Facile synthesis of lithium containing polyhedral oligomeric phenyl silsesquioxane and its superior performance in transparency, smoke suppression and flame retardancy of epoxy resin

Massive release of toxic volatiles and smoke during combustion is one of the biggest problems facing epoxy resin composites, therefore, it is still a huge challenge to obtain a flame retardant that can simultaneously improve the flame retardancy and reduce the evolution of smoke and toxic gases. Herein, a novel lithium containing polyhedral oligomeric phenyl silsesquioxane (Li-Ph-POSS) has been prepared via hydrolysis condensation of phenyltriethoxysilane in the presence of LiOH·H₂O. FTIR, NMR, and MALDI-TOF-MS were used to identify the structure of Li-Ph-POSS, which indicate that it is a hepta-phenyl POSS comprised of incompletely condensed Si–OH and Si–O–Li groups. The excellent compatibility and dispersion of Li-Ph-POSS in EP/Li-Ph-POSS nanocomposites were detected by SEM and TEM. The effective smoke suppression and flame retardancy of EP/Li-Ph-POSS nanocomposites were investigated using cone calorimeter, smoke density and limited oxygen index measurements. Compared with pure EP, the EP with 4 wt% Li-Ph-POSS made the peak of heat release rate (p-HRR), total heat release (THR), peak of smoke production rate (p-SPR) and peak of CO production rate (p-COP) reduce by 61%, 36%, 44%, and 72%, respectively. This work provides a new strategy of mitigating the fire hazard of EP using phosphorus- and halogen-free metal-POSS.