The production of thermally conductive thermoplastic polymers with metallic or carbon fillers

Abstract

Thermal conductivity values of organic polymers are extremely low. Therefore, they are used as thermal insulating materials in many applications. In recent years, especially in electrical and electronics industry, plastic materials are used due to their corrosion resistance, ease of manufacture and low price. However, to be able to remove the heat generated by the electronic circuits, the plastic used must have a high thermal conductivity. In this project, composites were made from a polymer containing carboxylic acid groups (ethylene-metacrylic acid copolymer Surlyn®) filled with highly thermally conductive fillers such as spherical aluminum, aluminum flakes, graphite flakes or carbon fiber in different weight ratios. Alkali metal surface of aluminum gives an acid-base neutralization reaction with carboxylic acid groups of Surlyn® by forming an ionic bond and, this creates an interface with high interfacial adhesion. When graphite used as filler material with Surlyn®, the possibility of having an interaction between the filler and the polymer matrix is very low; however, when carbon fiber is used as a filler material with Surlyn®, it is expected that there is a good interaction between the filler and the polymer matrix although carbon fiber has the same structure with graphite because during manufacturing of carbon fiber, it is partially oxidized to 1,4-diketone, quinone, hydroquinone, dicarboxylic acid structures on the edge groups. In these composites, polymer matrix-filler material interfacial interaction properties were determined by scanning electron microscope. It is the objective of this work to enhance the adhesion of filler to polymer matrix by using coupling agents and surface treatment of the fillers. The increase in the thermal conductivity of the composites produced was determined by the thermal camera experiments. At the end of this study, the thermal conductivity of Surlyn® was increased from 0.24 W/m∙K to 6.8 W/m∙K by the incorporation of 40% by weight graphite.