Fabric Mercerising Process

Mercerization, the treatment of cotton with a strong caustic alkaline solution in order to improve the luster, hand and other properties,was names after its discoverer, John Mercer.

Mercerization leads to a number of changes in fibre and fabric properties:

• a more circular fibre cross-section
• increased lustre
• increased tensile strength, a major factor for technical textile fabrics
• increased apparent colour depth after dyeing
• improved dyeability of immature cotton (greater uniformity of appearance)
• increase in fibre moisture regain
• increase in water sorption
• improved dimensional stability.

Types of mercerization

Mercerization is widely used, and in the mercerization of different kinds of cellulose products, including blended products, the machine used and the treatment conditions must be selected in accordance with the type of fiber, the form that it is in and its properties, and also in accordance with the aims and the timing of the mercerization.

The wide range of treatment methods can approximately be broken down into the following divisions. Parentheses denote established terminology.

1. Classification according to the form of the product

a) Yarn mercerization

• Batch : Hank mercerization
• Cheese mercerization
• Continuous : Single end mercerization
• Tow mercerization
• Warp mercerization

b) Knit Mercerization

• Open mercerization
• Closed mercerization (Round mercerization, tubular knit mercerization)

c) Cloth mercerization

• Chainless mercerization (Roller mercerization)
• Chain mercerization (Stenter mercerization)
• Batch-up mercerization

2. Classification according to the marcerizing conditions

a) Water content

• Dry mercerization
• Wet mercerization

b) Tension

• Fixed-length mercerization
• Tension mercerization
• Tensionless mercerization

c) Alkaline concentration

• Low-concentration alkaline mercerization
• High-concentration alkaline mercerization
• Two-step mercerization

d) Temperature

• Ambient-temperature mercerization
• High-temperature mercerization
• Low-temperature mercerization

3. Classification according to timing

• Gray mercerization
• Pre-dyeing mercerization
• Post-dyeing mercerization

4. Classification according to the number of treatments

• Single mercerization
• Double mercerization

5. Classification according to the type of alkali used

a. Caustic soda mercerization

b. Ammonia mercerization

Liquid ammonia treatment is a highly effective and well-controlled alternative to caustic soda mercerisation, but the high capital cost of the necessary equipment for recovery and reuse of the ammonia as well as the application step limits the adoption of this sophisticated approach more widely. The effect of liquid ammonia treatment on the dyeing of cotton depends on the way that the ammonia is removed. Aqueous washing gives a product almost as dyeable as mercerised cotton. As with mercerising, treated yarns and fabrics appear more deeply dyed than untreated material having the same amount of dye present

6. Other

a. Alkali pad-dry method
b. Alkali pad-steam method

While other variations are also used, mercerization in industry is generally implemented according to a combination of the basic factors as listed above.

Fabric Mercerising Machine
Chain Mercerizing Machines

In order to make up for the shortcomings of the roller mercerizing machine, a clip stenter is used for post-mercerization treatment, in which a widthwise tension is applied then most alkali is showered off the fabric kept on the stenter, followed by thorough alkali removal and neutralization using an open-width washing machine.

Chainless Mercerising Process

This method of mercerization running fabric through a number of rollers without the use of a clip stenter is also called roller mercerization. The machine used has a number of stainless rollers, or stainless and rubber rollers, of a relatively-large diameter tiered zigzag in close contact to each other inside a long trough, with the lower tier designed to submerge in alkaline solution for mercerization.

Cotton Fabric and Yarn mercerising process
What is mercerized cotton?
Mercerization Process Produces Quality Fabrics

Hot Mercerization
Main steps in hot mercerising process are
1. Saturation with mercerising-strength caustic soda solution at a temperature close to its boiling point
2. Controlled hot stretching for a brief dwell period
3. Controlled cooling and dilution of the caustic liquor
4. Traditional tension-controlled washing and final rinsing.
Advantages of Hot Mercerising
The main chemical and physical changes to achieve the desired improvement in fabric properties do not take place at the high temperature of the saturator but when the cooling fabric passes through the traditional caustic dilution and washing-off stages.
1. Shortening of the process sequence to provide cost savings

2. Increased efficiency and reproducibility
3. Use of chain or chainless mercerisers with fewer problems related to fabric width control
4. Improved lustre, tensile strength and dimensional stability because greater stretching of the fabric is practicable
5. Increased dye uptake at moderate tension, but excessive stretching can result in lower dyeability
6. Improved results from fabric qualities containing lower-grade cotton
7. Flash scouring effect obtained
8. Good desizing action
9. Enhanced penetration of the fibre by the hot caustic liquor.

Study of some important parameters of greig cotton after Hot mercerization
Effect of heat on mercerization
An Investigation on the Effect of Hot Mercerization on Cotton Fabrics Made up of Open-End Yarns
Effect of mercerization treatment on dimensional stability of weft knitted fabrics

Foam Mercerizing

Mercerizing strength sodium hydroxide may be foamed and this foam applied to cotton by conventional methods. Application of foamed sodium hydroxide offers the possible advantages of savings in sodium hydroxide and dyes as well as ability to treat selectively given areas of the fabric. This technology may be useful in areas other than mercerization.

The following advantages has been claimed by the experts in this area are,

1.No specialized machinery is required.

2.Less consumtion of alkali.

3.Better control of fabric dimensions

4.Preferential treatment of one face of fabric when needed.

5.Penetration of lye in pile fabrics with less lye.

6.Possibility of printing with sodium hydroxde.
7.Possibility of better coverage of dead cotton and resulting into uniform dyeing.

Slack Mercerizing :-Loose mercerizing or mercerizing without tension
Slack mercerizing is done by exhaust. The fabric is slacked and treated with NaOH solution by this process of mercerizing no  luster is obtained but absorption is increased.
Slack mercerization is different than normal mercerizimg  that it must be planned in advance and will result into a stretch fabric. Fabric to be slack mercerized  is woven with enough space left between the yarns to crimp up knowing it will be slack mercerized. Once the fabric is slack mercerized it will become tighter and narrower while at the same time giving  a permanently crimp that makes for 100% stretch cotton. It’s like giving hair a perm. It is possible to get up to 15% comfort stretch and in a twill utility stretch.

Technology highlights of Goller Mercerizing Machine

 Watch video of knit mercerizing here