Functional properties of microwave-absorbent nanocomposite coatings based on thermoplastic polyurethane-based and hybrid carbon-based nanofillers

This paper describes the effect of nanofillers, such as nanographite, nickelzinc ferrite (NiZnFerrite), and in-house developed hybrid nanographite particles (i.e. iron-coated nanographite [FeNG] and ironnickel co-deposited nanographite [FeNiNG] particles), on microwave-absorption properties of thermoplastic polyurethane (TPU) based nanocomposite coatings on textile substrate. The flexible coatings were tested for various functional properties such as microwave absorbency, gas barrier property, impedance, and weather resistance. The comparison has also been made with other fillers such as bulk graphite (G) and iron powder (Fe) and carbon nanofiber (CNF) in coating form. The nanoparticles' dispersion was observed through optical microscope and phase image analysis on atomic force microscopy. The impedance behavior of such coated samples with 10?wt% nanofillers is frequency dependent except for CNF, which shows frequency-independent behavior even at 2?wt% loading. The gas barrier property of the FeNG-based and FeNiNG-based coatings is better than that of pure TPU; however, G-based, NG-based, and NiZnFerrite-based coatings show excellent barrier property. The coatings were evaluated for their microwave absorbency at low-frequency (from 0.3 to 1.5?GHz) as well as high-frequency (818?GHz) ranges. The FeNG-based and FeNiNG-based nanocomposite coatings showed good absorbency over a frequency range of 8 to 14?GHz as compared with those of others. The flexibility of the nanocomposite films is almost retained even at 10?wt% nanofiller loading. The weather resistance of the films was also evaluated, and the FeNiNG-based coating outperformed the FeNG-based coating as the latter is prone to oxidation on exposure to environment. Copyright (C) 2011 John Wiley & Sons, Ltd.