{
  "spore": "profile",
  "id": "pbo-zylon",
  "spore_version": "0.2",
  "family": "high-performance-polymers",
  "name": "Poly(p-phenylene-2,6-benzobisoxazole) fibre (Zylon)",
  "abbreviation": "PBO (Zylon)",
  "role": "high-strength fibre",
  "category": "polymers",
  "type": "high-performance",
  "summary": "PBO (Zylon) is a rigid-rod polybenzoxazole fibre made from a liquid-crystalline polymer. NIST reports that virgin PBO yarn breaks at 5.34 GPa and has a modulus of 147.11 GPa. In low Earth orbit on the MISSE 2 PEACE tray, PBO eroded by 1.36e-24 cm3 per oxygen atom, a middle value in the NASA table. The fibre is very strong and stiff but weak in ultraviolet light: NIST cites a loss of more than 90 percent of tensile strength after 450 hours of 340 nm radiation.\n",
  "best_for": "Very high-strength, stiff fibre for ballistic armour and tensile lines, where the fibre is kept out of sunlight",
  "weakest_at": "Ultraviolet light, which cuts tensile strength sharply; and low compressive strength (NIST: about 10 to 15 percent of tensile strength)",
  "identity": {
    "formula": "Poly(p-phenylene-2,6-benzobisoxazole), repeat unit C14H6N2O2",
    "designations": [],
    "source": "nasa-tm",
    "where": "Table IV, row PBO (Zylon), repeat unit C14H6N2O2 and molar mass 258.2356 g/mol"
  },
  "tags": {
    "environments": [
      "low-earth-orbit"
    ],
    "stresses": [
      "atomic-oxygen",
      "uv"
    ],
    "applications": [
      "habitats-and-suits",
      "structures"
    ]
  },
  "properties": [
    {
      "benchmark": "atomic_oxygen_erosion_yield",
      "label": "Atomic oxygen erosion yield, MISSE 2 flight",
      "value": 1.36e-24,
      "bound": "exact",
      "unit": "cm3/atom",
      "scope": "material",
      "conditions": {
        "exposure": "low Earth orbit, ISS MISSE 2 PEACE polymers tray",
        "basis": "erosion yield as printed in the NASA predictive-tool report"
      },
      "method": "Flight-measured erosion yield as printed in the NASA report",
      "status": "flight",
      "source": "nasa-tm",
      "where": "Table I (MISSE 2 PEACE polymers erosion yield data, row PBO (Zylon))",
      "source_detail": {
        "title": "Atomic Oxygen Erosion Yield Predictive Tool for Spacecraft Polymers in Low Earth Orbit",
        "id": "NASA/TM-2008-215490 (Banks, Backus and de Groh, December 2008)",
        "url": "https://ntrs.nasa.gov/citations/20090011780",
        "year": 2008,
        "kind": "report",
        "license": "public domain (NASA)"
      }
    },
    {
      "benchmark": "density",
      "label": "Density, PBO sample from MISSE 2",
      "value": 1.3976,
      "bound": "exact",
      "unit": "g/cm3",
      "scope": "material",
      "conditions": {
        "basis": "measured density of the MISSE 2 PBO sample as printed"
      },
      "method": "Value from the NASA erosion report density table",
      "status": "ground",
      "source": "nasa-tm",
      "where": "Table II (density and ash content, row PBO (Zylon))",
      "source_detail": {
        "title": "Atomic Oxygen Erosion Yield Predictive Tool for Spacecraft Polymers in Low Earth Orbit",
        "id": "NASA/TM-2008-215490 (Banks, Backus and de Groh, December 2008)",
        "url": "https://ntrs.nasa.gov/citations/20090011780",
        "year": 2008,
        "kind": "report",
        "license": "public domain (NASA)"
      }
    },
    {
      "benchmark": "ash_content",
      "label": "Mass fraction of polymer that is ash, PBO sample",
      "value": 0.0109,
      "bound": "exact",
      "unit": "mass fraction",
      "scope": "material",
      "conditions": {
        "basis": "mass fraction of the MISSE 2 PBO sample that is ash, as printed in the NASA table"
      },
      "method": "Value printed in the NASA density and ash table",
      "status": "ground",
      "source": "nasa-tm",
      "where": "Table II, column Mass fraction of polymer that is ash, row PBO (Zylon)",
      "source_detail": {
        "title": "Atomic Oxygen Erosion Yield Predictive Tool for Spacecraft Polymers in Low Earth Orbit",
        "id": "NASA/TM-2008-215490 (Banks, Backus and de Groh, December 2008)",
        "url": "https://ntrs.nasa.gov/citations/20090011780",
        "year": 2008,
        "kind": "report",
        "license": "public domain (NASA)"
      }
    },
    {
      "benchmark": "molar_mass",
      "label": "Molar mass of repeat unit",
      "value": 258.2356,
      "bound": "exact",
      "unit": "g/mol",
      "scope": "material",
      "conditions": {
        "repeat_unit": "C14H6N2O2"
      },
      "method": "Value printed in the NASA table of polymer chemical structure",
      "status": "ground",
      "source": "nasa-tm",
      "where": "Table IV, row PBO (Zylon)",
      "source_detail": {
