Rayon
RAYON
Rayon, acetate, and lyocell are all regenerated cellulose fibers. They originate from chemical treatment of natural materials. The materials most often used are cotton fibers too short to spin into yarns or wood chips. The Federal Trade Commission establishes generic categories of fibers for regulation and labeling purposes. The generic classification "rayon" includes several variants. Viscose rayon is the most common form. A variation of viscose, high-wet-modulus rayon was produced in 1955 with trade names of Avril and Zantrel as a modification to generate high strength, reduce elongation, and improve washability of rayon. Cuprammonium rayon is subjected to slightly different processing. U.S. cuprammonium production ceased in 1975, but it is still produced in Japan (FiberSource Web site; Kadolph and Langford 2001).
Acetate has its own generic category, which also includes a variant, triacetate. Triacetate is a manufactured cellulosic that is similar to acetate but limited in production and usage. (Collier and Tortora 2000). Lyocell was given its own classification by the FTC for labeling purposes, but it was also designated as a sub-classification of rayon.
Rayon, the earliest manufactured fiber, was first patented in 1855 by the Swiss chemist Georges Audemars. It was called "artificial silk." Sir Joseph Swan, an English chemist, was inspired by Thomas Edison's incandescent electric lamp to experiment with extruding Audemars's cellulose solution through fine holes into a coagulating bath in order to create filaments for the electric light. His fibers were used in Edison's invention as well as for an 1885 exhibition of textiles his wife crocheted from his new fiber. "Artificial silk" was also exhibited at the Paris Exhibition in 1889 by the French chemist Count Hilaire de Chardonnet who is known as the "father of the rayon industry" because he built the first plant for commercial production of "Chardonnet silk" in Besancon, France.
The French chemist Louis-Henri Despeissis patented cuprammonium rayon producing what he called "Bemberg silk" as early as 1908. A British silk company, Samuel Courtaulds and Company, Ltd., began production of a rayon known as viscose rayon in 1905 and by 1911 helped start American Viscose Corporation in the United States (FiberSource Web site; Encyclopaedia Britannica 2003). Some researchers theorize that getting access to the science of producing rayon was such a benefit for the United States that it contributed to American involvement in World War I (Clairmonte and Cavanagh 1981).
The invention of acetate was rapidly followed by commercial production, as early as 1910. In Switzerland, Camille and Henry Dreyfus created acetate motion picture film and toilet articles and during World War I built a plant in England to help the war effort with cellulose acetate dope for airplane wings. The Dreyfus brothers were invited to build an acetate plant in Maryland to provide cellulose acetate dope for American airplanes. The Celanese Company began commercial production of acetate fiber in 1924. Both rayon and acetate garments were available to consumers by the 1920s. Confusion between the two fibers was partially due to the Federal Trade Commission designating both as rayon. This was not corrected until 1953 when rayon and acetate were given separate generic fiber classifications.
Cellulosic manufactured fibers reached peak production in the 1980s with a market share of 21 percent. Fiber was produced in North America, Europe, and Asia. By 2002, Asia had become the leading manufactured fiber producer with 65 percent of the market and cellulosics had dropped to 6 percent of fiber production (Fiber-Source Web site). Given that polyester production soared while cellulosics dropped, it seems that polyester became accepted as the most optimal "artificial silk."
Lyocell, developed as a "better" manufactured cellulosic, may be fundamental to reinventing enthusiasm for manufactured cellulosic fibers. Introduced to the U.S. market in the early 1990s, lyocell is sold under the trademark Tencel by Tencel, Inc., and by the Austrian producer Lenzing AG as Lyocell by Lenzing. Promoted as a designer level apparel textile that is more environmentally friendly than rayon, lyocell promotions tended to downplay association with rayon and focused on being a new textile with considerable potential for comfort and aesthetic appeal.
Producing rayon, acetate, and lyocell fibers. Although each manufacturing process has technical differences and variations in the steps, the basic procedure for the manufacture of rayon and lyocell begins with wood chips or cotton linters. These materials are treated with chemicals and subjected to various treatments, depending on the end product. Eventually these materials are reduced to a cellulosic solution. This solution passes through spinnerets, patterned after the small holes that silkworms use to extrude silk filament, and dries to become mostly pure cellulose filaments.
