Preparation and performance analysis of palygorskite reinforced silicone-acrylic emulsion-based intumescent coating

Aiming to improve the fire resistance, the synergistic effects of palygorskite and expandable graphite (EG) on water-based intumescent fire retardant (IFR) coatings were investigated in details by fire resistance test, limiting oxygen index (LOI) test, vertical burning (UL-94) tests, thermogravimetry (TGA)-differential scanning calorimeter (DSC) test, and cone calorimeter test. The char residues were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Brunauer-Emmett-Teller test (BET). The backside temperature of the substrate of sample 3-3 with 3 wt% of EG and 3 wt% of palygorskite addition (SP3-3) was recorded to be 150 °C after 120 min fire test, 46.5% lower than that of the sample 1 with no addition (SP1). The SP3-3 had the best fire retardant performance reflected by UL-94 V0 flammability rating and the LOI value as high as 35.8%. The TG-DSC analysis showed palygorskite can increase the thermal stability and decrease the decomposition rate of the coatings. The cone calorimeter test demonstrated SP3-3 remarkably reduce the value of peak heat release rate and peak smoke production release by 64.1% and 85.7%, respectively. The XRD analysis confirmed that the decomposition compounds of ammonium polyphosphate, fillers, and palygorskite can react and form a ceramic-like protective barrier, which enhanced the thermal stability and char yield. In addition, the SP3-3 had shown best results in char expansion and char morphology.