The natural mineral clay rectorite (which contains aluminium, calcium, silicon and sodium) was modified by reaction with sodium pyrophosphate then tested at 10% in a waterborne PIN intumescent fire retardant coating, consisting of ammonium polyphosphate, melamine, titanium oxide and pentaerythritol. A 2 mm coating was applied to 5 mm steel plates by brush. The coatings were tested with a non-standard test method, using alcohol burning on the steel plates’ surface as the heat source for 60 minutes. With no intumescent coating, the back of the steel plates reached 200°C in 30 minutes, whereas the temperature with the intumescent coatings was around 20% lower. At 60 minutes, the control and the standard intumescent coating plate both reached around 225°C whereas the plate with the coating including modified rectorite only reached around 200°C. The authors conclude that this modified rectorite clearly improved the intumescent coating on steel, enabling generation of a more uniform and compact intumescent foam structure, giving a ceramic-like effect protecting the foam and improving adhesion to the steel plate.
“An emerging mineral-based composite flame retardant coating: Preparation and enhanced fireproof performance”, W. Xie et al., Surface & Coatings Technology 367 (2019) 118–126 https://doi.org/10.1016/j.surfcoat.2019.03.073
See also the summary of UL fire testing of upholstered furniture in pinfa Newsletter n°102