High-performance EMI shielding materials with renewable characteristics are needed to address the issue of electromagnetic radiation pollution. The use of traditional metal-based EMI shielding materials is limited by their high density, corrosiveness, and expensive processing costs. At the same time, using regular fossil-fuel-driven conductive polymer composite-based EMI shielding materials creates environmental pollution, exacerbates resource consumption, and offers poor electromagnetic shielding effectiveness. Moreover, most of the processing methods used for conductive polymer composite-based EMI shielding materials are focused on a batch-scale process, which cannot easily be scaled up. We studied a sustainable foam injection molding-based method to efficiently fabricate renewable microcellular PLA/graphite nanocomposite foams, with improved mechanical and electrical properties for ultra-efficient EMI shielding applications. A microcellular PLA/graphite nanocomposite foam, with a density of 0.7 g cm⁻³ and a thickness of 2.0 mm, exhibits an outstanding EMI shielding performance with a total electromagnetic interference shielding effectiveness (EMI SE) of up to 45 dB. More importantly, thanks to the reduced reflection, which resulted from the strong thin-film interference effect, this lightweight porous nanocomposite foam has an absorption-dominated EMI shielding feature with a radiation energy reflection of less than 15%. The nanographite reorientation, which resulted from foaming, led to the microcellular PLA/graphite nanocomposite foam's electrical conductivity being dramatically increased by almost six orders of magnitude, in relation to the unfoamed sample. Furthermore, the microcellular PLA/graphite nanocomposite foam also exhibited outstanding mechanical properties. These were characterized by a strong specific strength and modulus, and super-ductile fracture behavior. Thus, this lightweight sustainable nanocomposite foam demonstrated great promise as an ultra-efficient EMI shielding material for future use in many applications such as aerospace and electronics.

Superinsulating materials play a pivotal role in achieving the sustainable development of our modern world by improving energy efficiency, and reducing energy consumption and CO₂ emission. Nanocellular polymer foams have been considered as a promising superinsulating material, but their development is yet to be achieved. The understanding of thermal transport through the nanocellular foam is crucial for developing this superinsulating material. Herein, we report an accurate mathematical model for the first time to quantitatively estimate thermal transport through the nanocellular polymer foam. This is realized by taking into account the phonon scattering effect, the Knudsen effect and the thin-film interference effect in modeling the thermal transport through solid conduction, gas conduction and thermal radiation, respectively. We demonstrate a quantitative relationship between the cellular structure and the equivalent thermal conductivity and present the optimum cellular structure scope for achieving the superinsulating performance. In particular, the significance of thermal radiation in the nanocellular polymer foam is emphasized. This mathematical model offers a very useful tool for deeply understanding thermal transport through the nanocellular polymer foams, and guiding the development of the new generation of superinsulating materials.