Regulation of dielectric and microwave absorption properties of needle-punched polyimide/carbon fiber nonwoven composites in X-band

Abstract

The application of nonwoven fabrics in the field of microwave absorption is becoming more and more extensive because of its advantages of light weight, short manufacturing process and strong designability. In this article, polyimide and carbon fiber (PI/CF) nonwoven fabrics were prepared by needle punching process, and then they were immersed in water-based polyurethane (WPU) solution containing different contents of short carbon fiber (SCF, 0–3 mm) to prepare a series of PI/CF/WPU composites. As could be seen from the microscopic morphology that the materials were well impregnated by WPU, and the prepared composites had dense structures. The tensile strength and elongation at break of pure WPU were 13.4 MPa and 161.9%, respectively. The addition of 2 wt.% SCFs in WPU increased the tensile strength to 14.4 MPa by 7.4%, while the addition of 5 wt.% SCFs decreased the tensile strength by 8.2%. Adding 2 wt.% and 5 wt.% SCFs to WPU had little effect on improving the dielectric of pure WPU. But when the PI/CF nonwoven fabrics were added, the dielectric properties of the material greatly improved. The real and imaginary parts of the PI/CF/WPU were 20.2 and 9.5 at 8.2 GHz without SCF addition, 30.4 and 15.7 with 2 wt.% SCFs addition, and 47.2 and 182.8 with 5 wt.% SCFs addition. For PI/CF/WPU without SCF, the reflectivity in the entire X-band was lower than −10 dB in the thickness of 2–2.2 mm. When the thickness was 2.2 mm, the reflectivity reached the minimum value of −25 dB at 12.4 GHz.

Keywords

• Nonwoven fabrics
• Microwave absorption
• Tensile strength
• Dielectric properties