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<p>This study investigates the enhanced flame retardancy and char-forming behavior of halogen-free thermoplastic polyurethane (TPU) incorporating ammonium dihydrogen phosphate–modified rice husk (ADP-RH) as an intumescent flame-retardant additive. Surface phosphorylation of RH introduced phosphorus- and nitrogen-containing functionalities, enabling its multifunctional role as acid, carbon, and gas sources during thermal degradation. Thermogravimetric analysis (TGA) revealed increased char yield and improved integral procedural decomposition temperature (IPDT) values for TPU composites containing ADP-RH. Kinetic analysis using the Ozawa model showed that the apparent activation energy increased from 112&#xa0;kJ·mol⁻¹ for neat TPU to 146&#xa0;kJ·mol⁻¹ for TPU/ADP-RH 20%, indicating enhanced thermal stability. Flammability evaluation demonstrated that TPU/ADP-RH 20% achieved a UL-94&#xa0;V-0 rating with a limiting oxygen index (LOI) of 31%. Cone calorimetry further confirmed a reduction of more than 40% in peak heat release rate compared with neat TPU. TG–FTIR analysis indicated the release of phosphorus- and nitrogen-containing species in the gas phase, which contributed to flame inhibition, while XPS and residue characterization revealed the formation of a dense, P–N–Si-rich protective char layer in the condensed phase. The synergistic action between gas-phase radical quenching and condensed-phase barrier formation accounts for the significant enhancement in flame retardancy. These findings demonstrate that phosphoric acid-modified rice husk effectively promotes stable char formation and improves the fire performance of halogen-free TPU through a well-defined intumescent mechanism.</p>

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Enhanced flame retardancy and char formation of halogen-free thermoplastic polyurethane composite incorporating phosphoric acid-modified rice husk

  • 期刊论文

  • 发表日期：

    2026年7月9日

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  • Chen-Feng Kuan,
  • Chin-Lung Chiang,
  • Chane-Yuan Yang,
  • Hsu-Chian Kuan,
  • Min-Chin Chung

摘要

This study investigates the enhanced flame retardancy and char-forming behavior of halogen-free thermoplastic polyurethane (TPU) incorporating ammonium dihydrogen phosphate–modified rice husk (ADP-RH) as an intumescent flame-retardant additive. Surface phosphorylation of RH introduced phosphorus- and nitrogen-containing functionalities, enabling its multifunctional role as acid, carbon, and gas sources during thermal degradation. Thermogravimetric analysis (TGA) revealed increased char yield and improved integral procedural decomposition temperature (IPDT) values for TPU composites containing ADP-RH. Kinetic analysis using the Ozawa model showed that the apparent activation energy increased from 112 kJ·mol⁻¹ for neat TPU to 146 kJ·mol⁻¹ for TPU/ADP-RH 20%, indicating enhanced thermal stability. Flammability evaluation demonstrated that TPU/ADP-RH 20% achieved a UL-94 V-0 rating with a limiting oxygen index (LOI) of 31%. Cone calorimetry further confirmed a reduction of more than 40% in peak heat release rate compared with neat TPU. TG–FTIR analysis indicated the release of phosphorus- and nitrogen-containing species in the gas phase, which contributed to flame inhibition, while XPS and residue characterization revealed the formation of a dense, P–N–Si-rich protective char layer in the condensed phase. The synergistic action between gas-phase radical quenching and condensed-phase barrier formation accounts for the significant enhancement in flame retardancy. These findings demonstrate that phosphoric acid-modified rice husk effectively promotes stable char formation and improves the fire performance of halogen-free TPU through a well-defined intumescent mechanism.