Fiber polarity

A clear trend is recognized between fiber polarity and moisture uptake. The amount of polar amide (NH-CO) linkages and hydroxyl (OH) pendant groups into the methylene chain structures of polyamide and poly(vinyl alcohol) fibers, respectively, render them significantly more moisture absorbent (4-5%) than the polyolefins and elastomeric fibers (less than 0.1%). Densely packed polymer networks, as in the cases of polyester, poly(vinyl chloride), and particularly Kevlar fibers, exclude the entry of water molecules, again resulting in low moisture content. 

CDT is perfoimed by the application of a large electrical field to the fibers through a sharp electrode. The polarity of the fibers and the number of OH and COOH groups increase, and consequently, fiber/polar-epoxy resin matrix adhesion improves after applying this treatment to the fibers. CDT can be applied as a continuous process, which is the common practice in textile or paper industry [6], This treatment can also be apphed as a preparation stage for grafting the cellulosic fiber surface to hydro-phobic, nonpolar polymers [9]. 

Unlike the fundamental and all other / = 0 modes, the fields of / 1 modes are not plane polarized. Instead, due to fiber polarization effects, the direction of the field depends on the position in the fiber cross-section, as is clear from... 

The analytes from a liquid or from the headspace above a sample are concentrated on a fused silica fiber coated with a polymer film, causing an equilibrium distribution of the analytes to be established between the stationary phase (the microfiber) and the aqueous or gas phase (the sample). Once equilibrium has been established between sample and fiber, the concentrated compounds are thermally desorbed in the injector of a gas chromatograph and transferred to the capillary column (Eig. 1). The parameters to be optimized here are the nature of the fiber coating (fiber polarity) and fiber film thickness, as well as the concentra-... 

The effect of fiber polarity on small amines was minimal. The polar fibers did not extract more of the polar analytes than the nonpolar analytes. However, the polar fibers exfracfed much less of the nonpolar analytes than the nonpolar fibers. The reduction in fhe extraction on nonpolar analytes by the polar fibers provides some selecfivify for polar analytes. 

Solution Polymerization. Solution polymerization is widely used ia the acryhc fiber iadustry. The reactioa is carried out ia a homogeaeous medium by usiag a solveat for the polymer. Suitable solveats can be highly polar organic compounds or inorganic aqueous salt solutions. 

Microscopy (qv) plays a key role in examining trace evidence owing to the small size of the evidence and a desire to use nondestmctive testing (qv) techniques whenever possible. Polarizing light microscopy (43,44) is a method of choice for crystalline materials. Microscopy and microchemical analysis techniques (45,46) work well on small samples, are relatively nondestmctive, and are fast. Evidence such as sod, minerals, synthetic fibers, explosive debris, foodstuff, cosmetics (qv), and the like, lend themselves to this technique as do comparison microscopy, refractive index, and density comparisons with known specimens. Other microscopic procedures involving infrared, visible, and ultraviolet spectroscopy (qv) also are used to examine many types of trace evidence. 

Ryton fibers are high performance products developed by Phillips Petroleum Co. by reaction of -dichloroben2ene with sodium sulfide in the presence of a polar solvent according to the following ... 

Fig. 23. Two types of hollow-fiber modules used for gas separation, reverse osmosis, and ultrafiltration applications, (a) Shell-side feed modules are generally used for high pressure appHcations up to - 7 MPa (1000 psig). Fouling on the feed side of the membrane can be a problem with this design, and pretreatment of the feed stream to remove particulates is required, (b) Bore-side feed modules are generally used for medium pressure feed streams up to - 1 MPa (150 psig), where good flow control to minimise fouling and concentration polarization on the feed side of the membrane is desired.

Optical properties also provide useful stmcture information about the fiber. The orientation of the molecular chains of a fiber can be estimated from differences in the refractive indexes measured with the optical microscope, using light polarized in the parallel and perpendicular directions relative to the fiber axis (46,47). The difference of the principal refractive indexes is called the birefringence, which is illustrated with typical fiber examples as foUows. Birefringence is used to monitor the orientation of nylon filament in melt spinning (48). 

In addition to the restrictions on their mobiHty caused by steric and polar interactions between chemical groups, the protein molecules in wool fibers are covalentiy cross-linked by disulfide bonds. Permanent setting only occurs if these disulfide bonds are also rearranged to be in equiHbrium with the new shape of the fiber. Disulfide bond rearrangement occurs only at high temperature (>70° C) in wet wool and at even higher temperatures (above 100°C) in... 

Adsorption and Surface Chemical Grafting. As with siHca and many other siHcate minerals, the surface of asbestos fibers exhibit a significant chemical reactivity. In particular, the highly polar surface of chrysotile fibers promotes adsorption (physi- or chemisorption) of various types of organic or inorganic substances (22). Moreover, specific chemical reactions can be performed with the surface functional groups (OH groups from bmcite or exposed siHca). 

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