Poor thermal conductivity of polymer composites has long been a deterrent to their mass use in aerospace and defense applications. New research finds that graphene embedded in polymer epoxy resins drastically improves their thermal conductivity, opening doors to their use in demanding thermal management applications.
Researchers from Tecnalia and Graphenea in Spain have carefully measured electrical and thermal conductivity of composites that include different types of graphene, such as reduced graphene oxide (rGO), graphene nanoplatelets (GNPs) and carbon nanotube buckypapers (CNT-BP). In contrast to previous work that generally involved dispersing graphene or CNTs in resins, this research employs a novel method of embedding whole sheets of graphene into the resin. Considerably higher thermal conductivity values are reported, and the complete proposed manufacturing process allows the production and processing in large batches.
Image: Improving epoxy thermal conductivity by adding graphene sheets (Bustero et al, Advanced Composites and Hybrid Materials (2020), CC BY 4.0 license)
Three different types of graphene films from three producers were tested, with results published in the journal Advanced Composites and Hybrid Materials. Graphene nanoplatelet films from Nanografi were compared to Graphenea’s thermally treated rGO and Tecnalia’s CNT-BPs. The three films were found to have different thicknesses, porosities and electrical sheet resistances, offering different interactions with polymer epoxies.
The composites were prepared by manual impregnation of the carbon films with liquid epoxy resin. In all cases the addition of the nanocarbon film to the epoxy increased thermal conductivity, with best results for GNP film at a concentration of 30% wt. With in-plane thermal conductivity of 20 W/mK, the GNP composite is comparable with nanocomposites of graphene powder dispersions and aligned GNP composites which, however, are made with processes that are difficult to scale up. The GNP film also exhibits strong thermal stability, with no weight loss up to 600 oC, although the epoxy itself starts degrading at 290 oC.
The results are promising for demanding applications such as in aerospace and defense. Introducing graphene sheets to polymer epoxies was shown to increase thermal conductivity by two orders of magnitude while also improving thermal stability.