Bio-functionalization of fillers with natural phytic acid for sustainable flame-retardant agents for natural rubber composites

The current challenge for sustainable flame retardants has led to innovative approaches, including the utilization of natural substances to enhance the fire resistance of elastomer composites. This paper presents the design of eco-friendly hybrid flame-retardant additives based on mineral fillers (hydrotalcite (LDH) and sepiolite (SEP)) modified with aminosilane (APTS) and phytic acid (PA) for natural rubber (NR) biocomposites. The synergistic effects of the PA and silanized mineral fillers resulted in NR composites with improved thermal, mechanical, and barrier properties, as well as increased flame retardancy. Importantly, it was proven that direct in-situ application of PA into elastomer cured with sulphur-based crosslinking systems is ineffective, due to its negative effect on the curing process (significantly reducing torque moment). Binding the PA onto silanized fillers enabled the creation of hybrid additives that leverage the flame-retardant benefits of PA without compromising the other properties of the polymer. The addition of PA-modified fillers to NR reduced the heat release rate (HRR) by around 40 %, indicating outstanding flame retardancy. This work makes a significant contribution and expands the understanding of using eco-friendly natural compounds to reduce the flammability of sulfur-cured elastomers.