Study on the effect of the density and incorporation amount of Coal Fly ash hollow microspheres on the fire performance of epoxy resin

Coal Fly ash hollow microspheres (CSs), owning the potential for flame retardancy, are currently being researched to reduce the fire hazard of polymers. In this article, a series of Coal Fly ash hollow microspheres/ epoxy resin (CSs/EP) composites have been fabricated. The effects of CSs density and incorporation amount on the flame retardancy and thermal stability of the CSs/EP system were investigated by cone calorimeter test (CC) and thermogravimetric (TG) analysis. The CC results demonstrated that the fire safety of CSs/EP composites first increased and then decreased when the CSs densities were 1.90 g/cm3, 1.83 g/cm3, 1.77 g/cm3, 1.70 g/cm3, and 1.65 g/cm3. When CSs was added in amount of 2 wt%, 4 wt%, 6 wt%, 8 wt%, and 10 wt%, the fire safety of CSs/ EP composites also increased initially and then decreased. Compared with pure EP, the FRI of CSs/EP composites containing the CSs density of 1.77 g/cm3 and incorporation amount of 8 wt% was enhanced to 2.69 times, the FGI was reduced by 38%, and the FPI was increased by 56%. The phenomenon corresponds to the TG results, and the addition of CSs did reduce the initial decomposition temperature of CSs/EP (1.77 g/cm3, 8 wt%), while increasing the carbon residue. Scanning electron microscope (SEM) give positive evidence that the CSs/EP composite (1.77 g/cm3, 8 wt%) has a continuous and complete corrugated char residue layer. In terms of me-chanical properties, the flexural strength of CSs/EP increased initially and then dropped as the decrease of density and the increase of CSs incorporation amount.