Highly stretchable and self-foaming polyurethane composite skeleton with thermally tunable microwave absorption properties

Synthesis of Lightweight Renewable Microwave-Absorbing Bio-Polyurethane/Fe3O4 Composite Foam: Structure Analysis and Absorption Mechanism

Sustainable renewable polymer foam used as a lightweight porous skeleton for microwave absorption is a novel strategy that can effectively solve the problems of the large surface density, high additive amount, and narrow absorbing band of absorbing materials. In this article, novel renewable microwave-absorbing foams were prepared using Sapiumse biferum kernel oil-based polyurethane foam (BPUF) as porous matrix and Fe₃O₄-nanoparticles as magnetic absorbents. The microstructure and the microwave absorption performance, the structural effects on the properties, and electromagnetic mechanism of the magnetic BPUF (mBPUF) were systematically characterized and analyzed. The results show that the mBPUF displayed a porous hierarchical structure and was multi-interfacial, which provided a skeleton and matching layer for the Fe₃O₄ nanoparticles. The effective reflection loss (RL ≤ −10 dB) frequency of the mBPUF was from 4.16 GHz to 18 GHz with only 9 wt% content of Fe₃O₄ nanoparticles at a thickness of 1.5~5 mm. The surface density of the mBPUF coatings was less than 0.5 kg/cm² at a thickness of 1.8 mm. The lightweight characteristics and broadband absorption were attributed to the porous hierarchical structures and the dielectric combined with the magnetic loss effect. It indicates that the mBPUF is a prospective broadband-absorbing material in the field of lightweight stealth materials.

Size-controllable porous flower-like NiCo2O4 fabricated via sodium tartrate assisted hydrothermal synthesis for lightweight electromagnetic absorber

Although the performance of NiCo₂O₄-based absorbers with multiple components has made great progress, the property of pure NiCo₂O₄ is still far from the requirements of high-performance electromagnetic wave absorbers. It is recognized that morphology control is an effective strategy to improve electromagnetic absorbing capacity of absorbers. Herein, this work reported the fabrication of porous flower-like pure NiCo₂O₄ via simple hydrothermal reaction with the assistant of sodium tartarate in where tartaric acid served as a structure-directing agent. It was demonstrated that size distribution and electromagnetic absorbing capacity of the obtained NiCo₂O₄ could be modulated easily by controlling addition of sodium tartrate. It was verified that dipole polarization originated from lattice defect and oxygen vacancy as well as interfacial polarization ascribing to adjacent and interconnected flakes are responsible for the excellent electromagnetic absorbing performance. The obtained porous flower-like NiCo₂O₄ exhibited broad absorption bandwidth at thin thickness as well as proper dissipation ability. This work offers a new strategy to fabricate size-controllable porous flower-like NiCo₂O₄ electromagnetic absorber. It is believed the obtained NiCo₂O₄ will be a promising candidate as a lightweight electromagnetic absorbing material.