Properties of Rayon Fiber | Physical and Chemical Properties of Viscose Rayon

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Rayon Fiber
Rayon is a manufactured fiber composed of regenerated cellulose, as well as manufactured fibers composed of regenerated cellulose in which substituents have replaced not more than 15% of the hydrogens of the hydroxyl groups. 
 
Rayon fiber
 Physical Properties of Viscose Rayon

Moisture Absorption
It absorbs more moisture than cotton. Moisture Content of Coton is 6% at 70 deg F and 65% RH, and for Viscose Rayon it is 13% under the same conditions.

Tensile Strength
The Tensile Strength of the fibre is less when the fibre is wet than when dry. It is 1.5-2.4 gpd in the dry state and 0.7-1.2 gpd in the wet state. For high tenacity variety the values are 3-4.6 gpd and 1.9 to 3.0 gpd.

Elasticity
The elasticity of Viscose Rayon is less than 2-3%. This is very important in handling viscose yarns during weaving, stentering etc when sudden tensions are applied.

Elongation at Break
Ordinary Viscose rayon has 15-30% elongation at break, whule high tenacity rayon has only 9-17% elongation at break.

Density
The density of Viscose rayon is 1.53 g/cc. Rayon filaments are available in three densities: 1.5, 3.0 and 4.5

Action of Heat and Light
At 300 deg F or more, VR loses its strength and begins to decompose at 350-400 deg F. Prolonged exposure to sunlight also weakens the fibre due to moisture and ultraviolet light of the sunlight.

Chemical Properties of Viscose Rayon
Viscose rayon consists of cellulose of lower DP than cotton cellulose. Also amorphous region of Viscose rayon is present to a greater extent, therefore, Viscose rayon reacts faster than cotton with chemicals. Acids like H2SO4 HCL breaks the cellulose to hydrocellulose. Oxidising agents like Na(OCl)2, Bleaching powder, K2Cr2O7, KMnO4- form oxycellulose. Cold acid solutions for a short time do not attack viscose rayon.

Action of Acids:
The resistance of regenerated cellulose rayon’s to acids is generally less than that of cotton to the same concentrations of the same acids. Therefore , acid treatments must not be too drastic with respect to concentration ,temperature and time .Organic acids can be safely used in 1 to 2 percent concentration without injury to the fiber. Inorganic acids such as hydrochloric & nitric can be used in surprisingly strong concentrations provided the temperatures are not too high and the treatment is brief. Oxalic acid for removal of iron stains is not recommended except at temperatures lower than 150°F.At high temperatures and concentrations all acid will destroy or carbonize regenerated rayon’s. No harmful action will result if applied at .5 to 3 percent solution at room temperature.

Action of Soaps:
Ordinary soaps in usual textile concentration have no direct effect on regenerated cellulose materials. Improper use of soap or use of poorly made soap results in rancidity and odor in rayon fabrics or yarns. When soaps alone is used ,there is a tendency for the ionized fatty acid from the soap to adhere tenaciously to the individual rayon filaments. During the drying filament of such materials and subsequent storage .The free fatty acid radical is very likely to turn rancid & to give the goods & objectionable odor. This phenomenon is specially Prevalent on oil-delustered rayons, because the fatty acid radical of the soap adheres Tenaciously to the minute oil globules in the structure of the yarn.If given time enough the fatty acid radical

Action of Dry Heat:
Most regenerated celluloses, under the influence of heat as well as light ,show rapid loss in strength, this change being accompanied by a increase in copper number and alkali solubility. In a study of effect of drying conditions of textile yearns, Wiegerink in 1940 showed that the quality index of cellulose fibers decreases either as the temperature is increased or as the moisture content of the surrounding atmosphere is increased .Both the breaking strength & fluidity of viscose rayon appear to be functions of the relative humidity to which the samples are exposed. Degradation of cellulose is lower in the absence of oxygen. Continued heating , however , in the absence of oxygen leads to deterioration of the cellulose but little is known about the course of the reactions. Short heating at high temperatures ,such as 140°c is less harmful than long heating at lower temperatures. A decrease of tenacity & eventually a yellow to brown discoloration occurs on aging.

Action of Solvents
Textile solvents can be used on Viscose rayon without any deteriorating effect. Viscose rayon dissolves in cuprammonium hydroxide solution.

Effect of Iron
Contact with iron in the form of ferrous hydroxide weakens viscose rayon yarns. Therefore staining, marking or touching of rayon to iron or iron surface should be avoided.

Action of Microorganisms
Microorganisms ( moulds, mildew, fungus, bacteria) affect the colour, strength, dyeing properties and lustre of rayon. Clean and dry viscose rayon is rarely attacked by moulds and mildew.
 
 

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