Hong-Wei He

Solventless electrospinning of ultrathin polycyanoacrylate fibers

Solvent recovery is a big challenge for industrial-level production of ultrathin fibers by solution electrospinning because more than 70 wt% of the precursor solution is volatilizable organic solvent. In this paper, we report an interesting solventless electrospinning technique for the fabrication of poly(ethyl-2-cyanoacrylate)/polymethylmethacrylate (PECA/PMMA) fibers. The spinning solution only contains two components: ethyl-2-cyanoacrylate (ECA) monomer and PMMA, which are nearly all (>90%) electrospun into fibers at room temperature. The fiber solidification mechanism during the electrospinning process could be ascribed to the rapid polymerization of the ECA monomer in the presence of water vapour (specifically hydroxide ions) in the atmosphere, which is quite different from the conventional solvent evaporation in solution electrospinning or the fiber cooling mechanism in melt electrospinning. In addition, the morphology, structure, and influence of temperature and PMMA concentration have also been studied. The results may give some stimulation for developing new ecofriendly electrospinning methods.

Twisted microropes for stretchable devices based on electrospun conducting polymer fibers doped with ionic liquid

We report an effective method to fabricate poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)–polyvinyl pyrrolidone (PEDOT:PSS–PVP) fiber arrays doped with ionic liquid (IL). The twisted microropes were obtained by twisting the electrospun aligned polymer fiber arrays. It was found that the twisted rope exhibited higher electrical conductivity (∼1.8 × 10−4 S cm−1) after IL doping (1.96 wt%) than those without doping (∼0.8 × 10−5 S cm−1), and its conductivity was linearly correlated with strain up to 35% (which is one magnitude larger than previous reports) and showed repeatable cycle loops of tensile-resilience. The extensible rate could reach up to more than 90%, considerably higher than that of ropes without IL doping (∼17%). The results indicate that the twisted PEDOT:PSS–PVP ropes may be used as elastic semiconductors and stretchable sensors.

Solvent-free electrospinning of UV curable polymer microfibers

The conventional solution electrospinning (e-spinning) process is facing the trouble of solvent recovery, especially for the industrial mass production of electrospun (e-spun) ultrathin fibers. This study provides a possible strategy, solvent-free e-spinning to solve this problem. By using a modified homemade e-spinning device and UV curable materials as the precursor liquid, all the spinning solution was successfully e-spun into ultrathin fibers without solvent evaporation (weight loss) in an atmosphere of nitrogen and under UV light radiation. The solidification mechanism of the fibers is ascribed to the quick curing of the acrylate bonds in the spinning stream under UV light radiation and without oxygen inhibition in the atmosphere of nitrogen. Such a break-through leads to fabrication of ultrathin fibers by solvent-free e-spinning without solution loss, and provides an eco-friendly approach to prepare new and functional (composite) ultrathin fibers by using a variety of UV curable materials and functional additions.

Solvent-free electrospinning: opportunities and challenges

Electrospinning (e-spinning) has attracted tremendous attention because this technology provides a simple and versatile method for fabricating ultrafine fibers from a rich variety of materials including polymers, composites, and ceramics. However, an overwhelming majority of publications focus on solution e-spinning that processes polymer solutions into continuous ultrafine fibers with a low precursor utilization (usually less than 20 wt%). Only a few groups have paid attention to solvent-free e-spinning such as melt e-spinning to avoid solvent emission into air and achieve highly efficient utilization of precursors (e.g., more than 90 wt%). More importantly, solvent-free electrospun (e-spun) fibers without any solvent residue provide opportunities in some interesting fields such as tissue engineering and wound dressings. Herein, we aim to highlight recent research studies and future trends of solvent-free e-spinning such as melt e-spinning, supercritical CO2-assisted e-spinning, anion-curing e-spinning, UV-curing e-spinning and thermocuring e-spinning, which may be further developed into efficient, controllable and ecofriendly processes for the generation of ultrafine fibers. Here, solvent-free e-spinning is defined as an e-spinning technique which never uses a conventional solvent, or nearly all of the precursor solution spins into ultrathin fibers so that only a few precursors enter air via evaporation, and the utilization ratio of precursor can reach more than 90%. Compared to solution e-spinning, solvent-free e-spinning may open the door to new horizons in modeling e-spinning without any risk of solvent residue in fibers, solvent evaporation into air and high cost of solvent recycling, and offers potentially broad applications in biomedicine, tissue engineering, textiles, filtration and other fields. Finally, some challenges in solvent-free e-spinning are discussed.

