In order to improve the performance of phenolic foam, an additive compound of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and Itaconic acid (ITA) were attached on the backbone of ethyl cellulose (EC) and obtained DOPO-ITA modified EC (DIMEC), which was used to modify phenolic resin and composite phenolic foams (CPFs). The structures of DOPO-ITA were verified by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (1H NMR). The molecular structure and microstructure were characterized by FT-IR spectra and SEM, respectively. Compared with EC, the crystallinity of DIMEC was dramatically decreased, and the diffraction peak positions were basically unchanged. Additionally, thermal stability was decreased and Ti decreased by 24 °C. The residual carbon (600 °C) was increased by 25.7%. With the dosage of DIMEC/P increased, the Ea values of DIMEC composite phenolic resins were increased gradually. The reaction orders were all non-integers. Compared with PF, the mechanical properties, flame retardancy, and the residual carbon (800 °C) of CPFs were increased. The cell size of CPFs was less and the cell distribution was relatively regular. By comprehensive analysis, the suitable dosage of DIMEC/P was no more than 15%.

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In order to improve the mechanical properties without reducing its flame retardancy of phenolic foams (PFs), 9, 10-dihydro-9-oxa-10phosphaphenanthrene-10-oxide (DOPO) was introduced in the structure of cashew nut shell liquid (CNSL) to improve its flame retardant, and the product of DOPO grafting CNSL (DOPO-g-CNSL) was obtained to modify phenolic resin, and to prepare DOPO-g-CNSL modified PFs (DCMPFs). The structures of DOPO-g-CNSL were verified by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (1 H-NMR). Compared with CNSL, thermal stability of DOPO-g-CNSL was decreased and Ti decreased by 3.53%, but the residual carbon (800°C) was increased by 35.05%. Compared with pure PF, the mechanical properties, toughness and flame retardancy of DCMPFs were increased when the ratio of DOPO-g-CNSL to phenol (DOPO-g-CNSL/P) was no more than 10%. With the dosage of DOPO-g-CNSL/P increased, Ti of DCMPFs was slightly increased, but the carbon residues (800°C) were almost unchanged. And the cell sizes of DCMPFs were basically the same as the pure PF. By comprehensive analysis, the suitable dosage of DOPO-g-CNSL/P was no more than 10%.

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