Rayon

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. 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. In 1893, they formed the Viscose Syndicate to grant licences and, in 1896, formed the British Viscoid Co. Ltd. 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. 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. 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. In 2004 Lenzing was producing 40,000 tons [sic, probably metric tonnes]. 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. Bernigaut's method (1884) The first rayon was made by Louis Marie Hilaire Bernigaut in 1884. Bernigaut's rayon was made of nitrocellulose produced from cellulose, where the cellulose was obtained from cotton and then reacted with a mixture of sulfuric and nitric acid. Nitration occurs as: [C6H7O2(OH)3]n + HNO3 ↔ [C6H7O2(NO3)3]n +H2O. The sulfuric acid is used take up the water formed in the reaction, leaving nitrocellulose. Tetraamminecopper(II) sulfate is also used as a solvent. Viscose method (1891) The raw material for viscose is primarily wood pulp (sometimes bamboo pulp), which is chemically converted into a soluble compound. It is then dissolved and forced through a spinneret to produce filaments, which are chemically solidified, resulting in fibers of nearly pure cellulose. Unless the chemicals are handled carefully, workers can be seriously harmed by the carbon disulfide used to manufacture most rayon. To prepare viscose, pulp is treated with aqueous sodium hydroxide (typically 16–19% by mass) to form alkali cellulose, which has the approximate formula [C6H9O4−ONa]. This material is allowed to depolymerize to an extent. The rate of depolymerization (ripening or maturing) depends on temperature and is affected by the presence of various inorganic additives, such as metal oxides and hydroxides. Air also affects the ripening process, since oxygen causes depolymerization. The alkali cellulose is then treated with carbon disulfide to form sodium cellulose xanthate: Production begins with processed cellulose obtained from wood pulp and plant fibers. The cellulose content in the pulp should be around 87–97%. The steps: "Lyocell" has become a genericized trademark, used to refer to the Lyocell process for making cellulose fibers. the Lyocell process is not widely used, because it is still more expensive than the viscose process. == Properties ==

Rayon is a versatile fiber and is widely claimed to have the same comfort properties as natural fibers, although the drape and slipperiness of rayon textiles are often more like nylon. It can imitate the feel and texture of silk, wool, cotton, and linen. The fibers are easily dyed in a wide range of colors. Rayon fabrics are soft, smooth, cool, comfortable, and highly absorbent, but they do not always insulate body heat, making them ideal for use in hot and humid climates, although also making their hand feel cool and sometimes almost slimy to the touch. The durability and appearance retention of regular viscose rayons are low, especially when wet; also, rayon has the lowest elastic recovery of any fiber. However, HWM rayon (high-wet-modulus rayon) is much stronger and exhibits higher durability and appearance retention. Recommended care for regular viscose rayon is dry-cleaning only. HWM rayon can be machine-washed. Regular rayon has lengthwise lines called striations and its cross-section is an indented circular shape. The cross-sections of HWM and cupra rayon are rounder. Filament rayon yarns vary from 80 to 980 filaments per yarn and vary in size from 40 to 5000 denier. Staple fibers range from 1.5 to 15 denier and are mechanically or chemically crimped. Rayon fibers are naturally very bright, but the addition of delustering pigments cuts down on this natural brightness. == Structural modification ==

The physical properties of rayon remained unchanged until the development of high-tenacity rayon in the 1940s. Further research and development led to high-wet-modulus rayon (HWM rayon) in the 1950s, with U.S. production starting in 1955. High-wet-modulus rayon is a modified version of viscose that is stronger when wet. It can be mercerized like cotton. HWM rayons are also known as "polynosic". Polynosic fibers are dimensionally stable and do not shrink or get pulled out of shape when wet like many rayons. They are also wear-resistant and strong while maintaining a soft, silky feel. They are sometimes identified by the trade name Modal. Modal is used alone or with other fibers (often cotton or spandex) in clothing and household items like pajamas, underwear, bathrobes, towels, and bedsheets. Modal can be tumble-dried without damage. == Producers and brand names ==