Wood pulp or cotton linters are also used in production of acetate, however, as a result of the chemical treatments, the fiber produced is no longer pure cellulose, but rather a form called cellulose acetate. As a result, the characteristics of acetate differ from those of the purely cellulose fibers. Acetate was the first thermoplastic fiber, a fiber that will soften and melt when exposed to high levels of heat (Kadolph and Langford 2001).
In the manufacture of lyocell, chemicals can be recovered and recycled, making lyocell one of the most environmentally friendly fibers to produce. Rayon and acetate involve considerable potential for hazardous chemical by-products. Efforts have been made to recycle chemicals and minimize environmental impacts, but the strict environmental pollution regulations in the United States have led many American manufacturers to discontinue rayon production.
Characteristics of rayon, acetate, and lyocell textiles. Rayon and lyocell have high absorbency, low heat retention, and soft, non-irritating surfaces that make them comfortable next to the skin in warm weather. Both can also be manipulated to emulate the aesthetic character of cotton, wool, silk, and linen. Additionally, lyocell has the capacity to simulate the aesthetics of silk, suede, and leather. By contrast, acetate has more heat retention and less absorbency and is subject to static electricity build-up.
Viscose rayon and lyocell tend to be produced as staple (short) fibers and thereby have a textured surface that softens light reflectance. Acetate fibers are typically produced as filament fibers, and as a result acetate is more successful in simulating the luster and body of silk in such fabrics as taffeta and satin. Both rayon and lyocell dye easily although color will fade over time and with abrasion. Acetate was difficult to dye and subject to fading until synthetic solution dyes were developed to solve this problem. Acetate now is produced in a wide color range and color stability is good when fabrics are exposed to sunlight, perspiration, air pollution, and cleaning. Acetate is dissolved by fingernail polish remover containing acetone and is damaged by extended exposure to sunlight.
Unless it is the high wet modulus type, rayon has poor durability and resiliency. Rayon and acetate perform better if dry-cleaned than if laundered because they are weaker when wet. Acetate also has poor abrasion resistance and is sensitive to chemicals. While rayon may shrink or be distorted after laundering unless given special finishes, acetate is dimensionally stable. Lyocell is much stronger when wet than rayon or acetate and is considered to have good durability and dimensional stability. Resiliency is better than either rayon or acetate. Lyocell can be successfully washed by using the gentle cycle and can be pressed with a warm iron. Wrinkle-resistant treatments do not greatly affect strength. Lyocell has potential to fibrillate, which results in a fuzzy appearance on the surface. This is beneficial for a textured surface but makes the fabric subject to abrasion damage. New variations developed to lower fibrillation contribute to the versatility of this promising textile. Lyocell is often manufactured in microfiber (ultrafine) form to enhance the extremely soft feel and drape.
A major concern with acetate is its reaction to heat and to fire. While acetate wrinkles easily, it fuses and melts if ironed at high temperatures. Acetate also burns readily, as do all cellulosics, but spits molten pieces while burning that melt and fuse to the skin. Acetate is mildew and insect resistant. (FiberSource Web site; Kadolph and Langford 2001; Collier and Tortora 2000).
Rayon, acetate, and lyocell in fashion across time. Early in the twentieth century, rayon and acetate were both explored as an economical alternative to silk. The marketing of both fibers became confused as acetate was first sold as a form of rayon labeled "acetate rayon." Following World War I, which temporarily disrupted fiber development, consumers experienced problems with shrinkage and distortion of rayon and the thermoplasticity of acetate that had to be addressed. World War II disrupted access to silk fiber. Manufacturers in the United States used this opportunity to expand the market for rayon and acetate, allowing them to be accepted as new fibers rather than silk substitutes.
New fibers competed with rayon and acetate in the postwar period. While consumers enjoyed their low cost, unpredictability of performance was a deterrent. Use of manufactured cellulosics has declined. The large market share of polyester in the 2002 market leads one to assume that the aesthetic of silk is still important, but better performance than either rayon or acetate tend to provide has become a higher priority (FiberSource Web site).
