https://orcid.org/0000-0001-6392-7880
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ABSTRACT
A graphite-modified adhesive was developed in order to simultaneously enhance the thermal conductivity and the strength of an adhesive joint. The thermal conductivity through the joint was investigated by using highly filled PP/graphite composite substrates, which were joined with an epoxy adhesive of different layer thicknesses. Similar measurements were carried out with a constant adhesive layer thickness, whilst applying an epoxy adhesive modified with expanded graphite (EG) (6, 10, and 20 wt%). By reducing the adhesive layer thickness or modifying the adhesive with conductive fillers, a significant increase of the thermal conductivity through the joint was achieved. The examination of the mechanical properties of the modified adhesives was carried out by tensile tests (adhesive only), lap-shear tests, and fracture energy tests (mode 1) with aluminium substrates. Modification of the adhesive with EG led to an increase of the tensile lap-shear strength and the adhesive fracture energy (mode 1) of the joint. In addition, burst pressure tests were performed to determine the strength of the joint in a complex component. The strength of the joint increased with the graphite content in the PP substrate and in the epoxy adhesive.
Acknowledgements
The authors thank the German Federal Ministry of Education and Research for financial support of this work (project no. 01LY1512 and 01LY1307). We also thank our industry partners Mr. M. Jasch (Protech GmbH, Pfullingen, Germany) for designing and Mr. Dr. T. Hickmann (Eisenhuth GmbH & Co. KG, Osterode am Harz, Germany) for providing the mould for the burst pressure samples as well as Mr. A. Cohnen (Institute of Plastics Processing, RWTH Aachen, Germany) for melt compounding of the PP/graphite Timcal Timrex KS500 composites. The authors would like to thank Mr. H. Scheibner and Mrs. K. Eichhorn for mechanical tests, Mrs. K. Arnhold for TGA measurements, Mrs. Ch. Steinbach for particle size distribution measurements, Mr. B. Kretzschmar for melt compounding of the PP/EG GFG600 composites and Andreas Scholze (all from IPF Dresden) for injection moulding of the burst pressure specimens.