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Manufacturing:
A conventional polymer processing technique (melt spinning) is the basis of this technique, with novel modifications. The process flow of manufacturing typical polypropylene auxteic fibre is illustrated below:
Applications:
Auxetic fibres can be used as fibre reinforcements in composite materials e.g. polyolefin auxetic fibres in a polyolefin matrix. The auxetic fibres improve resistance to fibre pull out and fibre fracture toughness, and give enhanced energy absorption properties. Sonic, ultrasonic and impact energy can be absorbed enabling superior composites to be made for sound insulation of walls of buildings, body parts for submarines or other vehicles, etc, bumpers for cars, etc.
Auxetic fibres can be used alone or in combination with other materials for personal protective clothing or equipment as a consequence of the superior energy absorption and impact resistance properties. Crash helmets and body armour (e.g. bullet proof vests) are examples of applications.
It may be desirable to make the protective material in the form of an auxetic macrostructure made from auxetic fibres (i.e. a hierarchical auxetic material). These properties should also lead to enhanced sports protective clothing, e.g. shin pads, knee pads, batting gloves etc. The possibility exists of producing protective clothing made from auxetic fibres which have equivalent protective performance to those made from non-auxetic fibres but which are lighter and/or thinner due to the benefits associated with the auxetic property.
Auxetic materials have pore size/shape and permeability variations leading to superior filtration/separation performance in several ways when compared to non-auxetic materials. Application of an applied tensile load on a non-auxetic porous material causes the pores to elongate in the direction of the applied load, which would tend to increase the filter porosity. Benefits for auxetic filter materials, therefore, include release of entrapped particulates (e.g. drug-release materials) and self-regulating filters to compensate for pressure build-up due to filter fouling.
SPECTRA
Introduction:
In this world very rapid developments are taking place in every field. Then how the field of textiles can remain untouched with it. Recently developed spectra fiber is one of the world’s strongest and lightest fibers. A bright white polyethylene, it is, pound-for-pound, ten times stronger than steel, more durable than polyester and has a specific strength that is 40 percent greater than aramid fiber. Spectra is best known as the super-fiber used in the Small Arms Protective Insert (SAPI) plates protecting American soldiers in Iraq and Afghanistan. Spectra fiber is used in numerous high-performance applications, including police and military ballistic-resistant vests, helmets, armored vehicles, sailcloth, fishing lines, marine cordage, lifting slings, and cut-resistant gloves and apparel..
Production (Spinning Process):
A process for making polymer filaments, which have a high tensile strength and a high modulas by stretching a polymer filamentwhich, contains a substantial amount e.g., at least 25 wt% of polymer solvent, at a temperature between the swelling point and the melting point of polymer. A solution of the polymer may be spun to a filament through a spinning aperture and the spun filament cooled to below the dissolution temperature of the polymer without substantial evaporation of solvent from the filament and then brought to a temperature between the swelling point and the melting point of the polymer and stretched.
Polymer solutions were prepared by dissolving the polymers in paraffin oil, decalin, or dodecane under a nitrogen atmosphere and in the presence of an antioxidant. The solutions were spun using the experimental setup. The extrusion temperature varied from 130 to 1750C for dilute solutions and was fixed at 1200C for concentrated solutions. The spun filaments were then quenched in cold water to form gel fibers and collected on a winder.
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