Graphitic Carbon Powders for Polymer Applications

Abstract

Carbon is used as filler in multifunctional polymer compounds. Carbon is present in nature or can be synthetized in different forms. Due to its valency, carbon is capable of forming many allotropes. Well-known forms of carbon include diamond and graphite. In recent decades many more allotropes and forms of carbon have been discovered and researched including ball shapes such as buckminsterfullerene and sheets such as graphene. More extended structures of carbon include nanotubes, nanobuds, and nanoribbons. Other unusual forms of carbon exist at very high temperature or extreme pressures. Graphite is the most common allotrope and is characterized by good electrical, thermal, and lubricating properties. The term “graphitic carbon” includes various types of carbon powders with different levels of crystallinity like natural and synthetic graphite. Natural graphite from ore deposits occurs in three main forms: flake graphite, lump or vein graphite, and amorphous graphite. Synthetic graphite is manufactured from natural or petroleum carbon precursors in high-temperature processes that transfer amorphous carbon to carbon of higher structural order.

The electrically and thermally insulating character of most polymers can be changed by the addition of electrically and thermally conductive fillers like graphite powders. Graphitic carbon powders especially represent a valid filler solution for thermally conductive polymer compounds in the case that electrical insulation is not a prerequisite. For applications where high electrical resistivity is required, graphite can still be used at low concentration when the resulting graphite polymer composite has not percolated to the electrically conductive state but already shows significant thermal conductivity. The two-dimensional crystal structure and anisometric particle shape of graphite lead to anisotropic properties of the final polymer compound. The degree of anisotropy can be influenced by the graphite type, polymer type, and processing conditions. Graphitic carbon powders can also be used as solid lubricant, infrared shielding filler, and gas barriers to reduce the gas penetration through polymer films. Graphitic carbons have been poorly considered in the past as fillers for electrically conductive polymers due to the, compared to carbon black, higher impact on the mechanical properties of the resulting polymer compounds. However, the recent search for metal-free polymer compounds with good thermal conductivity and light weight has offered new opportunities to further exploit the potential of graphite-filled polymer composites in various applications. We will review the main properties of graphitic carbon powders, alongside with processing and properties of the resulting graphite-filled polymer composites and the related final applications as well as the mechanisms for lubrication, electrical, and thermal conduction obtained in graphite-filled polymer compounds.