Tomiak, Florian
Verarbeitung und Brandverhalten blähgraphitgefüllter Polymere
Florian Tomiak
Thermoplastic material systems are easily ignitable and contribute significantly to the release of heat and smoke in case of fire. Today, flame retardant modifications of thermoplastic material systems are usually achieved by additivation. As halogen-containing flame retardant additives are increasingly replaced by halogen-free additives, due to health and environmental concerns, new solutions are required. A promising halogen-free alternative are solutions whose flame retardant mechanism is based on the formation of a highly intumescent residue. Expandable graphite represents such a system. The flame retardant effect of expandable graphites is largely dependent on the expansion capacity of the particles. High hydrodynamic stresses cause erosion and particle breakage during processing. This reduces the stacking height of layered graphene and consequently the expansion capacity of individual particles.
This work investigates the processing stability of expandable graphite and evaluates the influence of processing-induced particle damage on the flame behavior. The investigations were carried out experimentally by systematic processing condition variation in compounding (twin-screw extruder) and injection molding processes. It was shown that the degree of particle damage depends significantly on reaching a critical hydrodynamic stress of about 0.1 MPa. Hydrodynamic stresses commonly arise from the flow of polymeric melts and are therefore largely dependent on the viscoelastic properties of the matrix polymer. Particularly high-viscosity polymers generate high levels of stress, resulting in substantial damage to integrated expandable graphite. Regarding the resulting flame retardant performance, the degree of particle damage impacts the heat release rate, peak heat release and the total heat emitted. However, the flashover tendency (Petrella Index) as well as UL-94 classifications and the oxygen index remain stable and have been shown to be largely independent of the degree of particle damage.
pages: 159