Combined effect of silicate coating and phosphate loading on the performance improvement of a keratinous fiber-based flame retardant

Although the effectiveness of organic-inorganic combination on the flammability reduction in polymeric materials has been proved by the multi-layer coating method on fabric and foam, the technique has not been intensively investigated for bulk polymers. In order to impart the excellence of the combination to bulk polymers, the thermal barrier resulted from the hybrid has to be triggered in the entire region of the polymer during combustion. In this work, phosphate loaded chicken feather fibers (CFF) with layered silicate outer coatings are developed into an efficient intumescent flame retardant (IFR) material system for polypropylene (PP). The organic-inorganic hybrid material, designed for silicate reinforced composite char formation during combustion, allows the modified PP composite to achieve significantly improved flame retardancy compared to that of the composite modified by the only phosphate. A small silicate content (0.4 wt%) leads to 27 wt% reduction in phosphate to achieve the same level of flame retardancy for PP. Furthermore, the efficiency of loaded phosphate, measured by a cone calorimeter, is 14% higher than that of a commercial IFR, ammonium polyphosphate (APP). Thermal gravimetric analysis and cone calorimeter tests demonstrate a suppressed decomposition of phosphorus and CFF at a higher temperature due to robust char formation. The characterization of the char residue using SEM-assisted elemental analysis confirms the silicate reinforced char. Flame retardant mechanism and mechanical performance have also been investigated to aid a better understanding and furthering its performance improvement.

Automated summary

In this study, an organic-inorganic hybrid material with phosphate loaded chicken feather fibers (CFF) and layered silicate outer coatings was developed as an efficient intumescent flame retardant system for polypropylene. The addition of a small amount of silicate led to a significant improvement in flame retardancy compared to phosphate only modification, achieving a 27 wt% reduction in phosphate while maintaining the same level of flame retardancy for PP. The loaded phosphate showed 14% higher efficiency compared to a commercial IFR, ammonium polyphosphate, and thermal analysis confirmed the formation of a robust char residue during combustion.