RAYON

any man-made textile fibre produced from the plant substance cellulose. Developed in an attempt to produce silk chemically, the fibre was originally known by such terms as artificial silk and wood silk, but in 1924 it was given the coined name rayon. An anitrocellulose type of rayon, first produced commercially in France in 1891 in the form of a nitrocellulose fibre, was later discontinued because of its high flammability. Rayon is described as a regenerated fibre because the cellulose is converted to a liquid compound and then back to cellulose in the form of fibre. The cellulose, obtained from soft woods or from the short fibres adhering to cotton seeds (linters), is chemically treated to form a solution that is forced through tiny holes in a nozzle (spinnerets). This process of forcing a solution through spinneret holes is called spinning; the same name is applied to the production of yarn by twisting together fibres that may be of natural or man-made origin. Rayon emerges in the form of filament, a fibre of great length, and is hardened by drying in air or by chemical means. The filament is sometimes cut into shorter pieces having uniform length, called staple, and twisted together to make yarn. Viscose rayon, the most widely used type, was developed in 1892. The raw material is formed into thin sheets and subjected to various treatments that produce a viscous spinning solution resembling honey in consistency and colour. Colour is frequently incorporated at the solution stage (spun-dyed), although the fibre has good affinity for dyes. Substances may also be added to the solution to decrease the normal high lustre. Most viscose rayons have strengths approaching the regular grades of nylon and have similar stretch characteristics, but they are low in elasticity except when wet. Readily penetrated by water, the fibre absorbs up to 13 percent of its weight in moisture. It swells when wet and also loses strength. Viscose decomposes at about 185 to 205 C (365 to 400 F) and is readily ignited. Exposure to sunlight gradually reduces strength but does not affect colour. Viscose can be washed in mild alkaline solutions but loses strength if subjected to harsh alkalies. Common dry-cleaning solvents are not harmful. Viscose can be produced in a variety of forms adaptable to numerous uses. Its ability to absorb moisture contributes to the comfort of the wearer of viscose clothing, and it is widely used in both outer apparel and underwear. It is also used in carpets and other home furnishings and for such industrial applications as tire cords and surgical materials. High-tenacity viscose rayons, known by such trade names as Tenasco and Cordura, have improved strength imparted by application of a high degree of stretch immediately after spinning. Cuprammonium rayon, widely known by the trademarked name Bemberg, was developed in 1890 and is made with a spinning solution produced by dissolving cellulose in an ammoniacal copper solution. The fibre, of about the same strength and performing much like viscose rayon, has a fine diameter and is the rayon most resembling silk. It can be stretched 10 to 17 percent beyond its original length when dry and 17 to 33 percent when wet. Depending upon the amount and duration of stretching, its elastic recovery ranges from 20 to 75 percent. The fibre can absorb about 12.5 percent of its weight in moisture. It burns readily and begins to decompose at about 150 C (300 F). It is somewhat more costly than viscose and is lustrous, with soft hand (properties perceived by handling) and good draping properties. It is frequently used for lightweight, sheer fabrics and for satins.