Monday, November 6, 2017

Objects and Classification of Textile Finishes

Textile finishing:
In textile manufacturing, any operation for improving the appearance or usefulness of a fabric after it leaves the loom or knitting machine can be considered a finishing step. It improves the look, performance, or "hand" (feel) of the finish textile or clothing. Finishing is the last step in fabric manufacturing and is when the final fabric properties are developed. Finishing is mostly done in fabric form rather than in yarn form.

A fabric's finish can be either chemicals that change the fabric's aesthetic and/or physical properties or changes in texture or surface characteristics brought about by physically manipulating the fabric with mechanical devices; it can also be a combination of the two.

Textile finishing treatment
Fig: Textile finishing treatment
Textile finishing gives a textile its final commercial character with regard to appearance, shine, handle, drape, fullness, usability, etc. Nearly all textiles are finished. When finishing takes place in a wet state, it is called wet finishing, and while finishing in a dry state, it is called dry finishing. The finishing auxiliaries are applied using finishing machines, padders or mangles with one- or two-sided action or by impregnation or exhaustion. Altering the composition, rheology and viscosity of the finish applied can vary effects.

Objects of textile finishing:
The object of finishing is to improve the attractiveness and/or serviceability of fabric. There is a wide variation of techniques among different fabrics and different production units. In fact, many of them are trade secrets; that is why many details have not been published. There are actually very few published works available except about functional finishes, for which specific chemicals serve specific functions.

The variations of finishing depend on the following factors:
  • The type of fiber and its arrangement in yarn and fabric
  • The physical properties of fibers such as swelling capacity and behavior when pressure or friction is applied
  • The capacity of fibers to absorb chemicals.
  • The susceptibility of the materials to chemical modification.
  • The most important factor, the desirable properties of the material during its use.
Classification of finishes:
The finishing processes may be broadly classified into two groups:
  1. Physical or mechanical finishes
  2. Chemical finishes
The physical or mechanical processes encompass simple processes like drying on a steam-heated cylinder to various type of calenders, raising for soft effects on the surface of the fabric and breaking the finishing of filled goods for comfortable feel.

Most of the mechanical finishes are known from ancient times and few changes have occurred in their method of operations. Some physical properties, such as dimensional stability, can be improved with chemical finishing.

Mechanical finishing or ‘dry finishing’ uses mainly physical (especially mechanical) means to change fabric properties and usually alters the fabric's appearance as well. The mechanical finishes include calendering, emerising, compressive shrinkage, raising, brushing and shearing or cropping. The mechanical finishes for wool fabrics are milling, pressing and setting with crabbing and decatising. Mechanical finishing also encompasses thermal processes such as heat setting (i.e., thermal finishing). Mechanical finishing is considered a dry operation even though moisture and chemicals are often needed to successfully process the fabric.

Chemical finishing or ‘wet finishing’ involves the addition of chemicals to textiles to achieve a desired result. In chemical finishing, water is used as the medium for applying the chemicals. Heat is used to drive off the water and to activate the chemicals. The chemical methods have changed with time remarkably, and the newer finishes have been developed continually. Many chemical methods are combined with mechanical methods, such as calendering, to improve the effect. Typically, the appearance of the textile is unchanged after chemical finishing.

Some finishes combine mechanical processes along with the application of chemicals. Some mechanical finishes need an application of chemicals; for example, milling agents are needed for the fulling process or reductive and fixation agents for shrink proofing wool fabrics. On the other hand, chemical finishing is impossible without mechanical assistance, such as fabric transport and product application. The assignment to mechanical or chemical finishing depends on the circumstance; that is, whether the major component of the fabric's improvement step is more mechanical or chemical.

Mechanical devices are used in both categories; the major distinction between the two is what caused the desired fabric change, the chemical or the machine?

Another method of classification is to classify finishes as temporary and permanent finishes. In fact, no finish stands permanently till the material is serviceable, hence a more accurate classification would be temporary or durable.

Some of the temporary finishes are:
  • Mechanical: calender, schreinering, embossing, glazing, breaking, stretching, etc.
  • Filling: starch, china clay and other mineral fillers
  • Surface application: oil, different softeners and other finishing agents.
Some of the durable finishes are:
  • Mechanical: compressive shrinkage, milling of wool, raising and cutting processes, permanent setting, etc.
  • Deposition: synthetic resins—both internal and external, rubber latex, laminating, etc.
  • Chemical: mercerisation, perchmentising, cross-linking agents, water repellent finish, fire-resistant and fireproofing finishes, shrinkproofing of wool, etc.

It should be noted that any such classification is arbitrary. Accurate classification is difficult because durability depends on several factors. Durability can be varied, and it is not possible to draw any borderline between temporary and durable finishes.

References:

  1. https://en.wikipedia.org/wiki/Finishing_(textiles)
  2. http://textilelearner.blogspot.com/2011/03/description-of-textile-finishing_1796.html
  3. Chemical Finishing of Textiles by W D Schindler & P J Hauser
  4. Principles of Textile
  5. Finishing by Asim Kumar Roy Choudhury
  6. Chemistry and Technology of Fabric Preparation and Finishing by Dr. Charles Tomasino