Xin Ning

Flexible inorganic membranes used as a high thermal safety separator for the lithium-ion battery

A flexible SiO2 porous fiber membrane (SF) is prepared by electrospinning followed by calcination in this work. Compared with an organic substrate separator, the SF used as a separator will be an absolute guarantee of the battery thermal safety. The porosity of the SF is 88.6%, which is more than twice that of a regular PP separator. Hydrophilic SF shows better electrolyte wetting ability and its high porosity enables the SF to absorb 633% liquid electrolyte on average, while the lithium-ion conductivity reaches 1.53 mS cm−1. The linear sweep voltammogram testing of PP and SF suggested that SF, with great electrochemical stability, can meet the requirements of lithium-ion batteries. The cyclic and rate performances of batteries prepared with SF are improved significantly. Such advantages of the SF, together with its potential in mass production, make the SF a promising membrane for practical applications in secondary lithium-ion batteries.

Recent advances in melt electrospinning

With the emergence of one-dimensional (1D) functional nanomaterials and their promising applications, electrospinning (e-spinning) technology and electrospun (e-spun) ultrathin fibers have been widely explored. Melt e-spinning as an ecofriendly method which produces fibers from polymer melt has drawn much attention in recent years. Meanwhile, melt e-spun fibers without any residual solvent provide opportunities in many areas such as tissue engineering, wound dressings, filtration and textiles. In this review, we introduce the basic principles and recent developments of melt e-spinning, and then summarize various heating methods and various materials used in melt e-spinning, and the influence of several parameters. Particularly, several kinds of new melt e-spinning apparatuses (e.g., portable apparatus and apparatus for mass production), 3D fibrous structures and some applications developed recently are reviewed. Finally, we discuss the future prospects and challenges of melt e-spinning.

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.

Facile Fabrication of Multi-hierarchical Porous Polyaniline Composite as Pressure Sensor and Gas Sensor with Adjustable Sensitivity

A multi-hierarchical porous polyaniline (PANI) composite which could be used in good performance pressure sensor and adjustable sensitivity gas sensor has been fabricated by a facile in situ polymerization. Commercial grade sponge was utilized as a template scaffold to deposit PANI via in situ polymerization. With abundant interconnected pores throughout the whole structure, the sponge provided sufficient surface for the growth of PANI nanobranches. The flexible porous structure helped the composite to show high performance in pressure detection with fast response and favorable recoverability and gas detection with adjustable sensitivity. The sensing mechanism of the PANI/sponge-based flexible sensor has also been discussed. The results indicate that this work provides a feasible approach to fabricate efficient sensors with advantages of low cost, facile preparation, and easy signal collection.

Preparation of Polypropylene Micro and Nanofibers by Electrostatic-Assisted Melt Blown and Their Application

In this paper, a novel electrostatic-assisted melt blown process was reported to produce polypropylene (PP) microfibers with a diameter as fine as 600 nm. The morphology, web structure, pore size distribution, filtration efficiency, and the stress and strain behavior of the PP nonwoven fabric thus prepared were characterized. By introducing an electrostatic field into the conventional melt-blown apparatus, the average diameter of the melt-blown fibers was reduced from 1.69 to 0.96 μm with the experimental setup, and the distribution of fiber diameters was narrower, which resulted in a filter medium with smaller average pore size and improved filtration efficiency. The polymer microfibers prepared by this electrostatic-assisted melt blown method may be adapted in a continuous melt blown process for the production of filtration media used in air filters, dust masks, and so on.

Modeling of Braided Structures Based on Secondary Helix

In this paper, the relationship among primary helix, secondary helix and braiding curve is discussed and it concludes that the braiding curve is the projection of secondary helix on the braiding surface. Based on this conclusion, the equation of braiding curve is derived using Frenet frame. The geometrical models of braided strands are realized by two methods, one is based on the mathematical models; the braiding curves are obtained by their equations directly. The other is based on the projective relationship using SolidWorks™. A projective surface has been built and employed to realize the projection of secondary helix on the helical surface, the braiding curve is obtained by the intersection of projective surface and the helical surface. For both methods, the strands are built by sweeping the cross section along the braiding curve. The modeling methods introduced are not confined by the braiding angle and cross section of strand and could be used to simulate different braided structures.

Portable melt electrospinning apparatus without an extra electricity supply

Melt electrospinning has attracted a lot of interest due to its advantages such as being solvent-free, low-cost and so on. However, previously reported melt electrospinning devices were usually complicated due to their necessary heating system. Moreover, the electrical heating system may cause electrostatic interference during the melt electrospinning process. For simplification, we designed a portable melt electrospinning setup based on an alcohol lamp (or a candle/lighter) as a heat source, which could make the setup work well without an extra power supply and electrostatic interference. Polymers such as polycaprolactone (PCL), poly(lactic acid) (PLA) and polyurethane (PU) were electrospun successfully into fibers with diameters of 13–60 μm using this apparatus. We also study the influence of various experimental parameters, such as the temperature of the charging barrel (120–255 °C, which can be adjusted by changing the heating distance), electrospinning distance (6–14 cm) and the inner diameter of the spinneret (0.26–1.2 mm), on the PCL fibers. This simple and safe device can be used as a demonstrator for the melt electrospinning process.