Magnetic and microwave absorbing properties of magnetite–thermoplastic natural rubber nanocomposites

Magnetic and microwave absorbing properties of thermoplastic natural rubber (TPNR) filled magnetite (Fe3O4) nanocomposites were investigated. The TPNR matrix was prepared from polypropylene (PP), natural rubber (NR) and liquid natural rubber (LNR) in the ratio of 70:20:10 with the LNR as the compatibilizer. TPNR-Fe3O4 nanocomposites with 4–12 wt% Fe3O4 as filler were prepared via a Thermo Haake internal mixer using a melt-blending method. XRD reveals the presence of cubic spinel structure of Fe3O4 with the lattice parameter of a=8.395 Å. TEM micrograph shows that the Fe3O4 nanoparticles are almost spherical with the size ranging 20–50 nm. The values of saturation magnetization (MS), remanence (MR), initial magnetic susceptibility (χi) and initial permeability (μi) increase, while the coercivity (HC) decreases with increasing filler content for all compositions. For nanocomposites, the values of the real (εr′) and imaginary permittivity (εr′′) and imaginary permeability (μr′′) increase, while the value of real permeability (μr′) decreases as the filler content increases. The absorption or minimum reflection loss (RL) continuously increases and the dip shifts to a lower frequency region with the increasing of both filler content in nanocomposites and the sample thickness. The RL is −25.51 dB at 12.65 GHz and the absorbing bandwidth in which the RL is less than −10 dB is 2.7 GHz when the filler content is 12 wt% at 9 mm sample thickness.