Mechanism of a polyolefin based effervescent flame retardant material
Fire safety issues are becoming increasingly important in modern society and cables are one potential fire risk since they can start and/or spread a fire. As a result of environmental and safety issues having to do with flame retardants based on halogens, much attention has lately been given to finding halogen free alternatives. This work focuses on Casico, a halogen free flame retardant system used primarily for cable applications. It is based on poly(ethylene-co-acrylate), chalk and silicone elastomer.
Small scale fire tests, such as oxygen index, cone calorimetry and dripping, analytical studies, such as IR, NMR, ESCA, XRD, SEM and TEM microscopy, and visual observations were used to evaluate materials. An original methodology in which the temperature is measured within cone calorimeter specimens using thermo couples was successfully developed.
The flame retardancy of Casico is multifaceted and depends on some simpler factors, such as a volume and dilution effect of inert filler, and other more complex factors, such as the ionomer formation that occurs between acidic groups and calcium ions in the chalk after ester pyrolysis of the acrylate groups, formation and stabilisation of an intumescent structure, and the importance of the surface layer. These factors have successfully been linked to each other and, together with the effect of dispersion and viscosity, the flame retardant properties and behaviour of Casico can be explained satisfactorily.