Assessing metal powder fraction and inclusion method for optimized morphology and electromagnetic interference (EMI) shielding effectiveness of recycled low-density polyethylene (LDPE)-based composite foams

Conductive polymer composite foams can achieve impressive absorption of electromagnetic energy through the synergistic effects of conduction and polymer loss, as well as multiple internal-scattering mechanisms driven by the material discontinuities between walls and air cells. Although it is well known that the concentration of conductive fillers affects air cell formation and growth during the foaming process, the mechanisms of powder incorporation into the solid precursor mixture warrant further investigation. In this work, a design of experiment (DoE) was developed to examine how the type of metal particles, concentration, and method of inclusion affect the chemical foaming process, morphology, and shielding effectiveness (SE) of the composite foams. For the experiments, recycled low-density polyethylene (LDPE) and reused metal particles (AISI 316 L and Maraging 300 steels, Nickel superalloy, and Copper) at two concentrations (5% and 10% wt) were used as the polymer matrix and fillers, respectively. Before foaming, each metal powder amount was incorporated according to two distinct approaches: (i) mixing/stirring; (ii) settling metal powder layers in two phases onto the LDPE pellets, without stirring. The morphological analysis and scanning electron microscope (SEM) images reveal that settling a smaller amount of metal powder (5 wt%) provides lighter, porous structures with distributed air cell areas and more homogeneously dispersed metal particles. Furthermore, these characteristics enable achieving an average specific Shielding Effectiveness (SSE) of more than 25 dB/g/cm³ in the X-band, especially for lower amounts of Ni superalloy or Cu, as confirmed by Analysis of Variance (ANOVA). In contrast, mixing the metal powders generally resulted in more dense structures with significantly reduced electromagnetic absorption. • Recycled low-density polyethylene and reused metal powders are chosen to realize composite foams. • Morphology and EMI shielding effectiveness of Composite foams are investigated. • Including different metal particles in the LDPE matrix using two methods impacts the final foam morphology. • Settling a lower content of reused Ni or recycled Cu can accomplish morphology and SE optimization.