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Antistatic Finish | Mechanism of Antistatic Finishes on Textile

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



Antistatic Finish
Antistatic finish are used for the removal in synthetic fibres 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.

There are two types of Antistatic finish
  1. Non-durable finishes
  2. Durable finishes
Explain durable and non durable finish for antistatic effects.

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
1. 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.

2. 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.

3. 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.

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
  • 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
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.

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