A new approach to improve the efficiency of intumescent flame retardant for polypropylene fibers

Abstract

This study introduces an improved approach to enhance polypropylene (PP) flame retardancy. High intumescent flame retardant (IFR) loadings (30 wt%) often compromise PP's mechanical properties. The research investigates the impact of different mixing sequences, including novel direct and multi-step methods, on the flame retardancy and properties of PP/IFR-silane composites. Composites, prepared via a two-roll mill and melt-spun into fibers, showed significant performance improvement with a proper multi-step mixing sequence (M-1) where ammonium polyphosphate (APP) particles were pre-treated with silane. This approach allowed reducing IFR content from 30 wt% to 25 wt% while maintaining a V0 UL94-V rating. The M-1 sequence resulted in silane strongly coating APP and enhancing thermal stability because of reduced phosphorus degradation and strong C-N and C=N bond formation, indicating enhanced chemical interactions. Rheological analysis also showed greater early-stage char expansion, improving polymer protection during combustion. The PP/mod-IFR composite fibers exhibited homogeneous additive distribution and chemical compatibility.