A study on thermal and dielectric characteristics of solid glass microsphere filled epoxy composites

Abstract

This thesis reports on the research dealing with the processing and characterization of solid glass micro-sphere filled epoxy composites. The first part of the work includes the development of two theoretical correlations based on one dimensional heat conduction models for estimation of effective thermal conductivity of polymer composites with single and multiple fillers.The second part depicts the details of the test procedures and test results in regard tothe physical, mechanical and micro-structural characteristics of the epoxy composites filled with solid glass microspheres (SGM) and/or micro-sized boron nitride (BN). The last part throws light on the thermal and dielectric characteristics of the composites with different filler type and concentrations. The estimation of effective thermal conductivity of the composites using finite element method (FEM) and using the proposed theoretical models is done and the results are validated by corresponding experimental results. The effects of inclusion of SGM and/or BN on the effective thermal conductivity (keff), glass transition temperature (Tg), coefficient of thermal expansion (CTE), electrical resistivity (ρ) and dielectric constant (Dk) of epoxy composites are studied. With the addition of SGM, the thermal conductivity, dielectric constant as well as volume resistivity value decreases. Again, the embedment of both SGM and BN fillers results in lowering the CTE of the composites whereas the Tg of the composites is improvedsubstantially. This work shows that the FEM serves as a very good predictive tool for assessment of thermal conductivity of composites.The proposed theoretical correlations too can serve as very good empirical models for spherical inclusions to estimate keff for composites within the percolation limit. With light weight and improved insulation capability, the solid glass micro-spheres filled epoxy composites can be used for applications such as insulation boards, food containers, thermo flasks, building materials, space flight and aviation industry etc.Similarly, with enhanced thermal conductivity, improved glass transition temperature, reduced coefficient of thermal expansion and modified dielectric characteristics, the epoxy composites with appropriate proportions of solid glass micro-spheres and boron nitride can be used in micro-electronics applications like electronic packaging, encapsulations, printed circuit board substrates etc.