1% POSS significantly improved fire performance achieved by a phosphorus – nitrogen intumescent FR in polypropylene. Nano- octavinyl POSS (polyhedral oligomeric silsesquioxane) was supplied by Zhengzhou Alfa. The intumescent PIN FR was produced by thermal reaction of APP (from Clariant), melamine and PER (pentaerythritol), to produce a single-component PIN FR (RMAPP). This was tested at 25% loading in polypropylene, improving UL 94 (1.6 mm) from unrated to V2 and LOI from 18 to 28. Replacing 1% RMAPP by POSS considerably improved fire performance, to UL 94 V0 (with no dripping), LOI 31, and also reduced peak heat release rate (1023 kW/m3 for pure PP, 89 with 25% RMAPP and 66 with 1% POSS). Increasing POSS to 2% or 5% (replacing RMAPP) resulted in fire performance poorer than with 1% POSS. Similarly, mechanical performance was best with 1% POSS. The POSS was well mixed with the PP and the RMAPP before injection molding of the samples, and the authors suggest that the improved fire performance and mechanical properties with 1% POSS results from improved dispersion and compatibility between the PIN FR and the polymer and from silicon oxide reinforcement of the char layer.
“Synergistic and compatibilizing effect of octavinyl polyhedral oligomeric silsesquioxane nanoparticles in polypropylene/intumescent flame retardant composite system”, B. Yang et al., Composites Part A 123 (2019) 46–58 https://doi.org/10.1016/j.compositesa.2019.04.032 Image: Wikipedia.