Lyocell may be an exception to this downward trend. Manufacturers have been careful to differentiate lyocell from rayon. As a new fiber, it has a cachet of novelty and designer level taste that fits well with fashion. Recently, the versatility of Tencel lyocell is being expanded through new finishing processes that expand options for the aesthetic character of the final textile or garment (American Fiber Manufacturer's Association). Having the aesthetic of cellulosics with better performance and the aura of being good for the environment may help lyocell become the manufactured cellulosic of choice.
Common rayon, acetate, and lyocell textile uses. Rayon is used for a range of apparel as either 100 percent rayon or blended to create blouses, dresses, suiting, sport shirts, work clothes, slacks, and accessories. Interior products are also frequently blended and primarily include upholstery, draperies, slipcovers, bed coverings, and tablecloths. High wet modulus rayon tends to be used in knitwear and lingerie. Nonwoven applications for rayon are also extensive due to its high absorbency. These include cosmetic "cotton" balls, industrial wipes, reusable cleaning cloths, disposable diapers and sanitary products, and medical surgical materials. High tenacity rayon can be used for tire cords and other industrial products (Collier and Tortora 2000; Kadolph and Hollen 2001; Fiber-Source Web site).
Acetate fiber is primarily used for linings and also special occasion apparel, such as taffeta, satin, and brocade wedding and prom dresses. It is commonly found blended with rayon in interior textiles, such as antique satin or brocade draperies, textured upholstery, and bedspreads and quilts. Acetate is used for cigarette filters.
Because it is nearly twice the price of rayon, lyocell has been targeted primarily to upscale apparel, such as business wear, dresses, slacks, and coats. Recent innovations resulting from the Tencel Inc., Intellect research program has moved lyocell into more formal wear, such as men's suits. Lyocell is also being seen in lingerie, hosiery, and casual wear. Interior uses include upholstery and draperies. Lyocell can be blended with cotton, wool, linen, silk, nylon, and polyester, a broad range of possibilities for combining fiber characteristics. New modifications have made production of lyocell knitwear optimal.
bibliography
Clairmonte, Frederick, and John Cavanagh. The World in Their Web: Dynamics of Textile Multinationals. London: Zed Press; Westport, Conn.: L. Hill, 1981.
Collier, Billie, and Phyllis Tortora. Understanding Textiles. New York: Macmillan, 2000. Contains good illustrations.
Hatch, Kathryn. Textile Science. Minneapolis, Minn.: West Publishing, 1993. Contains good illustrations.
Kadolph, Sara, and Anna Langford. Textiles. 9th ed. New York: Prentice-Hall, 2002. Contains good illustrations.
Internet Resource
"A Short History of Manufactured Fibers." Available from <http://www.fibersource.com>.
Carol J. Salusso
Rayon
Rayon
Background
For centuries humankind has relied upon various plants and animals to provide the raw materials for fabrics and clothing. Silkworms, sheep, beaver, buffalo deer, and even palm leaves are just some of the natural resources that have been used to meet these needs. However, in the last century scientists have turned to chemistry and technology to create and enhance many of the fabrics we now take for granted.
There are two main categories of man-made fibers: those that are made from natural products (cellulosic fibers) and those that are synthesized solely from chemical compounds (noncellulosic polymer fibers). Rayon is a natural-based material that is made from the cellulose of wood pulp or cotton. This natural base gives it many of the characteristics—low cost, diversity, and comfort—that have led to its popularity and success. Today, rayon is considered to be one of the most versatile and economical man-made fibers available. It has been called "the laboratory's first gift to the loom."
In the 1860s the French silk industry was being threatened by a disease affecting the silkworm. Louis Pasteur and Count Hilaire de Chardonnet were studying this problem with the hope of saving this vital industry. During this crisis, Chardonnet became interested in finding a way to produce artificial silk. In 1885 he patented the first successful process to make a useable fiber from cellulose. Even though other scientists have subsequently developed more cost-effective ways of making artificial silk, Chardonnet is still considered to be the father of rayon.
For the next forty years this material was called artificial or imitation silk. By 1925 it had developed into an industry unto itself and was given the name rayon by the Federal Trade Commission (FTC). The term rayon at this time included any man-made fiber made from cellulose. In 1952, however, the FTC divided rayons into two categories: those fibers consisting of pure cellulose (rayon) and those consisting of a cellulose compound (acetate).
