Rayon

Rayon is one of the most peculiar fabrics in commercial use today. It is a commercial polymer fiber made from cellulose, more specifically wood pulp. It usually has a high luster quality giving it a bright sheen. Rayon is commonly used commercially for clothes and furnishings but also has uses in the fillings in Zippo lighters and other industrial sectors.

Common characteristics of rayon include:


 * poor durability
 * excellent comfort, with impressive absorbency and thermal retention
 * poor appearance retention due to weakness

(C6H12O6)n is the Rayon's chemistry formula.



Usually rayon is produced through wet spinning, in which the raw material, in this case wood pulp, is dissolved in chemical, spun in a chemical bath, and the fibers solidify in the bath during coagulation. Due to this form of spinning, rayon has striations, giving the cross sections an indented circular shape. This cross section becomes convenient later during dyeing because rayon has a greater surface area.



**STRUCTURE OF RAYON** The unit cell of cellulose is shown in Fig. 4.

Fig 4. Structure of unit cell of cellulose In regenerated celluloses, the unit cell structure is an allotropic modification of cellulose I, designated as cellulose II (other allotropic modifications are also known as cellulose III and cellulose IV). The structure of cellulose derivatives could be represented by a continuous range of states of local molecular order rather than definite polymorphic forms of cellulose which depend on the conditions by which the fiber is made. Rayon fiber properties will depend on: how cellulose molecules are arranged and held together; the average size and size distribution of the molecules. Many models describe ways in which the cellulose molecules may be arranged to form fiber fine structure. The most popular models of fiber fine structure are the fringed micelle and fringed fibrillar structures. Essentially, they all entail the formation of crystallites or ordered regions. The skin-core effect is very prominent in rayon fibers. Mass transfer in wet spinning is a slow process (which accounts for the skin-core effect) compared to the heat transfer in melt spinning. The skin contains numerous small crystallites and the core has fewer but larger crystallites. The skin is stronger and less extensible, compared to the core. It also swells less than the core; hence, water retention is lower in the skin than in the core although moisture regain is higher in the skin. This is explained by an increased number of hydroxyl groups available for bonding with water as a result of a larger total surface area of the numerous small crystallites.

Fig. 5: Cellulose structure When rayon fibers are worked in the wet state,the filament structure can be made to disintegrate into a fibrillar texture. The extent to which this occurs reflects the order that exists in the fiber structure, as a consequence of the way in which the cellulose molecules are brought together in spinning. Another important structural feature of rayon fiber is its cross-sectional shape. Various shapes include round, irregular, Y-shaped, E-shaped, U-shaped, T-shaped and flat.

History
For centuries, humankind relied upon various plants and animals to provide the raw materials necessary for fabrics and clothing. Rayon was the first manufactured fiber developed, it made from wood or cotton pulp and was first known as artificial silk. Georges Audemars (He is a Swiss chemist) invented the first crude artificial silk around 1855, by dipping a needle into liquid mulberry bark pulp and gummy rubber to make threads. The method was too slow to be practical. Hilaire de Charbonnet and Comte de Chardonnay (They are French chemists) patented an artificial silk that was a cellulose-based fabric known as Chardonnay silk in 1884." Pretty but very flammable, it was removed from the market. In 1894, British inventors, Charles Cross, Edward Bevan, and Clayton Beadle, patented a safe a practical method of making artificial silk that came to be known as viscose rayon. Avtex Fibers Incorporated first commercially produced artificial silk or rayon in 1910 in the United States. The term "rayon" was first used in 1924.

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.

**Environmental Concerns**
Although rayon is a natural fiber, there is large environmental concerns associated with production. First, since it is made of wood pulp, cutting down trees is obviously necessary to produce rayon. This can lead to animal endangerment and pollution. Also, the amount of acid needed to produce rayon is extreme. Organic matter, nitrates, phosphates, iron, zinc, oil, and grease are all released through the water used to make rayon. Air emissions from the factories used to make rayon include sulfur, nitrous oxides, carbon disulfide, and hydrogen sulfide is not treated correctly.

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Examples of where the use of rayon is found would be in fabrics such as velvets and taffeta.