Carbon Foams by Solid State Foaming of Short Vermicelli Bonded by Phenol-Formaldehyde for Thermal Insulation and Electromagnetic Interference Shielding

Abstract

A simple method of production of carbon foams by randomly assembling short vermicelli rods and bonding them using phenol-formaldehyde (PF) followed by foaming in the solid state during carbonization has been reported. The brittle vermicelli becomes ductile in the range of 200−250 °C during carbonization, which facilitates the nucleation and growth of bubbles in the solid state due to the water vapor generated by the -OH condensation of starch. The dense PF coating on the vermicelli surface facilitates the enlargement of cells by restricting the escape of water vapor during the solid state foaming. The dense carbon produced from the PF binds the carbonized vermicelli rods, affording structural integrity and mechanical strength. The foam body consists of open intervermicelli void space and closed cellular pores in the carbonized vermicelli rods. A broad cell size range of 4−142 μm with an average value of 29.2 μm is observed. The density, compressive strength, and thermal conductivity of the carbon foam are modulated in the ranges of 0.30−0.34 g cm −3 , 0.63−1.6 MPa, and 0.162−0.222 W m −1 K −1 , respectively, by changing the PF solution concentration in the range of 50−90 vol %. The carbon foams exhibit absorption-dominated electromagnetic interference shielding with total shielding effectiveness and specific shielding effectiveness in the ranges of 47.5−65.6 dB and 155.2−192.9 dB cm 3 g −1 , respectively, for the X band (8.2−12.4 GHz).

Recent Progress in Poly (3,4‐Ethylene Dioxythiophene): Polystyrene Sulfonate Based Composite Materials for Electromagnetic Interference Shielding

“…Electrospinning is one of the best methods to produce nanofibers in large scale. [3,4,6,82,[150][151][152] Lai et al [81] fabricated a composite with hydrophilically-engineered electrospun glycerol grafted polyacrylonitrile (PAN) nanofiber (GPNF) and PEDOT: PSS using fabric shrink strategy for EMI shielding in X-band. The conductive nanofiber films of PEDOT: PSS /GPNF composites were prepared by dip-coating.…”

“…Absorption dominant shielding directly depends on thickness (t) and skin depth (𝛿) of the materials as shown in equations (5,6). Skin depth (𝛿) of a material is termed as the distance at which the intensity of the incident EM wave decreases to 37% or (1/e).…”

“…As a result, EM waves are omnipresent in the surroundings and pave paths for the penetration of EM waves in all spheres of life. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] The stray and unwanted EM waves cause malfunctioning of electronic devices and can even disrupt the devices permanently. It can disrupt vehicular control systems, military activities, rail, road, and mass transit systems.…”

Recent advances in structural design of conductive polymer composites for electromagnetic interference shielding

“…Because of the fast growth of communication and electronic technology, electromagnetic radiation pollution and interference have attracted much attention 1 . The broadband electromagnetic waves (EMWs) with a frequency range of 10 3 to 10 21 Hz (wavelength: 3 × 10 −13 to 3 × 10 5 m) have flooded into modern life.…”

“…Because of the fast growth of communication and electronic technology, electromagnetic radiation pollution and interference have attracted much attention. 1 The broadband electromagnetic waves (EMWs) with a frequency range of 10 3 to 10 21 Hz (wavelength: 3 Â 10 À13 to 3 Â 10 5 m) have flooded into modern life. In the EM spectrum, almost all electronic devices can emit radio waves with a frequency region of 10 4 to 10 10 Hz and microwaves with a frequency region of 10 9 to 10 12 Hz (GHz frequency), as shown in Figure 1.…”