spore: profile
id: pbi
spore_version: 0.2
family: high-performance-polymers
name: Polybenzimidazole
abbreviation: PBI
role: High-temperature aromatic polymer used as flame-resistant fibre and moulded resin, and in NASA space textiles
category: polymers
type: high-performance
summary: |
  Polybenzimidazole (PBI) is an all-aromatic heterocyclic polymer, first developed in 1961 by Vogel and Marvel. It has no melting point and is usually yellow to brown. Goodfellow lists a density of 1.3 g/cm3, a heat deflection temperature of 435 degC at 0.45 MPa, a tensile strength of 160 MPa, a tensile modulus of 5.9 GPa and a limiting oxygen index of 58 percent. TotalMateria gives a glass transition of 425 degC. As a sample on the MISSE 2 PEACE experiment in low Earth orbit it had an atomic oxygen erosion yield of more than 2.21e-24 cm3/atom, which NASA prints as a lower bound (greater-than sign).
best_for: Flame-resistant protective fabrics and high-temperature parts that must keep stiffness, with a glass transition of 425 degC
weakest_at: Atomic oxygen in low Earth orbit (erosion yield of at least 2.21e-24 cm3/atom on MISSE 2); fine dust is flammable and explosive when suspended in air
identity:
  formula: Polybenzimidazole, repeat unit C20H12N4 (molar mass 308.34 g/mol), poly[2,2'-(m-phenylene)-5,5'-bibenzimidazole]
  cas: 32075-68-6
  source: wiki-pbi
  where: 'Wikipedia Polybenzimidazole page (infobox: repeat-unit formula and molar mass; chemical name). CAS 32075-68-6 is also printed on the Goodfellow PBI film page. The MCAM SDS gives CAS 25928-81-8 for polybenzimidazole, so both numbers are recorded and the difference is listed in gaps.'
tags:
  environments:
    - low-earth-orbit
  stresses:
    - atomic-oxygen
  applications:
    - habitats-and-suits
properties:
  - benchmark: density
    value: 1.2758
    unit: g/cm3
    scope: material
    conditions:
      basis: polymer density from the MISSE 2 PEACE polymer table, supplier information or density gradient
    method: Table II density column, reported with the mass fraction of sodium ash
    status: ground
    source: nasa-misse2-pbi
    where: Table II (MISSE 2 PEACE polymers density and fractional ash content), row Polybenzimidazole PBI
  - benchmark: density
    value: 1.3
    unit: g/cm3
    scope: material
    conditions:
      basis: polybenzimidazole film product listing, form not stated on the page beyond film
    method: Density value printed on the Goodfellow product page
    status: ground
    source: goodfellow-pbi
    where: Mechanical and Physical Properties table, Density( gcm-3 ) row
  - benchmark: glass_transition_temperature
    value: 425
    unit: degC
    scope: material
    conditions:
      basis: single glass transition value printed in the material data table for the PBI entry
    method: Value printed on the TotalMateria material data page (page lists temperature bands with the value)
    status: ground
    source: totalmateria-pbi
    where: Physical properties, row Glass Transition Temperature, Tg
  - benchmark: heat_deflection_temperature
    value: 435
    unit: degC
    scope: material
    conditions:
      stress: 0.45 MPa
    method: Heat-deflection temperature printed in the thermal properties table
    status: ground
    source: goodfellow-pbi
    where: Thermal Properties table, row Heat-deflection temperature - 0.45MPa( C )
  - benchmark: max_service_temp
    value: 260
    value_high: 400
    unit: degC
    scope: material
    conditions:
      basis: upper working temperature range printed on the product page
    method: Range printed on the Goodfellow product page as 260-400
    status: ground
    source: goodfellow-pbi
    where: Thermal Properties table, row Upper working temperature( C ) 260-400
  - benchmark: thermal_conductivity
    value: 0.41
    unit: W m-1 K-1
    scope: material
    conditions:
      temperature: 23 degC
    method: Value printed as 0.41@23 degC on the product page
