Improved Flame Retardant Properties of a Halogen-Free Material for Cable Applications

Licentiatavhandling, 2008

Due to the large amount of electric equipment in our surroundings, fire safety of cable materials is becoming increasingly important. Because of environmental and health issues, much focus is on development of halogen-free materials. In this thesis, a halogen-free flame retardant material named Casico™ is studied. The main constituents of Casico are ethylene-acrylate copolymer, calcium carbonate and silicone elastomer. The flame retardant mechanism of the system is multifaceted with swelling, ionomeric cross-linking and formation of a protective surface layer as the most important processes. The performance of a Casico material in a fire situation is much dependant on its dimensional stability and resistance to dripping. The flame retardant properties when using poly(ethylene-co-methacrylic acid) and poly(ethylene-co-butyl acrylate) as the copolymer have been compared. Ionomeric formation between acidic groups in the polymer and calcium ions results in a viscosity increase above 250 – 300°C. This increase occurs at lower temperatures with the EMAA material which has great impact on the fire performance as shown with cone calorimetry and dripping test. In addition, the effect of three different nanofillers (montmorillonite, sepiolite and POSS) on the rheological properties and fire behaviour of the system has been studied. Montmorillonite gave a significant increase in viscosity above 250°C resulting in reduced dripping and decreased heat release rate.