Fiber humidities

Shukla S.K., Parashar G.K., Mishra A.P., Misra P., Yadav B.C., Shukla R.K., Bali L.M., Dubey G.C., Nano-like magnesium oxide films and its significance in optical fiber humidity sensor, Sens. Actuat B 2004 98 5-11. 

S. Muto, A. Fukasawa, M. Kamimura, F. Shinmura, and H. Ito, Fiber humidity sensor using fluorescent dye-doped plastics, Jpn. J. Appl. Phys. 28, L1065-L1066 (1989). 

Arregui, F.J., et al.. An experimental study about hydrogels for the fabrication of optical fiber humidity sensors. Sensors and Actuators B Chemical, 2003. 96(1-2) p. 165-172. 

Scientists investigated on optical inteferometric stmctures that can be applied in toxic gas sensors. The sensor head consists of PANi and nafion layers deposited on the face of the telecommunication optical fiber. Humidity sensors are useful for the detection of the relative humidity (RH) in various environments. Polymer composites and modified polymers with hydrophilic properties have been used in humidity sensor devices. Researchers prepared nanocomposite pallets of iron oxide and PPy for humidity and gas sensing by a simultaneous gelation and polymerization process. This resulted in the formation of a mixed iron oxide phase for... 

Control of relative humidity is needed to maintain the strength, pHabiUty, and moisture regain of hygroscopic materials such as textiles and paper. Humidity control may also be required in some appHcations to reduce the effect of static electricity. Temperature and/or relative humidity may also have to be controlled in order to regulate the rate of chemical or biochemical reactions, such as the drying of varnishes, the appHcation of sugar coatings, the preparation of synthetic fibers and other chemical compounds, or the fermentation of yeast. 

Improved Hot—Wet Properties. Acryhc fibers tend to lose modulus under hot—wet conditions. Knits and woven fabrics tend to lose their bulk and shape in dyeing and, to a more limited extent, in washing and drying cycles as well as in high humidity weather. Moisture lowers the glass-transition temperature T of acrylonitrile copolymers and, therefore, crimp is lost when the yam is exposed to conditions requited for dyeing and laundering. 

Electrical Behavior. The resistivity of acetate varies significantly with humidity with typical values ranging from 10 ohm-cm at 45% rh to 10 ohm-cm at 95% rh (16). Because of the high resistivity both acetate and triacetate yams readily develop static charges and an antistatic finish is usually apphed to aid in fiber processing. Both yams have also been used for electrical insulation after lubricants and other finishing agents are removed. 

Requirements for space suits are more complex and frequently involve garments that can circulate water and/or air through the fibrous assembly. Laminated and/or coated garments with specific requirements to pressure, radiation, temperature, and humidity are more stmcturaHy complex as a textile product relative to the types of fibers used in this aerospace fabrication. 

Shipping and Storage. MaHc acid is shipped in 50-lb, 100-lb, and 25-kg, multiwall paper bags or 100-lb (45.5 kg) fiber dmms. A technical-grade, 50% solution may be shipped in tank cars or tank tmcks. MaHc acid can be stored in dry form without difficulty, although conditions of high humidity and elevated temperatures should be avoided to prevent caking. 

Because the mechanical properties of hydrophilic fibers are critically dependent on moisture regain, it is vital that such fibers be tested under constant conditions of temperature and humidity. Standard conditions used in the textile industry are 65% relative humidity and 21°C (1,2,21,96). ASTM D1909, D2118, and D2720 Hst accepted commercial moisture regain values used in the buying and selling of fibers. 

L-Ascorbic acid is screened or pulverized into a variety of particle sizes. It is usually packaged in 25-kg and 50-kg quantities in standard, polyethylene-lined containers, eg, fiber dmms, cormgated boxes, etc. The recommended storage conditions are low humidity and temperatures of <23 C. 

At equihbrium with relative humidity below 100%, the moisture ia wood is present primarily ia the cell wads. The moisture content at which the ceU wads would be saturated and the ced cavities empty is caded the fiber saturation poiat. Actuady, such distribution is impossible. Beginning at - 90% relative humidity, some condensation may occur ia smad capidaries. The determination of the fiber saturation poiat is based on the fact that certain properties of wood (eg, strength and volume) change uniformly at first with increasing moisture content and then become iadependent of the moisture content (Fig. 2). The equdibrium moisture content (usuady determined by extrapolation), at which the property becomes constant at 25 to 30% moisture, is represented by the fiber saturation poiat. 

Fig. 4. The stress—strain curves of a wool fiber at different relative humidities.

Static electrification may not be a property of the basic stmcture, but of a new surface formed by a monomolecular layer of water (82). All textile fibers at a relative humidity, at which a continuous monomolecular layer is formed, actually do have the same charge density. This is attributed to the absence of ionic transport which caimot occur in a monomolecular layer. At higher moisture levels than required to form a monomolecular layer, ionic conductivity can occur because of excess water molecules and by hydration of the ions. At very low moisture-regain levels, all materials acquire the same charge (83). 

The high electrical resistivity of asbestos fibers is weU-known, and has been widely exploited in electrical insulation appHcations. In general, the resistivity of chrysotile is lower than that of the amphiboles, particularly in high humidity environments (because of the availabiHty of soluble ions). For example, the electrical resistivity of chrysotile decreases from 1 to 2100 MQ/cm in a dry environment to values of 0.01 to 0.4 MQ/cm at 91% relative humidity. Amphiboles, on the other hand, exhibit resistivity between 8,000 and 900,000 MQ/cm. 

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