In 2018, viscose fiber production in the world was approximately 5.8 million tons, and China was the largest producer with about 65% of total global production. Trade names are used within the rayon industry to label the type of rayon in the product. Viscose rayon was first produced in Coventry, England in 1905 by Courtaulds. Bemberg is a trade name for cuprammonium rayon developed by J. P. Bemberg. Bemberg performs much like viscose but has a smaller diameter and comes closest to silk in feel. Bemberg is now only produced in Japan. Visil rayon and HOPE FR are flame retardant forms of viscose that have silica embedded in the fiber during manufacturing. North American Rayon Corporation of Tennessee produced viscose rayon until its closure in the year 2000. Indonesia is one of the largest producers of rayon in the world, and Asia Pacific Rayon (APR) of the country has an annual production capacity of 0.24 million tons. == Environmental impact ==

The biodegradability of various fibers in soil burial and sewage sludge was evaluated by Korean researchers. Rayon was found to be more biodegradable than cotton, and cotton more than acetate. The more water-repellent the rayon-based fabric, the more slowly it will decompose. Subsequent experiments have shown that wood-based fibres, like Lyocell, readily biodegrade whereas synthetic fibers such as polyester do not biodegrade at all. Silverfish—like the firebrat—can eat rayon, but damage was found to be minor, potentially due to the heavy, slick texture of the tested rayon. Another study states that "artificial silk [...] [was] readily eaten" by the grey silverfish. A 2014 ocean survey found that rayon contributed to 56.9% of the total fibers found in deep ocean areas, the rest being polyester, polyamides, acetate and acrylic. A 2016 study found a discrepancy in the ability to identify natural fibers in a marine environment via Fourier transform infrared spectroscopy. Later research of oceanic microfibers instead found cotton being the most frequent match (50% of all fibers), followed by other cellulosic fibers at 29.5% (e.g., rayon/viscose, linen, jute, kenaf, hemp, etc.). Further analysis of the specific contribution of rayon to ocean fibers was not performed due to the difficulty in distinguishing between natural and man-made cellulosic fibers using FTIR spectra. For several years, there have been concerns about links between rayon manufacturers and deforestation. As a result of these concerns, FSC and PEFC came on the same platform with CanopyPlanet to focus on these issues. CanopyPlanet subsequently started publishing a yearly Hot Button report, which puts all the man-made cellulosics manufacturers globally on the same scoring platform. The scoring from the 2020 report scores all such manufacturers on a scale of 35, the highest scores having been achieved by Birla Cellulose (33) and Lenzing (30.5). == Health issues ==

The most common rayon production method, the viscose process, uses carbon disulfide, which is highly toxic. It is well documented to have seriously harmed the health of rayon workers in developed countries, and emissions may also harm the health of people living near rayon plants Rates of disability in modern factories (mainly in China, Indonesia, and India) are unknown. about 250 g of carbon disulfide is emitted per kilogram of rayon produced. Control technologies have enabled improved collection of carbon disulfide and reuse of it, resulting in a lower emissions of carbon disulfide. Nazis used forced labour to produce rayon across occupied Europe. In the 1990s, viscose rayon producers faced lawsuits for negligent environmental pollution. Emissions abatement technologies had been consistently used. Carbon-bed recovery, for instance, which reduces emissions by about 90%, was used in Europe, but not in the US, by Courtaulds. Pollution control and worker safety started to become cost-limiting factors in production. Japan has reduced carbon disulfide emissions per kilogram of viscose rayon produced (by about 16% per year), but in other rayon-producing countries, including China, emissions are uncontrolled. Rayon production is steady or decreasing except in China, where it is increasing, Rayon production has largely moved to the developing world, especially China, Indonesia and India. Rates of disability in these factories are unknown, and concerns for worker safety continue. == Related materials ==

Related materials are not regenerated cellulose, but esters of cellulose. Nitrocellulose is a derivative of cellulose that is soluble in organic solvents. It is mainly used as an explosive or as a lacquer. Many early plastics, including celluloid, were made from nitrocellulose. Cellulose acetate shares many traits with viscose rayon and was formerly considered the same textile. However, rayon resists heat, while acetate is prone to melting. Acetate must be laundered with care either by hand-washing or dry cleaning, and acetate garments disintegrate when heated in a tumble dryer. The two fabrics are now required to be listed distinctly on US garment labels. Cellophane is generally made by the viscose process, but dried into sheets instead of fibers. == See also ==