The Effect of Foaming Process on the Radar Absorbing Properties of PMMA/MWCNT Composites

Alightweight polymer composite with a broad bandwidth، tunable absorption frequency and multi-functionality is an ideal material for making a radar absorber. In general، composite microcellular foams have many potential applications due to their lightweight، high mechanical properties and monotonous cell structure. In this research، the effect of foaming method on the radar absorbing properties of composite radar absorbers was investigated. In the first step، a controllable، repeatable and high pressure/temperature operation foaming system by supercritical CO2 gas as foaming agent was designed and built. The composites based on poly (methyl methacrylate) (PMMA) and multiwall carbon nanotube (MWCNT) at different weight percentages were prepared by solvent-anti solvent coagulation method. The sample sheets with 3 mm thickness were molded using hot compression molding method. Then، the foaming process was performed and the cell morphology of the prepared foams was studied using scanning electron microscopy. Monotonous cell structure of the composite foams revealed a good dispersion of nanoparticles in the polymer matrix. The data of the reflected radar waves (before and after foaming) showed that the foaming reduced the reflection of the radar waves to less than 10 percent in all the samples. It is important to note that the absorption of radar waveswas increased with the foaming of neat PMMA. It was observed that the foaming of composites increased the threshold of absorption of radar waves from less than 1 wt% nanotube for the unfoamed samples to 1-3 wt% nanotube for the foamed samples.