Thermally Conductive Boron Nitride/SEBS/EVA Ternary Composites: ‘‘Processing and Characterization’’ Sebnem Kemaloglu, Guralp Ozkoc, Ayse Aytac Department of Chemical Engineering, Kocaeli University, Kocaeli 41040, Turkey The aim of this study is to investigate the effect of hexagonal boron nitride (BN) particle shape/size and loading level on the thermal, mechanical, electrical properties, and morphology of styrene-ethylene-butyl- ene-styrene terpolymer (SEBS)/poly(ethylene-co-vinyl acetate) (EVA) blends to be used as thermal interface materials (TIM). It is observed from the scanning elec- tron microscopy (SEM) of BN powders that each type has a characteristic particle size distribution and parti- cle shape. SEM analysis conducted on matrices (i.e. SEBS/EVA blends) does not indicate any sign of interfacial delamination or phase separation between components. The surface energy measurements and subsequent wettability coefficient calculations point out that the dispersion of BN in SEBS is thermody- namically more favorable than that of BN in EVA. In other words, SEBS tends to encapsulate BN particles in comparison to EVA. Thermal conductivity of compo- sites increases with increasing filler loading level regardless of filler size and shape. It is found that the composites with smaller BN particles (i.e. high aspect ratio and plate-like particles) shows higher thermal conductivity than that of the composites with larger particles at the same filler content. The tensile strength of the composites reduces with the incorporation of BN regardless of BN content and matrix composition. The increasing content of BN in the matrix gradually improves the moduli of the composites. The hardness of composites enhances with BN loading level and SEBS/EVA ratio regardless of filler type. The increasing amount of EVA in the composites results in a decrease in dielectric constant of neat matrices and composi- tes. POLYM. COMPOS., 31:1398–1408, 2010. ª 2009 Society of Plastics Engineers INTRODUCTION Recent developments in electronic technology have brought the miniaturization as a trend. On the other hand, miniaturization in combination with increasing power of electronic devices results in increasing heat flux. Therefore the heat dissipation has become critical to the performance, reliability and further miniaturization of electronic devices [1–3]. The heat produced during the operation of the device is generally dissipated by thermal conduction [4–6]. The traditional method used for this purpose is heat sinks. However, in the absence of good thermal contact, heat dissipation capacity of a heat sink is tremendously decreases due to interfacial thermal resist- ance arising from surface roughness mismatch of both the device and the heat sink. This results in nearly 99% of the interface being separated by air gaps [4, 7]. To reduce the thermal resistance at the interface, the remaining air gaps are filled with suitable thermal interface materials (TIMs). An ideal TIM should have high thermal conductivity, low coefficient of thermal expansion (CTE) and low dielectric constant as well. Moreover the material must be soft enough to be easily deformed by applied contact pressure to fill all the gaps between the mating surfaces [4, 7]. TIMs can be classified as elastomeric thermal pads, thermal greases, solders, and phase change materials [4, 8]. Elastomeric thermal pads have been recently shown increasing interest due to ease of handling and high compressibility. Elastomeric thermal pads are typi- cally made of an elastomeric polymer, such as silicon rubber, and reinforced with highly thermally conductive but electrically insulating fillers, such as aluminum nitride (AlN), boron nitride (BN), silicon carbide (SiC), and alumina (Al 2 O 3 ) [9, 10]. The studies reported in the literature mostly focus on the processing and characterization of silicone rubber based elastomeric thermal pads. Zhou et al. investigated the thermal conductivity of poly(dimethyl siloxane) rein- forced with silicone nitride (Si 3 N 4 ) particles alone or in combination with silicone carbide whisker (SiC w ) [7]. It was found that the incorporation of 50% hybrid sized Si 3 N 4 into silicone rubber yielded the highest thermal conductivity compared to others. Moreover, the com- bined use of hybrid Si 3 N 4 /SiC w at a weight ratio of 9:1 provided higher thermal conductivity, improved thermal stability and reduced CTE. In other study, BN reinforced silicone rubber was developed [2]. The effects of content Correspondence to: Guralp Ozkoc; e-mail: guralp.ozkoc@kocaeli.edu.tr Contract grant sponsor: Turkish National Boron Research Institute (BOREN); contract grant number: 2008.C0148. DOI 10.1002/pc.20925 Published online in Wiley InterScience (www.interscience.wiley.com). V V C 2009 Society of Plastics Engineers POLYMERCOMPOSITES—-2010