The Ester

Acetate fibre:

Textile fibres which are composed of ester cellulose are called acetate fibres.

Acetate is a manufactured fibre in which the fibre forming substance is cellulose acetate. Where not less than 92% of the hydroxyl groups are acetylated the term tri acetated may be used as a generic description of the fibre.

The term acetate is derived from acet and ate. The former comes from acetic acid (The acid of vinegar), whilst the latter denotes a chemical salt. Acetate means a salt of acetic acid. In organic chemistry, a salt is known as an ester. As a result acetate fibres are at times referred to as cellulose ester. There are two types of acetate fibres —

I)             Acetate

II)          Triacetate

I)       Tri acetate:

 Tri acetate is a man made, natural polymer based, primary cellulose acetate filament or staple fibre. It is formed by the fully acetylation of purified cotton linters with acetic acid and anhydride. Six acetate groups are formed in each glucose unit, in six –OH groups.

n = 225

II)    Acetate:

 Acetate is a man made, natural polymer based, secondary cellulose acetate filament or staple fibre. To obtain acetate or secondary cellulose acetate fibre, triacetate is hydrolyzed, i.e. reacted with water so that only 2.3 to 2.4 acetyl groups are present per glucose unit.

n = 130

The raw materials & chemicals used in manufacturing acetate fibre:

The raw mtls and chemicals used in manufacturing acetate fibres in different stages are given:

1.      Raw mtls:

Cotton linters, wood pulp containing cellulose, acetic acid and active anhydride.

2.      Purified stage:

Sodium carbonate or caustic soda for bleaching sodium   hypochlorite.

3.      Steeping stage: Glacial acetic acid.

4.      Acetylation stage: Acetic acid, acetic anhydride, catalytic H₂SO₄.

5.      Hydrolysis: 95% acetic acid, H₂O.

6.      Precipitation: Na/Ca/Mg Acetate.

7.      dope preparation:        for acetate, 85% acetone + 15% ethanol

for triacetate, 90% methylene chloride + 10% ethanol

8.      Spinning: Acetone, methylene chloride.

Manufacturing process of acetate:

The main stages of manufacturing of acetate fibres as follows:

Purification of cellulose:

                                    The cotton linters are purified by kier boiling for 4-10 hrs with alkali solⁿ of Na₂CO₃ then they are bleached with NaOCl. Then the linters washed and dried.

Activation:

                                    In this stage, the purified cotton linters or wool pulp are steeped in glacial acetic acid (3:1) at room temperature for easy acetylation. To swell the fibre and to increase their chemical reactivity.

Acetylation:

a)      Non – solvent: Esterification is done by anhydride in presence of catalytic H₂SO₄.

b)      Solvent: The typical recipe of solvent process

-          100 lbs purified cellulose

-          300 lbs acetic anhydride

-          500 lbs glacial acetic acid

-          8-10 lbs H₂SO₄

Then the mixture is kept at a temp of 25^o-30^oC for 8-10 hrs. After acetylation a thick clear soln of primary cellulose acetate or triacetate is obtained.

Hydrolysis:

 Hydrolyse acetylated cellulose is performed by H₂O presence of 95% acetic acid, for 15-20 hrs. at a high temp of 40^o-50^oC. Thus an acetone soluble product is obtained.

Precipitation:

                                    After hydrolysis, for destroying catalytic H₂SO₄. Na/Mg/Ca acetate is added.

CH₃COONa +H₂SO4→NaSO₄ +CH₃COOH

Then dilute aqueous acetic acid is added and hence acetate is precipitated.

Washing and drying:

                                    In this step, acetate is washed and centrifuged so that the amount of water is not exceeding 20%, then dried.

Blending:

                                    Before dry spinning blending is performed —

þ  To control product quality.

þ  To decrease cost.

Dope preparation:

For acetate:— By dissolving acetate in the solvent of 85% acetone and 15% ethanol, spgⁿsolⁿ is prepared. In this time, pigment and dellustrantsetc are added.

For tri acetate: — Dope is prepared by dissolving primary cellulose acetate in 90% methylene chloride + 10% ethanol.