    status: ground
    source: goodfellow-pbi
    where: Thermal Properties table, row Thermal conductivity
  - benchmark: cte
    value: 23
    unit: 10-6 K-1
    scope: material
    conditions:
      basis: coefficient of thermal expansion as printed on the product page, temperature not stated
    method: Value printed as x10-6 K-1 on the product page
    status: ground
    source: goodfellow-pbi
    where: Thermal Properties table, row Coefficient of thermal expansion
  - benchmark: elastic_modulus
    value: 5.9
    unit: GPa
    scope: material
    conditions:
      basis: tensile modulus printed on the product page
    method: Value printed on the Goodfellow product page
    status: ground
    source: goodfellow-pbi
    where: Mechanical Properties table, row Tensile modulus( GPa )
  - benchmark: ultimate_tensile_strength
    value: 160
    unit: MPa
    scope: material
    conditions:
      basis: tensile strength printed on the product page (unnotched)
    method: Value printed on the Goodfellow product page; Wikipedia infobox gives the same 160 MPa
    status: ground
    source: goodfellow-pbi
    where: Mechanical Properties table, row Tensile strength( MPa )
  - benchmark: elongation
    value: 3
    unit: '%'
    scope: material
    conditions:
      basis: elongation at break printed on the product page
    method: Value printed on the Goodfellow product page
    status: ground
    source: goodfellow-pbi
    where: Mechanical Properties table, row Elongation at break( % )
  - benchmark: limiting_oxygen_index
    value: 58
    unit: '%'
    scope: material
    conditions:
      basis: oxygen concentration at which the sample burns, printed on the product page
    method: Value printed on the Goodfellow product page; the page also says Does not burn in its flammability row
    status: ground
    source: goodfellow-pbi
    where: Physical Properties table, row Limiting oxygen index( % )
  - benchmark: moisture_absorption
    value: 0.4
    unit: '%'
    scope: material
    conditions:
      time: over 24 hours
    method: Value printed as water absorption over 24 hours on the product page
    status: ground
    source: goodfellow-pbi
    where: Physical Properties table, row Water absorption - over 24 hours( % )
  - benchmark: dielectric_constant
    value: 3.2
    unit: '-'
    scope: material
    conditions:
      frequency: 1 MHz
    method: Value printed on the Goodfellow product page at 1 MHz
    status: ground
    source: goodfellow-pbi
    where: Electrical Properties table, row Dielectric constant @1MHz
  - benchmark: dielectric_strength
    value: 21
    unit: kV/mm
    scope: material
    conditions:
      basis: dielectric strength printed on the product page
    method: Value printed on the Goodfellow product page
    status: ground
    source: goodfellow-pbi
    where: Electrical Properties table, row Dielectric strength( kV mm-1 )
  - benchmark: electrical_resistivity
    value: 800000000000000
    unit: Ohm cm
    scope: material
    conditions:
      basis: volume resistivity printed on the product page
    method: Printed as 8x10 to the power 14 Ohmcm on the Goodfellow product page
    status: ground
    source: goodfellow-pbi
    where: Electrical Properties table, row Volume resistivity( Ohmcm )
  - benchmark: atomic_oxygen_erosion_yield
    value: 2.21e-24
    unit: cm3/atom
    bound: lower
    scope: material
    conditions:
      environment: low Earth orbit, ISS outside Quest airlock, MISSE 2 PEACE tray, 3.95 years
      bound: lower bound, printed as greater than 2.21e-24
    method: Measured erosion yield from the MISSE 2 flight sample, read from NASA Table I; NASA prints it as a lower bound
    status: flight
    source: nasa-misse2-pbi
    where: Table I (MISSE 2 PEACE polymers erosion yield data), row Polybenzimidazole PBI
  - benchmark: glass_transition_temperature
    value: 415
    unit: degC
    scope: material
    conditions:
      standard: ISO 11357-1,-2
