Low smoke halogen-free materials for wire and cable applications

Licentiate thesis, 2002

Fire safety issues are becoming increasingly important in modern society and cables are one potential fire risk since they can start a fire and/or spread one. Traditionally, materials containing halogen have been used as primary insulation in low voltage power and telecommunication cables and most cables used today therefore contain halogen. Today, as a result of concern with environmental and safety issues, the focus has recently been on halogen-free materials that perform well in fire situations. Casico is a halogen-free material used as insulation in low voltage applications. Its flame retardant properties have been evaluated in this study, including the flame retardant effect of each individual component of Casico: ethylene-acrylate copolymer, chalk and silicone elastomer. A system based on low density polyethylene, chalk and silicone elastomer has been used as a comparative material. Small scale fire tests, such as oxygen index and cone calorimetry, and visual and analytical studies, for instance IR, NMR, ESCA and XRD, of the residues left after thermal treatment were carried out. The results show that the Casico system has good flame retardant properties. This is due to different factors, such as dilution with an inert filler, ester pyrolysis of acrylate groups, ionomer formation and formation of an intumescent structure. Special emphasis is placed on the formation of the intumescent structure obtained at 500C and 1000C and it is shown that the initially formed structure consists mainly of chalk and silicon dioxide whereas the final structure consists of calcium silicate, calcium oxide and calcium hydroxide