Sheath-core spinning

Samuelson, H.V., 1993. Sheath-core spinning of multilobal conductive core filaments. U.S. Patent 5,202,185. 

Abstract Bi-component melt-spinning has been widely applied to produce functional and novel fibres such as hollow fibres, electrically conductive fibres, etc. This chapter details the extrusion of bi-component fibres and discnsses issnes affecting the structure-property of the fibres during the spinning process, interfacial interaction parameters and compatibility of the polymers to be chosen for sheath-core spinning. 

Bicomponent fibres are sjmthetic fibres composed of two firmly but separately combined polymers of different chemical and physical structures. The structure of the bieomponent depends on the shape of the spinnerette orifice (side-by-side, sheath eore, matrix - fibril and multi-fibrillary) and the type of spinning method. Due to the structural differences, the two components shrink differently on heat treatment and form crimp and greater bulk in the fibre. The first fully synthetic bicomponent was an acrylic (Sayelle, Orion 21). The use of sheath-core fibres composed of nylon 6,6 and nylon 6 (Heterofil, ICI) for floor coverings is described. 

There are variations of the spinning process that have not been mentioned here, e.g., bicomponent spinning. Usually, this operation is carried out by employing two extrusion systems that keep the resins separate until just before the streams exit the spinneret. Sheath-core or side-by-side yarns can be spun by this process. Simpler bicomponent yarns are spun with mixed incompatible resins from mixed-pellet blends. 

The results presented indicate that uniform sheath-core fibers of nano dimensions can be produced from two polymers by carefully adjusting the spinning conditions, in particular the applied voltage. As it is generally known, the polymer solution flow rates and concentrations directly controlled the core-sheath fractions and, therefore, the overall fiber size. 

The first study, conducted by Sun et al., demonstrated the feasibility of the approach by producing hbers from a polymer poly(dodecylthiophene) (PDT) and a metal salt [palladium (II) diacetate (Pd(OAc)2)], either of which can form hbers by themselves. A subsequent study, by Yu et al. showed that ultra-hne hbers can be produced using a highly dilute solution of a polymer in the core, which would otherwise produce droplets due to jet break-up when spun alone. This concept was illustrated by the use of dilute solutions of PAN (3 and 5 wt%) in the core wrapped in PAN-co-PS. Removal of the sheath after spinning resulted in very hne PAN hbers (100 nm or less) with narrow and unimodal distribution. More recently, in a study based on silk and PEO (core/sheath) polymers, with water as the solvent for both, it was reported that the crystallized silk hbers (converted from the random coil I conformation to the stable y -sheet silk II structure) could be produced after anneaUng at high humidity (90% RH at 25°C) and subsequent water extraction of the PEO sheath. ... 

H ollow acrylic fibres can be produced by a wet or dry spinning method or as bicomponents having sheath/core structure wherein the core is disposed or dissolved to get the hollow structure in the form of an internal linear continuous channel. Toray Industries has disclosed a process to manufacture hollow acrylic fibres by spinning a liquid containing acrylonitrile-methacrylic acid copolymer as a sheath and polyvinyl alcohol as a core. The resultant hollow acrylic fibre was used to produce hollow carbon fibres for use in composites. 

In sheath-core type bi-component spinning, Okamoto incorporated an improvement in US Pat. No. 3692423 by changing the converging angle of the funnel-shaped space from 6 to 75° (Fig. 6.6). 

Bicomponent technology has been used to introduce functional and novelty effects other than stretch to nylon fibers. For instance, antistatic yams are made by spinning a conductive carbon-black polymer dispersion as a core with a sheath of nylon (188) and as a side-by-side configuration (189). At 0.1—1.0% implants, these conductive filaments give durable static resistance to nylon carpets without interfering with dye coloration. Conductive materials such as carbon black or metals as a sheath around a core of nylon interfere with color, especially light shades. 

Armor-Piercing Discarding Sabot (APDS).. In this type of projectile, a carbide core, either capped or uncapped, is placed inside a steel or light-alloy sheath (fitted with a tracer) to give good exterior ballistic characteristics, and this subcaliber assembly is placed inside a full-caliber carrier. This carrier (sabot) is so designed that it will impart velocity and spin to the subcaliber projectile. 

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