Mercerization using Ammonia:

In this process cotton is treated with ammonia (NH3) to get similar effect as obtain using higher concentration of sodium hydroxide. The use of ammonia in mercerization has been known since the 1930’s and was developed commercially for fabric processing around 1970 in what was originally known as the Tedesco process, which was subsequently acquired by the Sanforized company and made well-known as the Sanfor-Set®process. Similar to mercerization process (using caustic soda), it also act as a swelling agent for  cotton and also bring changes in crystalline structure of cotton. Liquid ammonia penetrate cotton (Cellulose) very rapidly and form a complex with the hydroxyl group after breaking the hydrogen bonds in the crystalline and semi crystalline region. As ammonia molecule is very small it allows it to penetrate completely into every fiber of the fabric/yarn, unlike caustic which causes such rapid fiber swelling that the caustic is blocked at the surface of yarns, preventing further penetration. The surface tension of ammonia used in the mercerizing process is much lower than caustic soda cocentration (using mercerization). The lower surface tension overcomes the enormous resistance of air trapped in the fabric which is a characteristic of heavy cotton fabrics. Additionally, at normal mercerization concentrations of caustic (23%), sodium hydroxide forms a hepta-hydrate with water (NaOH·7H₂O), which results in a slow-moving, bulky group.

In the process of ammonia mercerization, the Cellulose I (native cellulose) is converted into ammonia cellulose complex, then to Cellulose III on heating and removal of ammonia. The main difference between Cellulose II (Obtain in caustic mercerization) and Cellulose III is that the cellulose III is recovered into Cellulose I, while Cellulose II could not be reconverted besides minor changes in the spacing and angle between crystalline lattices. The transition from Cellulose II to Cellulose I is possible through the application of water and heat, steam or by prolonged soaking in water at ambient conditions. 

Ammonia mercerization can be carried out on yarn as well as on fabric, which are discuss below:

Treatment of cotton yarn with ammonia:

Under this cotton yarns are first moist (30% moisture regain) and continuously treated in a liquid ammonia bath at -35oC (approximately 0.7 second contact time), then enter into hot water bath (95 degree C, 0.1 sec contact),  where it is stretched 10-30%. Subsequently, the yarn is would on a spool and dried continuously with hot water.

Treatment of cotton fabric with ammonia:

 Ammonia treatment is carried out in three steps as given below:

i) Padding fabric, ii) Tension control and iii) Removal of ammonia

In this dry fabric is impregnating for around 10 second in liquid ammonia bath to 100% wet pick up using padding mangle. After exposer, fabric is immediately dried using indirect steam under tension. As the removal of ammonia from the fabric is extremely sensitive to the applied tension, it is necessary to run over blanket. The small amount (5-10%) residual ammonia present in the fabric after drying is removed by steaming. The ammonia vapours are recovered, liquified and reuse.