Lecture 6
Acetate and Triacetate Fiber
Md. Shahabul Hossen
Lecturer,
Department of Textile Engineering
Mawlana Bhashani Science and Technology University
Cellulose derivatives
Cellulose derivatives are cellulose whose reactive hydroxyl
groups are chemically modified by various reactions
Classification of cellulose derivatives: Chemical structures:
Modified cellulosic fiber: Triacetate and Acetate Fiber
Federal Trade Commission Definition for
➢ Acetate and triacetate are manufactured/regenerated fibers
which are belong to modified cellulosic fibers. Acetate Fiber: A manufactured fiber in
➢ In this cellulosic fibers the main component is cellulose which the fiber forming substance
acetate.
➢ The fiber in which at least 92% acetate group is contained is is cellulose acetate, where not less than 92%
called Triacetate or primary acetate fiber. of the hydroxyl groups are acetylated, the
➢ On the other hand which contain at least 76% acetate group is
called di-acetate or acetate or secondary acetate . term triacetate may be used as a generic
description of the fiber.
Cotton Tri-Acetate
Cellulose Structure
Tri-acetate Fiber
Triacetate is known as a generic description or primary acetate containing no hydroxyl group. Tri
acetate is a man made, natural polymer based, primary cellulose acetate filament or staple fiber. It is
formed by the fully acetylation of purified cotton linters with acetic acid and acetic anhydride. Each
cellobiose unit generates six acetate groups in the place of six -OH groups.
Tri-Acetate
Cotton
Acetate Fiber
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 (reaction with water to
produce acetate or secondary cellulose acetate fiber).
Acetate
Tri-Acetate
Flow Chart of Acetate Fiber Manufacturing Process
Purification of Cellulose
↓
Activation
↓
Acetylation
↓
Hydrolysis (For acetate fiber)
↓
Precipitation
↓
Washing & Drying
↓
Blending
↓
Dope Preparation
↓
Dry Spinning
Flow Chart of Acetate Fiber Manufacturing Process
The major stages involves in the manufacturing process of acetate fibers are-
Cellulose Purification: Cotton linters are purified by kier boiling for 4-10 hours with an alkali solution of
sodium carbonate (Na2CO3) or caustic soda NaOH, followed by bleaching with sodium hypochlorite (NaOCl).
Following that, the linters were cleaned and dried.
Activation: Purified cotton linters or wood pulps are steeped in glacial acetic acid (CH3COOH) (3:1) at room
temperature to facilitate acetylation. It helps in swelling the fiber and boosting its chemical reactivity.
Flow Chart of Acetate Fiber Manufacturing Process
Acetylation (For triacetate): The swollen cellulose is loaded with an excess glacial acetic acid and
acetic anhydride into a closed vessel fitted with a powerful stirrer. These are thoroughly mixed together
and the mixture has the following weight ratio:
▪ Purified linters/ wood pulp/ cellulose – 1 parts
▪ Acetic anhydride – 3 parts
▪ Glacial acetic acid – 5 parts
Flow Chart of Acetate Fiber Manufacturing Process
Acetylation(Con’d): When the mixing has been accomplished, a small quantity (0.1 part) of H2SO4
dissolved in a glacial acetic acid is added. The acid reacts with the acetic anhydride to form sulpho-
acetic acid (C2H4O5S), which is the real acetylating agent. The acetylation of the cellulose now
proceeds. The reaction is exothermic, it is desired to keep the temperature low in order to avoid
unwanted degradation of cellulose. So the acetylation vessel has to be cooled. For the first
hour, the reaction temperature is kept below 200C and for next 7-8 hour at 25-300C. The mass
becomes gelatinous and very viscose. At the end of 8 hour all cellulose becomes cellulose triacetate.
Cotton Tri-Acetate
Flow Chart of Acetate Fiber Manufacturing Process
Hydrolysis (For Acetate): Hydrolyze acetylated cellulose is performed by H2O presence of
95% acetic acid, for 15-20 hrs at high temp of 40°-50° C. During this time, partial hydrolysis
of the cellulose triacetate takes place, some of the acetyl groups being removed and hydroxyl
groups formed again. Thus an acetone soluble product is obtained.
Flow Chart of Acetate Fiber Manufacturing Process
Precipitation: After hydrolysis, Na/Mg/Ca acetate is added for destroying catalytic H2SO4.
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.
• To control product quality.
• To decrease cost.
Flow Chart of Acetate Fiber Manufacturing Process
Dope Preparation ( Solution preparation for spinning):
For acetate = 85% (CH3COCH3) acetone +15% (CH3CH2OH) ethanol.
For triacetate = 90% (CH3Cl) methylene chloride + 10% (CH3CH2OH) ethanol.
Flow Chart of Acetate Fiber Manufacturing Process
Spinning: Dry spinning process is applied for acetate and acetone is used as solvent. The spinning
process consists of forcing the solution through spinneret into a chamber through which a counter
current of hot air flows. The solvent evaporates and is recovered and a secondary cellulose acetate
filament collected from the bottom of the chamber.
Dry spinning process is applied for
acetate and triacetate fiber spinning