        "title": "Atomic Oxygen Erosion Yield Predictive Tool for Spacecraft Polymers in Low Earth Orbit",
        "id": "NASA/TM-2008-215490 (Banks, Backus and de Groh, December 2008)",
        "url": "https://ntrs.nasa.gov/citations/20090011780",
        "year": 2008,
        "kind": "report",
        "license": "public domain (NASA)"
      }
    },
    {
      "benchmark": "ultimate_tensile_strength",
      "label": "Ultimate tensile strength, virgin PBO yarn",
      "value": 5.34,
      "bound": "exact",
      "unit": "GPa",
      "scope": "material",
      "conditions": {
        "basis": "unworn virgin yarn, mean of 6 replicates, as printed"
      },
      "method": "Mean value printed in the NIST tensile table",
      "status": "ground",
      "source": "nist-7237",
      "where": "Table 1, Virgin row, Ultimate Tensile Strength column",
      "source_detail": {
        "title": "NISTIR 7237: Chemical and Physical Characterization of Poly(p-phenylene-2,6-benzobisoxazole) Fibers Used in Body Armor",
        "id": "NIST NISTIR 7237 (Chin, Byrd, Forster et al.)",
        "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/IR/nistir7237.pdf",
        "year": 2005,
        "kind": "report",
        "license": "NIST public domain"
      }
    },
    {
      "benchmark": "ultimate_tensile_strength",
      "label": "Ultimate tensile strength, yarn from new unworn vest",
      "value": 4.78,
      "bound": "exact",
      "unit": "GPa",
      "scope": "material",
      "conditions": {
        "basis": "yarn from a new unworn PBO vest of the same model, mean of 6 replicates"
      },
      "method": "Mean value printed in the NIST tensile table",
      "status": "ground",
      "source": "nist-7237",
      "where": "Table 1, New row, Ultimate Tensile Strength column",
      "source_detail": {
        "title": "NISTIR 7237: Chemical and Physical Characterization of Poly(p-phenylene-2,6-benzobisoxazole) Fibers Used in Body Armor",
        "id": "NIST NISTIR 7237 (Chin, Byrd, Forster et al.)",
        "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/IR/nistir7237.pdf",
        "year": 2005,
        "kind": "report",
        "license": "NIST public domain"
      }
    },
    {
      "benchmark": "ultimate_tensile_strength",
      "label": "Ultimate tensile strength, yarn from officer vest",
      "value": 3.22,
      "bound": "exact",
      "unit": "GPa",
      "scope": "material",
      "conditions": {
        "basis": "yarn from a PBO vest worn by an officer that was penetrated, mean of 6 replicates"
      },
      "method": "Mean value printed in the NIST tensile table; NIST states it is a 30 percent decrease against new yarn",
      "status": "ground",
      "source": "nist-7237",
      "where": "Table 1, Officer row, Ultimate Tensile Strength column; Introduction text on the 30 percent decrease",
      "source_detail": {
        "title": "NISTIR 7237: Chemical and Physical Characterization of Poly(p-phenylene-2,6-benzobisoxazole) Fibers Used in Body Armor",
        "id": "NIST NISTIR 7237 (Chin, Byrd, Forster et al.)",
        "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/IR/nistir7237.pdf",
        "year": 2005,
        "kind": "report",
        "license": "NIST public domain"
      }
    },
    {
      "benchmark": "elastic_modulus",
      "label": "Modulus at break, virgin PBO yarn",
      "value": 147.11,
      "bound": "exact",
      "unit": "GPa",
      "scope": "material",
      "conditions": {
        "basis": "unworn virgin yarn, mean of 6 replicates, as printed"
      },
      "method": "Mean value printed in the NIST tensile table",
      "status": "ground",
      "source": "nist-7237",
      "where": "Table 1, Virgin row, Modulus at Break column",
      "source_detail": {
        "title": "NISTIR 7237: Chemical and Physical Characterization of Poly(p-phenylene-2,6-benzobisoxazole) Fibers Used in Body Armor",
        "id": "NIST NISTIR 7237 (Chin, Byrd, Forster et al.)",
        "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/IR/nistir7237.pdf",
        "year": 2005,
        "kind": "report",
        "license": "NIST public domain"
      }
    },
    {
      "benchmark": "elastic_modulus",
      "label": "Modulus at break, yarn from new unworn vest",
      "value": 141.8,
      "bound": "exact",
      "unit": "GPa",
      "scope": "material",
      "conditions": {
        "basis": "yarn from a new unworn PBO vest, mean of 6 replicates"
      },
      "method": "Mean value printed in the NIST tensile table",
      "status": "ground",
      "source": "nist-7237",
      "where": "Table 1, New row, Modulus at Break column",
      "source_detail": {
        "title": "NISTIR 7237: Chemical and Physical Characterization of Poly(p-phenylene-2,6-benzobisoxazole) Fibers Used in Body Armor",
