ABPBI fiber performs better than aramid in outer layer testing of firefighting suits: high thermal stability and carbonization ability are of concern

Research background and material properties

The outer layer of firefighter protective clothing usually uses intrinsic flame-retardant high-performance fibers such as aramid, polybenzimidazole (PBI), polyamide imide, and polyimide. PBI is known for its non flammability and low smoke release. A study published in Fire and Materials focuses on poly (2,5-benzimidazole) (ABPBI) – a synthetic monomer with lower carcinogenicity and higher heat and flame retardancy. The limit oxygen index (LOI) data provided by the study shows that ABPBI is about 72, PBI is about 38.3, and aramid is about 25. Despite its outstanding numerical value, research on ABPBI in the field of flame retardant textiles is still relatively limited.

Testing methods and main results

The research team used ABPBI and aramid fabric woven with 2/1 diagonal weave (surface density 260 gsm) to conduct vertical combustion tests and radiation heat and convective heat exposure experiments. Combined with density functional theory (DFT) calculations, the thermal stability of the two polymers was analyzed from the perspectives of HOMO-LUMO, bond dissociation energy, and Mayer bond order.

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• In the vertical combustion test, both fabrics did not show sustained or smoldering combustion, and the carbon residue was less than 5%.

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• Under convective heat exposure (84 kW m ⁻ ², 30 seconds), aramid fabric exhibits “rupture” behavior due to embrittlement, while ABPBI maintains flexibility and dimensional stability.

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• Dynamic mechanical analysis of ABPBI after thermal exposure shows a decrease of about ten times in storage modulus, while EDS analysis corresponds to a 26.2% loss of oxygen element and a 9.3% increase in carbon element.

; Aramid cannot complete the test under these conditions. Exposure to 10 kW m ⁻ ² radiant heat flux for 180 seconds did not result in significant loss of tensile strength for both fabrics. In terms of overall thermal protection performance (TPP), the ABPBI outer layer combination is 60 cal cm ⁻ ², and the aramid outer layer combination is 44 cal cm ⁻ ², both exceeding the minimum requirement of 35 cal cm ⁻ ².

The calculation and experimental results show that ABPBI has advantages in thermal stability, carbonization ability, and protective performance, and has the potential to be used as an advanced outer layer material for firefighting protective clothing.

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The significance of polymer additives and building materials industry

Although this study focuses on protective textiles, the dimensional stability, carbonization behavior, and weather aging performance of high-performance fibers involved in it at high temperatures have similarities with the demand for flame-retardant and durable materials in the fields of construction and home decoration.

. In applications such as PVC profiles, sealants, and architectural coatings, weather resistance and stability are always the core indicators. The formulation design of antioxidants and light stabilizers directly affects the service life of materials under heat, oxygen, and light conditions. The high LOI and carbonization ability demonstrated by ABPBI provide material level reference ideas for the design of flame-retardant building materials; The characterization methods of mechanical properties and elemental composition changes after thermal exposure in research can also provide reference for the evaluation of weather resistance and aging of building materials. It should be noted that this study focuses on the outer fabric of firefighting clothing, and its conclusions still need to be validated in conjunction with specific processing techniques, formulation systems, and relevant regulatory requirements when applied to building products.

Source: Wiley Online Library，《Fire and Materials》，DOI: 10.1002/fam.70090

Information source:Enhanced Fire Protection: Improved Efficacy of ABPBI Over Aramids as the Outer Layer in Firefighter Suits， Organized by Herun Chemical.