No abstract

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.

The aim of this work was to verify the influence of expandable graphite (EG) and aluminum hydroxide (ATH) fillers on the flammability of polyisocyanurate-polyurethane (PIR). Limited oxygen index increased to 72.5 with an incorporation of 16 phr (parts per hundred of matrix) EG and 50 phr ATH into the matrix (total weight percent was 39.76%). Cone calorimetry was employed to study the flammability properties of these PIR/ATH/EG composites. Scanning electron microscopy analysis was conducted to study the char characteristics of the composites after the cone calorimetry tests. It was found ATH could effectively induce villi like particles, which made the intumescent char denser, on the surface of EG. The compact char layer could effectively impede the transport of bubbles and heat. ATH and EG accelerated the initial degradation and fluffy char was quickly generated on the surface. Thus, degradation products of the composite were slowed down and the diffusion of volatile combustible fragments to flame zone was delayed.