Preparation and thermal conductivity of spherical graphite-filled glycerol-based thermal greases

Developing high-performance thermal greases incorporating bio-derived components is of considerable interest for reducing the interfacial thermal resistance between heat-generating components and heat sinks in electronic devices. In this study, a sustainable composite thermal grease based on bio-derived glycerol (Gly) was fabricated through a readily scalable mechanical mixing process, using spherical graphite (s-Gr) as the thermally conductive filler and tannic acid (TA), a naturally occurring polyphenol, as the interfacial modifier. The structural characteristics and microstructural morphology of the composite thermal greases were investigated by FTIR, XRD, and SEM, while the effects of filler loading and TA-mediated interfacial modification on their thermal stability and thermal transport performance were evaluated. The thermal conductivity of the unmodified s-Gr/Gly thermal greases increased monotonically with increasing filler content and reached 5.56 W m^-1 K^-1 at 75 wt% s-Gr loading. After TA modification, the thermal conductivity of the s-Gr@TA/Gly thermal grease further increased to 6.23 W m^-1 K^-1, corresponding to an enhancement of approximately 12%. This improvement is attributed to π-π interactions between the aromatic rings of TA and s-Gr, together with hydrogen bonding between the phenolic hydroxyl groups of TA and Gly. These interactions enhance filler-matrix affinity, reduce interfacial thermal resistance, and improve the dispersion of s-Gr, thereby facilitating the formation of more efficient heat-transfer pathways. This study broadens the application scope of Gly and provides a valuable reference for the development of more sustainable thermal greases.