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The rayon fibre is made with pure cellulose. Cellulose is the substance which is obtained from the cell walls of the woody part of trees and cotton plant. Cellulose is commonly used for making products such as paper. The rayon fibre that has been formed with regenerated or re-formed cellulose substance is called as regener-ated cellulose fibres.
Rayon is the first man -made fibre and its production has been prophesied as long ago as 1664 by Robert Hooke, an English naturalist. He believed that it is possible to make an “artificial glutinous” composition which can resemble the silk-worm fibre. Man-made textile fibres were officially recognized in 1925 when the Federal Trade Commission (FTC) per-mitted the use of the name “rayon” from yarns obtained from cellulose or its deriv-atives. With the increase in production of man -made fibres, FTC ruled again in 1937 that any fibre or yarn produced chemi-cally from cellulose must be designated as rayon.
Based on the method of manufacture, at present there are two principal types of rayon.
1. Rayon or Viscose
2. High Wet Modulus Rayon (regener-ated rayon)
In High Wet Modulus Rayon (HWM), the original material (cellulose) is changed chemically into another form, which is then changed or regenerated into cellulose again. These changes produce the final product that is purified cellulose in the fibre form.
For making viscose rayon, wood chips or cotton linters are treated with chemicals to produce sheets of purified cellulose that resembles white blotters. This purified cellulose is soaked in caustic soda which produces sheets of alkali cellulose. These sheets are then broken up into fluffy white flakes or grains called cellulose crumbs. The crumbs are aged for 2-3 days under controlled temperature and humidity.
Liquid carbon disulphide is then added to these cellulose crumbs which turn it into a light orange substance called cellulose xanthate. The cellulose xanthate crumbs are then dissolved in a weak solution of caustic soda, which turns it to a thick vis-cous solution resembling honey in colour and consistency. This thick solution is called viscose. The viscose is aged, fil-tered and vacuum treated to remove the air bubbles present, as they may cause the filament to break. This treated viscose solution is then forced through the holes of a spinneret into sulphuric acid which coagulates the cellulose of the cellulose xanthate to form pure regenerated cellu-lose filaments (Figure 3.1).
A wide variety of fabrics can be produced by viscose rayon. Spun rayon fabrics can be used for making fabrics that resem-ble cotton, linen or wool. Rayon filament yarns can be used for making fabric that resemble silk. Various finishes can be applied to these rayon fabrics to improve their serviceability and to enhance their appearance. The most common finishes given to rayon fabrics are as follows :
Shape : Thin long filament
Size : Diameter varies from 12 to 40 microns (controlled by manufacturer)
Luster : Varies from brightness to dullness
Strength : 2.4 – 3.0 Pa m3/kg
Elongation : 19 – 24%
Elasticity : 82%
Density : 1.5 g/cm3 for all rayon types
Moisture : Upto 10.7%
Dimensional stability : Poor
Resistance to acids : Not good, but can be improved in special conditions
Resistance to alkalies : Not good, but can be improved in special conditions
Sunlight : Can withstand sunlight to an extent
Insects : Silver fish damages all type of cellulose fibres
Reaction to heat : Can withstand heat, but longer exposure will eventually degrade the fibre
· The uses of Rayon are:
· The rayon is used to create clothing such as blouse, jackets, sportswear and dresses.
· It is used in textile industry for mak-ing textile belts.
· Rayon is used for making tyre.
· It is also used for making carpets and surgical dressings.
· Rayon is used for a wide range of fabrics for household.
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