Static electricity is electricity at rest and is built up when materials contact and then separate allowing for a transfer of electrons resulting in an unequal electron balance creating negative or positive charged items, this electron transfer is activated by frictional forces. Electricity generated in this manner is known as triboelectricity. It is static because it remains on the surface of insulative materials as they do not possess the property to conduct the electrical charge throughout the structure, resulting in the charge remaining static on the surface.
The way different materials behave is due to their properties, the Triboelectric series is a prediction of how materials will react based on these properties, ie which are more reactive and whether they become positive or negatively charged, the further apart in the series materials are listed illustrates that a greater charge will be created on their interaction.
Triboelectric series" />
Figure 1. Triboelectric Series
The Triboelectric series is useful in predicting results from material interactions, however this is a generalisation and a range of variable factors will ultimately influence the charge generated, such as;
· Area of contact
· Speed of separation
· Materials chemistry
From the Triboelectric series it is demonstrated that human skin is most likely to loose electrons, becoming positively charged, whereas materials such as polyester, polyurethane, polypropylene, PVC and Teflon, tend to gain electrons and become negatively charged. Therefore when synthetic fibres are worn in close to skin applications static electricity occurs, the amount of charge generated depends on variables such as the materials properties, mechanics of contact, surface contact and Relative humidity?.
Whereas static electricity in clothing applications can be troublesome for the wearer, the consequences are generally within the guidelines for safe working, in such applications anti-static finishes can be implemented to minimise the problem.
In Textile processing static electricity becomes more problematic, as materials are often processed at high speeds and contact with materials that create triboelectricity, which in insulating materials can result in a static charge remaining on the surface, which can result in an electrostatic discharge. As well as a possible safety risks for workers, charged surfaces can also attract and hold foreign matter that causes a contamination risk during process affecting the quality of the end product.
The Human body is the biggest generator of triboelectricity, when this electrostatic is then discharged a small shock can be experienced, but this mostly only causes mild discomfort, however in certain environments this electrostatic discharge can pose health and safety risks and the malfunction of electronic equipment. In areas where flammable of volatile liquids or gases are processed an electrostatic discharge can trigger fire or explosion. In areas where sensitive electronic equipment is manufactured or stored an electrostatic discharge can cause malfunction, which is costly, because of these risks controlling Electro Static Discharge ?is of high priority to many industries. Therefore means of controlling electrostatic discharge are implemented, and due to the human body being a main factor in its generation, clothing and accessories such as wrist straps are implemented in controlling it. Many environments requires workers to wear personal protective clothing with anti-static properties and these usually work by dissipating the charge, ie, not allowing it to sit static on the surface, this is done through the introduction of conductive materials which allow for flow through of the charge, often allowing it to flow into the ground.