Rayon is the generic term for fiber (and the resulting yarn and fabric) manufactured of regenerated cellulose by any one of six processes. Its importance as a fiber lies in its versatility, and in the fact that it was the first viable manufactured fiber. As far back as 1664, English naturalist Robert Hooke theorized that artificial filaments might be spun from a substance similar to that which silkworms secrete to make silk. This was often tried by scientists in the ensuing years who sought an "artificial silk", yet no one was to succeed until the Frenchman, George Audemars. By dipping a needle into a viscous solution of mulberry bark pulp and gummy rubber, he was able to make a thread. While interesting from a scientific standpoint, this process was hardly viable economically - it was very slow, and required a great deal of skill and precision. The first commercial synthetic fiber was produced by Louis-Marie-Bernigaud, Count of Chardonnet (1839-1924) after 29 years of research, was patented in 1884, and manufactured by him in 1889. Soon after, the English chemist Charles Frederick Cross and his collaborator Edward John Bevan discovered the viscose process (see below) in 1891 (1892?). Courtaulds Fibers produced the first commercial viscose rayon in 1905; the first in the United States was in 1910 by the American Viscose Company. Initially rayon was called "Artificial Silk", and many other names. In 1924 (1926?), a committee formed by the U.S. Department of Commerce and various commercial associations decided upon the name "rayon". It was called "rayon" for one of two reasons: either because of its brightness and similarities in structure with cotton (sun = ray, -on = cotton). Or because the naming committee couldn't find a name from the thousands entered in a contest they sponsored, and who hoped to shed a "ray of light" on the subject (from rayon, French for ray).
By using two different chemicals and manufacturing techniques, two basic types of rayon were developed - viscose rayon and cuprammonium. Other processes for rayon include the polynosic (modal) process and the now obsolete nitrocellulose and saponified acetate processes. The nitrocellulose process is likely obsolete not only because the viscose and cuprammonium processes are more effective, they are also safer; the nitrocellulose process results in a fiber with explosive properties.
As recently as 1992 there has been an entirely new process developed for producing regenerated cellulose fibers: the lyocell process, developed by Courtaulds. While it is sufficiently different from rayon to almost be in a class by itself, the U.S. Federal Trade commission has formally amended the textile rules to add lyocell as a subclass of rayon.
As viscose is the most common and recognized process for making rayon today, the process is outlined below. While the United States government considers fibers from all the above processes rayon, the International Organization for Standardization (ISO) prefers the name viscose for rayon (regenerated cellulose) obtained by the viscose process. The name viscose was derived from the word viscous, which describes the liquid state of the spinning solution.
The cellulosic raw materials for rayon are wood chips (usually from spruce or pine) or cotton linters. These are treated to produce sheets of purified cellulose containing 87-98% cellulose. They are then bleached with sodium hypochloride (NaOCl) to remove natural colour. These cellulose sheets are then soaked in 18% caustic soda for 1 to 2 hours producing sheets of alkali cellulose. Any excess alkali is pressed out. The substance is broken up into flakes or grains called cellulose crumbs, which are aged for two or three days under controlled temperature and humidity. Liquid carbon disulfide is added to the crumbs to change the cellulose into cellulose xanthate, a light orange substance that is still in crumb form. These crumbs are dissolved in a weak solution of caustic soda and transformed into a viscous solution called "viscose", honey-like in colour and consistency.
To produce the rayon filament, the viscose solution is aged, filtered, then vacuum-treated to remove any air bubbles that could weaken the filament and cause it to break. It is then pumped through spinnerets into a bath of sulfuric acid, which coagulates the cellulose xanthate to form regenerated filaments of 100% cellulose. The many variations and different properties of viscose such as luster, strength, softness and affinity for dyes, are influenced here by varying the technique and by the addition of external materials.
Once extruded, the freshly formed viscose must be purified and strengthened. It is thoroughly washed, treated with a dilute solution of sodium sulfide to remove any sulfur impurities. It may be bleached to remove a slight yellowness and to secure even white colour, and then given a final washing.
Cellulose in this process is instead treated with ammonia and cupric oxide. Rayon created by this process is also called cuprammonium cellulose or Cuprophan, cuprammoniam rayon, or saponified cellulose ester. One interesting use of this variety of rayon is in the manufacture of artificial kidneys and semi-permeable membranes for hemodialysis. This is possible because cellulose and regenerated cellulose allow molecules of a certain size and/or chemical composition to pass through them, while blocking others. Harmful substances are strained out, and the blood is purified.
