The principal mechanisms of antistatic finishes are increasing the conductivity of the fiber surface (equivalent to lowering the surface resistivity ) and reducing frictional forces through lubrication. The surface resistivity is defined (AATCC TM 76) as a ¡®material property of a substance whose numericalvalue is equal to the ratio of the voltage gradient to the current density¡±. The resistivity is in effect the resistance of the fiber to the 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 act 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 tivity from mobile molecule since the surface orientation for these materials places the hydrated layer at the air interface.