Regenerated Cellulose Fibers (Viscose Rayon)
Properties
Regenerated Cellulose or Rayon is made from purified cellulose, primarily from wood pulp, which is chemically converted into cellulose acetate to make the fiber soluble in solvents. It is the oldes manmade fiber. Because Rayon is manufactured from naturally occurring polymers, it is sometimes called a semi-synthetic fiber. Specific types of rayon include Viscose, Modal and Lyocell, and Bamberg, each of which differs in manufacturing process and properties of the finished product.
Different processes exist to convert the fiber to Rayon. In the case saponified cellulose acetate, the cellulose is first treated with glacial acetic acid to make the cellulose more reactive. Next, it is acetylated with an excess of glacial acetic acid and acetic anhydride with sulphuric acid to promote the reaction. The cellulose acetate is then de-acetylated by sodium hydroxide saponification under controlled conditions. This process was developed by Celanese who called the fiber “Fortisan”. Today, the generic term of this fiber is Rayon. The product is a true regenerated cellulose filament. Usually, only a portion of the hydrogen of the cellulose hydroxyl groups have been replaced with substituents. For this reason, it has good water absorbancy.
In the case of viscose Rayon, the cellulose is reacted with sodium hydroxide to form alkali celulose, which, in turn, is reacted with carbon disulfide (CS2) to convert it to cellulose xanthate. It is then dissolved in dilute sodium hydroxide and then extruded through spinnerets into an acid bath (wet spinning). The fibers generic name is Viscose Rayon. Usually, not more than 15 percent of the hydrogen of the cellulose hydroxyl groups have been replaced with substituents. For this reason, the fiber has excellent water absorbancy.
Bamberg or Cuprammonium Rayon is another important Rayon fiber. It is manufactured by dissolving cellulose in cupric ammonium hydroxide (ammonical copper oxide solution) and then extruding it in an acid bath to coagulate the fiber. The fiber is sometimes called Bamberg silk because of its similar properties. It is a less costly alternative to silk.
Rayon fibers have outstanding strength, low elongation and good water absorbancy and find many industrial uses where these three properties are required.
| Tensile Strength (Tenacity) | Fair (Regular) Good - Excellent (HWMR) |
| Abrasion Resistance | Fair - Good |
| Absorbency | Excellent |
| Static Resistance | Excellent |
| Heat Resistance | Good |
| Wrinkle Resistance | Poor |
| Resistance to Sunlight | Fair - Good |
| Elasticity |
Poor (Regular) Good (HWMR) |
| Flame Resistance | Burns Rapidly |
| Resilience | Poor |
HWMR = high wet-modulus Rayon
COMMERCIAL Viscose Rayon Fibers
There are two types of Rayon commercially available; these are viscose and high wet-modulus Rayon (HWMR). Major manufacturers of these fibers include Ashi-Kasei, Viscocel, and Lenzing.
Applications
Rayon fibers find many industrial applications. Major uses include apparel, upholstery, tire cords, hoses, surgical materials, feminine hygiene products, and linings for a variety of products.