Abstract: In this paper, the flame retardant system of aluminum hydroxide (ATH) and expandable graphite (EG) is used as to improve the fire retardancy of carbon fiber reinforced phenolic resin composites (CFPF). The flame retardancy and mechanical properties of the composites with different mass ratios of the two ingredients were investigated experimentally, including the smoke suppression performance, thermal degradation behavior, tensile and bending properties, and residual carbon morphology. The experimental results showed that the addition of the two flame retardants improved the flame retardancy, smoke inhibition performance, and thermal stability of the composites. The limiting oxygen index (LOI) of the flame retardant CFPF-2 sample in which the mass ratio of ATH and EG was 1∶2 is increased by 68.4% compared to the non-modified CFPF-0. The result of cone calorimetry test shows that the peak heat release rate (pHRR), total heat release (THR), total smoke generation (TSP), and average specific extinction area (ASEA) of the CFPF-2 composites are improved by the addition of the two flame retardants. The pHRR, THR, TSP and ASEA of CFPF-2 decrease by 49.73%, 65.30%, 94.89% and 94.63%, respectively, compared to CFPF-0. The result of smoke density test shows that the maximum specific optical density (D_s,max) of CFPF-2 decreases by 93.71%. This indicates that ATH and EG have a very good synergistic effect, especially in smoke suppression. The results of thermogravimetric analysis (TGA) show that the carbon residue of CFPF-2 is increased to 13.72%, a significant improvement compared to the 2.70% of CFPF-0. In addition, the mechanical property test results show that the ATH/EG flame retardant system can improve the tensile and flexural strengths of the CFPF composites.

Key words: phenolic resin, expandable graphite, aluminum hydroxide, flame retardant, smoke suppression, composites