Viscose Rayon Fiber Manufacturing Process

Introduction:

Viscose rayon can be found in cotton-like end uses as well as silk-like end uses. Viscose rayon is the oldest commercial man-made fiber. It is naturally regenerated cellulosic-based material such as wood pulp, cotton, linters. etc the degree of polymerization is 400 to 700 and the chemical structure of viscose resembles cotton to be specific cellulose.

What are the steps involved in the manufacturing of viscose rayon?

The manufacturing of viscose rayon involves the following steps, let us study them in the order they are performed:

• Steeping
• Shredding
• Aging
• Xanthation
• Ripening
• Preparation of spinning solution
• Filtration
• Spinning

The figure shows the production of Viscose rayon fiber in brief. Take a look at the detailed process:

Fig- Viscose Rayon Fiber Production

   

Steeping:

Steeping is the very first step in the manufacturing of viscose. In this process, the pulp is treated for mercerization in the presence of NaOH at the mercerizing strength. The pulp sheets are then steeped (immersed) in 18% NaOH. Alkali cellulose is generated as a product during the reaction.

Shredding:

During shredding, the alkali sheets are then, converted into a light fluffy mass with the help of a machine that consists of a pair of revolving blades rotating at a high speed in the opposite direction.

Ageing:

The crumbs obtained at the end of the shredding procedure are transferred to a steel container where they are stored under a specific temperature for 3 to 72 hours which may vary according to the catalyst and the alkali. The presence of air in the alkali reduces the chain length which in turn decreases the viscosity as it is essential to prepare the desirable spinning solution. As soon as the correct viscosity is obtained these pieces are then, transferred into a drum where it is kept in an inert atmosphere and kept at a low temperature.

Xanthation:

During the process of xantation the aged alkali cellulose crumbs are placed in vats and are allowed to react with carbon disulphide under a controlled temperature of 20-30 degree Celsius which forms cellulose xanthate.

Ripening:

In this process, the viscose is allowed to ripen for a stipulated period. During ripening, two major processes take place firstly, the xanthate groups are redistributed and then lost.  The viscosity of the solution first decreases and then rises to its original value.

Preparation of spinning solution:

The spinning solution contains the following:

• Water-69%
• Zinc sulphate-1%
• Sodium sulphate-18%
• Glucose-2%
• Sulphuric acid-10%

The sodium sulphate precipitates the dissolved sodium cellulose xanthate. The sulphuric acid converts xanthate into cellulose, carbon disulphide, and sodium sulphate. The glucose provides softness and pliability to the filaments whereas zinc sulphate helps in adding strength.

Filtration:

The viscose is filtered to remove undissolved materials that might disrupt the spinning process or cause defects in the rayon filament.

Wet Spinning:

In this process, the ripened viscose solution passes through a centrifugal pump due to pressure exerted on the solution by the compressed air. Then viscose solution is forced through a spinneret which has many fine holes with diameters ranging from 0.05- 0.1mm, as soon as a number of filaments emerge from the spinneret they are taken together to the surface of the spinning bath and then it is guided to two rollers from where they are wound on to a spindle.