Viscose Rayon

Rayon viscose

flat filament VFY high tenacity monofilament spun yarns fibers VSF tow/tops spun yarns Introduction Properties Applications Grades Processability Background info Supplier Partner

Rayon was the first manufactured fiber. The term rayon was officially adopted by the textile industry. Unlike most man-made fibers, rayon is not synthetic. It is made from wood pulp, a naturally-occurring, cellulose-based raw material. As a result, rayon's properties are more similar to those of natural cellulosic fibers, such as cotton or linen, than those of thermoplastic, petroleum-based synthetic fibers such as nylon or polyester.

Although rayon is made from wood pulp, a relatively inexpensive and renewable resource, processing requires high water and energy use, and has contributed to air and water pollution. Modernization of manufacturing plants and processes combined with availability of raw materials has increased rayon's competitiveness in the market.

History

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 in 1855  the Frenchman did so, 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 Hilaire de Bernigaud, Count of Chardonnay (1839-1924) after 29 years of research, was patented in 1884, and manufactured by him in 1889. This cellulose-based fabric known as Chardonnay silk was pretty but very flammable, it was removed from the market.  

Soon after, the English chemist Charles Frederick Cross and his collaborators Edward John Bevan and Clayton Beadle discovered the viscose process 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).

 

Properties Viscose Rayon has a silk-like aesthetic with superb drape and feel and retains its rich brilliant colors. Its cellulosic base contributes many properties similar to those of cotton or other natural cellulosic fibers. Rayon is moisture absorbent (more so than cotton), breathable, comfortable to wear, and easily dyed in vivid colors. It does not build up static electricity, nor will it pill unless the fabric is made from short, low-twist yarns. Rayon is comfortable, soft to the skin, and has moderate dry strength and abrasion resistance. Like other cellulosic fibers, it is not resilient, which means that it will wrinkle. Rayon withstands ironing temperatures slightly less than those of cotton. It may be attacked by silverfish and termites, but generally resists insect damage. It will mildew, but that generally is not a problem. One of rayon's strengths is its versatility and ability to blend easily with many fibers—sometimes to reduce cost, other times for lustre, softness, or absorbency and resulting comfort. Rayon has moderate resistance to acids and alkalis and generally the fiber itself is not damaged by bleaches; however, dyes used in the fabric may experience color change. As a cellulosic fiber, rayon will burn, but flame retardant finishes can be applied. Fiber Properties overview 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, 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.   Parameters  Comparative Rating Cotton Viscose Polyester Comfort  Moisture Regain Good  Very good  Poor Thermal protection  Good  Very good  Poor Air permeability  Very good  Good  Poor Softness  Good  Very good Poor Smoothness  Poor  Good  Very good Static dissipation  Good  Very good  Poor Aesthetic Drape  Good  Very good  Poor Luster  Poor  Very good  Very good Crease recovery  Poor  Poor  Very good Uniformity  Poor  Very good  Good Utility Performance Antipilling  Good  Very good  Poor Wash & wear  Good  Poor Very good     Applications Yarns: embroidery thread, chenille, cord, novelty yarns     Fabrics: crepe, gabardine, suiting,  lace, outerwear fabrics and linings for fur coats & outerwear. Apparel:  blouses, dresses,  saris, 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, conveyor belts, hoses), applications within the aerospace, agricultural and textile industries, braided cord, tapes Various: sausage casing, cellophane Grades flat yarn high tenacity monofilament fibers tow/tops spun yarns Types of Rayon There are four major types or modifications of rayon. Understanding each type should help clarify differences in product performance. "Regular rayon" has the largest market share. It is typically found in apparel and home furnishings and identified on labels by the term "viscose." The distinguishing property of regular rayon is its low wet strength. As a result, it becomes unstable and may stretch or shrink when wet. Dry cleaning is usually recommended to preserve the appearance of fabrics made from this fiber. If machine washed, untreated regular rayon can shrink as much as 10 percent. High Wet Modulus (HWM) rayon is a modified viscose that has virtually the same properties as regular rayon, plus high wet strength. HWM rayon can be machine washed and tumble dried and perform much like cotton in similar end uses. HWM rayon can also be mercerized, like cotton, for increased strength and lustre. The terms frequently used to describe HWM rayon in apparel include "polynosic" rayon or the trade name MODALTM. High Tenacity Rayon is a modification of "regular rayon" to provide exceptional strength (two times that of HWM rayon). High tenacity rayon is primarily found in tire cord and industrial end