Toward halogen-free flame resistant polyethylene extrusion coated paper facings

Extrusion coating experiments of flame retarded low density polyethylene (LDPE) onto a standard machine finished Kraft paper have been carried out. A pilot extrusion coating line was used in order to investigate the potential of halogen-free flame retardant system based on azoalkanes such as azocyclohexane (AZO) and 4′,4-bis(cyclohexylazocyclohexyl)methane (BISAZO) for fire resistant coating applications. In comparison, experiments were performed using FlameStab^®NOR116, magnesium dihydroxide (MDH) and a brominated additive Luvogard MB81/PE as reference flame retardants. The concentration of azoalkane flame retardants was varied between 0.5 and 1 wt.%. The maximum extrusion temperature was varied between 260 and 290 °C and the coating layer weight from 12.9 to 25.0 g/m². The obtained multilayer facings containing azoalkanes exhibited significantly improved flame retardant properties, especially at the low coating weight of 12.9 g/m². Under all of the used experimental conditions the runnability on the pilot line was flawless for azoalkane formulations. In contrast, our pre-trials using MDH/LDPE (50:50) formulations failed due to poor film quality and visible white aggregates. Moreover, the multilayer facings containing the FlameStab^®NOR116, Luvogard MB81/PE or mixtures thereof, showed inferior flame retardant properties compared to azoalkane based facings.