MOISTURE REGAIN

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. 

Fig. 7. Moisture regains of cellulose acetate (A) and triacetate (T) fibers. Moisture content on a bone-dry basis, measured at 22°C (—...

Among the bast textile fibers, the density is close to 1.5 g/cm, or that of cellulose itself, and they are denser than polyester, as shown iu Table 5. Moisture regain (absorbency) is highest iu jute at 14%, whereas that of polyester is below 1%. The bast fibers are typically low iu elongation and recovery from stretch. Ramie fiber has a particularly high fiber length/width ratio. 

Fiber type Breaking tenacity, N / tex Elongation, % Specific gravity Moisture regain, % Approximate melt point, °C... 

Fig. 3. Variation of moisture regain with rh at 20°C. Odon is an acryUc fiber Trevira, a polyester.

Polyamide CAS Registry Number Mp, °C T,°C Tenacity, N / tex Moisture regain, %... 

Foi example, nylon pile fabrics, exhibiting higher moisture regain, have different traction characteristics under wet and dry conditions than do polypropylene-based materials. Effects of artificial turf fabric constmction on shoe traction ate given in Table 2. Especially effective in aiding fabric surface uniformity is texturing of the pile ribbon, a process available for the two principal pile materials nylon and polypropylene. 

Comfort has been a merchandising point for cotton and much of cotton s success has stemmed from this property (159—162). This has not, however, prevented cotton interests from trying to modify the moisture regain or content of finished fabrics (163—165). One unique finish imparts... 

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. 

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). 

Moisture regain elongation) 0.4 elongation) 0.4 elongation) 0.4 0.4 elongation) 0.34... 

The moisture-regain of these hydrocelluloses at 70°F. and 65 % relative humidity was determined and is shown in Table VII. It is evident... 

Effect of Hydrolysis on Moisture-Regain (at 70°F., 65% rel. humidity) of Cotton Lintersl>... 

---