Acetate.pptx

textile fibre 3rd sem textile technology

1. MAN – MADE FIBRE ACETATE RAYON

2. ACET ATE RAYON Textile fibres which are composed of ester cellulose are called “acetate fibre”. Acetate means acet (i.e. come from acetic acid) and ate (denotes a chemical salt ) so acetate means a salt of acetic acid. These are basically of two types : ACETATE : man made , secondary cellulose acetate filament. TRIACETATE: man made , primary cellulose acetate filament.

3. Manufacturing of acetate Rayon Cellulose acetate is dissolved in suitable solvent (chloroform or acetone) and spun by evaporating the solvent. Thus , while viscose and cuprammonium are regenerated cellulosic fibres, acetate rayon is regenerated modified cellulosic fibre.

4. Raw materials : Cotton linters (fibres of short length ) Wood pulp Glacial acetic acid Acetic anhydride Sulphuric acid Acetone

5. Acetylation process The pre-treated cotton linters are fed to an acetylator ( closed jacketed vessel) containing a mixture of acetic anhydride, glacial acetic acid and small amount of conc. Sulphuric acid . For every 100 kg of cotton linters , 300kg of glacial acetic acid , 500kg acetic anhydride and 8-10 kg of sulphuric acid may be used. After adding the mixture circular door at the top is sealed. A stirrer having many blades rotates to mix the ingredients. The acetylation reaction is exothermic reaction i.e. heat is liberated during acetylation which should be removed by circulating cold water through a jacket fitted to the acetylator.

6. The reaction is completed in 7-8 hrs. at 25-30 degree Celsius. Triacetate is formed in the suspension form in the aceylation mixture , which is called ” acid dope ”.

7. Hydrolysis (partial deacetylation ) The acid dope is stored in jars for ageing. Water and sulphuric acid are added and allowed to stand for 10-20 hrs. During this period, called ripening period, partial converison of acetate groups to hydroxyl groups takes place. The mixture is then diluted with water and stirred constantly when the secondary acetate separates in the form of white flakes. The flakes are allowed to settle, water is removed and the jar is filled with fresh water .

8. The flakes are placed in the centrifugal machine. When the basket revolves at a high speed, the excess of water present in the flakes is forced out of the cage through perforations. The flakes are then dried in a horizontal drier, in which hot air is forced through them.

9. Dried acetate flakes are mixed with three times their weight of acetone with powerful stirrers. The acetate dissolves slowly in the solvent. It takes about 24 hrs for complete dissolution to give a thick colored liquid, called dope. The solution is filtered and deaerated . The spinning solution contains 25 to 35% of cellulose secondary acetate.

10. Spinning process The spinning dope is spun into acetate rayon filaments on the dry spinning system, which requires hot dry air. The dope is fed from a feed tank into spinning cabinets. The dope coming out of the spinnrette travel a distance of 2-5meters vertically downward to a feed roller from where it is guided onto a bobbin at a much greater speed than that of spinning.

11. MICROSCOPIC VIEW