Lyocell was created by Courtaulds Fibers in 1992, and first manufactured in the United States in 1993. It is marketed under the Tencel(TM) name. In the lyocell process (also called "solvent-spun"), wood pulp and amine oxide solution are mixed and heated until the cellulose dissolves. The clear solution that results is then extruded into a dilute aqueous solution of the amine oxide, which precipitates the cellulose as fiber. After washing in water, the fiber is ready for finishing processes. The dilute amine oxide from washing is purified and recycled by evaporating the excess water. The difference between this process and other cellulose spinning methods are considerable. Lyocell production uses a non-toxic solvent that is recovered, purified and recycled as an integral part of the manufacturing process. Waste products are thus minimal and harmless. The process uses less energy, less water and less non-renewable resources. While lyocell is classified as a subclass of rayon (see above), it has numerous advantages over conventional rayon fibers. Lyocell is much stronger, washable, shrink- and wrinkle-resistant than rayon, thus overcoming rayon's major faults. Yet it still has the soft hand and excellent drape of rayon, and its high absorbency, and excellent dye- and print-ability. Lyocell is environmentally friendly. It is produced from the wood pulp of trees specifically grown for this purpose. It is specially processed, using a solvent spinning technique in which the dissolving agent is recycled, reducing environmental effluents.
The structure of the rayon fiber is generally that of smooth, inelastic filaments like glass rods. However, different processes, additives and finishing techniques can vary the physical appearance and structure of the fiber.
In the burning test, rayon most resembles cotton. It ignites rapidly, sometimes even faster than cotton, burning with a large, bright, yellow flame. Burnt rayon leaves an odour like burnt paper, similar to cotton. The ash is also like cotton: light and feathery gray, which disintegrates rapidly.
In the feeling test, rayon is more difficult to identify. The variety of processes, modifications of technique and various treatments can make rayon look and feel like silk, cotton, wool or linen. In general, however, rayon has the smooth felling of silk. It is slippery because of the smoothness of the filaments, and has an almost brittle-feeling quality due to the fiber's inelasticity.
The breaking test can differentiate between rayon, cotton and linen yarns. Because of its inelasticity, rayon will tend to break shortly, with a short, uneven breaking pattern. It is even easier to distinguish when wet, as it breaks very easily then.
General Characteristics: Rayon as a cloth is soft and comfortable. It drapes well, which is one of the reasons it is so desirable as an apparel fabric. Most characteristics are variable depending on processing, additives and finishing treatments, not to mention fabric construction.
Absorbency: Rayon is the most absorbent of all cellulose fibers, even more so than cotton and linen. Because of this, rayon absorbs perspiration and allows it to evaporate away from the skin, making it an excellent summer fabric. Its high absorbency applies equally to dyes, allowing beautiful, deep, rich colours.
Strength: It loses a great deal of strength when wet. Because of this, it stretches and shrinks more than cotton.
Abrasion resistance: Poor due to inelasticity of the fibers. It is easily damaged by scraping and will pill on the surface of the cloth.
Flammability: Because of its excessive flammability (see burning test), it inspired the Flammable Fabrics Act. The FFA was enacted by the U.S. Department of Commerce in 1953 in response to public concern over a number of serious burn accidents involving brushed rayon high pile sweaters (referred to as "torch sweaters") and children's cowboy chaps which could easily catch fire and flash burn.
Static: No static build-up.
Chemical reactions: Because it is a cellulose fiber, it is damaged by even relatively weak acids.
Rayon fabric should always be dry-cleaned, unless it has been specifically treated for washability. Even then, great care should be taken to guard against shrinkage.
Rayon
Yarns: embroidery thread, chenille, cord, novelty yarns.
Fabrics: challis, crepe, gabardine, suitings, yarn-dyes, faille, gauze, prints, textured rayons & other novelties, outerwear fabrics, and linings for fur coats & outerwear.
Apparel: blouses, dresses, jackets, lingerie, linings, millinery (hats), slacks, sport shirts, sportswear, suits, ties, work clothes.
Domestic Textiles: bedspreads, blankets, curtains, draperies, sheets, slip covers, tablecloths, upholstery.
Industrial Textiles: high-tenacity rayon is used as reinforcement to mechanical rubber goods (tires, hoses), applications within the aerospace, agricultural and textile industries.
Viscose
Pulps: high-tenacity rayon cord (for tires, industrial belts, and hoses), textile fibers, sausage casing, cellophane.
Fabrics: lace, dress materials, dull crepe, satin, taffeta, brasso, velvet, georgette, and tapestry.
Apparel: dresses, saris.
Domestic Textiles: upholstery, curtain and finishing fabric.
Industrial Textiles: braided cord, tapes.
Lyocell
Pulps: premium textile fibers
Apparel: dresses, suits, sportswear, pants, jackets, blouses, skirts.