Viscose fiber

Definition:

A generic term for filaments made from various solutions of modified cellulose by pressing the cellulose solution through an orifice and solidifying it in the form of a filament.

History:

 Viscose or Rayon was the first manufactured fiber. In 1665, Robert Hooke, an English naturalist, theorized that it might be possible to spin artificial filaments. In 1855, George Audemars, a Frenchman succeeded but his process was slow and needed a great deal of skill. The first commercial fiber was patented in 1884 by the count of Chardonnay after 29 years research. In 1891 three English men, Charles Frederick Cross, Edward John Bevan and Clayton Beadle discovered the viscose process. Courtaulds produced the first commercial viscose rayon in 1905.

Viscose Fiber Characteristics

• Highly absorbent
• Soft and comfortable
• Easy to dye
• Drapes well

The drawing process applied in spinning may be adjusted to produce rayon fibers of extra strength and reduced elongation. Such fibers are designated as high tenacity rayons, which have about twice the strength and two-third of the stretch of regular rayon. An intermediate grade, known as medium tenacity rayon, is also made. Its strength and stretch characteristics fall midway between those of high tenacity and regular rayon[13].

DIFFERENT TYPES OF VISCOSE RAYONS

Rayon fibers are engineered to possess a range of properties to meet the demands for a wide variety of end uses. Some of the important types of fibers are briefly described.

High wet modulus rayon: These fibers have exceptionally high wet modulus of about 1 g/den and are used as parachute cords and other industrial uses. Fortisan fibers made by Celanese (saponified acetate) has also been used for the same purpose.

Polynosic rayon:

These fibers have a very high degree of orientation, achieved as a result of very high stretching (up to 300 %) during processing. They have a unique fibrillar structure, high dry and wet strength, low elongation (8 to 11 %), relatively low water retention and very high wet modulus.

Specialty rayons:

Flame retardant fibers: Flame retardance is achieved by the adhesion of the correct flame- retardant chemical to viscose. Examples of additives are alkyl, aryl and halogenated alkyl or aryl phosphates, phosphazenes, phosphonates and polyphosphonates. Flame retardant rayons have the additives distributed uniformly through the interior of the fiber and this property is advantageous over flame retardant cotton fibers where the flame retardant concentrates at the surface of the fiber.

Super-absorbent rayons:
This is being produced in order to obtain higher water retention capacity (although regular rayon retains as much as 100 % of its weight). These fibers are used in surgical nonwovens. These fibers are obtained by including water- holding polymers (such as sodium polyacrylate or sodium carboxy methyl cellulose) in the viscose prior to spinning, to get a water retention capacity in the range of 150 to 200 % of its weight.