Lyndon Arnold

Recent advances in nanofibre fabrication techniques

Over the past decade, there has been a tremendous increase in the demand for polymeric nanofibres which are promising candidates for various applications including tissue engineering, protective clothing, filtration and sensors. To address thisdemand, researchers have turned to the development of various techniques such as electrospinning, meltblowing, bicomponent spinning, forcespinning and flash-spinning for the fabrication of polymeric nanofibres. However, electrospinning is the widely used technique for the fabrication of continuous nanofibres. The ability to fabricate nanofibrous assemblies of various materials (such as polymers, ceramics and metals) with possible control of the fibre fineness, surface morphology, orientation and cross-sectional configuration, gives electrospinning an edge over other processes. Although several researches have been done in electrospinning, understanding some of the other processes is still in infancy. In this perspective article, we summarize the fundamentals of various techniques for the fabrication of nanofibres. This paper also highlights a gamut of recent advances in the techniques for nanofibre fabrication.

Effect of viscosity and electrical conductivity on the morphology and fiber diameter in melt electrospinning of polypropylene

The feasibility of fabricating polypropylene (PP) nanofibers has been explored by using different additives, such as sodium oleate (SO), poly(ethylene glycol) (PEG) and poly(dimethyl siloxane) (PDMS), during melt electrospinning. PP of high melt flow index (1000) was used with PEG and PDMS for the reduction of the melt viscosity; and it was used with SO for improving the electrical conductivity during melt electrospinning. It was observed that all the additives used in this study helped to reduce the fiber diameter. The most promising additive, SO, was effective in reducing the fiber diameter to the nanometer scale due to the increase in the electrical conductivity. The fiber diameter was decreased by the addition of PEG and PDMS due to the decrease in the melt viscosity. The effect of die shape on the fiber cross-sectional shape was analyzed and an interesting finding is that the die shapes did not have an effect on the cross-sectional shape of the fibers. That is, irrespective of the die shapes (i.e. trilobal, tetralobal, multilobal and circular) used in this study, the cross-sectional shapes of melt electrospun fibers were circular. The distribution of the additives in the fiber was analyzed by energy-dispersive X-ray analysis and was found to be uniform. Tensile tests were performed on single nanofibers with limited success, due to the problems in preparing fiber samples and successfully holding them in the jaws of the testing machine without slippage.

Application of Wool in High-velocity Ballistic Protective Fabrics

The protective power of typical aramid-based ballistic fabrics, when assembled into multi-layered panels designed to defeat high-velocity ballistic impacts, can be improved if wool is incorporated into the weave structure. Although the synthetic is still the primary energy-absorbent material, the wool plays a complementary role by increasing resistive interactions between the yarns and filaments. Wool restricts the lateral separation of the synthetic yarns and ensures that more directly impacted yarns are held in place to dissipate the impact energy. Wool increases the energy-absorption mechanism of yarn pull-in by increasing the longitudinal friction along the yarns/filaments, in particular near the free edges of the fabric layers. The wool absorbs water that may otherwise lubricate synthetic filaments and so improves the wet performance. Ballistics tests have shown that synthetic fabrics blended with wool can at least match the dry or wet ballistic performance of an equivalent pure Kevlar fabric when tested under National Institute of Justice (NIJ) Ballistic Standard Level III A. The inclusion of the wool can significantly improve the tear strength of pure synthetic ballistic fabrics.

Thermal comfort properties of Kevlar and Kevlar/wool fabrics

Recent research on ballistic vests has focused on comfort performance by enhancing thermal comfort and moisture management. Kevlar/wool fabric has been developed as a potential material for ballistic vests. This study investigates the thermal comfort properties of woven Kevlar/wool and woven Kevlar ballistic fabrics. In this context, the thermal resistance, water-vapor resistance, moisture management performance, air permeability and optical porosity of 100% Kevlar and Kevlar/wool ballistic fabrics were compared. The effects of fabric physical properties on laboratory-measured thermal comfort were analyzed. This study also presents the fabric bursting strength and tear strength for comparison. Experimental results showed a clear difference in thermal comfort properties of the two fabrics. It was found that Kevlar/wool possesses better moisture management properties and improved mechanical properties than Kevlar fabric.

Fabrication and Characterisation of Nanofibres by Meltblowing and Melt Electrospinning

Fabrication of nanofibres has become a growing area of research because of their unique properties (i.e. smaller fibre diameter and higher surface area) and potential applications in various fields such as filtration, composites and biomedical applications. Although several processes exist for fabrication of nanofibres, electrospinning is considered to be the simplest. Most of the research in electrospinning is based on solution rather than melt. The feasibility of fabricating nanofibres of polypropylene (PP) by meltblowing and melt electrospinning has been investigated in this paper. In meltblowing different fluids such as air and water were fed at different inlets along the extrusion barrel for the fabrication of nanofibres whereas in melt electrospinning it was achieved by using different additives. The results obtained by using water in meltblowing were better with respect to the morphology and fibre uniformity compared to air. In melt electrospinning although all the additives (i.e. sodium oleate (SO), polyethylene glycol (PEG) and polydimethyl siloxane (PDMS)) helped in reducing the fibre diameter, only SO was effective to reduce the diameter down to nanoscale. It was concluded that both the solvent-free processes have the potential to substantially increase the production of nanofibres compared to solution electrospinning.

