Flame retardant and mechanical properties of epoxy composites with ammonium polyphosphate and hyperbranched silicon‐containing polymers

ABSTRACT The epoxy resin was mixed with ammonium polyphosphate (APP) and hyperbranched silicon‐containing polymers (HBP‐B2). The cured composites were investigated by thermogravimetric analysis, Underwriters Laboratory standard for the flammability properties under vertical burning (UL‐94V), and limited oxygen index (LOI) test methods. The LOI of 43.5 and could be obtained at the weight ratio of 70:25:5 for the epoxy resin:APP:HBP‐B2, Sample A25B5, and the LOI was higher than that of the composite with 30 wt % APP only, Sample A30B0, of which the LOI was 34.5. It suggested that the HBP‐B2 could cooperate with the epoxy/APP composite to form a more effective protection layer during combustion, which resulted in a higher second‐stage thermal degradation temperature. During the UL‐94V test, the flame was extinguished immediately once the burner was removed. Furthermore, the tensile and impact strength of the epoxy/APP composite could also be improved by using HBP‐B2 compound as the toughening agent. The composite containing 20% of APP and 10% of HBP‐B2, Sample A20B10, still had excellent flame retardant properties with a V‐0 rating. Moreover, the tensile strength and impact strength of that composite got 19 and 25% increases compared with the Sample A30B0, which contained 30% of APP only. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48857. IR thermal images of the samples while the ignition burner had been moved away for one second during the UL94 test.