Flame retardant epoxy composites with epoxy-containing polyhedral oligomeric silsesquioxanes

A kind of polyhedral oligomeric silsesquioxanes (POSS) containing the propoxyl-epoxy and phenyl groups (pr-ep-Ph-POSS) was synthesized via hydrolytic condensation reaction. Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry identified the structure of the pr-ep-Ph-POSS, including major caged Si₆O₉ (T6), Si₁₀O₁₅ (T10), Si₁₂O₁₈ (T12), etc. The pr-ep-Ph-POSS was applied into the epoxy resin to achieve EP/pr-ep-Ph-POSS composites. Thermogravimetric analysis indicated that EP/pr-ep-Ph-POSS showed excellent thermal properties than pure EP. The fire behaviors of EP/pr-ep-Ph-POSS composites were evaluated based on the cone calorimetry, limiting oxygen index (LOI), UL-94 vertical burning test, and smoke density test. The smoke density decreased by ~30%, the LOI value reached to 26.4%, dripping was inhibited, and the peak of heat release rate decreased by ~62%. X-ray photoelectron spectroscopy analysis and FTIR indicated that protective-barrier effect is the main flame-retardant mode of action for pr-ep-Ph-POSS, due to the formation of the Si-O-Si, Si-O-C, and Si-C condensed phase, which improve the thermal stability, strength, and integrity of the char layer.