Abstract: The resol phenolic resin with high solid content was prepared with formaldehyde (1.24 mol), paraformaldehyde (7.28 mol) and phenol (4.26 mol), using NaOH as catalyst, via step polymerization. Three eco-friendly halogen-free flame retardants (ammonium polyphosphate (APP), melamine phosphate (MP) and LM-NPP 8081) were chosen. The effects of their presences on the mechanical properties, flame retardancy, fragility, thermal conductivity and heat resistance of PFs were investigated. The results showed that the flame retardancy of the PFs was significantly improved, while both thermal resistant and thermal conductivity of PFs were not enhanced. When the amount of flame retardant was 8%, machanical properties of PFs were the best, and the comprehensive performances of MP composite PFs was better than the other two. Limited oxygen index, compression strength, bending strength, fragitily properties, thermal conductivity and carbon residue of MP composite PFs were 55.22 %, 0.30 MPa, 0.28 MPa, 34.40%, 0.045 W/(m·K), 87.50 %(300 ℃) and 61.12 % (600 ℃) respectively. The results showed that MP was better flame retardant for PFs than the other two.

Key words: halogen-free flame retardants, phenolic resin, thermal resistance, phenolic foams