Certain natural cellulose fibres are treated and re-produced for specific purposes. The famous fibres such as Viscose Rayon, Acetate etc. are produced by processing various natural polymers.
Manmade Cellulosic Fibers
The first man-made fibres which were developed and produced used polymers of natural origin, more precisely of cellulose which is a raw material available in large quantities in the vegetable world.
Cellulose is the natural polymer that makes up the living cells of all vegetation. It is the material at the center of the carbon cycle, and the most abundant and renewable biopolymer on the planet.
Cotton linters and wood pulp, viscose rayon, Cupra-ammonium, Cellulose Acetate (secondary and triacetate), Polynosic, High Wet Modulus (HWM).
- Cellulose is one of many polymers found in nature.
- Wood, paper, and cotton all contain cellulose. Cellulose is an excellent fiber.
- Cellulose is made of repeat units of the monomer glucose.
- The three types of regenerated cellulosic fibres are rayon, acetate and triacetate which are derived from the cell walls of short cotton fibres called linters.
- Paper for instance is almost pure cellulose
Originally, the word rayon was applied to any cellulose-based manufac- tured ﬁber, and therefore included the cellulose acetate ﬁbers. However, the deﬁ- nition of rayon was clariﬁed in 1951 and now includes textiles ﬁbers and ﬁlaments composed of regenerated cellulose, excluding acetate. In Europe the ﬁbers are now generally known asviscose, the termviscose rayon being used whenever confusion between the ﬁber and the cellulose xanthate solution (also called viscose—see below) is possible. (In this article the termsregenerated cellu-losics, rayon, and viscose rayontend to be used interchangeably.)
- Rayon is a manufactured regenerated cellulosic fiber.
- It is the first man made fibre .
- It has a serrated round shape with smooth surface.
- It loses 30-50% of its strength when it is wet.
- Rayon is produced from naturally occurring polymers and therefore it is not a synthetic fiber, but a manufactured regenerated cellulosic fiber.
- The fiber is sold as artificial silk
There are two principal varieties of rayon namely viscose and cupra ammonium rayon.
A manufactured fiber in which the fiber forming substance is cellulose acetate.Acetate is derived from cellulose by reacting purified cellulose from wood pulp with acetic acid and acetic anhydride in the presence of sulfuric acid.
The Acetate Fiber Characteristics
- Luxurious feel and appearance
- Wide range of colors and lusters
- Excellent drapability and softness
- Relatively fast drying
- Shrink, moth and mildew resistant
- Special dyes have been developed for acetate since it does not accept dyes ordinarily used for cotton and rayon.
Acetate fibers are the manufactured fibers in which the fiber-forming substance is cellulose acetate. The cellulose esters triacetate and acetate are formed through acetylation of cotton linters or wood pulp using acetic anhydride and an acid catalyst in acetic acid.
Acetate and triacetate fibers are very similar in appearance to the regular-tenacity viscose rayons.Acetates and triacetates are moderately stiff fibers and possess good resil iency on bending and deformation, particularly after heat treatment.
The abrasion resistance of acetate and triacetate is poor, and these fibers cannot be used in applications requiring high resistance to rubbing and abrasion; however, the resistance of these fibers to pilling is excellent. While acetate and triacetate are moderately absorbent, their absorbencies cannot compare with the pure cellulosic fibers. The hand of acetate fabrics is somewhat softer and more pliable than triacetate, which possesses a crisp firm hand. Fabrics of both fibers possess excellent draping characteristics. Fabrics of acetate and triacetate have a pleasing appearance and a high degree of luster, but the luster of these fabrics can be modified through addition of delusterants.
Both acetate and triacetate are susceptible to attack by a number of household chemicals. Acetate and triacetate are attacked by strong acids and bases and by oxidizing bleaches. Acetate has only fair sunlight resistance, whereas the sunl ight resistance of triacetate is superior. Both fibers have good heat resistance below their melting points.
Acetate and triacetate cannot be dyed by dyes used for cellulosic fibers. These fibers can be satisfactorily dyed with disperse dyes at moderate to high temperatures to give even, bright shades. Acetate and triacetate dry quickly and may be tumble dried or drip dried.