SHAPE FORMING T
here are a number of standards relating to regulations for tyres and their electrical properties. As
is often the case with standards, their titles can be bit of a mouthful, such as the International Standard ISO 16392 Electrical resistance — Test methods to measure the electrical resistance of tyres on a test rig, or ASTM F 1971 – Standard test method for electrical resistance of tyres under load on the test bench. These requirements regulate and
ensure Electrostatic discharge (ESD) protection to remove static electricity from the surface of a tyre when it occurs at high speed and to prevent its accumulation in the long run. In some application areas, normal
tyres that are required to be anti- static are considered to be capable of safely dissipating electrical charge if the resistance measured does not exceed 1010
Ω. But there are a number of specific
cases, such as when the tyre is used in potentially explosive areas, that are strictly regulated by the ATEX Products Directive 2014/34/EU and EN 1755 – Industrial trucks – safety requirements and verification for example, which include supplementary requirements for operation in potentially explosive atmospheres. According to EN 1755, the outer material of castors and wheels should have a maximum surface resistance of 109
Ω. It is a well-known fact that most
tyre formulations contain carbon black and can easily achieve the requirements for being anti-static, but this is not the case with non- marking solid tyres. Using graphene nanotubes (also referred to single wall carbon nanotubes, SWCNTs) is an alternative solution to provide the required conductive properties as well as maintain colour and the basic formulation properties of non-marking solid tyres. It has been acknowledged by
both scientists and manufacturer communities that graphene nanotubes are one of the most advanced additives for improving almost all materials used in our daily life. When applied in rubber compounds, they enhance mechanical performance while also imparting conductivity.
Non-marking tyre
The key to achieving this previously unobtainable combination of properties is graphene nanotubes’ extremely low working dosage.
CONSISTENT CONDUCTIVITY VERSUS MECHANICAL PERFORMANCE Various types of inorganic nanofillers have proven to be an efficient way to enhance the mechanical and electrical properties of rubbers. Carbon black and silica are widely used in commercially produced rubbers, including for tyres. It is known that the shape of
the nanofiller affects the critical concentration required to create a connected network of filler (called the percolation threshold); the higher the aspect ratio of the nanoparticle, the lower the percolation threshold. That is why using 2D and 1D carbon nanofillers (i.e. graphene sheets and carbon nanotubes) in rubbers has attracted the attention of numerous
research groups in academic institutions and in industry. Graphene nanotubes are characterised by the smallest possible diameter of less than 2nm, and are of particular interest. One fairly new conductive additive
that has recently entered the polymer market is multi-wall carbon nanotubes (MWCNTs). However, MWCNTs are not able to fully meet manufacturers’
The atoms of the graphene nanotube wall are arranged in hexagons
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