Graphite as an effective solid lubricant for PS

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Graphite as an effective solid lubricant for PS

Replacing metals with plastics is a smart idea. Offering benefits including lighter weight, improved durability, reduced corrosion, design flexibility, and very often a lower overall production cost. However, to provide a real alternative to metals, polymers typically need to be compounded with suitable functional additives that allow them to fulfill the requirements of each application.

Graphite is a emerging as a potential multi-functional filler due to a novel combination of properties such as electrical and thermal conductivity, lubricity, low density, and chemical inertness. Moreover, graphite is available in large quantities and at relatively low prices compared to other functional fillers such as carbon nanotubes, carbon fibres, molybdenum disulphide or boron nitride.

Graphic can for example increase the thermal conductivity of polymers by two orders of magnitude, allowing the production of plastics heat sinks for applications such as LEDs or geothermal heat exchange pipes.

Graphite powders have also been used for many years as a solid lubricant in self-lubricating polymer formulations, either alone or in combination with other fillers such as molybdenum disulphide, PTFE, carbon fibres or glass fibres.

High loading levels (more than 30%wt) of graphite are typically necessary to achieve the desired properties. The effect of graphite type, particle size and loading level on tribological properties of polystyrene has been recently investigated and it has been determined that good results could be obtained using Timrex KS44 primary synthetic graphite at a 30% loading level. Other investigation have indicated that the special high aspect ratio C-Therm graphite can impart high thermal conductivity to polymer compounds at much lower loading levels compared to alternatives such as KS44 graphite. The results of this research show that the special C-Therm high conductivity graphite outperformed synthetic KS44 graphite.

Thermal conductivity and structure play an important part in tribological modification.

R.Gilardi, D. Bonacchi, M.E.Spahr: “Graphitic carbon powders for polymer application”, Springer Verlag(2016)