Synergistic effect of aluminum hydroxide and expandable graphite on the flame retardancy of polyisocyanurate-polyurethane foams

摘要

For the first time, expandable graphite (EG) and aluminum hydroxide (ATH) was combined to improve the flame retardancy of polyisocyanurate-polyurethane (PIR-PUR) foam. The limited oxygen index increased from 26.5 for the PIR-PUR matrix to an incredible value of 92.8 when 24 phr (parts per 100 of matrix) EG and 60 phr ATH were incorporated into the matrix. Based on morphology observation and thermogravimetric analysis, it was speculated that two factors contributed to the improvement of flame retardancy primarily. First, ATH could effectively induce "villi" like particles, which was useful to form a dense char. The compact char layer could effectively impede the transport of bubbles and heat. Second, ATH and EG accelerated the initial degradation and fluffy char was quickly generated on the surface of the composites. Thus, the degradation of the composite was slowed down and the diffusion of volatile combustible fragments to flame zone was delayed.