Mechanical and EMI shielding properties of solid and microcellular TPU/nanographite composite membranes

Abstract

Tough, flexible, and conductive polymer composites show numerous advantages over conventional metal-based materials for EMI shielding applications, for example, in enclosures and packages of electronic devices, due to their low density, high flexibility, excellent corrosion resistance, and easy processing. Herein, thermoplastic polyurethane (TPU) was compounded with flake-shaped nanographite to prepare flexible polymer composite membranes with enhanced mechanical and EMI shielding properties. To regulate TPU/graphite composite's properties, microcellular foaming with carbon dioxide was used to prepare microcellular TPU/graphite composite membranes. Nanographite can significantly promote cell nucleation and hence lead to a refined cellular structure. With 20 wt% nanographite, cell density can be increased by two orders of magnitude. By adding the optimal amount of nanographite, the tensile strength and modulus can be increased up to 28% and 39%, compared to TPU. Although microcellular foaming compromises the tensile properties of the composites, it can significantly enhance their elasticity with more than a 20% decrease in hysteresis loss in comparison to solid ones. Moreover, it is also found that TPU composites with high graphite contents significantly enhanced EMI shielding properties, and microcellular foaming leads to relatively worse EMI shielding performance. Both solid and foamed TPU/graphite composites show promising prospects in EMI shielding applications.