Ammonia Mercerization

Submitted To: Dr. Ummul Khair Fatema Presented By : ID Name 2011-1-017 Shahanaz Parvin 2011-1-018 Rifat Jahan 2011-1-098 Nazmun Nahar 2011-1-128 Humayra Akhter Himu 2011-1-208 Nigar Rashida

What is MERCERIZATION? Mercerization is a pre-treatment or finishing treatment of cellulosic materials with higher concentrated Alkali (NaOH) for short period at lower temperature. Mercerization gives cotton woven cloth a silky luster, and is the foundation of many improved and beautiful finishes. Mercerization was discovered by John Mercer and the process is named after him : Mercerizing. Later Horace Lowe found that the glazing effect became even more pronounced when cold caustic soda acted on cotton under tension. He discovered the actual mercerizing process.

Objectives of mercerization To improve luster of cotton materials To increase ability to absorb dye and moisture To improve reactions with a variety of chemicals To improve dimensional stability of materials To improve strength/elongation and mechanical properties To improve smoothness To improve hand

Effect of mercerization on cotton fiber

What is AMMONIA MERCRIZATION? Ammonia Mercerization is a treatment of cotton fibre with Ammonia (NH3) produces effect similar to that obtained with caustic soda. Among various amines, the Liquid Ammonia appears to be unique in its swelling action on cellulose and its effect on crystal structure. Liquid ammonia treatment was first developed by Coats in 1960.

Why Ammonia mercerization? Liquid Ammonia treatment is a highly effective and well controlled alternative to caustic soda mercerization. Anhydrous liquid ammonia, being smaller molecule, penetrates cellulose very rapidly and complexes with hydroxyl groups of cellulose after breaking hydrogen bonds in crystalline regions and increases distance between cellulose chain in crystallites. Ammonia treatment results in a more rounded cotton fiber, which scatters light more, in turn resulting in a luster that is less bright.

Why Ammonia mercerization? ( Contd.) This processing makes the inside of the fiber swell equally. There is less fiber- swelling, therefore the fibers are more pliable, which allows them to bend and recover more easily when tension or stress is applied. The permanent-press effects are achieved without the use of cross-linking resins. The ammonia process was intended as a replacement for conventional mercerizing for both fabrics and in mercerizing sewing threads (Prograde process). The lower pH of ammonia allows safe treatment of more sensitive fibers like linen (flax) or silk.

Application on types yarns & fabrics

Sewing Thread Denim Corduroy Chambray

Pillow Material Jute Linen Cotton PET Blend Cotton Nylon Blend

Physical changes Improvement in strength. Change in cross section from bean shape to almost circular. Change in longitudinal view convoluted to cylindrical.

Cross section of cotton fiber After Mercerization After Ammonia Mercerization

CHEMICAL CHANGES Formation of cellulose-III Improvement in moisture regain properties (more hydroxyl groups) Improvement in dye uptake

Absorption of ammonia in cotton fabric 1 Cross section before mercerization 2-5 Swelling process in ammonia 6 Rinsing process after swelling 7 After state

Process parameter Concentration of Ammonia Time of treatment Tension applied Temperature Surface tension of Ammonia Impurities of Ammonia

Chemicals Ammonia Wetting agent Temperature : -33ºc Absorption period : 0.6 sec

Schematic Diagram of Ammonia Mercerizing Machine Two processes known as PROGRADE for yarn mercerizing and SANFORSET for woven and knitted fabrics are widely used. Schematic Diagram of Ammonia Mercerizing Machine

Main Parts Of Ammonia Mercerization Machine Ammonia Impregnation zone Ammonia Evaporation Zone Washing Zone

Principle Of Ammonia Mercerization Machine Process consist of passing the fabric though a bath of liquid ammonia with 100% pickup for approximately 10 seconds. Ammonia is removed with dry heat applied by passing over blanketed, steam heated dry cans which removes about 90% of the ammonia which is recovered by a recovery plant and made available for recycling. The rest of the ammonia, which chemically bonded to the cellulose, was removed by light steaming.

Diagram of the “Sanfor-set" process

Ammonia Impregnation zone The untreated fabric in dry condition, is passed over smoothing rolls and then around some heated dry cans. The dry cans assure an adequate level of dryness(water content less than 10%) in the fabric. Then the fabric is cooled by a fan before entering through a gas lock to the processing chamber . In the treatment chamber, the fabric passes over a guide roller and is directed downward and around an immersion roll disposed in the lower portion of a liquid pan, which retains liquid ammonia . The liquid ammonia bath is at a temperature of - 33° C. After passing the liquid ammonia bath, fabric is directed upward to a guide roller. The fabric web advances at a rate such that its immersion in the liquid ammonia bath may be for only a fraction of a second.

Ammonia Impregnation zone (Contd.) The atmosphere within the chamber is saturated with ammonia vapor, such that the liquid ammonia does not evaporate from the impregnated fabric emerging from the bath. The guide roll serves to smooth and apply a slight widthwise tension to the fabric before it enters the pad rollers. After having passed through the pad rollers , the fabric passes over a tension control roller ,to impart a desired amount of warpwise tension.

Ammonia Evaporation Zone The fabric passes around some guide rollers and is brought into a pressure contact with the surface of a heated dryer drum. The dryer includes a blanket which serves to both press the fabric tightly against the surface of the heated drum and to geometrically confine the fabric by frictional forces. The dryer drum typically may be heated by high temperature steam. Thus, when the fabric, saturated with liquid ammonia at -33° C, comes into contact with the heated drum surface, the ammonia is almost instantly washed off, to a level at which no further substantial reaction occurs. Thus, the reaction period is effectively terminated almost instantly upon contact of the fabric with the heated drum. In this heat treatment some 90-95% of the ammonia is removed.

Recovery of ammonia Recovery of ammonia occurs by the reaction between ammonia water and gas that is discharged. Ammonia water is to mix with air, it goes outside and is then separated through the distillation column. Ammonia is distilled then send to the storage unit finally. In the recovery device of ammonia, there are gas vents to wash the top of the tower, to control the ammonia content, and to lower than the amount for environment protection.

Comparison among different mercerization process Property Conventional Mercerization Hot Ammonia mercerization Swelling speed Low Fast Very fast Evenness Uneven Good Luster Very good Dye up take Not quite good Dimensional stability Alkaline chemical Sodium hydroxide

EFFECT OF AMMONIA MERCERIZATION More rounded yarn structure and orientation. Excellent form stability ( having good Wash & Wear properties) Low shrinkage in post washing. Increase in wrinkle resistance. Increase in fiber elasticity. Enhanced tear resistance as well as tensile strength. This process add gentle, elegant luster to the fiber. Fibers keep their soft feel as no damage is done by this processing. Highly uniform dyeing properties. Dye uptake % increased.

ADVANTAGES OF AMMONIA MERCERISATION Evenness and uniformity of swelling comparatively better. Less pollution. Jute and linen can be mercerized. Safe treatment of more sensitive fibers like flax or silk. Higher productivity. Higher quality fabric. Longer life after long periods of wear and repeated washing.

DISADVANTAGES OF AMMONIA MERCERIZATION Very costly equipments. Non-availability of machine. Lower color yield. Large capital investment for NH3 recovery. NH3 recovery problem. Leakages cause great harm to personnel working.

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