Assignment on acetate fiber

Acetate Fibre :

Basically it is chemically regenerated fibre obtain from cellulose.It is also called derivative of cellulose fibre.Chemical composition of acetate contain ester group.

Chemical Structure of Acetate:

Chemical Structure of Viscose:

Manufacturing Of Acetate:

The basic raw material for acetate is cotton.After that it is treated with other chemical and TRI-Acetate is formed.Then from TRI-Acetate Di-Acetate or Acetate is form.

In this report we will discuss production of Acetate from the raw material to its finished products

Its uses Many other Interesting things.

Production Of VISCOSE:

Cellulose:

Purified cellulose for rayon production usually comes from specially processed wood pulp. It is sometimes referred to as dissolving cellulose or dissolving pulp to distinguish it from lower grade pulps used for papermaking and other purposes. Dissolving cellulose is characterized by a high a -cellulose content, i.e., it is composed of long-chain molecules, relatively free from lignin and hemicelluloses, or other short-chain carbohydrates.

Steeping:

The cellulose sheets are saturated with a solution of caustic soda (or sodium hydroxide) and allowed to steep for enough time for the caustic solution to penetrate the cellulose and convert some of it into soda cellulose , the sodium salt of cellulose. This is necessary to facilitate controlled oxidation of the cellulose chains and the ensuing reaction to form cellulose xanthate.

Pressing:

The soda cellulose is squeezed mechanically to remove excess caustic soda solution

Shredding:

The soda cellulose is mechanically shredded to increase surface area and make the cellulose easier to process.

This shredded cellulose is often referred to as white crumb

Ageing:

The white crumb is allowed to stand in contact with the oxygen of the ambient air. Because of the high alkalinity of white crumb, the cellulose is partially oxidized and degraded to lower molecular weights. This degradation must be carefully controlled to produce chain lengths short enough to give manageable viscosities in the spinning solution, but still long enough to impart good physical properties to the fibre product.

Xanthation:

The properly aged white crumb is placed into a churn, or other mixing vessel, and treated with gaseous carbon disulfide. The soda cellulose reacts with the CS2 to form xanthate ester groups. The carbon disulfide also reacts with the alkaline medium to form inorganic impurities, which give the cellulose mixture a characteristic yellow color - and this material is referred to as yellow crumb . Because accessibility to the CS2 is greatly restricted in the crystalline regions of the soda cellulose, the yellow crumb is essentially a block copolymer of cellulose and cellulose xanthate.

Dissolving:

The yellow crumb is dissolved in aqueous caustic solution. The large xanthate substituents on the cellulose force the chains apart, reducing the inter chain hydrogen bonds and allowing water molecules to solvate and separate the chains, leading to solution of the otherwise insoluble cellulose. Because of the blocks of un-xanthated cellulose in the crystalline regions, the

yellow crumb is not completely soluble at this stage. Because the cellulose xanthate solution (or more accurately, suspension) has a very high viscosity, it has been termed viscose .

Ripening:

The viscose is allowed to stand for a period of time to ripen . Two important processes occur during ripening: Redistribution and loss of xanthate groups. The reversible xanthation reaction allows some of the xanthate groups to revert to cellulosic hydroxyls and free CS2. This free CS2 can then escape or react with other hydroxyl on other portions of the cellulose chain. In this way, the ordered, or crystalline, regions are gradually broken down and more complete solution is achieved. The CS2 that is lost reduces the solubility of the cellulose and facilitates regeneration of the cellulose after it is formed into a filament.

Filtering:

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

Degassing:

Bubbles of air entrapped in the viscose must be removed prior to extrusion or they would cause voids, or weak spots, in the fine rayon filaments.

SPINNING:

The viscose is forced through a spinneret, a device resembling a showerhead with many small holes. Each hole produces a fine filament of viscose. As the viscose exits the spinneret, it comes in contact with a solution of sulphuric acid, sodium sulphate and, usually, Zn++

ions. Several processes occur at this point, which cause the cellulose to be regenerated and precipitate from solution. Water diffuses out from the extruded viscose to increase the concentration in the filament beyond the limit of solubility. The xanthate groups form complexes with the Zn++, which draw the cellulose chains together. The acidic spin bath converts the xanthate functions into unstable xantheic acid groups, which spontaneously lose CS2 and regenerate the free hydroxyls of cellulose. (This is similar to the well-known reaction of carbonate salts with acid to form unstable carbonic acid, which loses CO2). The result is the formation of fine filaments of cellulose, or rayon.