Spinning:

Dry spinning process is applied for acetate, tri acetate spinning Acetone and methylene chloride used as solvent.

Physical properties:

1.      Tenacity:

 Both types of acetate fibres are weak due to the amorphous nature of their polymer systems, which limits the number of inter polymer forces of attraction which can occur.

Acetate and triacetate become weaker when wet. This is because water molecules enter the amorphous regions of the fibres polymer systems. The fibre polymers move further apart, the cohesive effect of the Vander Waal’s forces is sufficiently reduced to cause a loss in tenacity of the filament or staple fibre.

Tenacity of acetate fibre 1.1-1.3 gm/den when dry and 0.65-0.75 gm/den when wet and

For triacetate fibre 1.2-1.4 gm/den when dry and 0.7-0.8 gm/den when wet.

2.      Elastic – plastic nature:

 Both acetate and triacetate are plastic because of their amorphous polymer systems.

Both acetate and triacetate fibres become more plastic when wet as sufficient water molecules can enter their amorphous polymer systems to break a significant number of inter polymer forces of attraction.

3.      Elongation:

 For acetate fibre 23-30% (standard) when dry and 35-45% when wet and

For triacetate fibre 25-30% when dry and 30-40% when wet.

4.      Hygroscopic nature:

 Despite their very amorphous polymer system, both acetate and triacetate fibres have only a fair of moisture absorbency because of the relatively low polarity of the acetate and triacetate polymers.

Standard moisture regain of acetate fibre is about 6.5% and

 For triacetate, regain before heat treatment 4.5%, after treatment 2.5-3.0%.

5.      Specific gravity:

 Specific gravity for acetate fibre is 1.30 and

 For triacetate fibre 1.32.

Thermal properties:

Acetate:         

þ  It is thermoplastic mtls.

þ  It becomes sticky at 190⁰C.

þ  It becomes soft at 205⁰C.

þ  It melts about 232⁰C.

þ  It is not readily flammable.

þ  Exposed to a naked flame cause melt and burn.

Triacetate:

þ  It is thermo plastic.

þ  Heat treatment of triacetate increases the crystallinity and molecular orientation.

þ  It’s softening point 225⁰C.

þ  Melting point 300⁰C.

þ  Triacetate melts and shrivels to a molten bad when ignition.

Chemical properties:

1.      Acid:

Acids hydrolyze both type of acetate, causing polymer degradation and resulting in weakening and eventual destruction of their textile mtls.

Dilute solutions of weak acids do not affect acetate, but the fibres are decomposes by strong acids in concentrated solution.

Triacetate is resistant to dilute acids but is attacked by strong acids in high concentration.

2.      Alkali:

Alkaline hydrolysis occurs on the surface of the filaments resulting in the yellowing of white or the dulling of colored acetate and triacetate textile mtls.

For acetate,     Alkali up to 9.5 — little effected.

                        Strong alkali — causes saponification and cell-acetate

                                                changed to regenerated cellulose.

For triacetate, dilute alkali — greater resistance

hot strong alkali — attacked and hydrolyzed.

3.      Bleaches:

Acetate is attacked by strong oxidizing agents, but is not affected by normal bleaching solutions of hypochlorite or peroxide .

Triacetate is not affected significantly by common bleaching agents including hypoclorites, chlorites, per acetic acid and hydrogen peroxide.

4.      Organic solvent:

Acetate swells or dissolves in many solvents including acetones and other Ketones, Phenol, Chloroform etc. and insoluble in petroleum chemicals.

Triacetate dissolves in Methylene chloride, Chloroform, Formic acid and swelled by Acetone, Ethylene chloride and Trichloro ethylene and not affected by Benzene, Toluene, Xylene.

5.      Color fastness:

The acetate fibres are not easy fibres to dye or print. The disperse dyes, which are the only dyes which will readilydye or print. Acetate or triacetate textile materials had to be specially developed.

6.      Light:

For acetate deterioration after prolonged exposure, resulting in some loss of strength, the color remains good. Retention of tenacity is improved by certain colored pigments.

But triacetate is highly resistant on exposure to severe outdoor weathering there is little loss in strength and no yellowing.

7.      Heat:

For acetate, after a week at 120^oC, it remains much of its original tensile strength.

