PROPERTIES OF VISCOSE YARN

PHYSICAL PROPERTIES

X ray pattern is similar to that of Mercerised cotton Cellulose hydrate.

Degree of polymerization of cellulose hydrate in ordinary viscose fiber is 280 320.

Structure of viscose fiber is looser due to the less orderly arrangement of the main chains.

Ordinary viscose fiber has non uniform structure caused by processing conditions.

Hygroscopicity is higher.

Swelling in water is greater.

It has more moisture content. About 13 % at 65 % relative humidity. This is more than that for cotton (6%).

Moisture content increases with relative humidity.

Absorption of water at saturation is 40 %.

In wet condition loses a considerable part of their strength. (50 60%)

Tensile strength is less when fiber is wet than when it is dry (this is inverse for cotton and linen).

Elasticity is less than 2-3 %. after which creep develops and permanent elongation sets in. this should be considered in weaving and stentering.

When sudden tension is applied, it affects luster, appearance, & chemical reactions, resulting in streaky dyeing, streaky printing, shifting of yarn in fabric in final finishing process.

Ordinary viscose has 15 30 % elongation at break. While high tenacity viscose 9-17 % elongation at break.

In wet state viscose is easy to stretch and has higher percentage elongation.

Density of viscose: 1.53 gm /cc

Short exposure to high temperature has less harmful effect than long exposure to relatively lower temperature.

Long exposure to high temperature yellows viscose rayon.

At 150 0C or more viscose looses its strength and begins to decompose at 1800C or higher temperature.

Prolonged exposure to sunlight weakens viscose rayon due to moisture and UV rays.

Combined action of heat and light brings about rapid losses of strength.

Degradation is slower in the absence of oxygen than its presence. But continued exposure to heat in the absence of oxygen leads to degradation of viscose rayon.

Weakening of viscose rayon: Condition % Loss in strength

6 hour UV light 4 % 6 hour daylight 57 %

CHEMICAL PROPERTIES

Viscose has lower degree of polymerization than cotton cellulose. It has more amorphous region than cotton cellulose. Hence it reacts faster than cotton.

Less resistant to the action of acids, much less resistant to alkali.

Caustic alkali solutions cause strong swelling of viscose which can pass in to the solution.

Acids like HCl, H2SO4 break down cellulose macromolecules and produce hydro cellulose.

Oxidizing agents oxidize viscose very faster and oxy cellulose is formed.

Cold acid solution for a short time does not attack viscose.

2 % acetic or formic acid is safe at room temperature.

2 % Oxalic acid can be used up to 60 0C to remove rust stains.

HCl, H2SO4 , HNO3 can be used safely at high concentration for short time at moderate temperature. Acids must be neutralized or washed before drying.

Acids in contact with viscose rayon make it hard and brittle.

Solvents like pine oil, PCE, TCE, benzene, toluene, xylene, gasoline, CCl4

can be used without any deteriorating effect. But highly polar solvents like phenols should be avoided.

Viscose dissolves in cupra ammonium hydroxide solution.

Contact with iron in the form of ferrous hydroxide Fe(OH)2 weakens viscose rayon yarns.

Fe(OH)2 ( O) Fe2(OH ) 3

Viscose ( O) Oxy cellulose Hence staining, marking, touching with iron surfaces should be avoided.

All traces of iron stains should be removed in 5 15 min by using 1 2 % Oxalic acid solution at 60 0C or below.

Micro organisms ( moulds, mildews, fungus, bacteria etc) affect the colour strength, dyeing property and luster of rayon.

Presence of micro organism depends on type of size, temperature and humidity during storage.

It should be treated with anti mildew agents.

Moulds and mildew rarely attack dry and clean viscose rayon.

Micro solubility of fiber in different solvents:

Solvent Micro solubility Cupra ammonium hydroxide Dissolves 80 % Acetone Insoluble Gl. Acetic acid Insoluble Conc. HCl at room temperature Dissolves after 20 30 min Conc. HNO3 at room temperature Insoluble

Resistance of fiber:

Chemical Action Hot dilute strong acid Dissolves Cold conc. Strong acid Dissolves Weak acids Strength deteriorates on prolonged

hot contact. Strong alkali Swells and fiber losses strength Weak alkali No effect in cold. Strength reduces

in hot condition. Organic solvents Resistant Organic highly polar solvents Reduces strength

Polynosic Fiber:

Variety of viscose staple fiber

Propeties close to cotton fabric.

Higher degree of cellulose polymerization (450 500 D.P.)

More orderly structure.

Better uniformity.

Higher strength.

Reduced elongation in the dry state.

Less swelling in water.

Smaller loss of strength in the wet state. (25 35%)

Reduced solubility in alkali.

Cupra ammonium fibers (Bemberg):

Finer

Structure is more uniform. The skin is absent.

Higher strength in the dry state and loss of strength in the wet state is somewhat lower.

(Compiled from various sources by Chirag Panchigar)

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