Investigation of mechanical and EMI shielding performance of polypropylene/carbon nanotube/glass fiber microcellular foam

Polypropylene (PP)/Carbon-Nanotube (CNT) nanocomposites and PP/CNT/Glass fiber (GF) hybrids were foamed using supercritical carbon dioxide (CO2) through a batch foaming process. Uniform nanofiller dispersion was assessed by field emission scanning electron microscopy (FE-SEM). By incorporating CNTs in the matrix, the average cell size was reduced to less than one-second that of neat foam (from 49 to 22.5 µm), and cell density increased. As a matter of fact, high electrical conductivity is crucial to achieving a great electromagnetic interference (EMI) shielding performance. Hence, CNTs were loaded up to 3 wt%. By incorporation of CNTs, electrical conductivity increased from ~10-16 to ~10-4 and ~10-5 S/cm for unfoamed and foamed PP/CNT3 samples, respectively, and EMI shielding effectiveness increased to 11 dB and 9.5 dB for unfoamed and foamed PP/CNT3 samples, respectively. After evaluating the microstructural and electrical properties of the nanocomposites and their foams, as well as elucidating the foaming process's role in the EMI shielding performance of the hybrids and foams, there was a great need to investigate the mechanical properties of hybrid systems and the effect of fiber concentration. Tensile properties revealed that by increasing the fiber content, young modulus and tensile strength increased for unfoamed samples and decreased for foams. The compression test of hybrid foams showed that by loading nanotubes and glass fibers, compressive mechanical properties increased. Also, by adding CNTs and glass fibers, impact properties increased and decreased, respectively, for solid and foamed hybrids. Moreover, by loading both additives impact properties enhanced.