    method: Value printed on the APSOplast PBI technical data sheet (compound PBI 00.004-00)
    status: ground
    source: apso-pbi
    where: Thermal attributes, row Glass transition temperature (ISO 11357-1,-2)
  - benchmark: max_service_temp
    value: 310
    unit: degC
    scope: material
    conditions:
      basis: maximum operating temperature, long term
    method: Value printed on the APSOplast PBI technical data sheet
    status: ground
    source: apso-pbi
    where: Thermal attributes, row Max. operating temperature long term
  - benchmark: min_service_temp
    value: -50
    unit: degC
    scope: material
    conditions:
      basis: minimum operating temperature
    method: Value printed on the APSOplast PBI technical data sheet
    status: ground
    source: apso-pbi
    where: Thermal attributes, row Min. operating temperature
  - benchmark: moisture_absorption
    value: 7.5
    unit: '%'
    scope: material
    conditions:
      basis: at saturation in air of 23 degC and 50 percent relative humidity
    method: Value printed on the APSOplast PBI technical data sheet
    status: ground
    source: apso-pbi
    where: Other attributes, row Moisture absorption
  - benchmark: atomic_oxygen_erosion_yield
    value: 2.27e-24
    unit: cm3/atom
    scope: material
    conditions:
      environment: low Earth orbit prediction, MISSE 2 exposure
    method: Predicted erosion yield from the NASA atomic oxygen predictive tool, compared with the measured value in Table VII
    status: calculated
    source: nasa-misse2-pbi
    where: Table VII (comparison of the predicted and actual erosion yields), row Polybenzimidazole PBI, predicted column
corrosion:
  - environment: Low Earth orbit, atomic oxygen (MISSE 2, ISS outside the Quest airlock, 3.95 years)
    headline: PBI erodes under atomic oxygen, and the MISSE 2 flight value is only a lower bound.
    effect: The flight erosion yield was greater than 2.21e-24 cm3/atom. NASA gives a predicted value of 2.27e-24 cm3/atom for the same exposure, so the prediction and flight value are close.
    rating: moderate
    conditions:
      fluence: not printed on the PBI row of Table I
      duration: 3.95 years
    source: nasa-misse2-pbi
    where: Table I and Table VII (NASA/TM-2008-215490)
  - environment: Elevated temperature in air
    headline: PBI keeps its service range to about 400 degC.
    effect: The product page gives an upper working temperature of 260 to 400 degC and a heat-deflection temperature of 435 degC at 0.45 MPa. Wikipedia says PBI is stable above 400 degC and does not melt.
    rating: low
    conditions:
      basis: upper working temperature range from the product page
    source: goodfellow-pbi
    where: Thermal Properties table
  - environment: Humid air and water
    headline: Water uptake is low.
    effect: Water absorption over 24 hours is 0.4 percent. Wikipedia gives a moisture regain of 13 percent, close to cotton at 16 percent.
    rating: low
    conditions:
      time: 24 hours
    source: goodfellow-pbi
    where: Physical Properties table, Water absorption row
  - environment: Phosphoric acid in fuel-cell membranes
    headline: Phosphoric acid-doped PBI leaches out of the membrane.
    effect: Leaching and condensation on the phosphate groups limited phosphoric acid-doped PBI membranes. A higher acid loading degrades mechanical properties.
    rating: moderate
    conditions:
      basis: doped membranes, not the neat polymer
    source: pmc-pa-pbi-review
    where: Introduction and PBI membrane sections
risks:
  hazards:
    - text: 'The MCAM safety data sheet gives no GHS classification for polybenzimidazole: classification none, no signal word, no hazard statements.'
      ghs: []
      source: mcam-sds-pbi
      where: Section 2 (GHS classifications)
    - text: Dust is flammable and explosive when finely divided and suspended in air, so dust control and grounding apply during handling.
