Antistatic Finishes in Textile: Mechanism and Importance

Last Updated on 03/05/2021

Antistatic Finishes in Textile: Mechanism and Importance

Anju Singh
M.Sc. in Fabric and Apparel Science
Delhi University, India
Email: anjusingh292@gmail.com

Antistatic Finishes
Antistatic finish is used for the removal in synthetic fibers of the unwanted effects of electrostatic charge produced during production and wear of fabrics and knits. Electrostatic charge causes an undesirable adhesive power and a resultant shabbiness. It is applied by means of an anti-static chemical treatment, the effect of which may be temporary or permanent.

antistatic finished fabric — Fig: Antistatic finished fabric

Why Antistatic Finish is Essential?
The garments made purely from hydrophobic fibers such as polyester, have tendency to develop static charge, resulting in clinging of garments to the wearer’s body and / or annoying crackling sound while wearing on or taking off a garment. Static electricity can cause many processing problems for textile materials, especially those made from hydrophobic synthetic fibers. Antistatic finishes are applied as an effective antistatic agent on the surface of the fiber and to the surface with which frictional contact is causing the potential charge accumulation.

The tendency to accumulate static charge can be decreased by increasing the fabric conductivity and / or reducing the frictional forces by applying suitable lubricating agents. The hygroscopic finishes can be used to increase the fabric conductivity. Some examples of non-durable antistatic finishes include polyethylene glycol and polyethylene oxide compounds.

Some polyamines may be reacted with polyglycols for durable hydrophilic finishing of textiles. Deposition of carbon or metallic (e. g. nano-silver) coatings may also result in increased fabric conductivity and reduced static charge accumulation.

Fig: Problems of static electricity on fabric

Static electricity appears at many stages of textile production and during wear, namely, use of textile products. The problem of static electricity is observed in fibers that contain very low humidity; thus, it is often observed in hydrophobic synthetic fibers, for example, polyester, polyamide and polyacrylic fibers. Natural fibers can develop static charging in overdried state, for example, at the outlet of a tenter, and in an environment with low humidity, for example, in winter.

During yarn production, static electricity on filament yarns leads to repulsion of filaments and ballooning of the yarn. Thus, appropriate preparation steps are added during fiber production to reduce the static electricity.

Static charges on fabrics can make handling difficult and can also lead to clinging of garment, which results in reduced wear comfort and aesthetic appearance.

Even small electric shocks can result from the development of static charge. At the end of continuous textile drying machines where the fabric is transported over a longer distance without direct contact to any metal part e.g. tenter driers, the dried material exhibits high static charging at the outlet.

Static charge also contributes to an enhanced adsorption of dust and soil from air. A serious problem of static electricity arises from clothing worn in workshops for electronic equipment. Through ongoing miniaturisation, the electrical power required to damage an integrated circuit or a device has decreased. In medical devices static charge can lead to malfunction and related risk of failure.

Types of Antistatic Finishes:
There are two types of Anti-static finish

Non-durable finishes
Durable finishes

Explain durable and non durable finish for antistatic effects.

1. Non-durable finishes
Non- durable antistatic agents are preferred for fiber and yarn processing finishes since ease of removal is important. Other important requirements of spin finish and fiber lubricants are heat resistance and oil solubility. This group of mostly hygroscopic materials includes surfactants, organic salts, glycols, polyethylene glycols, polyelectrolyte, quaternary ammonium salts with fatty alkyl chains, polyethylene oxide compounds and esters of salts of alkyl phosphonium acids. The general requirements for non durable antistats are:

Low volatility
Low flammability
Non yellowing (heat stable)
Non corrosive
Low foaming

a. Esters of phosphoric acid form the largest group of non-durable antistats.

The alkyl groups are usually derived from fatty acids. Ethoxylated fatty alcohols are also used to form the esters. The durability of these phosphoric acid esters increases with molecular size.

b. Quaternary ammonium compounds are the next largest group of non durable antistats. The most widely used are ditallowdimethylammonium chloride and dehydrogenated tallowdimethylammonium chloride.

