Dependence of Dielectric Constant and Mechanical Properties of Expanded Polystyrene Foam on Cell Wall Thickness

Hypothesis:

 The technology of preparing materials with desired dielectric constants is used in designing and manufacturing telecommunication equipment. Foaming of the polymers is an effective method to reduce their dielectric constant further, as the influence of the microstructural characteristics of the expanded polystyrene foams is important for their dielectric characteristics and mechanical properties. This article focuses on the effect of cell wall thickness of the expanded polystyrene foams on their dielectric constant, loss factor, hardness and resilience.

Many samples of the expanded polystyrene foam with different porosity and overall thickness values were prepared using a specific thermal procedure in a programmable oven. At first, the physical properties such as density and porosity of the expanded polystyrene foams were measured. Next, their microstructural characteristics such as the average cell wall thickness of the expanded polystyrene foams were investigated using a scanning electron microscope. The dielectric constant and loss factor of the samples were assessed with a vector network analyzer with a lens horn antenna. The mechanical properties of the expanded polystyrene foams were evaluated according to Shore D hardness, and the value of mechanical energy stored in them was measured by a resilience tester.

By increasing cell wall thickness in samples at equal overall thickness, the dielectric characteristics such as dielectric constant and dielectric loss factor increase by 12% and 53%, respectively. Moreover, the mechanical properties such as hardness and resilience reveal an increase of 40 and 42%, respectively, due to the increase of cell wall thickness in samples at the same overall thickness. While the dielectric constant and the dielectric loss factor decrease with the reduction of the overall thickness at the same cell wall thickness, the variation of the overall thickness depicts no effect on the hardness and resilience.