Sheath polymer blends

The polymer industry traces its beginning to the early modifications of shellac, natural rubber (NR — an amorphous c -l,4-polyisoprene), gutta-percha (GP — a semi-crystalline trfl i-l,4-polyisoprene), and cellulose. In 1846, Parkes patented the first polymer blend NR with GP partially co-dissolved in CSj. Blending these two isomers resulted in partially crosslinked (co-vulcanized) materials whose rigidity was controllable by composition. The blends had many apphcations ranging from picture frames, table-ware, ear-trumpets, to sheathing the first submarine cables. 

The references noted well demonstrate the ability to utilize polymer blend technology to achieve the desired balance of mechanical properties and conductivity. The promise of electrical conductive polymers with lower cost, processability, and mechanical durability can thus be envisioned for applications such as electrical dissipative coatings, printable circuits, electromagnetic shielding, resistive heating, conductive sheathing, battery applications, elastomeric conductors, fuses, electronic uses, sensors, specialty electrical devices for corrosive atmospheres, photovoltaic devices, catalysts, optical switches, and semiconductor devices. 

Cheng, K. K. T.C. Hsu, and L.H. Kao, A microscopic view of chemically activated amorphous carbon nanofibers prepared from core/sheath melt-spiiming of phenol formaldehyde-based polymer blends. J. Mater. Sci. 2011,46(11), 3914-3922. 

M. Wei, J. Lee, B. Kang, and J. Mead, Preparation of core-sheath nanofibers from conducting polymer blends, Macromolec. Rapid Commun., 26, 1127-1132 (2005). 

Wei, M., B. W. Kang, C. M. Sung, and J. Mead (2006a). Core-sheath structure in electrospun nanofibers from polymer blends. Macromolecular Materials and Engineering 291(11) 1307-1314. 

Several reinforcement techniques have been introduced for the fabrication of composite fibres, such as (i) the introduction of thermotropic liquid crystalline polymers (TLCP) to produce a matrix-fibril stmcture, (ii) use of multiphase polymer blends and hard/soft segmented thermoplastics, and (iii) bicomponent extrusion, where different polymers are brought in contact as separate streams just before the spinnerette to produce a sheath-core structure (Salem, 2000). However, the inapplicability of these techniques to high-commodity commercial polymers and other serious drawbacks has limited the appeal. For instance, fabrication of TLCP is very expensive and postprocessing may destroy its unique matrix-fibril structure. Incomplete microphase separation in some polymer blends often leads to a less desirable morphology in multiphase fibres and bicomponent spirming is sensitive to differences in viscosity between the polymers. 

If the melt viscosities of polypropylene and poly(ethylene terephthalate) polymers are reasonably matched under extrusion conditions, a finely dispersed blend may be produced in fiber form. Orientation of such fibers yields strong filaments in which microfibrils of the two partially crystallized polymers are intertwined and unable to separate. Similar fibers with a sheath of one polymer surrounding a core of the other have no mechanical integrity [27]. 

Plastics find extensive use in several areas of fiber optic cables. Buffer tubes, usually extruded from high-performance plastics such as fluoropolymers, nylon, acetal resins, or polybutylene terephthalate (PBT) are used for sheathing optical fibers. A blend o PVC and ethylene vinyl acetate (EVA) polymer, such as Pantalast 1162 of Pantasote Incorporated, does not require a plasticizer, which helps the material maintain stability when in contact with water-proofing materials. PVC and elastomer blends, Carloy 6190 and 6178, of Cary Chemicals are also used for fiber optic applications (Stiffening rods for fiber optics are either pultruded epoxy and glass or steel. Around these is the outer jacketing, which is similar to conventional cable.)... 

The core-sheath (c-s) configuration is adaptable because many different polymers may be applied as a sheath over a solid polyester core, thus giving a variety of modified surface properties while maintaining all the major fiber and textile properties of PET. An early patent by Shima and coworkers uses an eccentric core-sheath configuration to achieve spiral crimp in a yarn [67]. A recent patent by Chang and coworkers discloses the use of side-side or eccentric c-s bicomponent fibers to achieve a self-crimping yarn made from polytrimethylene terephthalate, where one component is a melt-blend of PTT with a small amount of polystyrene [68]. 

Being able to produce sheath-core bicomponent nanoliber structures using two different polymers can provide unique properties not achievable from a single material. The approach can be broadly viewed as a blending of materials, except that the two maintain their separate identities, v dth the core of one completely surrounded by the sheath of the other. Core-sheath liber formation can also be viewed as a one-step process for obtaining a surface-modified product. 

In extrusion of PP/PET blends, although PET had lower t than the blends, the blends extruded at higher volumetric rates, indicating that the output was controlled either by melting or the interlayer slip. It was shown that even if the sheath-and-core monofilaments of PP/PET blends could not be oriented (because of poor adhesion between the two polymers), melt blending still produced useful oriented product. The maximum draw ratio for PET was 7, whereas for PP/PET blends it was 11. The dynamic mechanical testing of blend monofilaments, containing le(PET) = 50 and 70 wt.%, indicated that Tg(PET) remained constant and the dynamic moduli were approximately additive. 

We have for a number of years developed polymer-based piezoelectric textile filaments and yarns [44]. Filaments are melt spun and bicomponents core-and-sheath type based on a blend of a normal bulk polymer like high-density polyethylene and the piezoelectric material (PVDF), surrounding a core of a conductive polyethylene-carbon black mixture (see Fig. 28.25). The core is electrically conductive and will act like an electrode. 

A. K. Sen, B. Mukherjee, A. S. Bhattacharya, L. K. Sanghi, P. P. De, and A. K. Bhowmick, Preparation and characterization of low-halogen and non-halogen fire-resistant low-smoke (FRLS) cable sheathing compound from blends of functionalized polyolefins and PVC. Journal of Applied Polymer Science, 43 (1991), 1673-84. 

Multi-component PCM fibers can be prepared using a PCM as the core and other polymer materials as the sheath. The PCMs are often micro-encapsulated and blended with other fiber-forming polymers prior to spirming, using the melt spinning or wet spirming process. 

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