Synergistic enhancement of thermal conductivity in polymer composites filled with self-hybrid expanded graphite fillers

• Hybrid of differently sized fillers induced a synergistic enhancement in properties.
• The size of expanded graphite was controlled using a high-speed crusher.
• Synergistic enhancement in thermal conductivity of composite was found by self-hybrid.
• Construction of thermally conductive pathways was the most important physical factor.
• X-ray computed tomography was suitable for evaluation of the conductive pathways.

The size of expanded graphite (EG) was controlled using a high-speed crusher because a hybrid of differently sized fillers can induce a synergistic enhancement of the thermal conductivity in polymer composites. We found that the thermal conductivity of a polymer composite filled with both 10 wt% EG and 10 wt% high-speed crusher treated EG (wEG) was synergistically improved by 12.0 and 20.7% compared to that of polymer composites filled with 20 wt% EG and 20 wt% wEG alone, respectively. A three-dimensional (3D) non-destructive analysis using X-ray micro-computed tomography (micro-CT) was applied to explain the synergistic enhancement and to identify the dispersion and 3D network of EG fillers in the composites accurately. According to the non-destructive analysis results, the synergistic enhancement was caused by the formation of efficient thermally conductive pathways due to the hybrid of the differently sized EG and wEG fillers.

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