The process of making viscose was discovered by C.F.Cross and E.J.Bevan in 1891. ******* Rayon, a textile material, is composed of cellulose obtained from cotton linters or from the pulp of trees such as spruce. Since the introduction of rayon about 1900, it has been used in many textile fields. At first rayon was called artificial silk because, in its filament form, it somewhat resembles silk. The manufacture of rayon filaments (and all manufactured fibers) is done by means of an extrusion process called spinning. In this procedure the fiber-forming liquid is forced through tiny holes in a nozzle or spinneret into a liquid bath containing a solution that produces filaments of pure cellulose, which can be spun into yarn. The filaments are drawn together to form both fibers and yarn in a single, continuous process. ************** Rayon has been around for more than 250 years but not as a fabric. The term rayon has only been with us since 1924. The idea to artificially duplicate the silk worm process was advanced in 1665 by an English scientist. It lay dormant until 1754 when a French scientist reported it was possible to make varnishes into threads, which imitated silk. More than 100 years later another Frenchman, Count Chardonnet, produced the first fiber having commercial success as a textile. In 1884 rayonne was born from his nitrocellulose process. Right on its heels the cuprammonium process was developed, a third in 1982 by two Englishmen called viscose , followed by acetate. The Chardonnet process is no longer in production. Rayonne was more widely known as artificial silk. The name was outlawed in 1924 and the name rayon was given to the fabric. Manufactured in this country in 1911, artificial silk got a cold reception from the public. It was not good looking nor good wearing and as late as 1920, wound up on bargain counters. Eventually, rayon started to catch on. In 1930 Sears offered yard goods in rayon and cotton flat crepe, rayon and cotton brocaded flat crepe, rayon and cotton alpaca and an assortment of washable all-rayon flat crepes. In 1933 Sears offered rayon taffeta guaranteed not to crack, rayon twill satin, textured rayon crepes and rayon seersucker, all sunfast. By 1939, Montgomery Wards was offering Petalspun, an all-spun washable rayon; Petalqeen, all rayon flat crepe prints with only 1% shrinkage; and Spunblend, a spun rayon and cotton blend. All rayons were advertised as being brilliant new patterns However, even as late as the 1950s rayon or rayon blends in yard goods and ready to wear were still suspect. Anyone who is familiar with butcher linen knows the horrors of this fabric stretching lengthwise while shrinking crossgrain, of bemburg-type sheers stretching unevenly causing hemline havoc and in general, the rotting of fibers around armholes and seam puckering and splitting. Fortunately research continued to improve the production process, making rayon an essential fiber that proved it could be attractive and desirable on its own or as blend with natural fibers. For quick reference, here is a summary of how rayon is made and the three methods by which cellulose is transformed into rayon yarn: VISCOSE cellulose is treated with caustic soda and carbon bisulphide, converting it into a gold liquid about the color and consistency of honey, called viscose. Viscose is forced through fine holes in end of a nozzle, called a spinnerette, directly into a chemical bath where it hardens into fine strands. When washed and bleached these strands become rayon yarn. Viscose was first introduced commercially in this country in 1911 and by 1950 accounted for 66% of US rayon production. ACETATE cellulose is combined with acetic acid [refined vinegar] making a substance called cellulose acetate. This is dissolved in acetone, then forced through the holes in a spinnerette directly into a tube. In the tube, warm air evaporates the acetone and the cellulose acetate emerges as dry filaments. Acetate was first introduced in this country on a commercial basis in 1919 and by 1950 accounted for 32% of rayon production. CUPRAMMONIUM purified cotton linters or wood pulp are treated chemically with copper ammonia which dissolves cellulose. The liquid thus obtained is pumped through the holes in a spinnerette into a solution which coagulates it into filaments. Cuprammonium was first produced commercially in this country in 1927. Filament Rayon rayon yarn, regardless of process, is produced in the form of a continuous thread and is known as filament rayon. Spun Rayon rayon can be made or cut in short lengths and are called rayon staples. They are twisted together [spun] into yarn and known as spun rayon fabrics. By 1950, 104 fabrics were available as rayon blends. That interest in vintage rayon flourishes is evidenced by collectors of vintage Hawaiian aloha shirts. Many are made of rayon and a book is being written on the history of this subject. ********** Federal Trade Commission Definition for Rayon Fiber: A manufactured fiber composed of regenerated cellulose, in which substituents have replaced not more than 15% of the hydrogens of the hydroxyl groups. http://www.ftc.gov/os/statutes/textile/textlact.htm *********** Rayon Fiber (Viscose) Rayon Staple Fiber Rayon Textile Filament Fiber Rayon Industrial Filament Fiber First U.S. Commercial Rayon Fiber Production: 