Rayon

Rayon, also called viscose, is a semi-synthetic fiber made from natural sources of regenerated cellulose, such as wood and related agricultural products. It has the same molecular structure as cellulose. Many types and grades of rayon fibers and films exist. Some imitate the feel and texture of natural fibers such as silk, wool, cotton, and linen. It can be woven or knitted to make textiles for clothing and other purposes. Rayon production involves solubilizing cellulose fibers. Three common methods are as follows:

The cuprammonium process (obsolete), using ammoniacal solutions of copper salts The viscose process (most common) using alkali and carbon disulfide The Lyocell process, using amine oxide, avoids neurotoxic carbon disulfide but is more expensive

History French scientist and industrialist Hilaire de Chardonnet (1838–1924) is known as the "father of rayon" for his early development and commercialization of nitrocellulose rayon, the first commercial semi-synthetic fiber. He patented his production process in 1885. Rayon was and still is also known by the name artificial silk. In Moroccan textile crafts, rayon yarn is also known as sabra and is marketed as cactus silk. Swiss chemist Matthias Eduard Schweizer (1818–1860) discovered that cellulose dissolved in tetraamminecopper dihydroxide. Max Fremery and Johann Urban developed a method to produce carbon fibers for use in light bulbs in 1897. Improvement of cuprammonium rayon for textiles by J. P. Bemberg in 1904 made the artificial silk a product comparable to real silk. English chemist Charles Frederick Cross and his collaborators, Edward John Bevan and Clayton Beadle, patented their artificial silk in 1894. They named it "viscose" because its production involved the intermediacy of a highly viscous solution. Cross and Bevan took out British Patent No. 8,700, "Improvements in Dissolving Cellulose and Allied Compounds" in May, 1892. In 1893, they formed the Viscose Syndicate to grant licences and, in 1896, formed the British Viscoid Co. Ltd. The first commercial viscose rayon was produced by the UK company Courtaulds Fibres in November 1905. Courtaulds formed an American division, American Viscose (later known as Avtex Fibers), to produce their formulation in the US in 1910. For the next decade, American Viscose was the sole producer of rayon in the United States. By the 1920s, the United States was the largest producer of rayon in the world. By 1929, the US output of rayon was more than double that of Italy, the second largest producer. There were half a dozen US rayon companies, but American Viscose produced more than half of the total rayon output in the US. Manufacturers' search for a less environmentally-harmful process for making rayon led to the development of the Lyocell method for producing rayon. The Lyocell process was under development in the late 1970s by a team at the now defunct American Enka fibers facility near Asheville, North Carolina, with a landmark patent granted in 1979 to employees Neal E. Franks and Julianna K. Varga. In recognition of this work, the American Association of Textile Chemists and Colorists (AATCC) awarded Neal E. Franks their 2003 Henry E. Millson Award for the Invention for Lyocell. In 1966–1968, D. L. Johnson of Eastman Kodak Inc. studied NMMO solutions. In the decade 1969 to 1979, American Enka tried unsuccessfully to commercialize the process. The operating name for the fibre inside the Enka organization was "Newcell", and the development was carried through pilot plant scale before the work was stopped. The basic process of dissolving cellulose in NMMO was first described in a 1981 patent by Clarence McCorsley III for Akzona Incorporated (the holding company of Akzo). In the 1980s the patent was licensed by Akzo to Courtaulds and Lenzing. The fibre was developed by Courtaulds Fibers under the brand name "Tencel" in the 1980s. In 1982, a 100 kg/week pilot plant was built in Coventry, UK, and production was increased tenfold (to a ton/week) in 1984. In 1988, a 25 ton/week semi-commercial production line opened at the Grimsby, UK, pilot plant. The process was commercialized at Courtaulds' rayon factories at Mobile, Alabama. In January 1993, the Mobile Tencel plant reached full production levels of 20,000 tons per year, by which time Courtaulds had spent £100 million and 10 years on Tencel development. Tencel revenues for 1993 were estimated as likely to be £50 million. A second plant in Mobile was planned. By 2004, production had quadrupled to 80,000 tons. Lenzing began a pilot plant in 1990, and commercial production in 1997, with 12 metric tonnes per year made in a plant in Heiligenkreuz im Lafnitztal, Austria. When an explosion hit the plant in 2003 it was producing 20,000 tonnes/year, and planning to double capacity by the end of the year. In 2004 Lenzing was producing 40,000 tons [sic, probably metric tonnes]. In 1998, Lenzing and Courtaulds reached a patent dispute settlement. In 1998 Courtaulds was acquired by competitor Akzo Nobel, which combined the Tencel division with other fibre divisions under the Accordis banner, then sold them to private equity firm CVC Partners. In 2000, CVC sold the Tencel division to Lenzing AG, which combined it with their "Lenzing Lyocell" business, but maintained the brand name Tencel. It took over the plants in Mobile and Grimsby, and by 2015 were the largest lyocell producer at 130,000 tonnes/year.

Process

Rayon is produced by dissolving cellulose, then converting this solution back to insoluble fibrous cellulose. Various processes have been developed for this regeneration. The current industrial methods for creating rayon are the cuprammonium method, the viscose method, and the Lyocell process. The cuprammonium and viscose methods have been practiced for more than a century with the viscose method contributing most of production.

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