Fibers dimensional changes

The CLTE is an important consideration if dissimilar materials like one plastic to another or a plastic to metal and so forth that are to be assembled where material expansion or contraction is restricted. The CLTE is influenced by the type of plastic (liquid crystal, for example) and RP (particularly the glass fiber content and its orientation). It is especially important if the temperature range includes a thermal transition such as Tg. Normally, all this activity with dimensional changes is available from material suppliers. 

Roggli VL, George MH, Brady AR. 1987a. Clearance and dimensional changes of crocidolite asbestos fibers isolated from lungs of rats following short-term exposure. Environ Res 42 94-105. 

Wood is subject to water iafiltration by both Hquid and vapor. As the moisture content iacreases, the wood wiU sweU imtU it reaches its maximum dimension at its fiber-saturation point (about 30% moisture). Variation in the bound water content between zero and 30% wfll aUow the wood to shrink and sweU. Rapid dimensional changes resulting from changes in the level of bound water cause the wood to crack and spHt. These cracks wfll then aUow moisture to absorb easily and quicldy into the wood. At moisture content levels above the fiber-saturation point, moisture wfll be present as free water, which in turn promotes the rate of wood decay. 

This difference is confirmed in the case of water-degraded wood by Rosenqvist (39), who showed that the adsorption-desorption isotherms of oak treated with PEG 400 were less responsive below 60% relative humidity to moisture-affected dimensional change than untreated oak. Her comparative X-ray diffraction analysis, between PEG-treated and untreated wood fiber, seemed to show the growth of more crystallinity with slightly increased intensity and sharpness of the difiraction image in the PEG 400-treated sample. Rosenqvist s results are based on a low concentration of PEG 400 in the wood and are certainly not comparable to the total replacement of water by heavier-molecular-weight PEG 3350. 

Although human hair fibers vary in cross-sectional shape, from nearly circular to elliptical, normalizing most elastic and other properties to fiber thickness can significantly reduce experimental scatter. Thickness is usually characterized as fiber diameter or cross-sectional area. Corrections to diameter for ellipticity are generally not employed. Hair fiber dimensions are also necessary to calculate fundamental elastic properties, and dimensional changes are often employed to follow the course of chemical reactions with hair. 

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