Intumescent Ethylene-Vinyl Acetate Copolymer

Le Bras and co-workers [50] developed flame retardant intumescent formulations using the association of APP as the acid source and PA-6 as the carbonisation agent in an EVA (8%) copolymer matrix. 

Insertion of APP-PA-6 in EVA leads to a significant improvement in the fire performance of the material [51, 52]. Interesting results are obtained in EVA with the intumescent (APP/PA-6) system at 30 wt% or 40 wt% loading. The optimal LOI ratio for APP/PA-6 is 5 wt%/wt and the UL 94 VO rating (vertical flame test) is achieved [25, 48, 53, 54]. 

The virgin polymer has a RHR maximum at about 1800 kW/m whereas the RHR of the EVA-APP/PA-6 formulation is only about 400 kW/m.  

In order to understand the fire behaviour of the EVA-APP/PA-6 formulation, Le Bras and co-workers [50] deal with the chemical characterisation of the intumescent materials formed during combustion in the conditions that occur in a cone calorimeter. 

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Wang, B., Wang, X., Shi, Y. et al. 2012. Effect of vinyl acetate content and electron beam irradiation on the flame retardancy, mechanical and thermal properties of intumescent flame retardant ethylene-vinyl acetate copolymer. Radiation Physics and Chemistry 81 308-315. 

Ethylene-vinyl acetate copolymers, usually known as EVA, are used in many applications, but especially for low voltage cables. These polymers are easily flammable and flame retardants are added to reduce their flammability. The classic solution is to incorporate aluminium hydroxide or magnesium hydroxide that develop endothermic reactions when heated. Nevertheless, large amounts have to be incorporated, often around 60% and this can lead to a loss of mechanical properties in the compound. Intumescent technology that works well with polypropylene has also been tried for EVA polymer systems. 

E. Leroy, L. Ferry, and J. Cuesta, Intumescence in ethylene-vinyl acetate copolymer filled with magnesium hydroxide and organoclays. In Fire Retardancy of Polymers, ed. Michel Le Bras (London The Royal Chemical Society, 2005), pp. 302-12. 

Siat, C. Bourbigot, S. Le Bras, M. Combustion behaviour of ethylene-vinyl acetate copolymer-based intumescent formulations using oxygen consumption calorimetry. 

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