# A Green P–N–Al Synergistic System for Eco-Friendly Flame-Retardant Polystyrene

## TL;DR

A green flame-retardant system using bio-based components improves fire safety and mechanical strength in polystyrene without halogens.

## Contribution

A novel eco-friendly P–N–Al synergistic system achieves high flame retardancy and retains mechanical performance in polystyrene.

## Key findings

- The PS/10ADP/15PA–TETA composite achieved a 28.5% limiting oxygen index and UL-94 V-0 rating.
- Peak heat release rate was reduced by 73.8%, with 78.4% tensile strength retention compared to neat PS.
- The system works via cooperative condensed-phase charring and gas-phase dilution mechanisms.

## Abstract

What are the main findings?
Developed a green flame-retardant strategy using bio-based PA and halogen-free components for PSAchieved 28.5% LOI, UL-94 V-0, 73.8% pHRR reduction, and 78.4% tensile strength retentionRevealed cooperative condensed- and gas-phase flame-retardant mechanisms via in situ P-N-Al network

Developed a green flame-retardant strategy using bio-based PA and halogen-free components for PS

Achieved 28.5% LOI, UL-94 V-0, 73.8% pHRR reduction, and 78.4% tensile strength retention

Revealed cooperative condensed- and gas-phase flame-retardant mechanisms via in situ P-N-Al network

What are the implications of the main findings?
Offers an eco-friendly strategy for high-performance flame-retardant PS materialsProvides a new approach to overcome the flame-retardancy/mechanics trade-off in polymersDemonstrates a design strategy for multifunctional composites with balanced safety and performance

Offers an eco-friendly strategy for high-performance flame-retardant PS materials

Provides a new approach to overcome the flame-retardancy/mechanics trade-off in polymers

Demonstrates a design strategy for multifunctional composites with balanced safety and performance

Polystyrene (PS) is widely used yet highly flammable, and developing halogen-free flame retardants that ensure both high fire safety and mechanical performance remains a challenge. A green intumescent system comprising ammonium dihydrogen phosphate (ADP) and phytic acid–triethylenetetramine (PA–TETA) was incorporated into PS powder via sequential solution grinding and hot pressing. The optimal formulation, PS/10ADP/15PA–TETA, achieved a limiting oxygen index of 28.5% with a UL-94 V-0 rating, and reduced the peak heat release rate and total heat release by 73.8% and 46.2%, respectively, while retaining 78.4% of the tensile strength of neat PS. The ADP/PA–TETA system operates via a cooperative condensed-phase charring and gas-phase dilution mechanism, achieving superior flame retardancy in PS composites. This work provides an effective and eco-friendly strategy for fabricating high-performance PS composites with balanced flame retardancy and mechanical properties.