By the 1950s, most of the rayon produced was being used in industrial and home furnishing products rather than in apparel, because regular rayon (also called viscose rayon) fibers were too weak compared to other fibers to be used in apparel. Then, in 1955, manufacturers began to produce a new type of rayon—high-wet-modulus (HWM) rayon—which was somewhat stronger and which could be used successfully in sheets, towels, and apparel. The advent of HWM rayon (also called modified rayon) is considered the most important development in rayon production since its invention in the 1880s.
Today rayon is one of the most widely used fabrics in our society. It is made in countries around the world. It can be blended with natural or man-made fabrics, treated with enhancements, and even engineered to perform a variety of functions.
Raw Materials
Regardless of the design or manufacturing process, the basic raw material for making rayon is cellulose. The major sources for natural cellulose are wood pulp—usually from pine, spruce, or hemlock trees—and cotton linters. Cotton linters are residue fibers which cling to cotton seed after the ginning process.
Strictly defined, rayon is a manufactured fiber composed of regenerated cellulose. The legal definition also includes manufactured fibers in which substitutes have not replaced more than 15 percent of the hydrogens.
While the basic manufacturing process for all rayon is similar, this fabric can be engineered to perform a wide range of functions. Various factors in the manufacturing process can be altered to produce an array of designs. Differences in the raw material, the processing chemicals, fiber diameter, post treatments and blend ratios can be manipulated to produce a fiber that is customized for a specific application.
Regular or viscose rayon is the most prevalent, versatile and successful type of rayon. It can be blended with man-made or natural fibers and made into fabrics of varying weight and texture. It is also highly absorbent, economical and comfortable to wear.
Regular viscose rayon does have some disadvantages. It's not as strong as many of the newer fabrics, nor is it as strong as natural cotton or flax. This inherent weakness is exacerbated when it becomes wet or overexposed to light. Also, regular rayon has a tendency to shrink when washed. Mildew, acid and high temperatures such as ironing can also result in damage. Fortunately, these disadvantages can be countered by chemical treatments and the blending of rayon with other fibers of offsetting characteristics.
High-wet-modulus rayon is a stronger fiber than regular rayon, and in fact is more similar in performance to cotton than to regular rayon. It has better elastic recovery than regular rayon, and fabrics containing it are easier to care for—they can be machine-washed, whereas fabrics containing regular rayon generally have to be dry-cleaned.
The Manufacturing
Process
While there are many variations in the manufacturing process that exploit the versatility of the fiber, the following is a description of the procedure that is used in making regular or viscose rayon.
Regardless of whether wood pulp or cotton linters are used, the basic raw material for making rayon must be processed in order to extract and purify the cellulose. The resulting sheets of white, purified cellulose are then treated to form regenerated cellulose filaments. In turn, these filaments are spun into yarns and eventually made into the desired fabric.
Processing purified cellulose
- 1 Sheets of purified cellulose are steeped in sodium hydroxide (caustic soda), which produces sheets of alkali cellulose. These sheets are dried, shredded into crumbs, and then aged in metal containers for 2 to 3 days. The temperature and humidity in the metal containers are carefully controlled.
- 2 After ageing, the crumbs are combined and churned with liquid carbon disulfide, which turns the mix into orange-colored crumbs known as sodium cellulose xanthate. The cellulose xanthate is bathed in caustic soda, resulting in a viscose solution that looks and feels much like honey. Any dyes or delusterants in the design are then added. The syrupy solution is filtered for impurities and stored in vats to age, this time between 4 and 5 days.
Producing filaments
- 3 The viscose solution is next turned into strings of fibers. This is done by forcing the liquid through a spinneret, which works like a shower-head, into an acid bath. If staple fiber is to be produced, a large spinneret with large holes is used. If filament fiber is being produced, then a spinneret with smaller holes is used. In the acid bath, the acid coagulates and solidifies the filaments, now known as regenerated cellulose filaments.
Spinning
- 4 After being bathed in acid, the filaments are ready to be spun into yarn. Depending on the type of yarn desired, several spinning methods can be used, including Pot Spinning, Spool Spinning, and Continuous Spinning. In Pot Spinning, the filaments are first stretched under controlled tension onto a series of offsetting rollers called godet wheels. This stretching reduces the diameter of the filaments and makes them more uniform in size, and it also gives the filaments more strength. The filaments are then put into a rapidly spinning cylinder called a Topham Box, resulting in a cake-like strings that stick to the sides of the Topham Box. The strings are then washed, bleached, rinsed, dried, and wound on cones or spools.
