Polyethylene fibers oriented

The higher thermal conductivity of inorganic fillers increases the thermal conductivity of filled polymers. Nevertheless, a sharp decrease in thermal conductivity around the melting temperature of crystalline polymers can still be seen with filled materials. The effect of filler on thermal conductivity for PE-LD is shown in Fig. 2.5 [22], This figure shows the effect of fiber orientation as well as the effect of quartz powder on the thermal conductivity of low density polyethylene. 

Almost all of these examples involve diffusion of a chemical species measuring diffusion rates has long been a specialty of NMR spectroscopy. The studies of KBr and drawn polyethylene produced unique information in the latter case, the known orientation of the deuterium electric field gradient in C-D bonds is used to determine the orientation, with respect to the magnetic field, of a polymer chain of a uniaxially ordered polyethylene fiber. The real time imaging of the polymerization of methyl methacrylate is very interesting and may represent a major direction for NMR imaging applications to polymer science. 

Extended-chain polyethylene fiber became available commercially in 1984 when DSM, a Dutch firm in the Netherlands, introduced Dyneema , and Mitsui Petrochemicals in Japan announced Tekmilon . Allied Signal of the United States entered the field in 1985 when it introduced Spectra fibers. These materials are characterized by very high strength and modulus, which are achieved by the use of ultrahigh molecular weight polyethylene spun by the gel spinning method into fibers having extended-chain structures and near perfect orientation. 

An interesting aspect of the work on UHMW polyethylene was the possibility of studying the anisotropy of the conductivity since aligned samples of stretch-oriented fibers could be produced and the effect of fiber orientation investigated. These experiments showed charge transport to be favored by a factor of approximately 20 along the direction of the oriented fibers compared with perpendicular to the fibers. This represented the first measurement of anisotropic conduction using the PR-TRMC technique. 

High performance polymer fibers (HPPF) have excellent mechanical properties compared to traditional textile fibers such as nylon. The typical HPPFs are aramid and polyethylene fibers (6). Aramid is a generic name for a class of aromatic polyamide fibers, most of which are varieties of poly(p-pheny-lene terephthalamide). Kevlar is the trade name of the varieties of aramid polymers introduced conunercially by Dupont. The molecules in the fibers of these materials are oriented in the axial direction. Poly(p-phenylene terephthalamide) is a rigid molecule with the following structure ... 

Biaxial orientation effects are important in the manufacture of films and sheet. Biaxially stretched polypropylene, poly(ethyleneterephthalate) (e.g., Melinex) and poly(vinylidene chloride) (Saran) produced by flat-film extrusion and tentering are strong films of high clarity. In biaxial orientation, molecules are randomly oriented in two dimensions just as fibers would be in a random mat the orientation-induced crystallization produces structures which do not interfere with the light waves. With polyethylene, biaxial orientation often can be achieved in blown-film extrusion. 

The tensile moduli of unorientated and orientated polyethylene fiber are 1.67-4.18 and 117 GNm , respectively [20]. These values may seem quite high for thermoplastic materials, but the theoretical tensile modulus (334 GNm ) is much higher than these values [20]. The large difference is because the polymer chains are not fully aligned and extended. In contrast, the tensile modulus of aromatic polyester LCP fibers is 125-175 GNm. These values approach the theoretical value 188 GNm [20]. 

W. Chinsirikul, T. C. Hsu, and I. R. Harrison, Liquid crystalline polymer (LCP) reinforced polyethylene blend blown film Effects of counter-rotating die on fiber orientation and film properties, Polym. Engr. and Sci., vol. 36, No. 22, 2708-2717, November (1996). 

The matrices used in sisal fiber-reinforced composites include thermoplastics (polyethylene, polypropylene, polystyrene, PVC, etc.), thermosets (epoxy, polyester, and phenol-formaldehyde resin, etc.), rubber (namral rubber, styrene-buta-diene mbber, etc.) gypsum, and cement. The effects of fiber length, fiber orientation, processing methods, fiber volume fi-action and fiber surface treatment on the mechanical and physical properties of sisal fiber reinforced composites have been smdied. 

Fig. //. Calculated stress-strain curves for perfectly ordered and oriented polyethylene fibers. The curves are for different molecular weights. The testing temperature is set equal to room temperature and the rate of elongation equals 100%/min.

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