Günter Beyer, Fire & Polymer, Belgium, discussed nano organoclays as PIN FRs in LS0H formulations (Low Smoke Zero Halogen). They are effective if the polymer enters between the molecular layers of the organoclay, resulting in a nanocomposite. This depends on compatibility of the organoclay with the polymer, and is controlled by the polymer´s polarity. Without this nano-scale infusion of the polymer into the clay, dripping will not be prevented in fire. Cone calorimeter results show that an organically modified layered silicate (organoclay) in EVA-ATH formulations can reduce peak heat release by around one third, increase time to ignition and to peak heat release, and reduce smoke emission, with formation of a compact char. Improved FR properties of nanocomposites allow cheaper medium voltage cable construction because a fire-protective mica tape underneath the cable jacket can be avoided, whilst still passing IEC 60332 Cat D. Although MFI (Melt Flow Index) data for such nanocomposite compounds may indicate increased viscosity, they nonetheless show good processing by extrusion, because of higher shear rates, often better than classical EVA-ATH compounds. Further challenges are that the high surface area of properly dispersed organoclays may immobilise polar antioxidants or UV stabilisers and that transition metals (such as iron) present in organoclay may accelerate long term polymer degradation, but these can be addressed by stabilisers. Also, quaternary ammonium compounds used as organic modifiers in organoclays can pose problems during processing if temperatures are too high, such as with PET or PC.
Günter Beyer, Fire & Polymer, Belgium
BACK TO NEWS