1910, Avtex Fibers Inc. (Formerly FMC Corporation and American Viscose) Current U.S Rayon Fiber Producers: Acordis Cellulosic Fibers, Inc., Lenzing Fibers Corporation. Federal Trade Commission Definition for Rayon Fiber: A manufactured fiber composed of regenerated cellulose, in which substituents have replaced not more than 15% of the hydrogens of the hydroxyl groups. (Complete FTC Fiber Rules here.) http://www.ftc.gov/os/statutes/textilejump.htm Basic Principles of Rayon Fiber Production — In the production of rayon, purified cellulose is chemically converted into a soluble compound. A solution of this compound is passed through the spinneret to form soft filaments that are then converted or "regenerated" into almost pure cellulose. Because of the reconversion of the soluble compound to cellulose, rayon is referred to as a regenerated cellulose fiber. There are several types of rayon fibers in commercial use today, named according to the process by which the cellulose is converted to the soluble form and then regenerated. Rayon fibers are wet spun, which means that the filaments emerging from the spinneret pass directly into chemical baths for solidifying or regeneration. Viscose rayon is made by converting purified cellulose to xanthate, dissolving the xanthate in dilute caustic soda and then regenerating the cellulose from the product as it emerges from the spinneret. Most rayon is made by the viscose process. -------------------------------------------------------------------------------- Viscose Process Most commercial rayon manufacturing today utilizes the viscose process. This process dates to the early 1900s, with most of the growth in production occurring between 1925 and 1955. In the early period, production was mainly textile filament, although the first staple was produced in 1916. High performance rayons, such as tire cord, did not appear until the late 1930s, with the advent of hot-stretching and addition of larger amounts of zinc to the spin bath. Invention of modifiers in 1947 brought on super tire cords and marked the beginning of the high-performance rayon fibers. All of the early viscose production involved batch processing. In more recent times, processes have been modified to allow some semi-continuous production. For easier understanding, the viscose process is a batch operation. Click on each process step for a brief explanation. Cellulose Purified cellulose for rayon production usually comes from specially processed wood pulp. It is sometimes referred to as "dissolving cellulose" or "dissolving pulp" to distinguish it from lower grade pulps used for papermaking and other purposes. Dissolving cellulose is characterized by a high a -cellulose content, i.e., it is composed of long-chain molecules, relatively free from lignin and hemicelluloses, or other short-chain carbohydrates. Steeping The cellulose sheets are saturated with a solution of caustic soda (or sodium hydroxide) and allowed to steep for enough time for the caustic solution to penetrate the cellulose and convert some of it into "soda cellulose", the sodium salt of cellulose. This is necessary to facilitate controlled oxidation of the cellulose chains and the ensuing reaction to form cellulose xanthate. Pressing The soda cellulose is squeezed mechanically to remove excess caustic soda solution. Shredding The soda cellulose is mechanically shredded to increase surface area and make the cellulose easier to process. This shredded cellulose is often referred to as "white crumb". Aging The white crumb is allowed to stand in contact with the oxygen of the ambient air. Because of the high alkalinity of white crumb, the cellulose is partially oxidized and degraded to lower molecular weights. This degradation must be carefully controlled to produce chain lengths short enough to give manageable viscosities in the spinning solution, but still long enough to impart good physical properties to the fiber product. Xanthation The properly aged white crumb is placed into a churn, or other mixing vessel, and treated with gaseous carbon disulfide. The soda cellulose reacts with the CS2 to form xanthate ester groups. The carbon disulfide also reacts with the alkaline medium to form inorganic impurities which give the cellulose mixture a characteristic yellow color – and this material is referred to as "yellow crumb". Because accessibility to the CS2 is greatly restricted in the crystalline regions of the soda cellulose, the yellow crumb is essentially a block copolymer of cellulose and cellulose xanthate. Dissolving The yellow crumb is dissolved in aqueous caustic solution. The large xanthate substituents on the cellulose force the chains apart, reducing the interchain hydrogen bonds and allowing water molecules to solvate and separate the chains, leading to solution of the otherwise insoluble cellulose. Because of the blocks of un-xanthated cellulose in the crystalline regions, the yellow crumb is not completely soluble at this stage. Because the cellulose xanthate solution (or more accurately, suspension) has a very high viscosity, it has been termed "viscose". Ripening The viscose is allowed to stand for a period of time to "ripen". Two important process occur during ripening: Redistribution and loss of xanthate groups. The reversible xanthation reaction allows some of the xanthate groups to revert to