Finishing Processes of Woolen Fabrics and Its Blends

Finishing in textile include all the mechanical and chemical process employed to improve and modify the physical aspects of the textile material thus increasing the value of the product. These processes are done following the process of manufacturing the fabric. In this article, we are going to discuss the finishing process of wool and its blends.

Textile processing

After the production of fabric, it passes through various finishing processes most of which are independent of each other. And since all the fabrics made, need to be finished based on the order requirement there is no predefined sequence of the finishing processes.

Following are the finishing processes generally carried out in a woollen/worsted or its blended finishing department.

1. Heat setting
2. Relax scouring
3. Denier reduction
4. Zero-zero Finish
5. Singeing
6. Calendaring
7. Paper press
8. Shearing
9. Decofast

#1. Heat setting

Heat setting is a term used in the textile industry to describe a thermal process usually taking place in either a steam atmosphere or a dry heat environment. It imparts higher fabric dimensional stability with other desirable attributes like higher volume, wrinkles resistance or temperature resistance. With heat setting, there is also change in strength, softness and stretchability. Very often, heat setting is also used to improve attributes for subsequent process.

Heat setting is done in a stenter machine which is also able to carry out an application of finishing chemicals, dyeing and stretching, curing along with pigment dyeing. This process is very important for polyester or polyester blend fabrics.

2. Relax scouring

The purpose of scouring is to remove all the waxes, stains, pectin and make the textile material hydrophilic or water absorbent for further processes. For synthetic fibres the amount of impurities is very less, mostly coming from machine oil which impairs the level of dyeing and finishing. In scouring the fabric is treated with detergents and alkali (soda ash or ammonium) in controlled temperatures which are followed by the acid treatment to balance the pH of the fabric.

3. Denier reduction

This process may be referred to as the controlled degradation of fabric to enhance their appearance. The use of concentrated sodium hydroxide etches away the outer filaments of the yarns in the fabric to reduce the effective denier. Temperature, caustic percentage and process time must be closely controlled for obtaining optimum fabric results. Denier reduction is always followed after scouring, drying and heat-setting for optimum results.

4. Zero-zero finish

Zero-zero finish, also known as sanforization, is the controlled compression shrinkage of the fabric which is obtained by passing the fabric through a rubber press. The stress formed during the movement through the rubber forces the yarns closer together making the fabric thicker and heavier with improved dimensional stability. In the zero-zero machine, the fabric is pressed between a hot cylinder and a rubber unit in presence of steam resulting in fabric shrinkage.

5. Singeing

Singeing refers to the burning-off of loose fibres not firmly bound into the yarn and/or fabric structure. It is an important part of pre-treatment. If not done properly there remain unclear print patterns, melted fabric surfaces and pilling with prolonged use. In the singeing process, the fabric is passed through the burning flame at high speed. Slower speed can damage the fabric or may result in burning. Since the protruding fibres are burned off, there comes a smooth shiny finish to the fabric.

6. Calendaring

Calendaring is a finishing process producing a flat, glossy and smooth surface by passing the fabric under pressure between multiple cylinders. The number of cylinders varies but grater the heat and pressure more will be the lustre. The calendaring process also improves the opacity of the fabric with reduced thickness. It also reduces yarn slippage. The drawback of it is that the finish imparted is not permanent, although sometimes calendar rolls are used to apply some of the so-called permanent finishing.

7. Paper-press

Paper-press is a finishing process wherein the fabric is pressed between paper which results in improved lustre and finish.

8. Shearing

Shearing in textile is cutting of raised nap of a pile fabric to a uniform height to enhance the appearance of the fabric. It can also be used to create stripes and other patterns by varying surface height. It is always almost employed for worsted or woollen fabrics.

9. Decofast

In the process,  the fabric is submitted to the action of direct steam with pressure settable at different levels. The steam is removed thus setting the fabric modifications occurred during the process.

Also See: Textile Finishing processes - an introduction