Effect of Zinc Borate on Flame Retardancy of Humic Acid-based Intumescent Fire Retardant Coatings
Biomass humic acid(HA),ammonium polyphosphate(APP),melamine(MEL)and zinc borate(ZB)were used to prepare intumescent coatings via melt-mixing,and then applied to the surface of steel structure for fire protection.The thermal stabilities of intumescent coatings were determined by thermogravimetric analysis(TGA),and the fire-retardancy were characterized and analyzed by cone calorimeter.The results showed that the coating(C4)with 2%ZB replacing the intumescent component of APP-MEL-HA exhibited the best fire performance.The peak heat release rate(PHRR)and total heat release(THR)were 53.2 kW/m2 and 22.7 MJ/m2,respectively,showing a reduction of 86%and 61%as compared to the control coating(C1).The mechanism of action was revealed according to the analysis of SEM and Raman results of char residue after cone calorimeter test.The combination of APP,MEL,HA and ZB promoted the formation of a continuous and dense graphitized expanded char layer on the surface of the steel plate,effectively preventing the heat and mass transfer,thereby improving the performance of the intumescent coating.
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