What is static electricity?
Dry skin, leather, fur, or human hair and also some metals like lead or aluminium tend
to give up electrons while other materials tend to become negatively charged such as wood, gold, platinum, polyurethanes, polyesters, polyolefins, polyvinyl chloride, silicones, and polytetrafluoroethylene.
Electrons are what “charge” a material and conductors allow the charges to be carried away removing the potential difference, NOT the electrons, but the difference in the number of electrons between the conductors. In other words, conductors let electrons even out so current (electrons) has no reason to flow and risk damage to sensitive parts. Insulators can build up electrons and because they are insulators, they stay there and huge potential differences can build up. One source of this build-up is caused by the mechanical moving of different materials against each other, called "triboelectric" charging. Triboelectric charging takes place when two materials come together, or rubbed together and then are separated. "Tribo" means to rub
Two differing substances in contact with each other will often generate an electric charge. Whenever two insulators have opposite charge tendencies, one tends to create a negative charge, and one tends to create a positive charge, and they are rubbed together, a sizable charge can be created.
For example, the human body will become positively charged when wearing polyester cloths also dry hair will “fly away” when combed with a plastic comb. The electrostatic charges are not stable and the attractive or repulsive forces will disappear with time. The rate of discharging depends on the material type, the humidity, and environmental and other conditions.
This process of charging is caused when one material loses electrons, thus making it more positive, and the other gains electrons, thus making it more negative. The triboelectric series (see below) is a list that ranks materials according to their propensity to gain or lose electrons. Steel is near the middle of the list and these materials do not show a strong tendency to behave either way. Note that the propensity of a material to become more positive or more negative after charging has nothing to do with the level of conductivity of the material.
Antistatic Agents
Antistatic agents are used in a wide range of applications to increase the surface conductivity of a range of materials to facilitate the dissipation of static electricity. The build-up of static electricity can cause a range of problems including, sparks with the resulting safety concerns, damage to sensitive electronic equipment, processing issues in fast-moving production processes such as textile spinning, pick up of dust and dirt particles by electrostatic attraction.
Antistatic agents can be internal where they are distributed within polymers to provide long term protection from static built up or can be applied as an external coating, in this case, the protection from static build-up is transient and will require periodic reapplication.
Antistatic agent work by increasing the electrical conductivity of the surface, this is achieved by either being conductive or by adsorbing water onto the surface, or a combination of both. The choice of antistatic agent is dependent on the application, the most effective products tend to be based on cationic materials these which work well in application requiring maximum performance, however, they can cause issues in a wide range of applications, therefore anionic and nonionic antistatic agents are widely used.
Plastics and textiles are the biggest markets for antistatic agents. They are both related to the antistatic build up in polymer substrates. Antistatic prevention in polymers is achieved by two methods or by a combination of both. One is the ability to provide an effective barrier on the polymer film, the other is to aid the dissipation of electrons.
Antistatic Agents - The Barrier Effect
Most polymers are insulators by nature, with conductivities ranging from 10-12 to 10-20 S cm-1. All electrons are localized in covalent bonds and cannot move in the bulk of the material as in metals. The electrical properties of the polymers are directly related to their chemical structure. Impurities such as ionic additives or moisture also can significantly contribute to the conductivity measured in polymers.
Lankem Antistatic Agents - The barrier effect method
Lansurf AE33 and Lansurf OA7 are recommended as surfactants that have the correct molecular size to leach slowly over time towards the polymer surface ( including PVC ).
Antistatic Agents - Charge Dissipation
As in the barrier effect, the anti-static agents migrate to the polymer or substrate surface. As the molecule is positively charged the electrons associated with static build-up can easily dissipate across the surface of the substrate. The additional effect of attracting water molecules also creates a barrier effect to help further improve the static build-up protection.
The diagram above depicts the migration of the antistatic agent to the surface that then allows the dissipation of electrons.
Lankem Antistatic Agents - Charge Dissipation method
Lanquat CAE-D is a highly effective antistatic agent it combines the conductivity of a quaternary ammonium group within the molecule with a polyether chain that increases water absorption, it is used in application requiring maximum protection from static build-up. This product is the most powerful anti-static agent for polymer films (non PVC) and high spinning textile applications.
Lansurf TA15 is a highly effective antistatic agent and although generally classed as a nonionic surfactant it also has mild cationic properties due to the nitrogen charge on the amine group. It has the advantage that is certain applications such as textile polymer processing can provide additional properties such as lubricity.
Amphokem CAB and Amphokem CAPB are effective antistatic agent, with the conductivity of a quaternary ammonium group providing effective dissipation of static electricity, these products being water-based can only be used in aqueous formulations.