Study on Structure and Composition of Residual Compounds From Air Environment Thermolysis of Phenolic/Siloxane Modified Epoxy Blends
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1.School of Materials Science and Engineering, Wuhan University of Technology,Wuhan 430070;2.Hubei Institute of Aerospace Technology Research,Wuhan 430040

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TB332

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    Abstract:

    The epoxy-polysiloxane copolymer (ES) was synthesized by condensation reaction of hydroxy-terminated polydimethylsiloxane (HTPDMS) and bisphenol A epoxy resin (CYD-128),and then blended with phenolic resin to modify and obtain polysiloxane modified epoxy/phenolic blend (ES/PF).Thermal properties of ES/PF blend and the chemical structure and composition of pyrolysis residues at different temperatures were investigated by thermogravimetry-differential scanning calorimetry (TGA-DSC), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy with energy dispersive spectrometer (SEM-EDS),and X-ray photoelectron spectroscopy (XPS).The results show that, compared with pure phenolic resin, the residual yield of ES/PF blend increases by 438% at 800 ℃ in air atmosphere, and the maximum heat release rate decreases from 21.98 W/g to 14.93 W/g. However, under N2 atmosphere, the residual yield decreases slightly by 14.3%.In addition, the hybrid structure rich in Si-Ox in the pyrolysis condensed phase of ES/PF blend system within 430-600 ℃ plays a key role in the stable formation of carbon layer, effectively delaying and inhibiting the further degradation of resin, and thus improving the carbon residue rate.When the temperature exceeds 430 ℃, the existing form of silicon element in the residue changes significantly,from SiO2 (accounting for more than 80%) at 430 ℃ to hydrated silica (SiO2·nH2O) at 600 ℃. These results fully indicate that the silicon element can significantly improve the carbon residue and thermal stability of phenolic resin under thermal oxygen condition, but its influence is suppressed to a certain extent under N2 conditions, which may be attributed to the oxygen absorption mechanism of siloxane groups during pyrolysis process. In addition, the structure and composition of pyrolysis residues of ES/PF blend system have a positive effect on improving the thermal residual strength and ablation resistance of the material.

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History
  • Received:March 07,2022
  • Revised:April 30,2022
  • Adopted:June 02,2022
  • Online: September 03,2024
  • Published: August 31,2024