Properties of Cuprammonium Rayon :
1. Produce a soft silk like handle.
2. Have same properties as cotton except the average DP is lower, and a larger part of this fiber is occupied by amorphous region.
3. It burns rapidly and chars at 180 deg C.
4. On ignition, it leaves behind ash containing copper.
Production of Cuprammonium Rayon :
It is produced by making cellulose a soluble compound by combining it with copper and ammonia. The solution of this material in caustic soda is passed through the spinneret and cellulose is regenerated in the hardening baths that remove the copper and ammonia and neutralize the caustic soda.
The reactions involved are as follows :NaOH (aq) + CuSO4 (aq) → Cu(OH)2 (s) + Na2SO4 (aq)
Cu(OH)2 (aq) → Cu2+ (aq) + 2 OH− (aq)
n Cu2+ (aq) + (cellulose)n + 2n OH− → (CuC6H8O5)n + 2n H2O
Acetate Rayon :
If the cellulose is treated with acetic acid under certain conditions the free hydroxyl groups of cellulose are converted into ester groups.
Alcohol + Acid -------- Ester
Raw Material :
Cotton linters and wood pulp are the most common employed raw materials for the manufacture of acetate rayon.
Production Process of Acetate Fiber :
Acetate fiber is produced by reacting high purity wood pulp with acetic anhydride. The acetate flakes that are produced through this chemical reaction are dissolved in a solvent, filtered, and adjusted to obtain spinning stock solution. The spinning stock solution is extruded through controlled nozzles with extremely small pore diameters ranging from 30 to 50μm. The solvent is then evaporated, and the yarns are formed. The cross section of acetate fiber is called a “chrysanthemum,” and is shaped uniquely with many lobes. After the spinning stock has been extruded through the pores, it takes on a round-shaped cross section.
However, rapid evaporation of the solvent from the surface results in the formation if a skin layer on the surface of the fiber. After that, evaporation of the solvent from the inside of the fiber causes the skin layer to cave in toward the fiber cross-section, giving rise to the final multi-location cross-section.
To be continue......