Mercerisation Using Liquid Ammonia 13471c

Fabric & Garment Finishing MERCERISATION USING LIQUID AMMONIA

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Usually cotton fabric is mercerized by high concentration NaOH solution. It improves in luster, strength, dyeability, etc.

But when the fabric is washed in many times, the handling of it becomes harsh.

Introduction • The liquid ammonia treatment of natural cellulosic fibre materials was introduced in the 70s by Sanforized Company at first under the “Sanfor-Set” name, and first of all only for the final finishing of denim fabric. • Since 1984, there has been another variant of the liquid ammonia treatment, the Veramtex “Beau-Fixe” process, which is also well established in practical finishing. • Both liquid ammonia treatments are used in the finishing cycle in Europe predominantly as a pre-treatment for easy care finishes.

Difference Between Two Treatments The two ammonia treatment methods differ particularly in the method of ammonia removal following the swelling process, which has some effect on the characteristic of the treated fabric. After impregnation with liquid ammonia, with swelling medium amounts to a few seconds only (“Sanfor-Set” 4 to 8 secs, “Beau-Fixe” 10 to 20 secs ).

• In the “Sanfor-Set” process, the ammonia is largely removed dry over drying cylinders at 130 to 145 degree Celsius and by blowing out residual ammonia gas with superheated steam, approx. 0.1% or more of residual ammonia remaining in the woven fabric, and generally removed by water action prior to chemical finishing. •

With “Beau-Fixe” process, part of the ammonia is removed first by blowing out with ammonia gas to approx. 80% residual ammonia, followed by washing out with water, first cold then hot, and drying on stenters and/or perforated cages at 100 to 120 degree Celsius. Practically, no ammonia residues are present in the material after this treatment.

General Characteristics of Ammonia Mercerized Fabrics • The difference in effect as opposed to caustic mercerization is because with ammonia, 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.

• As a rule, fabric shrinkage depends on the time of exposure to the ammonia, with 80% of the shrinkage occurring in the initial 6 seconds. Very close control of final shrinkage is achieved by fabric tension in the ammonia application in combination with compressive shrinkage.

• The much smaller molecular size of ammonia allows it to penetrate completely into every fiber of the fabric, unlike caustic which causes such rapid fiber- swelling that the caustic is blocked at the surface of yarns, preventing further penetration.

• Tension control is important in both ammonia and caustic mercerization for improved fabric tenacity and elongation. Moisture regain is improved in both if tension is applied prior to fiber swelling. • In garments that are fabricated from ammonia treated-fabrics, the garment life is longer after long periods of wear and repeated washings, improving sustainability.

• Ammonia- mercerization provides a higher dry-crease recovery and higher shrinkage consistency than caustic mercerization, especially with the dry-steam method of recovery. • However, caustic mercerization still has an advantage with regard to luster and improved depth of color in dyeing, although the uniformity of dyeing after mercerization is significantly improved with ammonia. Ammonia treatment results in a more rounded cotton fiber, which scatters light more, in turn resulting in a luster that is less bright. • An additional advantage of ammonia mercerization is the absence of alkaline oxycellulose that results with caustic treatments, which is evidenced by strength-losses and dyeing variation. The lower pH of ammonia allows safe treatment of more sensitive fibers like linen (flax)or silk.

• The permanent-press effects are achieved without the use of cross-linking resins, however, the commonly-used resins are soluble in ammonia and a combination resin finish and mercerizing, plus Sanforizing can be achieved if a soluble catalyst is employed. •

Additionally, ammonia acts as a formaldehyde-scavenger and resin-treated fabrics that are ammonia treated will produce no free-formaldehyde.

• With caustic treatments of fabrics like denim, the elimination of washing required in caustic mercerization avoids the problems with removing caustic. • Mercerizers are not normally equipped with drum washers for removal of caustic from heavy cotton fabrics and contamination remains on the fabric at the time of drying which results in damage to cotton. • The use of acetic acid to neutralize creates a problem with the formation of sodium acetate , which produces a very harsh feel. • The ammonia process on denims also produces a much flatter, richer appearance and improves the performance on stretch denim improving fit.

References • http://www.ssdc-tigertex.com/home/?page_id=20 LIQUID AMMONIA -“S-finish” New Development of Cotton by the Liquid Ammonia Process • http://www.veramtex.com/wa_files/20121031144651749.pdf International Textile Bulletin Practical Aspects of the ammonia treatment of natural cellulose textiles

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• https://www.denimsandjeans.com/denim/manufacturing-process/advances-in-the-ammonia-mercerizationof-denim/3022 Advances in the Ammonia Mercerization And Finishing in Denim By Harry Mercer, March 21, 2011 Slide 7 - 11