Developing sustainable and recyclable high-efficiency electromagnetic interference shielding nanocomposite foams from the upcycling of recycled poly(ethylene terephthalate)

The demand for high-performance electromagnetic interference (EMI) shielding composite foams with satisfactory environmental friendliness and high sustainability has increased considerably. However, considerable obstacles are frequently encountered in the practical development of incorporating upcycling of plastic wastes and environmentally friendly foaming technologies into the manufacture of such EMI shielding systems. In this research, we developed a lightweight sustainable nanocomposite foam system with outstanding EMI shielding performance from the integration of chemical upcycling of recycled poly(ethylene terephthalate) (PET) and supercritical carbon dioxide (sc-CO2) microcellular foaming. First, a green thermoplastic polyamide elastomer (TPAE) system was synthesized using a renewable bis(6-aminohexyl)terephthalamide (BAHT) monomer derived through the aminolysis of recycled PET, followed by adding single-walled carbon nanotubes (SWCNTs) into the TPAE system for the manufacture of TPAE/SWCNT nanocomposites. The π–π stacking of BAHT efficiently enhanced the melt strength of the material system, which was conducive for microcellular foaming process. After sc-CO2 foaming, a series of highly expanded nanocomposite foams with uniform microporous structure that could enable multiple reflections of electromagnetic waves were fabricated. Upon adding only 2 wt% SWCNTs, the foam system achieved a favorable conductivity of 0.15 S/cm and an extremely high specific shielding effectiveness (SSE) of 213.26 (dB cm3/g). Furthermore, the green nanocomposite foam possessed excellent durability. After being bent or twisted 1000 times, the foam maintained EMI shielding effectiveness of > 90% of the original value. Moreover, the foam could be easily recycled, reprocessed, and refoamed. For developing sustainable EMI shielding products, we believe that this study provides a promising direction with benefits of alleviating waste accumulation and reducing the use of virgin plastics in manufacture of foams, showing potential for advanced sustainable electronic applications.