Acetate Rayon Introduction

• First prepared in 1865 by heating cotton with acetic anhydride at 130-140 degree centigrade • In 1894, Cross and Bevan developed a more practical approach, in which acetylation was carried at atmospheric pressure using sulphuric acid or zinc chloride as catalyst • Can be produced as primary acetate( cellulose triacetate) or • Secondary acetate or acetate rayon Primary acetate: Completely acetylated cellulose in which all three hydroxyl groups of glucose unit in cellulose molecules are acetylated It was obtained as tough solid It is soluble in toxic and expensive solvents like chloroform Secondary acetate: Discovered in 1906 that triacetate could be partially hydrolyzed of i.e. by removing some of acetate group of triacetate and reconverting into hydroxyl group this new material was formed by complete acetylation and subsequent partial hydrolysis and is called secondary acetate It is soluble in relatively cheap and non toxic solvent like acetone Commercializationon

• In world War 1, the usage of acetate rayon started to increase • But the commercialization started in 1921 when all technical difficulties were removed and filament yarn was being made in Britain by the name “ Celanase ” • 1934 million pound yarn was exported to USA and also at that time the problem of dyeability was solved Acetate Rayon

Trade name Manufacturer Acele du pont, USA Aceta Bayer, Germany Albuna Snia Viscose, Itlay Arnel Celanase Corp, USA Atlon Toho Rayon Co., Japan • Raw Material: • Cotton linters or wood pulp

• Chemicals: Glacial Acetic Acid Acetic Anhydride

• Catalyst: Sulphuric Acid or Zink chloride Introduction: Acetate Rayon is modified regenerated cellulose fiber Cotton linters or wood pulp sheets are used for manufacturing “Acetate Yarn” Cellulose acetate is manufactured by dissolving cellulose and then regenerating into cellulose acetate: (primary or secondary) • The two acetates are formed by following reaction: The triacetate ( Primary acetate) is soluble in

chloroform (CHCl 3) but insoluble in Acetone (CH3COCH3) the secondary acetate (Acetate Rayon) is soluble in “ Acetone” and is obtained from triacetate

Manufacturing of Acetate Rayon: Takes place in four stages;

• Acetylation process • Hydrolysis • Preparation of Dope solution • Spinning a. Acetylation process:

Purified cotton linters/ purified waste cotton/ bleached pulp sheets are fed to the reactor A mixture of acetic anhydride , glacial acetic

acid and small amount of conc. H2SO4 are added to reactor the reactor is sealed after adding the mixture of chemicals and cotton linters • A stirrer is used to mix the ingredients thoroughly • Acetylation reaction is an exothermic reaction • The heat liberated during acetylation is removed by circulating cold water through jacket fitted outside the reactor • The acetylation reaction is completed in 7-8 hrs at 25-30 degree centigrade • Triacetate is formed at this stage Hydrolysis (Partial deacetylation)

• Triacetate is stored for ageing • Acetic acid, water and sulphuric acid are added and allowed to stand for 10-20 hrs • During this period, partial conversion of acetate groups to hydroxyl groups takes place • Careful control is necessary during hydrolysis • The mixture is then diluted with water and stirred constantly • The secondary acetate separates in the form of white flakes • The water is removed and then reaction vessel is filled with fresh water • The water is changed several times to obtain all the secondary acetate formed • The white flakes are centrifuged and excess of water is removed • The flakes are then dried Preparation of dope solution:

Dried flakes are dissolved in a solvent Acetone and a viscous solution is formed this viscous solution is known as “ Dope solution” the dried acetate flakes are mixed with three times their weight of acetone in the enclosed tank provided with powerful stirrer • The acetate is dissolved slowly in the solvent • It takes about 24 hours for complete dissolution to give a thick (viscous) clear liquid • The solution is filtered. • The spinning solution contains 25-35% of secondary acetate. Spinning:

A dope is fed from the feed tank A dope is filtered through a filter to avoid trouble due to solid particles interfering with smooth flow of dope through jets A metering pump ensures a constant flow of dope to spinneret The spinneret consists of metal plate through which number of small holes are made • The number of holes in the jet determines the number of filaments in the yarn • As the dope is squeezed out of jets, it emerges in filaments form into spinning cabinet • The filaments travel vertically down towards a feed roller from which it is guided on to bobbin • A slight twist is inserted as it is taken up • Take up speed is normally between 200 and 400 meter per minute • A slight stretch is also imparted to yarn to give some degree or orientation to the molecules • The stretched yarn become stronger than unstretched yarns due to orientation of molecules • The diameter of filaments depend on following three factors: ‹ Rate at which dope is fed by pump ‹ Diameter of jets ‹ Rate of stretching filaments • The hot air at 100 ◦C is fed from the bottom of cabinet • The hot air evaporates all acetone in the dope from the jets • The acetone is withdrawn from the top of cabinet and taken away to recovery plant • The acetone air mixture is scrubbed in water towers • The efficient recovery of acetone and acetic acid is essential for economic manufacture of Acetate Rayon • Important factors in the spinning process are: ‹ Temperature ‹ Moisture Content ‹ Velocity of Air

• The filaments are collected on spinning bobbin • Filaments are available from 45-600 denier • Staple fibers are 3-20 denier and cut into 1.5’’, 2’’, 2.5’’, 3’’, 3.5’’ and 5’’ ` Acetate Fiber Blends: a. Acetate and Wool b. Acetate and Viscose Rayon Properties

Tensile strength In dry state the tenacity is 1.1-1.3 g/denier It does not lose strength as viscose does when wet; the tensile strength of acetate is 18000-22000 lb/sq inch Elongation: 23-30 % dry 35-45 % wet Elastic recovery: At 4% extension , acetate has recovery 48-65%. When stretched further , the fiber undergoes plastic flow and becomes permanently deformed and does not return to its original position Luster : Very bright Handle: Soft Drape: Very satisfactory quality Effect of Moisture: In acetate the hydroxyl groups have been replaced by acetate groups: the inherent attraction of acetate for water molecules is less than that of viscose Acetate does not absorb as much water as the rayons the standard moisture regain is 6.5% • Melting point: It is a thermoplastic material. It becomes sticky at 190 ◦C and at 205 ◦C soften enough to deform under pressure. It melts at 232 ◦C Effect of High temperature: After a week at 120 ◦C, it retains much of its original strength Effect of age: Slight decline in tensile strength over prolonged period of time Effect of sunlight: Deterioration after prolonged exposure resulting in some loss of strength . Retention of tenacity is improved by addition of certain color pigments

Effect of acids: Dilute acids does not attack acetate but fibers are damaged by strong conc. acids Effect of alkalis: Strong alkali can cause saponification: the acetate groups are replaced by hydroxyl groups and cellulose acetate is gradually changed to regenerated cellulose

Biological Resistance: Acetate is highly resistant to mildew, moulds and bacteria • Shrinkage: Acetate has good dimensional stability and retain its shape in washing and laundering

Heat Conductivity: It act as insulator

Solubility: Soluble in Acetone, Methyl Ethyl Ketone • Cleaning and washing: soaps and mild detergents can be used safely in warm water. the garments should not be rubbed vigorously and warm water must be squeezed

• Effect of strong oxidizing agent/ Bleaching: Acetate is attacked by strong oxidizing agents but not affected by normal bleaching solutions the chemical properties depend on degree to which acetate groups have replaced hydroxyl groups in cellulose molecule End uses:

Dresses and fabrics Curtains, Bed sheets Pillow covers Wedding dresses