Cellulosic Fibres | Chemical Technology - Chemical Engineering PDF Download

Figure M-VIII 8.1: Process flow diagram for Viscose Rayon Manufacture 

Variables in Spinning:

• Temperature and composition of bath.
• Speed of coagulation
• Length of immersion
• Speed of spinning
• Stretch imparted 

Poly Sonic FIbres(VINCEL, ZANTREL): Polysonic fibres are new kind of viscose rayon  and have uniformity, length luster and microfibrillar structure. During the process steps are taken to maintain higher degree of polymerization by reducing the severity of chemical processing. During the initial stage cellulose  sheets bathed in weaker caustic soda. Higher degree  of polymeristion ( around 500-700 against viscose rayon around 250) is achieved by precipitating the viscose gently and slowly. The fibre is much like cotton 

Acetate Rayon 

The purified cotton linters or cellulose is fed to the acetylator containing acetic anhydride and acetic acid and conc. Sulphuric acid and acelylation is carried out at 25-30oC. The reaction mixture called acid dope is allowed for ripening for about 10-20 hrs. During reopening conversion of acetate groups takes place. After reopening, the mixture is diluted with water with continuous stirring. During the process flakes acetate rayon is precipitated which is dried and send to spinning bath where dry spinning of acetate rayon takes place by dissolving in solvent and passing trough spinnerated. The solvent is evaporates by hot air. The dope coming from the spinnerate is passed downwards to feed roller and finally to bobbin where spinning is done at higher speed.

Raw Material 

Purified cotton linters, wood pulp, acetic anhydride, acetic acid and sulfuric acid. 

Process Steps 

Activation with Acetic Acid: The process involves steeping of purified cotton in acetic acid which makes. Swelling and makes cellulose more reactive  

Acetylation: The pretreated cotton with acetic acid is then acetylated with excess acetic acid, acetic anhydride, with sulphuric acid to promote the reaction.

• One part of purified cellulose
• Three part of acetic anhydride
• Five parts of acetic acid
• Sulfuric acid 0.1 part (as catalyst)
• Reaction exothermic
• Temperature 20 oC for the first hour
• 25-30oC for the next 7-8 h

Hydrolysis of Triacetate: The triacetate formed is hydrolysed to convert triacetate to diacetate. The resultant mixture is poured in water to precipitate the cellulose acetate DP 350-400 

2.35 – 2.4 acetyl groups per anhydro glucose unit.

Spinning: Secondary acetate is dissolved in acetone, fitered, dearerated and passed through spinerrate in hot air environment, which evaporates the solvent.

Economical Production

• Low cost and availability of acetic acid and acetic anhydride
• Recovery of acetic acid
• Recovery of acetone

Process flow diagram for the manufacture of acetate Rayon is given in Figure M-VIII 8.2

Properties: Tenacity 1.4 g/denser, M.P. 230oC and decompose when melted, readily soluble in acetone, methyl ethyl ketone, methyl acetate, ethyl acetone, chloroform, ethylene chloride. 

Figure M-VIII 8.2: Process flow diagram for the manufacture of Acetate rayon 

Cupraammonium Rayon: Cupraammonium rayon is made from reaction of Cellulose with copper salt and ammonia. After bleaching celullose is added in ammonical solution of copper sulphate resulting in formation of cuprammonium cellulose which is spun into water and the yarn is washed with acid to remove traces of ammonia and dried. Process flow diagram for the manufacture of cuprammoium rayon is given in Figure M-VIII 8.3. 

Figure M-VIII 8.3: Process flow diagram for the manufacture of