Mechanical and flame-retardant properties and thermal decomposition of vinyl ester resin modified by different phenyl silsesquioxanes

The mechanical properties and fire resistance of vinyl ester resin (VER) composites containing cage-shaped octaphenyl silsesquioxane (OPS), incompletely cage-shaped phenyl silsesquioxane (PhT₇POSS), and ladder-shaped phenyl silsesquioxane (PPSQ) were investigated. The POSS structure and dispersion have a great influence on the mechanical properties, thermal stability, and decomposition process of VER composites. The bending strength at break and modulus of the VER-POSS composites were enhanced obviously, especially for VER-PPSQ composite and VER-OPS composite, respectively. In addition, PhT₇POSS-based VER composites revealed the lower values of the peak heat release rate, total heat release, and total smoke release in cone calorimetry tests due to the formation of dense carbon/silica protective layers that acted as a barrier to heat and mass transfer. Moreover, the flame-retardant mechanisms of condensed phase and gas phase were also investigated in detail. These results illustrate VERs modified by OPS, PhT₇POSS, and PPSQ are providing an applicable method to fabricate the composites with excellent flame-retardant and mechanical properties.