Spool Spinning is very similar to Pot Spinning. The filaments are passed through rollers and wound on spools, where they are washed, bleached, rinsed, dried, and wound again on spools or cones.
In Continuous Spinning, the filaments are washed, bleached, dried, twisted, and wound at the same time that they are stretched over godet wheels.
- 5 Once the fibers are sufficiently cured, they are ready for post-treatment chemicals and the various weaving processes necessary to produce the fabric. The resulting fabric can then be given any of a number of finishing treatments. These include calendaring, to control smoothness; fire resistance; pre-shrinking; water resistance; and wrinkle resistance.
High-Wet-Modulus Rayon
Manufacture
The process for manufacturing high-wet-modulus rayon is similar to that used for making regular rayon, with a few exceptions. First, in step #1 above, when the purified cellulose sheets are bathed in a caustic soda solution, a weaker caustic soda is used when making HWM rayon. Second, neither the alkali crumbs (#1 above) nor the viscose solution (step #2) is aged in the HWM process. Third, when making HWM rayon, the filaments are stretched to a greater degree than when making regular rayon.
Quality Control
As with most chemically oriented processes, quality control is crucial to the successful manufacture of rayon. Chemical make-up, timing and temperature are essential factors that must be monitored and controlled in order to produce the desired result.
The percentages of the various fibers used in a blended fabric must be controlled to stay within in the legal bounds of the Textile Fiber Identification Act. This act legally defines seventeen groups of man-made fibers. Six of these seventeen groups are made from natural material. They include rayon, acetate, glass fiber, metallics, rubber, and azion. The remaining eleven fabrics are synthesized solely from chemical compounds. They are nylon, polyester, acrylic, modacrylic, olefin, spandex, anidex, saran, vinal, vinyon, and nytril.
Within each generic group there are brand names for fibers which are produced by different manufacturers. Private companies often seek patents on unique features and, as could be expected, attempt to maintain legal control over their competition.
Byproducts
As one of the industry's major problems, the chemical by-products of rayon have received much attention in these environmentally conscious times. The most popular method of production, the viscose method, generates undesirable water and air emissions. Of particular concern is the emission of zinc and hydrogen sulfide.
At present, producers are trying a number of techniques to reduce pollution. Some of the techniques being used are the recovery of zinc by ion-exchange, crystallization, and the use of a more purified cellulose. Also, the use of absorption and chemical scrubbing is proving to be helpful in reducing undesirable emissions of gas.
The Future
The future of rayon is bright. Not only is there a growing demand for rayon worldwide, but there are many new technologies that promise to make rayon even better and cheaper.
For a while in the 1970s there was a trend in the clothing industry toward purely synthetic materials like polyester. However, since purely synthetic material does not "breath" like natural material, these products were not well received by the consumer. Today there is a strong trend toward blended fabrics. Blends offer the best of both worlds.
With the present body of knowledge about the structure and chemical reactivity of cellulose, some scientist believe it may soon be possible to produce the cellulose molecule directly from sunlight, water and carbon dioxide. If this technique proves to be cost effective, such hydroponic factories could represent a giant step forward in the quest to provide the raw materials necessary to meet the world wide demand for man-made fabric.
Where To Learn More
Books
Corbman, Bernard P. Textiles: Fiber to Fabric, 6th ed. McGraw-Hill, 1983.
Hollen, Norma, Jane Saddler, Anna Langford, and Sara Kadolph. Textiles, 6th ed. Macmillan, 1988.
Periodicals
Foley, Theresa M. "Rayon Fiber Manufacturer Shuts Down, Threatening U.S. Booster Production." Aviation Week & Space Technology. November 7, 1988, p. 29.
Smith, Emily T. "A Safe Shortcut around the Toxic Road to Rayon." Business Week. February 11, 1991, p. 80.
Templeton, Fleur. "From Log to Lingerie in a Few Easy Steps." Business Week. April 6, 1992, p. 95.
"Turning Corn and Paper into Rayon." USA Today. June, 1991, p. 7.
—Dan Pepper