LDPE/MWCNT and LDPE/MWCNT/UHMWPE self-reinforced fiber-composite foams prepared via supercritical CO2: A microstructure-engineering property perspective

•Microstructure-property study of LDPE/MWCNT and LDPE/MWCNT/UHMWPE self-reinforced nanocomposite foams.•Applying Solid-state batch foaming process via supercritical CO2 to introduce cellular structure.•Evaluating microstructure of solid nanocomposites microstructurally based on SEM, XRD, and rheological characteristics.•DSC thermograms relied on competition between changes in crystalline degree entropy and cellular structure.•Superior mechanical and electrical properties of self-reinforced nanocomposite foams due to the presence of nanofiller and fiber interactions simultaneously. [Display omitted] Low-density polyethylene (LDPE)/Multiwall-Carbon-Nanotube (MWCNT) nanocomposites were foamed using supercritical carbon dioxide (CO2). Uniform nanofiller dispersion was assessed by scanning electron microscopy (SEM), rheological measurements, and wide-angle X-ray diffraction (WAXD). By incorporating MWCNTs in the matrix, the average cell size was reduced to less than one-third that of neat foam (from 32.92 to 9.24 µm), and cell density jumped from 0.205 × 109 to 5.26 × 109 cell/cm3. After evaluating the thermal, mechanical, and electrical properties of the nanocomposites and their foams, as well as elucidating the foaming process's role in the crystalline structure, there was a great need to boost the mechanical performance. Hence, ultra-high molecular-weight-polyethylene (UHMWPE) fiber was embedded in the system, which is a reliable reinforcement for, and compatible with, the polyethylene, owing to its basic similarity to the matrix. The electrical conductivity of the solid and foamed materials was greatly improved by the addition of 15 wt% UHMWPE fibers and 1.4 wt% filler.