Synergistic effect of basalt fiber on the thermal properties of intumescent fire retardant coating

This research work presents the enhancement of thermal performance of intumescent fire-retardant coatings (IFRCs) to investigate the synergistic effects of novel type of fiber reinforcement (basalt fibers) towards heat shielding capability for steel structures. The coating basis consists of bisphenol-A epoxy resin (NPEL-128) cross-linked with polyamide amine (ACR Hardener (H-2310)), mixed with expandable graphite (EG), ammonium polyphosphate (APP), melamine and boric acid. Various formulations with different fiber loading were synthesized and characterized. Bunsen burner test in accordance to UL-1709 was performed to examine their fire retardant properties. Moreover, furnace test was carried out to investigate the char expansion. The results showed that 2 wt% basalt fibers (IFRC-B2) greatly enhanced the heat insulation performance, the steel plate backside temperature reaching 187°C after 1-h fire test compared to 375°C for the control formulation (CF) without fiber reinforcement. Char expansion measurements carried out after furnace test show that in the presence of basalt fibers the expansion of IFRC-B2 was twice that of CF. Char was also analyzed by Field Emission Scanning Electron Microscopy (FESEM). Micrographs revealed deep cracks on CF char surface, allowing the heat to diffuse more rapidly and explained the poor fire performances. The char of IFRC-B2 was smooth and dense, while distribution of basalt fibers and char cells were homogenous, with presence of small voids of about similar size, which limited heat transfers. Thermogravimetric analyses (TGA) in pyrolysis conditions showed that residual weight increases by 10 wt%, confirming the increase in thermal stability of the basalt containing formulation.