‐SiO₂ particles were dispersed evenly within the starch/PVA coating and an intermolecular hydrogen bond and a strong chemical bond C? O? Si were formed in the nano‐SiO₂ and starch/PVA. That the blending of starch, PVA and nano‐SiO₂ particles led to uniform starch/PVA/nano‐SiO₂ blend films with better mechanical properties. In addition, the nano‐SiO₂ particles can improve the water resistance and light transmission of the blend films. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Fabrication and characterization of chitosan/poly(vinyl alcohol) electrospun nanofibrous membranes containing silver nanoparticles for antibacterial water filtration

Electrospun nanofibrous membranes (ENMs) were fabricated based on chitosan/poly(vinyl alcohol) (CS/PVA) with a 70/30 mass ratio containing silver nanoparticles (AgNPs) via the electrospinning method. AgNPs were produced on the surface of CS/PVA nanofibers by adding AgNO₃ to a CS/PVA blend solution as a silver rendering component. The presence of AgNPs in the polymer blend solution was detected by UV spectrophotometry. The morphology of nanofibers before and after cross-linking with glutaraldehyde was investigated by the field emission scanning electron microscopy. The formation and size distribution of AgNPs onto the surface of nanofibers were observed by transmission electron microscopy and confirmed by energy dispersing X-ray spectroscopy. As-spun and cross-linked CS/PVA nanofibers revealed a smooth surface with diameters ranging from 58 to 73 nm and 95 to 109 nm, respectively. The effect of AgNP formation on the chemical structure of nanofibers was explored by Fourier transform infrared spectroscopy. Static and dynamic antibacterial filtration efficiencies of CS/PVA ENMs, containing differing amounts of AgNO₃, have been tested against Escherichia coli, a gram negative bacterium. The antibacterial assessment results exhibited a significant increase in both static and dynamic antibacterial filtration efficiencies of the prepared CS/PVA ENMs by addition of AgNO₃ as a bactericidal agent.     

Biocompatibility studies of electrospun nanofibrous membrane of PLLA‐PVA blend

Electrospinning, self‐assembly, and phase separation are some of the techniques available for the synthesis of nanofibers. Of these techniques, electrospinning is a simple and versatile method for generating ultrafine fibers from a wide variety of polymers and polymer blends. Poly L ‐lactide (PLLA) and Poly (vinyl alcohol) (PVA) are biodegradable and biocompatible polymers which are mainly used for biomedical applications. Nanofibrous membranes with 1:9 ratio of PLLA to PVA (8 to 10 wt % and 10 wt %) were fabricated by electrospinning. The percentage porosity and contact angle of PVA in the PLLA‐PVA nanofibrous mat increased from 80 to 83% and from 39 ± 3° to 55 ± 3°, respectively. The water uptake percentage of PVA nanofibers decreased from 190 to 125% on the addition of PLLA to PVA in the PLLA‐PVA nanofibrous mat. The nanofiber morphology, structure and crystallinity were studied by Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT‐IR), and X‐ray diffraction (XRD), respectively. The thermal properties were studied by thermogravimetric analysis (TGA) and differential scanning calorimetery (DSC). The biocompatibility studies of PLLA‐PVA blend were performed using fibroblast cells (NIH 3T3) by MTT assay method. The release of Curcumin (0.5, 1.0, and 1.5 wt %) from PLLA‐PVA blend was found to be ～ 78, 80, and 80%, respectively, in 4 days. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Fabrication and characterization of a novel polypropylene/poly(vinyl alcohol)/aluminum hybrid layered assembly for high‐performance fibrous insulation

A novel hybrid layered assembly based on aluminum‐coated poly(vinyl alcohol) (PVA) nanofibers supported on a polypropylene (PP) web was fabricated via electrospinning and physical vapor deposition. The PVA nanofibers and coated aluminum were characterized by field emission scanning electron microscopy and transmission electron microscopy. The results indicate that PVA nanofibers approximately 430 nm in diameter and an aluminum coating approximately 37 nm in thickness were successfully embedded on the supporting PP web. Fourier transform infrared spectra and the water vapor transmission rate were used to determine the IR spectral transmission and water vapor transmission through the materials with or without the nanofiber or metal coating, respectively. Compared to the uncoated PP web, the novel hybrid layered assembly showed a significant increase in thermal radiation extinction due to both the radiation reflection of the metal coating and the radiation absorption of the nanofibers without noticeable weight gain or water vapor permeable deterioration. This method represents a simple and practical approach for the production of a lightweight hybrid layered assembly that is highly beneficial in the efficient reduction of heat loss in low‐density fibrous insulations without a noticeable deterioration in the water vapor permeability and that could be used for wide applications such as protective clothing, sleeping bags, building construction, and aircraft. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation of poly(vinyl alcohol)/poly(acrylic acid)/TiO2/carbon nanotube composite nanofibers and their photobleaching properties

The composite nanofibers of poly(vinyl alcohol) (PVA)/poly(acrylic acid) (PAAc)/titanium(IV) oxide (TiO₂) were prepared by electrospinning for a novel photocatalytic treatment of waste water. To improve the photoelectronic properties of PVA/PAAc/TiO₂ composite nanofibers, carbon nanotubes (CNTs) were used as an additive. The TiO₂ and CNTs were immobilized in the PVA/PAAc hydrogels as electrospun nanofibers for an easier recovery after the wastewater treatment. The improved efficiency of pollutant dye removal was observed at pH 10 due to the pH-sensitive swelling behavior of the PVA/PAAc/TiO₂/CNTs composite nanofibers. The photocatalytic activity of TiO₂ was improved noticeably by applying electric field to the CNTs-embedded composite nanofibers.     

