Polypyrrole-Coated Zein/Epoxy Ultrafine Fiber Mats for Electromagnetic Interference Shielding

To reduce the environmental pollution and meet the needs for wearable electronic devices, new requirements for electromagnetic interference(EMI) shielding materials include flexibility, biodegradability, and biocompatibility. Herein, we reported a polypyrrole-coated zein/epoxy(PPy/ZE) ultrafine fiber mat which was inherently biodegradable and skin-friendly. In addition, it could maintain its ultrafine fibrous structure after coating, which could provide the mat with mechanical compliance, high porosity, and a large specific area for high EMI shielding. With the assistance of the epoxide cross-linking, the breaking stresses of the PPy/ZE fiber mats could achieve 3.3 MPa and 1.4 MPa and the strains were 40.1% and 83.0% in dry and wet states, respectively, which met the needs of various wearable electronic devices. Along with the extension in the PPy treatment duration, more PPy was loaded on the fiber surfaces, which formed more integrated and conductive paths to generate increasing conductivities up to 401.76 S·m^(-1). Moreover, the EMI shielding performance was raised to 26.84 dB. The biobased mats provide a green and efficient choice for EMI shielding materials, which may be a promising strategy to address EMI problems in multiple fields.

Electrospun Food-Grade Ultrafine Fibers from Pectin and Pullulan Blends

Electrospinning was used to produce ultrafine fibers and fibrous mats from aqueous solutions containing two edible polysaccharides: pectin (PEC) and pullulan (PUL). The process excluded the use of a synthetic carrier polymer or non-aqueous solvents thus maintaining the food-grade status of the components. The inclusion of PUL reduced the surface tension and electric conductivity of pectin solution, and promoted molecular entanglement between PEC and PUL as confirmed by rheological analysis. The spinnability of either polysaccharide was promoted by inclusion of the other. Cross-linking PEC networks were obtained by soaking the fibrous mats in successive Ca2+ solution. The fibrous mats can be used to carry bioactive compounds as demonstrated using probiotic bacteria Lactobacillus rhamnosus GG (LGG) as a model bioactive compound. The research is significant for the development of food products with unique textures and functionalities.

Release characteristics of different diameter ultrafine fibers as antibacterial materials

Although the electrospinning technique has been devoted to promoting therapeutic purposes as a drug carrier,however,there are still many fundamental problems in this area.This work focuses on a comparison of various diameter polyethersulfone(PES)electrospun ultrafine fibers as an-timicrobial materials.The fibrous morphology,antimicrobial agent distribution,thermally property,and biocompatibility evaluation of PES-based ultrafine fibers were systematically in-vestigated.The results demonstrated that the PES-based ultrafine fibers were suitable as anti-microbial material.Furthermore,the drug release behavior and mechanism were studied through total immersion.The release mechanism was confirmed to Fickian diffusion.It was revealed that the drug max release amount(71.5%)and release rate(7.71)are the highest for the smallest diameter ultrafine fibers.Meanwhile,the antimicrobial activity of PES ultrafine fibers is also inversely correlated with the diameter of fiber.The electrospun PES fibers would control their release behavior through the diameter and have a potential application in the wound dressings,such as chronic osteomyelitis and exposure injury.

Formation of Ultrafine Apatite Fibers by Sol-gel/Electrospinning

Ultrafine apatite fibers were prepared by electrospinning of sol-gel precursor/poly（ vinyl pyrrolidone） （PVP） solutions followed by subsequent calcination. The as-electrospun and calcinated fibers were observed under a scanning electron microscope and an optical polarizing microscope. Results show that the morphology and the diameter of as-electrospun fibers strongly depend on the viscosity and the surface tension of sol-gel precursor/PVP solutions. After calcination, the smooth as-electrospun fibers shrink and the fiber diameter decreases because of the removal of the polymer. The chemical evolution upon the transformation of the precursor from a gel to the final apatite fibers was investigated by thermogravimetric-differenfial thermal analysis, X-ray diffraction, and Fourier transform infrared spectroscopy. It is thus suggested that the crystalline structure of the calcined fibers is largely influenced by the calcination temperature. After being calcined at 600 ℃, the apatite fibers with a diameter of about 280 nm containing β-tricalcium phosphate were obtained.

A polarization method for quickly distinguishing the morphology of electro-spun ultrafine fibers

In the fields of tissue engineering and controlled drug release, electro-spun fibers are often required to have structural characteristics such as high porosity and large specific surface area. The traditional scanning electron microscope can observe the microscopic appearance of the sample clearly, but it damage to the polymer electro-spun fiber, and the detection takes a long time. In view of this, we have tested a polarization method to quickly distinguish different morphological features of the samples, such as smooth surface, microporous, and beaded microspheres using the depolarization parameter MMDD-△,which is obtained by the Mueller matrix polar decomposition. The preliminary results show that this method is simple, fast, and potentially capable of non-destructive evaluation of the microstructure properties of the object surface.

Experimental investigation on flow modes of electrospinning

Electrospinning experiments are performed by using a set of experimental apparatus, a stroboscopic system is adopted for capturing instantaneous images of the cone- jet configuration. The cone and the jet of aqueous solutions of polyethylene oxide （PEO） are formed from an orifice of a capillary tube under the electric field. The viscoelastic con- stitutive relationship of the PEO solution is measured and discussed. The phenomena owing to the jet instability are described, five flow modes and corresponding structures are obtained with variations of the fluid flow rate Q, the electric potential U and the distance h from the orifice of the cap- illary tube to the collector. The flow modes of the cone-jet configuration involves the steady bending mode, the rotat- ing bending mode, the swinging rotating mode, the blurring bending mode and the branching mode. Regimes in the Q-U plane of the flow modes are also obtained. These results may provide the fundamentals to predict the operating conditions expected in practical applications.

Recent Advances in Ultrafine Fibrous Materials for Effective Warmth Retention

Extremely cold environment has led to a variety of serious public health issues and posed huge burden on the social econ-omy,which is an urgent challenge to the human worldwide.Featured with comfort,convenience,and cost-effectiveness,fibrous materials have been selected as heat insulation materials to protect the human body against the cold for centuries.The advanced ultrafine fibers,with remarkable softness,small average diameter and pore size,and high porosity,have found extensive attention,as promising candidate for application in reducing the heat loss.In this review,the heat transfer mechanisms for single fiber and fiber assembly are provided,and the typical categories of ultrafine fibrous materials for warmth retention,classified as fibrous membrane and fibrous sponge in terms of aggregate structures,are systematically summarized.In particular,this review comprehensively discusses the fabrication strategies,structure characteristics,and significant properties of various ultrafine fibrous materials.Finally,the current challenges and future development prospects of ultrafine fibrous materials for effective warmth retention are highlighted.