What is a rayon fiber? Describe the rayon fiber production method.

What is a rayon fiber?

Rayon fiber is a regenerated natural fiber that is made from 100% cellulose. The molecular structure of the rayon fiber is the same as that of cotton and linen, except that the molecular chains are shorter and do not form as many small crystals. The many types and grades of rayon fibers can imitate the feel and texture of natural fibers such as silk, wool, cotton, and linen. Fiber is used to make textiles for clothing and other needs.

Rayon production method

For rayon production, the viscose method can use wood as a source of cellulose, whereas other routes to rayon require lignin-free cellulose as a starting material. The use of wood sources of cellulose made viscose cheaper, so it was traditionally used on a larger scale than other methods. Mineral acids such as sulfuric acid are used to make rayon fibers from ripe solutions. In this step, the xanthate groups are hydrolyzed to regenerate cellulose and carbon disulfide.

Production of the process begins with cellulose obtained from wood pulp and plant fibers. The cellulose content in the pulp should be about 87-97%.

The steps of rayon production-

1. At first, the cellulose is treated with caustic soda.

2. The treated cellulose is then pressed between rollers to remove excess liquid.

3. The pressed sheets are crumbled or shredded to produce what is known as a white crumb.

4. The white crumb is aged through exposure to oxygen. This is a depolymerization step and is avoided in the case of polynosics.

5. The aged white crumb is mixed in vats with carbon disulfide to form the xanthate. This step produces an Orange-Yellow crumb.

6. The yellow crumb is dissolved in a caustic solution to form viscose. Viscose lets it ripen, standing for a certain period of time. At this stage the molecular weight of the polymer changes.

7. After ripening, the viscose is filtered, degassed, and then extruded through a spinneret into a bath of sulfuric acid, resulting in the formation of rayon filaments. The acid is used as a regenerating agent. It converts cellulose xanthate back to cellulose. The regeneration step is fast which does not allow the correct direction of the cellulose molecules. So to delay the process of regeneration, zinc sulfate is used in the bath which converts cellulose xanthate to zinc cellulose xanthate thus providing time for proper orientation to take place before regeneration.

a. Spinning: The spinning of rayon fiber is done using a wet-spinning process. The filaments are allowed to pass through the frozen bath after coming out of the spinneret hole. Bidirectional masses are transferred.

b. Drawing: The rayon filaments are stretched, in a procedure known as drawing, to straighten out the fibers.

c. Washing: The fibers are then washed to remove any residual chemicals from them.

d. Cutting: If filament fibers are desired, then the process ends here. The filament shoots are cut while producing the main fiber shots.