cellulosic hydroxyls and free CS2. This free CS2 can then escape or react with other hydroxyl on other portions of the cellulose chain. In this way, the ordered, or crystalline, regions are gradually broken down and more complete solution is achieved. The CS2 that is lost reduces the solubility of the cellulose and facilitates regeneration of the cellulose after it is formed into a filament. Filtering The viscose is filtered to remove undissolved materials that might disrupt the spinning process or cause defects in the rayon filament. Degassing Bubbles of air entrapped in the viscose must be removed prior to extrusion or they would cause voids, or weak spots, in the fine rayon filaments. Spinning - (Wet Spinning) The viscose is forced through a spinneret, a device resembling a shower head with many small holes. Each hole produces a fine filament of viscose. As the viscose exits the spinneret, it comes in contact with a solution of sulfuric acid, sodium sulfate and, usually, Zn++ ions. Several processes occur at this point which cause the cellulose to be regenerated and precipitate from solution. Water diffuses out from the extruded viscose to increase the concentration in the filament beyond the limit of solubility. The xanthate groups form complexes with the Zn++ which draw the cellulose chains together. The acidic spin bath converts the xanthate functions into unstable xantheic acid groups, which spontaneously lose CS2 and regenerate the free hydroxyls of cellulose. (This is similar to the well-known reaction of carbonate salts with acid to form unstable carbonic acid, which loses CO2). The result is the formation of fine filaments of cellulose, or rayon. Drawing The rayon filaments are stretched while the cellulose chains are still relatively mobile. This causes the chains to stretch out and orient along the fiber axis. As the chains become more parallel, interchain hydrogen bonds form, giving the filaments the properties necessary for use as textile fibers. Washing The freshly regenerated rayon contains many salts and other water soluble impurities which need to be removed. Several different washing techniques may be used. Cutting If the rayon is to be used as staple (i.e., discreet lengths of fiber), the group of filaments (termed "tow") is passed through a rotary cutter to provide a fiber which can be processed in much the same way as cotton. -------------------------------------------------------------------------------- Other forms of regenerated cellulose fibers that are classified by the Commission as rayon without separate, distinctive names include high wet modulus rayon, cuprammonium rayon and saponified rayon. High wet modulus rayon is highly modified viscose rayon that has greater dimensional stability in washing. Cuprammonium rayon is made by converting the cellulose into a soluble compound by combining it with copper and ammonia. The solution of this material in caustic soda is passed through the spinneret and the cellulose is regenerated in the hardening baths that remove the copper and ammonia and neutralize the caustic soda. Cuprammonium rayon is usually made in fine filaments that are used in lightweight summer dresses and blouses, sometimes in Combination with cotton to make textured fabrics with clubbed, uneven surfaces. When extruded filaments of cellulose acetate are reconverted to cellulose, they are described as saponified rayon, which dyes like rayon instead of acetate. Rayon 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-thirds 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. Some Major Rayon Fiber Uses Apparel: Accessories, blouses, dresses, jackets, lingerie, linings, millinery, slacks, sportshirts, sportswear, suits, ties, work clothes Home Furnishings: Bedspreads, blankets, curtains, draperies, sheets, slipcovers, tablecloths, upholstery Industrial Uses: Industrial products, medical surgical products, nonwoven products, tire cord Other Uses: Feminine hygiene products General Rayon Fiber Care Tips — Most rayon fabrics should be dry-cleaned, but some types of fabric and garment construction are such that they can be hand or machine washed. For washable items, use the following as a guide: Fabrics containing rayon can be bleached; some finishes, however, are sensitive to chlorine bleach. Use mild lukewarm or cool suds. Gently squeeze suds through fabric and rinse in lukewarm water. Do not wring or twist the article. Smooth or shake out article and place on a non-rust hanger to dry. Rayon sweaters should be dried flat. Press the article while damp on the wrong side with the iron at a moderate setting. If finishing on the right side is required, a press cloth should be used. Between wearings, rayon articles may be pressed with a cool iron. (For specific instructions, refer to garment's sewn-in care label.) http://www.fibersource.com/f-tutor/rayon.htm 10aug02 **************** RULES AND REGULATIONS UNDER THE TEXTILE FIBER PRODUCTS IDENTIFICATION ACT 16 CFR Part 303 § 303.7 (d) Rayon. A manufactured fiber composed of regenerated cellulose, as well as manufactured fibers composed of regenerated cellulose in which substituents have replaced not more than 15 percent of the hydrogens of the hydroxyl groups. Where the fiber is composed of cellulose precipitated from an organic solution in which no substitution of the hydroxyl groups