      ghs: []
      source: mcam-sds-pbi
      where: Section 5 (fire-fighting measures) and Section 7 (dust handling)
  failure_risks:
    - mode: Atomic oxygen erosion in low Earth orbit
      trigger: Atomic oxygen fluence in LEO (MISSE 2, 3.95 years)
      consequence: Surface erosion, with a flight erosion yield greater than 2.21e-24 cm3/atom
      source: nasa-misse2-pbi
      where: Table I
    - mode: Acid leaching in phosphoric acid-doped membranes
      trigger: Phosphoric acid doping in fuel-cell electrolytes
      consequence: Loss of acid and conductivity; higher acid loading degrades mechanical properties
      source: pmc-pa-pbi-review
      where: PBI membrane section
  side_effects:
    - text: Processing can release dust; the primary route of entry is inhalation of particulates.
      source: mcam-sds-pbi
      where: Section 11 (toxicological information), primary route of entry
  handling:
    - text: 'Keep particulate exposure under the limits in the SDS: ACGIH TLV 10 mg/m3, OSHA PEL 15 mg/m3 total and 5 mg/m3 respirable.'
      source: mcam-sds-pbi
      where: Section 8 (exposure controls), particulates table
    - text: Use local exhaust ventilation and ground transfer equipment where dust can form, and remove ignition sources.
      source: mcam-sds-pbi
      where: Section 7 (handling and storage)
  mitigations:
    - text: Use local exhaust ventilation and dust control as the SDS directs.
      source: mcam-sds-pbi
      where: Section 8 (exposure controls)
uses:
  - application: habitats-and-suits
    device: Apollo-era tethers, belts and restraints
    example: NASA reports that PBI multifilament yarns were used in tethers, belts and restraints in the Apollo program.
    source: ntrs-flame-fibers-2017
    where: Section on the development of polybenzimidazole fibers
  - application: habitats-and-suits
    device: Space Shuttle stowage partitions and Skylab apparel
    example: NASA reports that PBI staple fibre was used in apparel fabrics for Skylab and in stowage partitions for the Space Shuttle programme.
    source: ntrs-flame-fibers-2017
    where: Section on the development of polybenzimidazole fibers
  - application: habitats-and-suits
    device: Protective apparel and flame-resistant clothing
    example: Wikipedia lists protective apparel as the first application of PBI fibre, and the Goodfellow page lists flammability as Does not burn.
    source: wiki-pbi
    where: Applications, 4.1 Protective apparel; Goodfellow Physical Properties table
supply:
  - subject: Producer
    abundance: PBI fibre and filament were developed by Hoechst Celanese under US government contracts from the Department of Defense and NASA. The company dedicated a facility to PBI filaments. No current production volume or country share was found in a source read in this run.
    producers:
      - name: Hoechst Celanese
        note: Named as the developer and the producer of PBI filaments in the NASA report
        country: United States
    critical_lists: []
    recycling: Not sourced.
    substitutes:
      - Wikipedia names phosphoric acid-doped PBI as one of the most mature membrane options for high-temperature PEM fuel cells.
    source: ntrs-flame-fibers-2017
    where: Section on the development of polybenzimidazole fibers and the closing section on the Hoechst-Celanese facility
  - subject: Feedstock
    abundance: PBI is made by condensing diphenyl isophthalate with 3,3',4,4'-tetraaminodiphenyl, then the intermediate cyclises (Wikipedia, Synthesis). No feedstock tonnage or price was found.
    producers: []
    critical_lists: []
    recycling: Not sourced.
    substitutes: []
    source: wiki-pbi
    where: Synthesis section
story:
  recipe:
    line: PBI is an all-aromatic polymer. Its repeat unit is C20H12N4, with a molar mass of 308.34 g/mol, built from benzimidazole rings linked through a meta-phenylene group (Wikipedia). It is made by condensing diphenyl isophthalate with 3,3',4,4'-tetraaminodiphenyl, and the intermediate cyclises spontaneously (Wikipedia, Synthesis).
    parts:
      - name: Carbon
        symbol: C
        role: Forms the aromatic benzimidazole rings and the meta-phenylene link of the backbone.
      - name: Hydrogen
        symbol: H
        role: Sits on the aromatic rings; the all-aromatic backbone gives the high thermal stability.