In triacetate after two weeks exposure at 130^oC, triacetate retained 68% of its strength.

Biological properties:

1.      Insects:

Moths and other insects do not normally attack acetate.

Triacetate is not attacked by moths or most topical insects or larvae which commonly attack textile fibres.

2.      Micro-organisms:

Fungi and bacteria may cause surfaces damage and discoloration bet resistance is greatly high.

Triacetate is highly resistant to attack by micro-organisms.

Electrical properties:

Excellent insulator in case of acetate.        

The electrical resistance of triacetate is very high.

Difference between viscose & cell – acetate:

Viscose Rayon	Cell-acetate or Acetate rayon
1.      Tenacity- 1.5-2.4 gm/den in dry 0.7-1.2 gm/den in wet	1.      Acetate 1.1-1.3 gm/den in dry 0.65-0.75 gm/den in wet Triacetate 1.2-1.4 gm/den in dry 0.7-0.8 gm/den in wet
2.      Elongation at break 15-30% in dry 20-35% when wet	2.      25-40% in dry 30-45% when wet
3.      MR- 13%	3.      MR- 6.5%
4.      Specific gravity 1.5	4.      Specific gravity 1.30
5.      D.P. 250-300	5.      D.P. 130
6.	6.

Difference between triacetate and acetate:

	Subject		Triacetate		Acetate
	1.		Primary cellulose acetate fibre.		Secondary cellulose acetate fibre.
	2.		Triacetate is produce at first by acetylation in presence of acetic acid and catalytic H2SO4.		Acetate is formed by hydrolyzed of triacetate adding of water.
	3.		Six acetate groups (-OOCCH3) are formed in place of the six –OH groups of the cellulose unit.		Only 2.3 or 2.4 acetate groups or per glucose unit occur.
	4.
	5.		Degree of polyn, n = 225		Degree of polyn, n = 130
	6.		Triacetate is more crystalline that acetate.		Acetate is less crystalline (40%).
	7.		Triacetate polymer 240 nm long about 2.6 nm thick.		Acetate 160 nm long and 2.3 nm thick.
	8. Tenacity		1.2-1.4 when dry 0.7-0.8 when wet		1.1-1.3 when dry 0.65-0.75 when wet
	9. Elongation		25-30% when dry 30-40% when wet		25-30% when dry 35-45% when wet
	10. M.R.		Before heat treatment 4.5% After heat treatment 2.5-3.0%		6.5%
11. Specific gravity		1.32		1.30
12. Softening point		225oC		205oC
13. Melting point		300oC		232oC
Chemically:
14. Acid		Dilute acid — resistant Strong acid — attacked		Dilute acid — not affected Strong acid — decomposed
15. Alkali		Dilute alkali — greater resistance Strong alkali — attacked and hydrolyzed.		Alkali up to pH 9.5 — little affected Strong acid — causes saponification, cell acetate change to regenerated cellulose.
16. Bleaches		Not effected significantly by common bleaching agents such as hypochlorite.		Attacked by strong oxidizing agents.
17. Heat		After two weeks exposure at 130oC, triacetate remain 68% of its strength.		After a weak at 120oC it remains much of its original strength.
18. Organic solvents		Dissolved in methylene chloride, chloroform.		Swells or dissolves in chloroform acetones.
19.		Primary cellulose will remain a heat set more satisfactory than acetate.		Acetate cannot be heat set satisfactory.
20.Fabric		Fabrics are dimensional higher than acetate.
21.		Crisper hand than acetate.
22.		More expensive		Less expensive

End use of acetate fibre:

þ  Lingerie.

þ  All kinds of women dress.

þ  Gowns.

þ  Ties and underwear for men’s wear.

þ  Shirts, pajamas, socks.

þ  Sportswear

þ  Insulator for electrical wiring and coils.

þ  Household fabrics such as drapery and upholstery fabrics

End use of triacetate fibre:

þ  Many warp knitted fabrics and garments.

þ  Ladies dress goods.

þ  Blended with wool & acetate for making suiting.

þ  In staple fibre form triacetate is blended with wool nylon and viscose.

þ  Table cloths.