Production Of Tri-Acetate:

Cellulose sheets are steeped in acetic acid for a time to make material more reactive, after further treatment with more acetic acid, acidic anhydride is added. The mixture is stirred througly blended but no reaction take place until and unless Sulphuric acid is added . This begins a acetylation reaction. The temperature is kept low because it gives out great amount of heat. The

mixture stand for 7-8 hours until it take it on a thick gelatin like. The material form is Tri-Acetate. To produce tri-acetate fibre water is added to the solution. This precipitated out collected , washed and dried. This dissolves in methylene chlorine and small quantity of alcohol

Production Of Acetate or Di-Acetate:

The material form tri-acetate flakes are combined with water . The solution strands for 24 hours. This cause acid hydrolysis and some of acetylated hydroxyl group regain their original position back.Tri-acetate is poured into water and cellulose acetate precipitated out into chalky white flakes that are connected washed and dried. This is secondary acetate. The flakes are soluble in acetone. A common nontoxic solvent. This takes 24 hours to make the solution. This solution is extruded through spinneret into warm air that evaporated acetone.

Molecular Of Acetate or Di-Acetate:

Acetate is a polymer composed of units of cellulose acetate in which an average 2 to 2.5 of the three OH units per glucose residue have been re placed by acetyl radical CH3COO

The degree of polymerization is between 350 to 400

Microscopic properties Of Acetate or Di-Acetate:

In longitudinal view, acetate can be seen uniform In width several parallel lines to the length of fiber. The cross section of acetate shows that the fiber

are lobed in outline, with regular curves, but there are no sharps point such as sometimes appear in viscose

Physical Properties Of Acetate or Di-Acetate:

Shape And Appearance:

They have the flexibility of such products that they can be made to any length and in varity of diameters from very fine to relatively heavy fibers.

Spinnerettes can be made orifices shaped other then round, this makes possible the production of variety of different-shaped acetate.

Luster:

The luster of acetate can be controlled. Thus fiber can be obtained that are very dull, very

bright and shiny or at any stage between.

Tenacity:

Acetate has a dry tenacity of 1.2 to 1.4 grams per denier

In wet conditions it drops to 0.8 to 1.0 g/d It has low tenacity when compared to other fibers To make it more attractive other properties are

added which may outweight the low strength

Elongation And Elastic Recovery:

It has good elastic recovery If stretch more then 1 % acetate undergoes some

permanent deformation and will not return to its size back

Resiliency:

Regular acetate does not have good recovery from crushing or wrinkling.

Its resiliency is low.

Moisture Regain:

Standard moisture regain of acetate is 6.5% In saturation acetate will absorb 14% moisture.

Density:

Having density of 1.32 It is lighter then cellulose. Making it possible

Dimensional Stability:

It is comparatively resistant to shrinkage or strength , except when relaxation shrinkage might occurs because of tension applied in contrasting a fabric.

It may shrink when exposing to the high temperature.

Thermal Properties:

Regular acetate is easily soften by by temperature above 177C

The fiber melts and burns evenly forming a hard black bead ash.

It gives chemical odor or an odor similar to hot vinegar.

Because of sensitivity to high temperature the fiber should be ironed to low temperature.

Chemical Properties:

Effect of Alkalies:

Dilute alkalies have little effect on acetate or tei-acetate.

Concentrated alkali causes saponification of both and eventual lost in fiber weight and reduction in the soft hand of fabrics.

Effect Of Acids:

Concentrated acid both organic and inorganic weaken the fibers and in most instant cause complete fiber degradation.

Hot acid both diluted or concentrated may cause decomposition or at least a loss of strength.

Cold diluted weaken the fiber if exposure is prolonged.

Effect Of Organic Solvents:

Most petroleum solvents used in dry cleaning do not damage the fibers.

Solvents such as acetone , phenol , chloroform will destroy the fiber.

Trichloroethylene will swell them. One should be cautions when using finger nail

polish remover near acetate, as it often contain acetone.

Acetate should be handle carefully when removing stains, as some stain removers contain chemicals that might damage the fibers.

Effect Of Sunlight, Age, And Miscellaneous Factors:

Acetate loses strength and may develop splits after prolonged exposure to sunlight.

Over time acetate will become weaker from aging. Although storage away from sunlight and circulating air will delay the process.

Static Charges:

All acetates, both regular and tri-acetate develop static charges when air is very dry.

The fibers are poor conductors or electricity, which contributes to development of static..

Biological Properties:

Micro Organisms:

Fungi such as mildew and bacteria may discolour acetate and tri-acetate.

Some weakening of acetate may occurs but tri-acetate retain its strength.

Insects:

Moths and other household pets do not damage acetate fibers.

However, silverfish may attack any sizing on acetates or tri-acetates.

Uses And Care Of Acetate:

It is used by many designers for its outstanding drapability and its desirable hand.

Acetate can be made into fabrics of varying weight , thickness , degree of stiffness and appearance.

Because of its thermoplastic property one should make sure that laundering or dry cleaning is carried out at temperature below those that might cause damage.

Acetate fabrics should not be twisted when wet because they retain wrinkles and crease would be require considerable ironing or steam pressing.

Acetate fibers are use in various industrial applications. One of the most important use of acetate fiber as filter media for cigarettes.

Apparel- Blouses, dresses, linings, special occasion apparel, Home Fashion - Draperies, upholstery, curtains, bedspreads