Intumescent Polypropylene and Polyethylene

Polypropylene (PP), for example, burns very easily and dripping is observed during its combustion. The use of virgin PP is thus limited when flammability properties are required. Several approaches have been developed to increase its fire-retardant properties. Hornsby [1] reviewed the approach of using classical fillers in PP to increase its fire-retardancy behaviour. With classical fillers, the main problem is the loading (typically between 40% and 60% of total mass), which directly affects the mechanical properties of the polymer. Another problem is that the filler must be treated to increase its interfacial adhesion with the matrix. 

Another solution to improve the fire-retardant (FR) properties of polymers is the use of intumescent additives [2, 3]. Intumescent technology [4, 5] has found a place in polymer science as a method of imparting flame retardancy to polymeric materials. On heating, FR intumescent materials form a foamed cellular charred layer on their surfaces [6, 7], which protects the underlying materials from the action of heat flux and flame. The proposed mechanism [8] is based on the charred layer acting as a physical barrier, which retards heat and mass transfer between the gas and the condensed phase. 

A solution of limiting the burning mechanism can be by developing on the outer surface of the polymer, a glassy [15] or an expanded shield [16] which may at least 

Three different types of halogen-free intumescent charring agents have been identified [17] (Table 7.1). All those compounds lead to the formation of a superficial char layer that prevents further decomposition but they act in three different ways  

Reproduced with permission from M. Modesti and A. Lorenzetti, Polymer Degradation and  

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