uses. It may be finished, chemically coated, or rubberized for protection from moisture and potential loss of dimensional stability and strength during use. Cupramonium Rayon is another type with properties similar to those of viscose or regular rayon. The manufacturing process differs somewhat from that of regular rayon and is less environmentally friendly. As a result, cupramonium rayon is no longer produced in the United States. Other types of rayon have been developed for specialized end uses. These include disposable, non-woven markets, and high-absorption rayon fibers with moisture-holding properties for disposable diapers, hygiene and incontinence pads, as well as medical supplies. Microfibers are not a type of rayon, but rather a very fine fiber that can be manufactured from either regular or HWM rayon. Microfibers are generally less than one denier in diameter. Rayon microfibers have been successfully produced at 0.9 denier. Fabrics from microfibers are very drapable and silk-like in hand and appearance.   Processability Fiber Production 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. Dissolution 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. Extrusion 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. Purification 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.   Fiber Structure 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.   Fiber Identification 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 odor 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 feeling 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.   Care of Rayon The critical element in successful care of rayon is the type of fiber.  Regular or viscose rayon usually require dry cleaning for best results high wet modulus, high wet strength or polynosic rayons, will normally machine wash and tumble dry satisfactorily.  The low wet strength of untreated viscose rayon is likely to cause shrinkage and loss of body if fabrics made from these fibers are hand or machine washed. Viscose rayon are usually labeled "dry clean only." Check and follow garment labels for care and instructions. Consumers who do not follow care instructions will have no recourse to manufacturers should damage occur during laundering. Since many dyes and finishes applied to viscose rayon are moisture-sensitive, consumers should protect garments from contact with moisture. Raincoats should be worn on stormy days. Also, care should be used when washing hands or working in the kitchen to avoid splashing water. The problem with sizing or dye migration increases the longer the area remains damp. Spills or moisture should be blotted with absorbent cloth to remove moisture. Avoid spilling acid or alkali, such as foodstuffs or perfume, as certain dyes used on rayon are especially sensitive to these substances. Use caution or avoid treating stained areas with water. Take the garment to a dry cleaner for stain removal. Rings or darker shading caused by sizing migration and lighter areas resulting from dye migration may be permanent. When viscose rayon can be hand washed, do so with care. Always support wet fabrics, since rayon has low wet strength and is unstable when wet. Avoid wringing moisture from fabrics. Gently squeeze out moisture and roll in a towel. Smooth and shape, then lay flat to dry. If the garments are not too heavy when wet, they can be hung on a non-rusting hanger. When pressing regular rayon garments at home, guard against spitting by steam irons that may cause water spots. Also, if possible, press on the wrong side or use a press cloth on the right side to avoid shine or iron imprints. Use a rayon or synthetic setting on the iron. When pressing blends, use the iron temperature for the most heat-sensitive fiber. Normally, a synthetic setting will be satisfactory. High wet modulus or polynosic rayons can usually be machine washed or dried without special care. Blends, dark colors, and permanent press fabrics should be washed on a gentle cycle with warm water; however, 100 percent high wet modulus rayons are normally not damaged by hot water temperatures (more than 140°F). Tumble dry on a warm setting and remove immediately, or while slightly damp. Smooth and hang to reduce wrinkling. Polynosic rayons can be line dried; however, heavy items should be supported by clotheslines to avoid stretching or loss of shape.   Background information Summary Rayon is probably the most misunderstood of all fibers. It is not a natural fiber, yet it is not synthetic. It is a fiber formed by regenerating natural materials into a usable form. Rayon fibers and fabrics made from them have many desirable properties. However, consumers sometimes expect performance characteristics beyond those for which rayon fibers were designed. Although rayon can look like wool, silk, cotton, or linen and is a manufactured fiber like polyester, this does not mean it behaves like or has the same properties or care requirements of these fibers. Rayon is a fiber on its own. Consider each garment made from rayon individually when determining use and care practices. And, always read and follow care labels for best performance.   Our supplier partner Newstartex for viscose rayon filament and fibers in rawwhite and spundyed