These are common ingredients in laundry and dryer applied consumer softeners. Like many other cationic antistats have an affinity for textile fibers and can be applied by exhaustion processes.

c. The last group of non-durable antistats is composed of non-ionic compounds such as ethoxylated fatty esters, alcohol and alkyl amines. Mixtures of cationic and non-ionic surfactants demonstrate synergistic antistatic properties. Non ionic materials provide increased moisture absorption and the cationic products provide the mobile counter ions.

2. Durable antistats
Obtaining antistatic properties that are durable to repeated launderings from a single finish application is difficult to achieve.

The basic principle is to form a cross linked polymer network containing hydrophilic groups. Typically, polyamines are reacted with polyglycols to make such structures. These polymers can be formed prior to application to fabrics, or they can be formed in situ on the fiber surface after pad application.
A variety of cross linking approaches can be used. One based on polyepoxides is shown below.

Fig: Crosslinking of polyamines to form durable antistats

The amount of hydrophilic character in the final polymer can be varied to meet individual requirements. The larger the hydrophilic portions, the more moisture are absorbed and the greater the antistatic effects obtained.
However, at high levels of absorbed moisture, the polymer surface film softens and is more easily removed by abrasion during laundering. Higher degrees of cross linking will reduce the moisture absorption and subsequent swelling, but the antistatic effectiveness decreases.
Additional difficulties with cross linked hydrophilic polymers include interferences with soil release and soil redeposition properties.
Owing to the difficulties in achieving the perfect balance of desired properties, the use of durable antistatic finishes is limited.
Other wash-fast antistatic agents are described in the literature, including polyhydroxypolyamines (PHPA) or polyalkylene and polyacrylic copolymers.

Mechanism of Antistatic Finishes on Fabric:
In garment antistatic properties often are developed by using appropriate finishing techniques. By the addition of chemicals, a layer of material is deposited on the electrically insulating fiber, which then exhibits substantial electrical conductivity to permit rapid neutralisation of static electricity.

The major principle is based on the deposition of hygroscopic substances that adsorb sufficient amounts of water to form a conductive layer. As a result these types of anti static finishes will depend on the sorption of water and thus on the climatic conditions near the sample.

The principle mechanisms of antistatic finishes are increasing the conductivity of fiber surface (equivalent to lowering the surface resistivity) and reducing frictional forces through lubrication. The surface resistivity is defined as a ‘material property of a substance whose numerical value is equal to the ratio of the voltage gradient to the current density. The resistivity is in effect the resistance of the fiber to electrical flow. Increasing conductivity produces a lower charge buildup and a more rapid dissipation while increased lubricity decreases the initial charge buildup.

Antistatic agents that increase fiber surface conductivity form an intermediate layer on the surface. This layer is typically hygroscopic. The increased moisture content leads to higher conductivity. The presence of mobile ions on the surface is very important for increased conductivity. The effectiveness of hygroscopic antistatic finishes depends greatly on the humidity of the surrounding air during actual use; lower humidity leads to lower conductivity (higher resistance) and greater problems with static electricity.

Most non-polymeric antistatic finishes are also surfactants that can orient themselves in specific ways at fiber surfaces. The hydrophobic structure parts of the molecule acts as lubricants to reduce charge buildup. This is particularly true with cationic antistatic surfactants that align with the hydrophobic group away from the fiber surface, similar to cationic softeners. The main antistatic effect from anionic and non ionic surfactants is increased conductivity from mobile ions and the hydration layer that surrounds the hydrophilic portion of the molecule since the surface orientation for these materials places the hydrated layer at the air interface.

References:

Chemical finishing of textiles by W. D. Schindler and P. J. Hauser
Textile Chemistry by Thomas Bechtold, Tung Pham
Textile Engineering-An Introduction Edited by Yasir Nawab

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Mazharul Islam Kiron

Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.