Synergistic fire‐retardancy properties of melamine coated ammonium poly(phosphate) in combination with rod‐like mineral filler attapulgite for polymer‐modified bitumen roofing membranes

Abstract

A novel intumescent (carbonization, acid donor and foaming) fire retardant that mimics carbon nanotubes was introduced into bitumen roofing and characterized using cone calorimetry as the main analytical tool. The experimental results indicate that 18% (by mass) attapulgite mineral (ATTP) mixed with base bitumen decreased the peak heat release rate per unit area (pHRRPUA) by 10%. Further, incorporation of melamine coated ammonium polyphosphate (MAPP) decreased the pHRRPUA by 52% and a mixture of these (3:1, ATTP:MAPP) decreased the pHRRPUA by 25% as compared to adding CaCO 3 as a filler. The residual mass loss after the cone test was also improved with up to 3%. The indication of a positive synergistic flame retardant effect of the ATTP-MAPP mixture is supported by thermogravimetric analysis. The addition of this rod-like mineral improved the general fire retardant properties of the base bitumen and increased the viscosity. Therefore, the polymer-modified bitumen with both fire retardant and rheological properties (providing mechanical strength) is a promising novel approach in the design of bitumen roofing membranes. K E Y W O R D S cone calorimetry, fire retardant, intumescent fire retardant, melamine coated ammonium polyphosphate, polymer-modified bitumen, thermogravimetric analysis 1 | INTRODUCTION Bitumen is a crude oil by-product that is dark brown to black, almost non-volatile, highly viscous, adhesive, and waterproof at normal temperature. Chemically, it is composed of thousands of small and large aliphatic to aromatic hydrocarbon molecules. 1 Bitumen can be separated into four generic fractions denoted as SARA (saturates, aromatics, resins and asphaltenes). 2 Bitumen is primarily used as a binder in asphalt road construction and as a waterproofing agent in roofing applications. 3 Upon heating beyond approximately 300 C, bitumen will ignite and the ensuing combustion process releases enough heat to sustain itself while releasing a substantial amount of smoke. 4 There are crucial points that must be considered in the manufacturing of bituminous roofing membranes. For example, viscosity measurements are of critical importance for use and performance reasons. 5 Indeed, a too low viscosity could give poor adhesion. The roofing membranes can catch fire during, for example, heat gun applications and, once a fire has started it is difficult to control due to the very high heat release rate of the material. Therefore, it is of interest to reduce both the ignitability and flammability of bitumen roofing membranes with the addition of fire retardants, which preferably should be environmentally friendly. However, only limited scientific research with focus