      - name: Nitrogen
        symbol: 'N'
        role: Forms the imidazole rings. Their hydrogen-bond network helps the polymer stay stiff and oxidation resistant.
  risk_groups:
    - title: For people
      level: 1
      verdict: Dust is the watch point
      lead: The MCAM SDS gives no GHS hazard classification, but it warns that fine dust is flammable and explosive, and that inhalation of particulates is the main route of entry.
    - title: For the mission
      level: 2
      verdict: Atomic oxygen erodes it
      lead: The MISSE 2 flight sample shows an erosion yield greater than 2.21e-24 cm3/atom, a lower bound from NASA Table I.
  why: PBI keeps its shape and stiffness at high temperature and does not burn easily. Its glass transition is 425 degC (TotalMateria), and its limiting oxygen index is 58 percent (Goodfellow). NASA used it for Apollo tethers and Shuttle-era textiles.
  uses:
    - where: Space textiles
      line: NASA reports that PBI staple and multifilament fibres were used in Apollo tethers and restraints, Skylab apparel and Space Shuttle stowage partitions.
    - where: Protective clothing
      line: Wikipedia lists protective apparel as the main use of PBI fibre.
  can_do:
    - label: Hold a heat
      value: 435 degC
      line: Holds a heat-deflection temperature of 435 degC at 0.45 MPa (Goodfellow).
    - label: Resist a flame
      value: 58 percent
      line: Limiting oxygen index of 58 percent (Goodfellow); the page says the material does not burn.
    - label: Survive orbit
      value: 2.21e-24 cm3/atom
      line: Atomic oxygen erosion yield on MISSE 2 is greater than 2.21e-24 cm3/atom, a lower bound (NASA Table I).
  compare: The Goodfellow PBI product page gives a density of 1.3 g/cm3 and a tensile strength of 160 MPa, with a tensile modulus of 5.9 GPa, a glass transition of 425 degC on TotalMateria and a limiting oxygen index of 58 percent. Its density in the NASA polymer table is 1.2758 g/cm3. The APSO datasheet gives a glass transition of 415 degC and a long-term maximum service temperature of 310 degC.
  compare_rows:
    - label: Density
      benchmark: density
    - label: Glass transition
      benchmark: glass_transition_temperature
    - label: Atomic oxygen erosion yield in LEO
      benchmark: atomic_oxygen_erosion_yield
  handling:
    - 'Keep dust levels within the SDS limits: 10 mg/m3 ACGIH TLV, 15 mg/m3 OSHA PEL total and 5 mg/m3 respirable.'
    - Use local exhaust ventilation and grounding where dust forms, and keep ignition sources away from processing areas.
  good_for:
    - High-temperature parts that must keep stiffness near 400 degC, such as flame-resistant textiles and space stowage.
    - Space textiles where flame resistance matters more than atomic oxygen resistance.
  watch_out:
    - The atomic oxygen erosion yield is a lower bound. The true erosion is higher than 2.21e-24 cm3/atom.
    - Values come from different grades and forms (film, rod, fibre, bulk). Check the grade named on each row.
    - The two CAS numbers (32075-68-6 and 25928-81-8) appear in different sources.
  verdict: PBI is a high-temperature, flame-resistant aromatic polymer with a glass transition near 425 degC and a limiting oxygen index of 58 percent. Its weakness in low Earth orbit is atomic oxygen erosion, where NASA gives a flight lower bound of 2.21e-24 cm3/atom.
gaps:
  - No PBI composition or CAS number was read from PubChem; the PubChem lookup by name and by CAS 25928-81-8 returned no CID in this run.
  - No flight result beyond the MISSE 2 erosion yield; no UV, radiation or thermal-cycling result for PBI was found in a fetched page.
  - 'Two CAS numbers are printed for PBI: 32075-68-6 (Wikipedia, Goodfellow) and 25928-81-8 (MCAM SDS). The source of each is recorded.'
  - No production volume or country share was found in a fetched source; the only producer named is Hoechst Celanese from the NASA report.
