Using the Thermal Conductivity in the Design of Thermoplastic Composites
Scientists from Shanghai Second Polytechnic University and Dongua University, both in Shanghai, China, recently published work in the Journal of Applied Polymer Science concerning designing thermoplastic composites with improved thermal transport properties. The paper, which may be found here, characterizes the synergistic effect of alumina and graphene addition to the thermal properties, including thermal conductivity, of the thermoplastic polymer material under study.
Alumina, with a thermal conductivity of approximately 30 W/mK, is a relatively good thermal conductor compared to most ceramics. It is also chemically inert, which makes it an attractive material for thermal conductivity improvement of polymer materials. However, relatively large wt % loadings are typically needed to attain good thermal transport properties, resulting in a heavy material which may be unattractive for applications where low weight is important.
Graphene, by contrast, has an extremely high intrinsic thermal conductivity. While the initial work in Nano Letters measured a thermal conductivity of single-layer graphene approaching 5300 W/mK, most research since then has measured a considerably lower, though still extremely large, thermal conductivity ranging between 1500W/mK and 2500 W/mK. Graphene is highly sensitive to its environment owing to the sensitivity of its phonon transfer efficiency to disruption, so graphene supported on an amorphous substrate has a much lower thermal conductivity, on the order of 500 W/mK to 600 W/mK. As an allotrope of carbon with high aromaticity, graphene is fairly chemically inert. In addition to its chemical stability, it has greatly superior thermal conductivity relative to alumina, and is considerably lighter than alumina, which makes it an attractive candidate for designing thermoplastic composites with improved thermal conductivity.
Figure 1. C-Therm TCi Thermal Conductivity Analyzer.
Using a C-Therm TCi Thermal Conductivity Analyzer (Figure 1), the researchers were able to characterize their materials for thermal conductivity at a variety of graphene and alumina loadings, in addition to examining the thermal conductivity of both materials.
Figure 2. Effect of Graphene and Alumina loading on thermal conductivity of thermoplastic polymers.
One of the key results the researchers were able to obtain is shown in Figure 2. Here, improvement of thermal conductivity relative to the base polymer material is plotted for various thermoplastic composites. It can be seen that the greatest synergistic effect occurs at a loading of 64 wt% alumina, 1 wt% graphene, and the balance thermoplastic polymer. The researchers go on to detail the postulated mechanism of this synergistic effect. Graphs of thermal conductivity as a function of weight % loading of each constituent, SEM characterization data, and powder X-ray diffraction data are also presented.
For those who are interested in more information, a link to where the paper may be purchased from the Journal of Applied Polymer Science may be found here.