2.5 Bio-based Flame Retardants, Phosphorus Nitrogen Flame Retardantsh

Bio-based flame retardants, as environmentally friendly finishing agents, represent one of the most attractive directions for next-generation flame retardants.

Studies have shown that incorporating nitrogen phosphorus flame retardant containing biomacromolecules into fabrics imparts excellent flame resistance. Phytic acid (IP6), a major phosphorus-containing component in grains, oil plants, and legumes, can be added as a single effective component to PA66 fabrics to enhance their flame retardancy.

Analysis revealed that during the finishing process, hydration reactions occur between IP6 molecules, forming a bio-based coating containing P—O—P groups. The treated PA fabrics exhibited a maximum LOI of 32.3%, no dripping or self-extinguishing behavior, and good wash durability.

Further utilizing IP6's metal ion coordination ability, a low concentration of IP6 was combined with, Al3+ ions to form insoluble Al3+-IP6 composite salts in situ on the fabric surface, through layer-by-layer deposition technology, eliminating the need for high-temperature curing. This approach maintained high LOI, and no dripping while enhancing fabric wash durability. Chitosan, calcium alginate, and oxidized sucrose are also well-studied bio-based flame retardants.

2.6 Multi component Synergistic Flame Retardants, Phosphorus nitrogen flame retardant.

The synergistic effect refers to the enhancement of system performance, when two or more components are combined at the same addition level, surpassing the sum of their individual contributions. This phenomenon is commonly observed in flame retardant systems, such as the phosphorus nitrogen synergism.

[(6-Oxo-(6H)-dibenzo[c,e][1,2]oxaphosphinine-6-one)methyl]succinic acid (DDP) is a DOPO derivative renowned for its high thermal stability, antioxidant properties, and excellent water resistance, making it an outstanding reactive flame retardant.

Li Yuanyuan et al. achieved phosphorus nitrogen synergistic flame retardancy in PA66 resins, through the combined use of melamine cyanurate (MCA) and halogen free flame retardant DDP. By integrating in-situ polymerization and copolymerization, the researchers prepared flame retardant PA66 resins via melt polycondensation.

When MCA was present at 2% and halogen free flame retardant at 4%, the resin achieved UL94 V-0 rating in vertical burn tests, with a limiting oxygen index (LOI) of 30.6%. This demonstrates that the combination of metal and phosphorus-based flame retardants, can lead to synergistic flame retardant effects.

Zhang et al. synthesized three dicyclohexylphosphinic acid metal salts, and found that aluminum and zinc salts, exhibited higher thermal stability than magnesium salts. When blended with PA66, aluminum salts demonstrated the best overall performance, balancing mechanical properties and flame retardancy. Optimal flame retardancy, achieving V-0 rating in vertical burn tests, was achieved at a loading of 15%.

The phosphorus-silicon combination (AlPi-polydimethylsiloxane) was investigated, for its flame retardancy in PA66 glass fiber composites. It was found that the phosphorus-silicon flame retardant improved the thermal decomposition of the composites, reducing the maximum mass loss rate, and enabling their application in high-temperature environments.

Kundu et al. functionalized green phosphorus compounds such as graphene oxide, lignin, and IP6 to enhance the flame retardancy of PA66 fabrics. This study highlights that nanomaterials and biobased flame retardants can also achieve synergistic flame retardant effects.

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