  - Limiting oxygen index, compressive modulus and atomic oxygen erosion yield are not in the canonical property list; they use short names (limiting_oxygen_index, atomic_oxygen_erosion_yield).
  - Hazard data rest on one MCAM SDS for the polymer. The Newtex sulfonated PBI SDS was not fetched.
  - Glass transition in Wikipedia is given as about 430 degC; only the TotalMateria value (425 degC) is recorded as a property.
sources:
  nasa-misse2-pbi:
    title: 'NASA/TM-2008-215490: Atomic Oxygen Erosion Yield Predictive Tool for Spacecraft Polymers in Low Earth Orbit (Banks, Backus and de Groh, 2008)'
    kind: report
    url: https://ntrs.nasa.gov/api/citations/20090011780/downloads/20090011780.pdf
    year: 2008
  wiki-pbi:
    title: Polybenzimidazole (Wikipedia)
    kind: web
    url: https://en.wikipedia.org/wiki/Polybenzimidazole
    year: 2026
  goodfellow-pbi:
    title: 'Goodfellow: Polybenzimidazole Film, PBI, CAS 32075-68-6 (product page)'
    kind: datasheet
    url: https://www.goodfellow.com/usa/polybenzimidazole-film-group
  totalmateria-pbi:
    title: 'TotalMateria: PBI material data page (material 5094597)'
    kind: datasheet
    url: https://www.totalmateria.com/en-us/material/5094597
  mcam-sds-pbi:
    title: 'Mitsubishi Chemical Advanced Materials: Duratron CU60 PBI safety data sheet (SDS-2700, revised 23 October 2019)'
    kind: datasheet
    url: https://www.boedeker.com/Portals/0/Safety Data Sheets SDS/MCAM/MCAM-Duratron-CU60-PBI-EN-SDS-2700-191023.pdf
  ntrs-flame-fibers-2017:
    title: 'Flame Retardant Fibers for Human Space Exploration: Past, Present, and Future (NASA NTRS 20170008542)'
    kind: report
    url: https://ntrs.nasa.gov/api/citations/20170008542/downloads/20170008542.pdf
    year: 2017
  apso-pbi:
    title: APSOplast PBI technical data sheet (compound PBI 00.004-00)
    kind: datasheet
    url: https://www.apsoparts.com/media/downloads/asset//std.lang.all/0_/en/PBI_00_004-00_EN.pdf
  pmc-pa-pbi-review:
    title: 'Ionic Liquid in Phosphoric Acid-Doped Polybenzimidazole (PA-PBI) as Electrolyte Membranes for PEM Fuel Cells: A Review (PMC8541579)'
    kind: paper
    url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8541579/
documents:
  - title: APSOplast PBI technical data sheet (compound PBI 00.004-00)
    type: datasheet
    url: https://www.apsoparts.com/media/downloads/asset//std.lang.all/0_/en/PBI_00_004-00_EN.pdf
  - title: MCAM Duratron CU60 PBI safety data sheet (SDS-2700)
    type: sds
    url: https://www.boedeker.com/Portals/0/Safety Data Sheets SDS/MCAM/MCAM-Duratron-CU60-PBI-EN-SDS-2700-191023.pdf
    year: 2019
  - title: NASA/TM-2008-215490 (MISSE 2 PEACE polymers erosion yield and density tables)
    type: report
    url: https://ntrs.nasa.gov/api/citations/20090011780/downloads/20090011780.pdf
    year: 2008
status: draft
updated: '2026-10-20'
review: {}
license: CC-BY-4.0
meta:
  status: draft
  method: assistant
  checked_values: 21
  unreachable: 1
  caveats: 4
  note: 'Written on 2026-10-20 by an AI assistant from pages read in this run: the NASA PDF (NTRS 20090011780) read with curl and pdftotext, Wikipedia, the Goodfellow PBI page, the TotalMateria PBI page, the MCAM SDS PDF, the NASA NTRS 20170008542 PDF and the PMC8541579 review. The PubChem record was not found.'