Highly thermal and electrical conductive composites with connected filler networks : preparation, characterization and applications

Abstract

In past decades, polymer-matrix composites for higher thermal and electrical conductive purposes have been studied extensively. All of the common mixing methods such as solution-mixing and melt-mixing led to the similar results that the fillers are randomly located in the continuous polymer matrix. However, this random filler distribution may not be the most effective way for thermal and electrical conduction. Therefore the purpose of the thesis is to control the dispersion state of the filler and to fabricate composites with special connected filler structure. These kinds of composites show a higher thermal conductivity as well as electrical conductivity (depended on the filler we used) compared with the composites made by traditional methods. Based on the idea above, PP/AlN composites with a 3-D segregated structure were successfully prepared by sintering of the composite particles with PP core and AlN shell. The composites showed about 23% higher thermal conductivity than the composites made by traditional solution mixing and melt mixing methods. To further enhance the connectivity between the fillers, BN fillers have been modified by surface treatment agent. And the thermal conductivity of UHMWPE/BN composites with BN treated by silane was about 20% higher than that with neat BN. To fabricate composites with connected filler networks at high filler loadings, porous interconnected AlN preforms were prepared and the corresponding epoxy/AlN composites were fabricated accordingly by infiltrating epoxy into the resulting preforms. The resulting composite exhibited a high thermal conductivity of 5.80 W/(m∙K), which was about 80% higher than that of epoxy/AlN composites at same AlN loading fabricated by traditional solution-mixing method. In addition, a connected preform composed by AlN/A₂O₃ was fabricated and the thermal conductivity of the corresponding epoxy/AlN/Al₂O₃ composites was as high as 14.5 W/(m∙K). At last, we promoted the idea in electrical conductive composites with connected filler network, and PP/UHMWPE/CF composites were prepared using similar method. The composite with 10vol%CF exhibited a very low log resistivity (Ω ∙ cm) of 1.25 and a double PTC effect was found. As temperature increased, volume expansion of UHMWPE particles due to melting was directly observed under optical microscope. In conclusion, the connected filler structures we designed in the thesis served as thermal and electrical conduction paths, and thus the corresponding composites with such filler structure exhibited a higher thermal and electrical (depended on the filler) conductivity than the ones prepared by common solution-mixing or melt-mixing methods.

Date of Award	2015
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology