A Study on Thermal Behavior of Lightweight Carbon/Polymer Composites

Abstract

To investigate thermal behavior of lightweight carbon/polymer composites and to explore the potential applications of composites are the main topics of this study. Present study dealt with unique experimental results such as synergistic improvement in thermal conductivity of multiphase composites and enhancement in surface hardness of graphene aerogel-based composites. To explore dominant factors determining the thermal conductivity of the carbon/polymer composites is also an important goal of this study. In Chapter 2, the thermal conductivity of composites with a polyphenylene sulfide (PPS) matrix and a mixture of boron nitride (BN) powder and multi-wall carbon nanotube (MWCNT) fillers was investigated. Synergistic improvement in thermal conductivity of the composite was obtained by introducing a combination of BN and MWCNT. The improvement of thermal conductivity was strongly depended on surface treatments of the MWCNTs, such as hydrogen peroxide and acid treatments. The thermal conductivity of the composite was affected by the interaction and interfacial thermal resistance between the PPS matrix and the BN filler. The interfacial thermal resistance of PPS/BN/MWCNT composites was investigated quantitatively by finite element method. The highest thermal conductivity was 1.74 W/m·K achieved by the composite with 1 wt% MWCNT that had been treated by hydrogen peroxide., This result indicated that we successfully fabricated a pelletizable, injection moldable, thermally conductive carbon/polymer composite, considering the specific thermal conductivity of the prepared composite. In Chapter 3, three-dimensional carbon nanomaterial reinforced composite aerogel was fabricated using a freeze-drying method. Graphene nanoplatelets (GNPs) were used as the reinforcement and poly vinyl alcohol (PVA) as the organic binding material to produce the composite aerogel. Two different methods were employed to control the internal structure of the aerogel: a variation of solvent composition and the formation of cross-linking. The internal structure of the aerogel was affected by the types and composition of the solvent. In addition, the subsequent cross-linking of the aerogel influenced the morphology and physical properties. This study is expected to provide a simple and efficient way to control the internal structure and resulting properties of the GNP aerogel. In Chapter 4, the thermal and electrical conductivity of composites with a graphene aerogel and an epoxy matrix were investigated. We fabricated a core-shell structured composites with the graphene aerogel core and the epoxy/graphene composite shell in order to enhance the poor surface hardness of graphene aerogel, resulting in increased resistance of graphene aerogel to the external forces. The thermal conductivity of the core-shell structured epoxy/rGO composites was 0.077 W/m·K which is similar to that of thermal insulating materials. On the other hand, the electrical conductivity of composite was found to exhibit 0.5 S/m which is almost 10 orders of magnitude higher than that of neat epoxy. This result indicated that carbon/polymer composites have a great potential in numerous engineering applications.