High-Efficiency EMI Shielding Polymer Composites: Using Recycled Polymers, Structure-Property Relationships

Abstract

The rapid expansion of electronic devices in modern society has intensified concerns regarding the protection of both electronic systems and the surrounding environment from undesired electromagnetic radiation. Addressing this challenge requires the development of advanced electromagnetic interference (EMI) shielding materials that are not only efficient but also environmentally friendly and economically feasible. This thesis focuses on the design, fabrication, and evaluation of high-performance EMI shielding polymer composites for applications in electronics, construction, and wearable technologies. A systematic approach was adopted to engineer composites with different structural architectures, including bulk, sandwich, and multilayer configurations, while prioritizing recycled materials, reduced filler content, and cost-effective components. In the first study, a bulk composite was developed using polypropylene (PP), calcium carbonate (CaCO₃), carbon nanotubes (CNTs), and mechanically recycled EPDM rubber. The effect of EPDM recycling on EMI shielding, electrical conductivity, rheological behavior, and mechanical properties was investigated. An optimal composition of 30 wt% recycled EPDM and 5 vol% conductive filler was identified. At 1 vol% filler, enhanced electromagnetic wave absorption (A = 0.7) was achieved, which was utilized for designing a sandwich structure. The second study examined a PP/CaCO₃ sandwich composite incorporating recycled ground tire rubber (GTR). This structure achieved an EMI shielding effectiveness of 55.2 dB, driven by strong absorption (A = 0.8) and multiple internal reflections due to impedance mismatch. It also exhibited good mechanical performance, with a tensile strength of 25 MPa, making it suitable for construction applications. The final study focused on a multilayer composite fabricated via a modified solution-casting method with reduced use of toxic DMF solvent. The composite demonstrated 26 dB shielding effectiveness at 0.6 mm thickness, along with absorption of 0.45, UV protection, and flexibility, highlighting its suitability for wearable electronics. Overall, this work presents sustainable and efficient strategies for developing EMI shielding materials using recycled polymers and cost-effective methods.