Highly Aligned Polyethylene Composite Films for Thermal Management


Yanfei Xu


Yanfei Xu, Jianjian Wang, James Loomis, Hadi Ghasemi, Xiaopeng Huang, Xiaobo Li, Cheng-Te Lin, and Gang Chen*

Author Affiliation: 

Department of Mechanical Engineering, Massachusetts Institute of Technology


While polymers are ubiquitous materials in modern society, low thermal conductivity values associated with bulk polymers (typically 0.1 – 0.4 W/mK) have hindered widespread development of these materials in heat transfer applications. One such solution, molecular chain alignment by mechanical drawing, has been demonstrated to greatly improve thermal properties. For example, previous reports on drawn ultra-high molecular weight polyethylene (UHMWPE) nanofibers have demonstrated thermal conductivity values greater than 100 W/mK (higher than that of most metals) [1]. High thermal conductivity in drawn fibers is attributed to polymer chain orientation along preferred direction by ultra-drawing, which improves the fiber quality toward an ‘ideal’ single crystalline fiber. Another direction commonly used to improve thermal conductivity in polymers is through the addition of filler materials – such as metals and ceramics, to create polymer-based composites. While effective, typically high filler loadings are required to achieve substantial increases in composite thermal conductivity values. Such high filler loadings have several unintended consequences. Therefore, we present a UHMWPE/graphite film with low filler loadings (<15 wt% graphite) that is achieved via mechanical drawing-induced molecular chain alignment and filler orientation. Using a combination of UHMWPE and highly thermally conductive 2D carbon fillers (exfoliated graphite or few-layer graphene), our fabrication method consists of custom extrusion, drying, and drawing platforms. This stretching results in macroscopic UHMWPE deformation and orientation of 2D filler network along the film in-plane direction to achieve higher alignment structure. The high-aspect-ratio structure of the filler material combined with draw-induced orientation of the polymer chain matrix makes for an ideal composite structure, as continuous percolation network and aligned filler particulate interfaces reduces phonon scattering sites. Structural characterization (XRD, SEM, and TEM) of these films suggests highly aligned polymer chains and crystallinity. We believe that further development of 2D graphite-based polymer composites will extend the promising potential of these versatile materials in a range of heat transfer applications. This work was supported by the U.S. Department of Energy/Office of Energy Efficiency and Renewable Energy/Office of Advanced Manufacturing Program (DOE/EERE/AMO) under award number DE-EE0005756. Reference [1] Shen, S.; Henry, A.; Tong, J.; Zheng, R.; Chen, G., Polyethylene nanofibers with very high thermal conductivities. Nat. Nanotech. 2010, 5 (4), 251-255.