Ecofriendly fabrication of ultrathin colorful fibers via UV-assisted solventless electrospinning

A new technique to fabricate ultrathin colorful fibers has been developed via ultraviolet (UV)-assisted solventless electrospinning. The precursor solution contains UV curable polyurethane acrylate (PUA) and colorful UV gel nail polish, and can be electrospun into ultrathin fibers without solvent evaporation in the atmosphere of nitrogen, owing to rapid curing of the acrylate bonds in the spinning jet under the radiation of UV light. The resulting fibers have good color fastness and high stretchability (more than 140%). In addition, various fiber colors can be conveniently adjusted and obtained through formulating the recipe of the precursor solution. Compared to the traditional dyeing process, this method is ecofriendly and promising to prepare colorful fibers, which may be used in textiles, clothing, and anticorrosive coatings.

Solvent-free two-component electrospinning of ultrafine polymer fibers

Solvent recovery is a big challenge in conventional solution electrospinning for the large-scale production of ultrafine fibers because the precursor utilization ratio is usually less than 20 wt%. In this paper, we report an eco-friendly two-component electrospinning technique for the fabrication of acrylate composite fibers using a homemade device at room temperature. During this electrospinning process, the two-component spinning solutions (component A: t-butyl peroxy-2-ethyl hexanoate (BPOEH), isobornyl methacrylate (IBOMA), nitrile rubber (NBR), methacrylic acid (MAA); component B: N,N-dimethylaniline (DMA), IBOMA, NBR and MAA) are nearly all electrospun into ultrafine fibers, and the utilization ratio of the precursor can reach more than 90 wt%. The fiber solidification mechanism can be ascribed to the rapid polymerization of the IBOMA monomer in the presence of free radicals formed by a redox initiation system (BPOEH + DMA), which is different from the solvent evaporation in solution electrospinning or cooling solidification in melt electrospinning. Such a two-component electrospinning technique may stimulate the development of an eco-friendly approach to fabricate composite and functional ultrafine fibers.

One-Step Synthesis Heterostructured g-C3N4/TiO2 Composite for Rapid Degradation of Pollutants in Utilizing Visible Light

To meet the urgent need of society for advanced photocatalytic materials, novel visible light driven heterostructured composite was constructed based on graphitic carbon nitride (g-C3N4) and fibrous TiO2. The g-C3N4/TiO2 (CNT) composite was prepared through electrospinning technology and followed calcination process. The state of the g-C3N4 and fibrous TiO2 was tightly coupled. The photocatalytic performance was measured by degrading the Rhodamine B. Compared to commercial TiO2 (P25®) and electrospun TiO2 nanofibers, the photocatalytic performance of CNT composite was higher than them. The formation of CNT heterostructures and the enlarged specific surface area enhanced the photocatalytic performance, suppressing the recombination rate of photogenerated carriers while broadening the absorption range of light spectrum. Our studies have demonstrated that heterostructured CNT composite with an appropriate proportion can rational use of visible light and can significantly promote the photogenerated charges transferred at the contact interface between g-C3N4 and TiO2.

Electrospinning of Ultrafine Conducting Polymer Composite Nanofibers with Diameter Less than 70 nm as High Sensitive Gas Sensor

Polyvinyl alcohol/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PVA/PEDOT:PSS) composite ultrafine fibers were successfully fabricated by high pressure airflow assisted electrospinning. The electrical properties of PVA/PEDOT:PSS nanofibers with different diameters were characterized. The average diameter of the nanofibers can be down to 68 nm. Due to its large specific surface area, ammonia sensing of the ultrafine nanofibers is more sensitive than the traditional electrospun fibers (average fiber diameter of 263 nm). The ammonia sensing properties of the samples were tested by impedance analysis. The results show that ultrafine PVA/PEDOT:PSS nanofibers are more suitable for detecting low concentrations of ammonia with higher sensitivity.