takes place and no chemical intermediates are formed, the term lyocell may be used as a generic description of the fiber. http://www.ftc.gov/os/statutes/textile/rr-textl.htm ************* Manufacturing: Synthetic and Cellulosic Fiber Formation Technology Most synthetic and cellulosic manufactured fibers are created by "extrusion" — forcing a thick, viscous liquid (about the consistency of cold honey) through the tiny holes of a device called a spinneret to form continuous filaments of semi-solid polymer. In their initial state, the fiber-forming polymers are solids and therefore must be first converted into a fluid state for extrusion. This is usually achieved by melting, if the polymers are thermoplastic synthetics (i.e., they soften and melt when heated), or by dissolving them in a suitable solvent if they are non-thermoplastic cellulosics. If they cannot be dissolved or melted directly, they must be chemically treated to form soluble or thermoplastic derivatives. Recent technologies have been developed for some specialty fibers made of polymers that do not melt, dissolve, or form appropriate derivatives. For these materials, the small fluid molecules are mixed and reacted to form the otherwise intractable polymers during the extrusion process (if you are interested in the latest information on extrusion, click here to go to the PolySort chat board on the topic). The Spinneret The spinnerets used in the production of most manufactured fibers are similar, in principle, to a bathroom shower head. A spinneret may have from one to several hundred holes. The tiny openings are very sensitive to impurities and corrosion. The liquid feeding them must be carefully filtered (not an easy task with very viscous materials) and, in some cases, the spinneret must be made from very expensive, corrosion-resistant metals. Maintenance is also critical, and spinnerets must be removed and cleaned on a regular basis to prevent clogging. As the filaments emerge from the holes in the spinneret, the liquid polymer is converted first to a rubbery state and then solidified. This process of extrusion and solidification of endless filaments is called spinning, not to be confused with the textile operation of the same name, where short pieces of staple fiber are twisted into yarn. There are four methods of spinning filaments of manufactured fibers: wet, dry, melt, and gel spinning. Wet Spinning Wet spinning is the oldest process. It is used for fiber-forming substances that have been dissolved in a solvent. The spinnerets are submerged in a chemical bath and as the filaments emerge they precipitate from solution and solidify. Because the solution is extruded directly into the precipitating liquid, this process for making fibers is called wet spinning. Acrylic, rayon, aramid, modacrylic and spandex can be produced by this process. Dry Spinning Dry spinning is also used for fiber-forming substances in solution. However, instead of precipitating the polymer by dilution or chemical reaction, solidification is achieved by evaporating the solvent in a stream of air or inert gas. The filaments do not come in contact with a precipitating liquid, eliminating the need for drying and easing solvent recovery. This process may be used for the production of acetate, triacetate, acrylic, modacrylic, PBI, spandex, and vinyon. Melt Spinning In melt spinning, the fiber-forming substance is melted for extrusion through the spinneret and then directly solidified by cooling. Nylon, olefin, polyester, saran and sulfar are produced in this manner. Melt spun fibers can be extruded from the spinneret in different cross-sectional shapes (round, trilobal, pentagonal, octagonal, and others). Trilobal-shaped fibers reflect more light and give an attractive sparkle to textiles. Pentagonal-shaped and hollow fibers, when used in carpet, show less soil and dirt. Octagonal- shaped fibers offer glitter-free effects. Hollow fibers trap air, creating insulation and provide loft characteristics equal to, or better than, down. Detailed production flowcharts: • Acrylic • Nylon (Polyamide) • Polyester Gel Spinning Gel spinning is a special process used to obtain high strength or other special fiber properties. The polymer is not in a true liquid state during extrusion. Not completely separated, as they would be in a true solution, the polymer chains are bound together at various points in liquid crystal form. This produces strong inter-chain forces in the resulting filaments that can significantly increase the tensile strength of the fibers. In addition, the liquid crystals are aligned along the fiber axis by the shear forces during extrusion. The filaments emerge with an unusually high degree of orientation relative to each other, further enhancing strength. The process can also be described as dry-wet spinning, since the filaments first pass through air and then are cooled further in a liquid bath. Some high-strength polyethylene and aramid fibers are produced by gel spinning. Stretching and Orientation While extruded fibers are solidifying, or in some cases even after they have hardened, the filaments may be drawn to impart strength. Drawing pulls the molecular chains together and orients them along the fiber axis, creating a considerably stronger yarn. http://www.fibersource.com/f-tutor/techpag.htm 10aug02 *********************