Structural and mechanical properties of polypropylene nanofibres fabricated by meltblowing

In this paper, a novel technique for the fabrication of nanofibres of polypropylene by meltblowing process with the injection of different fluids (such as nitrogen and water) has been explained. Low molecular weight polypropylene polymers were used in this study. The surface morphology of nanofibres was analysed by scanning electron microscopy. It was observed that the use of water gave better results compared to nitrogen for the fabrication of nanofibres. Nuclear magnetic resonance studies revealed similar chemical shifts for polymers and nanofibres, which indicated no change to the chemical functionality of the nanofibres by the application of fluids and high temperature during meltblowing. The mechanical properties of the nanofibres were investigated by using dumb-bell-shaped specimens in a universal tensile tester. The fibres fabricated with nitrogen were weaker and lower in tensile modulus compared to the fibres fabricated with water. The use of a rotating collector increased the tensile strength compared to a stationary collector due to higher degree of fibre alignment in the rotating drum. The tensile strength and modulus values were increased after annealing due to the increase in the crystallinity. The meltblown nanofibres showed hydrophobic nature as indicated by the high values of water contact angle. The hydrophobicity of the nanofibres fabricated with the injection of fluids did not change noticeably from the as-spun fibres fabricated without the fluids.

Design of knitted three-dimensional seamless female body armour vests

Seams and stitching in a body armour could affect their protective and comfort performance. The seamless technology is a method used to eliminate cutting and sewing processes in making knitted garments. This method is adopted to avoid the traditional cut and sew method used to accommodate the bust contour for female body armour design. The 3D knitting technology Shima Seiki SES-S.WG® and its whole garment WG-SDS-ONE APEX3 program were used to develop a seamless female body armour for fit and comfort. The Kevlar–wool and 100% Kevlar fabrics were produced as weft-knit single jersey using the whole garment knitting machine. The physical properties of the fabrics produced were measured. These properties were used to design two different styles of 3D seamless female body armour vests, the loose-vest and bra-vest. The knitted fabrics and the 3D seamless female body armour vests were engineered to confirm the design.

Comparison and Characterisation of Regenerated Chitosan from 1-Butyl-3-methylimidazolium Chloride and Chitosan from Crab Shells

Chitosan is a biopolymer derived from chitin which is naturally occurring in the exoskeleton of crustaceans. This paper reports dissolution and regeneration of chitosan by directly dissolving in an ionic liquid solvent, 1-butyl-3-methylimidazolium chloride (BMIMCl). This will provide an ideal platform to solubilise these kinds of polymers to achieve the dissolution. The current study dissolved chitosan from crab shell utilising BMIMCl as a solvent and characterised the resultant regenerated polymer. The regenerated chitosan showed increased hydrogen bonding when characterised by Fourier transform infrared (FTIR) spectral analysis. In addition, the study also compared the characteristics of regenerated and generic chitosan. The regenerated chitosan was also evaluated for antimicrobial properties and showed to possess antibacterial features similar to the commercial grade. This method can be utilised in future for blending of polymers with chitosan in a dissolved phase.

Surface Deposition of Chitosan on Wool Substrate by Electrospraying

Electrospraying or electrohydrodynamic spraying is a technique of liquid atomisation by utilising electrical forces. In the electrospraying technique, the liquid at the outlet of a nozzle is subjected to an electrical shear stress by maintaining the nozzle at high electric potential. This produces a fine mist of extremely small and in some cases down to nanometer size droplets. The charge and size of the droplets can be controlled by adjusting the flow rate and voltage applied to the nozzle. Extending the scope of electrospraying, textile substrates can be coated with suitable polymer solution to enhance the surface functionalisation. This paper highlights the deposition of chitosan on wool subtrates using elctrospraying and its potential application in medical textiles.

Mechanism of Nanofibre Fabrication by Meltblowing

Fabrication of nanofibres has become a growing area of research because of their unique properties (i.e. smaller fibre diameter and higher surface area) and potential applications in various fields such as filtration, composites and biomedical applications. The mechanism of nanofibre fabrication by meltblowing process with the injection of different fluids (such as air and water) has been investigated in this paper. In the meltblowing equipment the fluids were injected at a vent port along the extrusion barrel, for the fabrication of nanofibres. The injection of water resulted in better fibre morphology compared to the injection of air. Nanofibres were fabricated by the drafting action of the high-velocity flow of the heated air and the steam in the extruder. The fibres collected were straight prior to the fluid injection and coiled fibres were collected with the injection of fluids. Three types of fibres such as ribbon shaped, fused and branched fibres were obtained in addition to the circular fibres.