Through-thickness thermal conduction in glass fiber polymer–matrix composites and its enhancement by composite modification
نویسندگان
چکیده
Continuous glass fiber polymer–matrix composites are electrically insulating and used for printed wiring boards, but their thermal conductivity needs to be increased without sacrificing the electrical insulation ability. The through-thickness thermal conductivity of these epoxy–matrix composite laminates with in-plane fibers is found to be effectively modeled using the Rule of Mixtures with fibers and matrix mainly in parallel in the throughthickness direction, in contrast to the series model that is effective for previously studied carbon fiber composites. For the glass fiber composites, the through-thickness conductivity is similar to the in-plane conductivity. The conductivity for woven fiber composites is increased by up to 80 % by curing pressure increase (from 0.69 to 4.0 MPa), up to 50 % by solvent (toluene or ethanol) treatment of the prepreg for partial surface resin removal, and up to 90 % by boron nitride nanotube (BNNT) incorporation along with solvent treatment. The highest through-thickness thermal conductivity reached is 1.2 W/(m K), which is higher than those of all prior reports on glass fiber composites. The interlaminar interfaces are negligible in through-thickness thermal resistance compared to the laminae, as for previously studied carbon fiber composites. The fiber contribution dominates the lamina resistance. The fiber–fiber interface contribution to the lamina resistance decreases significantly with curing pressure increase or composite modification involving BNNT incorporation or solvent treatment of the prepreg. Introduction Polymer–matrix composites with continuous glass fibers are important for lightweight structural applications, including wind turbines, automobile body, boats, concrete structural repair, bridge decks, and oil pipelines. Due to their electrical insulation ability, they are also used for printed wiring boards and electrical insulation. However, they exhibit low thermal conductivity. Thermal conduction is important for heat dissipation, which is one of the most critical issues that limit the performance, power, and further miniaturization of microelectronics and light-emitting diodes. With the continuous fibers in the plane of the composite panel, in-plane thermal conduction is important for heat spreading, while through-thickness thermal conduction is important for heat removal, particularly when a planar heat sink is used. Increased thermal conductivity is also desired for temperature gradient reduction (hence thermal stress reduction) and thermal fatigue resistance enhancement. There is considerable prior work on increasing the thermal conductivity of polymers by using fillers in the absence of continuous fibers. These fillers include boron nitride (BN) particles [1, 2], graphite flakes [3], silicon carbide particles [2, 3], silicon nitride particles [2], alumina particles [2], and aluminum particles [4]. However, the science is quite different and little addressed when continuous fibers are present. This is because the continuous fibers are the major constituent (typically C50 vol%) in the composite and are aligned. Moreover, the continuous glass fibers are in the form of plies (laminae) and are more thermally conductive than the polymer matrix. As a result, a simple model in which the fibers are unidirectional and perfectly aligned, with no fiber–fiber contact, would point to anisotropy in the thermal conductivity, such that the & D. D. L. Chung [email protected] 1 Composite Materials Research Laboratory, University at Buffalo, State University of New York, Buffalo, NY 14260-4400, USA 123 J Mater Sci (2016) 51:3463–3480 DOI 10.1007/s10853-015-9665-x Author's personal copy
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