In a cone-calorimeter study by some of the same authors as above, 5% zinc- copper- and nickel-ferrite were separately tested as smoke suppressants in flame retarded polyurethane-polyisocyanurate foams (the flame retardant used was 20% TCPP tri (2-chlorylpropyl) phosphate and 10% DMMP dimethyl methylphosphonate).
Smoke density and carbon monoxide production of the FR foam was 25-42% lower with ferrite addition, with the best results for the zinc ferrite, but was still significantly higher than non-FR foam. The zinc ferrite also reduced the peak heat release rate, and the ferrite + FR foams all show lower heat release than non FR foam. The authors suggest that the increased smoke production increase is a result of the gas phase action of the flame retardants used. Based on TG-FTIR and XRD, they suggest that the metal ferrites are reducing release of gaseous products by phosphonate pyrolysis of the polymer and generating metal phosphate residues which can contribute to char formation.
“Smoke and toxicity suppression properties of ferrites on flame-retardant polyurethane–polyisocyanurate foams filled with phosphonate”, X. Liu et al. J Therm Anal Calorim (2016) 125:245–254 http://dx.doi.org/10.1007/s10973-016-5356-3