Viscose Rayon

Rayons

According to FTC (Federal trade commission):

A manufactured fiber composed of regenerated cellulose in which substituent have replaced not more than 15 % of hydrogen of hydroxyl groups

Viscose Rayon

Rayon is the oldest commercial manmade

fiber.The process of making viscose was

discovered by C.F.Cross and E.J.Bevan in 1891

It is now manufactured abundantly as its raw material is cellulose and is available in large quantities in timber and vegetable matter

Initially there were so many names of Rayon.

Viscose RayonThe viscose method is relatively

inexpensive and of particular significance in the production of nonwoven fabrics.

It is not synthetic.Its properties are more similar to cotton

and flax rather than polyester and nylon.Viscose Rayon has silk like aesthetic and

good feel.The name viscose was derived from the

word viscous, which mean liquid state of spinning solution.

Manufacturing of viscose rayonPreparation of wood pulpSteeping and pressingRecovery of Caustic sodaShreddingAgingChurning (Xanthation or Sulphidising)MixingRipeningSpinning

Preparation of Wooden pulp

Soft wood trees are usedWood is chipped into pieces about

0.9’’ X 0.5’’ X 0.25’’Chips are treated with Calcium bi sulphite

Ca(HSO3)2 for 8 -12 hoursChips are cooked with steam under

pressure for 14 hours to convert into pulp form

Pulp is washed with water to remove Calcium bi sulphite

Pulp is bleached with sodium hypo chlorite (NaOCl) solution

Pulp is converted into paper board

Steeping and pressingThe cellulose pulp sheets are steeped

in 17.5 % NaOH solution for 1-4 hoursIt is then pressed to remove excess

solutionThis process is called “ steeping”Cellulose is swollen and liquid turn

brownExcess of alkali is pressed outThis process is known as “ pressing”Moist soda cellulose mass is obtained

Recovery of caustic sodaMoist soda cellulose is allowed to

diffuse through parchment membranes to obtain pure caustic soda

Recovery of caustic soda is important for economic purpose

Used Caustic soda is concentrated and mixed with fresh caustic soda to reuse it

Empirical formulae of cellulose = (C6H10O5)n

Steeping:

(C6H10O5)n + NaOH = [C6H9O4-ONa]n

(Soda cellulose)

Xanthation:

[C6H9O4-ONa]n + nCS2 → [C6H9O4-OCS2Na]n

ShreddingThe shredding machine consists

of drum inside which high speed revolving blades with serrated edges are installed

Moist soda sheets are shredded and converted into fine crumbs

Shredding Machine

AgeingCarried out in stirring vessel

Very important for properties of fabric

Polymeric chains of cellulose are degraded in the presence of atmospheric oxygen at temp 20-25 degree centigrade

Completed in 1-2 days

ChurningStainless steel air-tight rotating drumIt can rotate at about 2 rpmSoda cellulose crumbs contain about

30% cellulose10% CS2 solution is added to soda

cellulose crumbsSoda cellulose and CS2 are churned

together to form deep orange gelatinous mass of sodium cellulose xanthate

Churning is completed after 3 hoursAfter completion of churning, sodium

cellulose xanthate is discharged

Mixing and blendingDilute NaOH soln is added in sodium cellulose

xanthate and mixing is carried out for 4-5 hours

A clear viscous liquid is obtained which is known as viscose

Viscose contains 6.5 % NaOH and 7.5 % of cellulose

Different viscose solutions obtained from different mixers are blended together along with TiO2 to balance inequalities and to obtain uniform homogeneous mixture

Uniform homogeneous mixture produces better quality of Rayon

It is filtered to remove any un dissolved particles

Air bubbles are removed

RipeningIt is very important part of

manufacturing process

The uniform homogenous viscous solution is stored in stainless steel vessel at 10-18 ◦C for 4-5 days for ripening

During ripening, first of all the viscosity of solution falls down and then again reaches to its original viscosity

When original viscosity reaches, this is the proper time to spin the solution and solution is immediately spun

SpinningA ripened viscose solution is forced to a

centrifugal pump by compressed air, which delivers it to filtering media and then glass tubing which carries a spinneret jet

The centrifugal pump delivers the viscose solution constantly and regularly

The spinneret is submerged in acid bathViscose solution comes out into acid

bath after passing through “spinneret” solidifies into filaments owing to regeneration of cellulose

Temp. of acid bath = 40~55 ⁰C

Longitudinal view

Cross sectional view

Properties of viscose rayon:

Tensile strength:The tensile strength of normal viscose rayon is 30000 – 46000 lbs per square inch.

Elongation:Normally it will elongate 17-25 % of its original length before breaking.

Elastic properties:At 2% extension it has elastic recovery of 60%

Specific gravity:1.50 to 1.52

Effect of moisture:It has moisture regain of 13%.

Effect of heat:It begins to lose strength at 150 degree centigrade and decomposes at 205 degree centigrade.

Effect of sunlight:It can withstand exposure to sunlight without discoloration.

Chemical properties:It can be attacked by oxidizing agents like hydrogen peroxide.

Effect of Acids:Can be attacked by hot dilute acids and cold concentrated acids.

Effect of alkali:It has high resistance to dilute alkali and can be attacked by strong alkalis.

Resistance to insects:Resistance to insects is good but can be attacked by silver fish.

Microorganisms:Resistance to mildews is much better than cotton.

Major uses of Rayon:

Apparel: Accessories, dresses, jackets, sport shirts, sportswear, suits, ties, work clothes etc.

Home Furnishings: Bedspreads, blankets, curtains, sheets, tablecloths.