Urchinlike Shells of TiO2 Hollow Spheres for Improving the Fire Safety of Epoxy Resin

Titanium dioxide (TiO2) is widely studied because of its excellent properties, which make TiO2 materials suitable for various applications. Here we introduce TiO2 particles with different hierarchical structures which can improve the fire safety of epoxy resin (EP). Both amorphous hydrous TiO2 solid spheres and urchinlike mesoporous TiO2 hollow spheres (UMTHS) can enhance the thermal stability of EP composites. Moreover, cone test results demonstrate that EP/UMTHS with a 2 wt % loading has the lowest heat release rate, total heat release, smoke production rate, and total smoke production values among all the samples. The following plausible mechanism is proposed: urchinlike shells of UMTHS come into contact with each other during the stirring process and partly form a larger shell structure through a fusion process. The physical barrier formed by the fused shell can both shield the composites from external radiation and postpone the transfer of heat and flammable pyrolysis gases.