Investigation of the microwave attenuation performance and structure‐property relationship for graphite‐filled cyclo‐olefin copolymer composites

Abstract

This study examined the morphological, rheological, viscoelastic, electrical, and microwave attenuation properties (RADAR absorbent and EMI shielding) of cyclo‐olefin copolymer (COC) composites prepared with the melt mixing method by using different amounts of graphite (0‐75 phr). Rheological percolation threshold of the graphite was determined as ∼38 phr. The RL analyses of the composites showed that the composites containing a moderate filler content (45 phr) exhibited the best radar absorption performance. Absorption bandwidth and minimum reflection loss (RL) value for the sample containing 45 phr of graphite were determined as 2.335 GHz (10.165‐12.5 GHz) and −39.89 dB, respectively. Total shielding effectiveness (SET) values of the sample including 75 phr of graphite varied in the ranges of 30 to 47.5 dB for the sample thicknesses of 7 mm. The correlation of the microstructural parameters and microwave attenuation properties of the composites indicated that the minimum RL value could be obtained at a filler concentration close to the rheological and electrical percolation thresholds. However, it was also revealed that acceptable shielding effectiveness values for commercial applications could be obtained by the samples with higher filler concentrations than the electrical percolation threshold.

Nickel‐coated carbon fillers for polyurethane foam with improved microwave absorption performance: A comparative analysis

“…It is striking that the dielectric and magnetic permittivity/permeability values that were obtained in this study were quite low compared to non-foam composites prepared using similar filler types and concentrations in the literature. 11,48 This difference may be attributed to the decrease in the functional filler concentration per unit volume during the foaming process and the breakage of the connection between the agglomerated filler particles between the cell walls.…”

“…8,9 Various materials with matching permittivity and permeability in the target frequency range can be used as MAMs. Most MAMs are prepared by the dispersion of one or more types of functional fillers, such as carbon derivatives, [10][11][12][13] metals, 14 or magnetic powders 15,16 in a polymer phase. Each type of MAM has specific advantages and disadvantages in terms of performance depending on the functional filler content.…”

“…There is no considerable microwave absorption below this critical concentration, while reflections from the composite surface increase due to electrical conductivity above this value, making it impossible to use the material as an absorber. 11 Similarly, relatively lower RL values and a broader absorption bandwidth are the main advantages of magnetic particle-filled polymer composites. However, the main drawbacks of these materials are the requirement of high filler concentrations to obtain acceptable absorption performance and high composite density and thickness values.…”

Cyclic olefin copolymer‐based copper clad laminate and the application for low loss broadband baluns

“…Moreover, the COC is used for the application of ultracompact dielectric waveguide window, with 20 dB return loss and 0.5 dB insertion loss in the related frequency range of 49% 18 . Thus, we think the COC has obvious advantages over many other thermoplastics for various applications, for example, EMI shielding in military applications which require high mechanical strength, long life and good processability 19 …”

A modified blister mixing element for generating extensional flow in a twin‐screw extruder: Process characterization and dispersion state of carbon nanotubes in cyclo‐olefin polymer

“…COP is a relatively new class of amorphous olefin-based thermoplastic polymers and demonstrates outstanding transparency, thermal stability, and mechanical properties. [20][21][22] SWCNTs with excellent mechanical properties and electrical conductivity have a higher aspect ratio of length to diameter and specific surface area than multiwalled CNTs. [20] Although adding SWCNTs into COPs can improve the mechanical properties and electrical properties, [21,22] achieving a good SWCNT dispersion in COPs is challenging because COPs have hydrophobic chemical structures, [23] and SWCNTs strongly aggregate due to their high specific area.…”