Gelatin shells strengthen polyvinyl alcohol core–shell nanofibers

In this study, polyvinyl alcohol (PVA) and gelatin are coaxially electrospun into core–shell nanofibers to derive mechanical strength from PVA and bioactivity from gelatin. The core–shell nanofibers with PVA in the core and gelatin in the shell display an increased Young's modulus, improved tensile strength, and reduced plastic deformation than PVA nanofibers. When the order of gelatin and PVA is reversed in the core–shell nanofibers, however, the mechanical strengthening effects disappear. It thus suggests that the bioactive yet mechanically weak gelatin shell improves the molecular alignment of PVA in the core and transforms the weak, plastic PVA into a strong, elastic PVA. The use of a gelatin shell as a biological coating and a protecting barrier to strengthen the core in electrospinning presents a new strategy for fabricating advanced composite nanofibers.     

5-Fluorouracil-loaded poly(vinyl alcohol)/chitosan blend nanofibers: morphology,drug release and cell culture studies

Electrospun polymeric nanofibers as carriers for anticancer drugs have received a great deal of attention to treat tumor cells. This work was aimed to prepare an optimized nanofibrous sample based on poly(vinyl alcohol) (PVA)/chitosan (CS) blend, and then evaluate it containing 5-fluorouracil (5-FU) in terms of morphology, drug release, and cell culture. The electrospinning conditions to produce PVA/CS (50/50) blend nanofibers with an average diameter of approximately 150.8 nm were adjusted as follows: applied voltage 17 kV, needle tip to collector distance 60 cm, and flow rate 0.1 mL/h. The obtained results from Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) showed that there were no chemical interactions between the polymers and drug during the electrospinning process and the uniform morphology without beads. Moreover, to prolong 5-FU release from the blend nanofibers, three layered samples consisting of PVA/CS blend and poly (ε-caprolactone) (PCL) [PVA/CS-PCL 3-layers] were electrospun. On the other hand, by adding PCL in the PVA/CS blend nanofibers, the samples showed more hydrophobic property. Eventually, thiazolyl blue (MTT) assay along with NIH 3T3 cells culture proved that the sample could kill more than 80% of the cells. This formulation could be a promising candidate for cancer therapy potentially.

     

Nanoencapsulation of intercalated montmorillonite‐urea within PVA nanofibers: Hydrogel fertilizer nanocomposite

This study describes the preparation and characterization of nanofibers with poly(vinyl alcohol) (PVA) as the wall matrix to encapsulate montmorillonite (MMT) clay and intercalated MMT‐urea nanocomposite using an electrospinning technique. Nanofibers encapsulated with (1–5%, w/w) MMT clay were successfully produced and characterized in relation to morphological, spectroscopic, structural, surface, and thermal properties. The electrospinning conditions for voltage, flow‐rate, and emitter to collector distance were 20 kV, 0.5, and 0.25 mL/h, and 10 cm, respectively. The surface roughness increased from 43.5 (empty fibers) to 56 nm in the PVA/MMT‐3% and bead‐less nanofibers were formed with the maximum diameter distribution and mean diameter value of 45–80 and 62 nm, respectively. The d‐spacing was increased significantly from 1.004 in MMT to 1.684 nm in MMT‐urea, indicating the intercalation of urea occurred successfully. Furthermore, elemental analysis results showed that the intercalated MMT‐urea contained 30.4% nitrogen. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45957.     

Self‐assembled honeycomb polyurethane nanofibers

Electrospinning uses a high voltage electric field to produce fine fibers. A new phenomenon of self‐assembly in the electrospinning of polyurethane nanofibers is observed. This report is the first known self‐assembling phenomenon in polyurethane electrospun nanofibers. Electrospun polyurethane nanofibers self‐assemble into unique honeycomb patterns on the collector surface. This novel observation opens up new and interesting opportunities for electrospun fibers in the areas of drug delivery devices, protective clothing, filters, and tissue scaffolds. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3121–3124, 2006     

ZrO2 fibers obtained from the halide free synthesis of non-beaded PVA/Zr n-propoxide electrospun fibrous composites

The composite fibers of polyvinyl alcohol (PVA) and zirconium (Zr) n-propoxide were produced by an electrospinning process using the mixed solution of PVA and sol of zirconium n-propoxide. Effects of process parameters, viz. applied voltage, needle to collector distance and flow rate, were studied on the composite fibrous morphology. Bead-free composite fibers, with fiber diameter ranging from 155 nm to 850 nm, were produced with different process parameters. The morphology of the fibers varies significantly with the heat treatment. Heat treatment of the composite fibrous mats results in the removal of PVA, which causes the surface rough while retaining the fibrous morphology. The XRD studies reveal that the structure of PVA free ZrO₂ fibers is tetragonal.