        "id": "NIST NISTIR 7237 (Chin, Byrd, Forster et al.)",
        "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/IR/nistir7237.pdf",
        "year": 2005,
        "kind": "report",
        "license": "NIST public domain"
      }
    },
    {
      "benchmark": "elastic_modulus",
      "label": "Modulus at break, yarn from officer vest",
      "value": 136.61,
      "bound": "exact",
      "unit": "GPa",
      "scope": "material",
      "conditions": {
        "basis": "yarn from a PBO vest worn by an officer, mean of 6 replicates"
      },
      "method": "Mean value printed in the NIST tensile table",
      "status": "ground",
      "source": "nist-7237",
      "where": "Table 1, Officer row, Modulus at Break column",
      "source_detail": {
        "title": "NISTIR 7237: Chemical and Physical Characterization of Poly(p-phenylene-2,6-benzobisoxazole) Fibers Used in Body Armor",
        "id": "NIST NISTIR 7237 (Chin, Byrd, Forster et al.)",
        "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/IR/nistir7237.pdf",
        "year": 2005,
        "kind": "report",
        "license": "NIST public domain"
      }
    },
    {
      "benchmark": "elongation",
      "label": "Strain at break, virgin PBO yarn",
      "value": 3.52,
      "bound": "exact",
      "unit": "%",
      "scope": "material",
      "conditions": {
        "basis": "unworn virgin yarn, mean of 6 replicates, as printed"
      },
      "method": "Mean value printed in the NIST tensile table",
      "status": "ground",
      "source": "nist-7237",
      "where": "Table 1, Virgin row, Strain at Break column",
      "source_detail": {
        "title": "NISTIR 7237: Chemical and Physical Characterization of Poly(p-phenylene-2,6-benzobisoxazole) Fibers Used in Body Armor",
        "id": "NIST NISTIR 7237 (Chin, Byrd, Forster et al.)",
        "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/IR/nistir7237.pdf",
        "year": 2005,
        "kind": "report",
        "license": "NIST public domain"
      }
    },
    {
      "benchmark": "decomposition_temperature",
      "label": "5 percent mass-loss temperature in air, virgin yarn",
      "value": 633.6,
      "bound": "exact",
      "unit": "degC",
      "scope": "material",
      "conditions": {
        "atmosphere": "air",
        "basis": "temperature at 5 percent mass loss, virgin yarn, as printed with standard uncertainty 2.5"
      },
      "method": "Thermogravimetric analysis value printed in the NIST table",
      "status": "ground",
      "source": "nist-7237",
      "where": "Table 2, Air Atmosphere, Virgin row, 5 percent decomposition temperature column",
      "source_detail": {
        "title": "NISTIR 7237: Chemical and Physical Characterization of Poly(p-phenylene-2,6-benzobisoxazole) Fibers Used in Body Armor",
        "id": "NIST NISTIR 7237 (Chin, Byrd, Forster et al.)",
        "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/IR/nistir7237.pdf",
        "year": 2005,
        "kind": "report",
        "license": "NIST public domain"
      }
    },
    {
      "benchmark": "decomposition_temperature",
      "label": "5 percent mass-loss temperature in nitrogen, virgin yarn",
      "value": 699.4,
      "bound": "exact",
      "unit": "degC",
      "scope": "material",
      "conditions": {
        "atmosphere": "nitrogen",
        "basis": "temperature at 5 percent mass loss, virgin yarn, as printed with standard uncertainty 8.2"
      },
      "method": "Thermogravimetric analysis value printed in the NIST table",
      "status": "ground",
      "source": "nist-7237",
      "where": "Table 2, Nitrogen Atmosphere, Virgin row, 5 percent decomposition temperature column",
      "source_detail": {
        "title": "NISTIR 7237: Chemical and Physical Characterization of Poly(p-phenylene-2,6-benzobisoxazole) Fibers Used in Body Armor",
        "id": "NIST NISTIR 7237 (Chin, Byrd, Forster et al.)",
        "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/IR/nistir7237.pdf",
        "year": 2005,
        "kind": "report",
        "license": "NIST public domain"
      }
    },
    {
      "benchmark": "ultimate_tensile_strength",
      "label": "Tensile strength, secondary summary",
      "value": 5.8,
      "bound": "exact",
      "unit": "GPa",
      "scope": "material",
      "conditions": {
        "basis": "secondary figure quoted in Wikipedia for the PBO fibre, no test conditions given"
      },
      "method": "Figure printed in Wikipedia; not a test result and not used for design",
      "status": "ground",
      "source": "wiki-zylon",
      "where": "Mechanical properties list, Tensile strength line",
      "source_detail": {
        "title": "Wikipedia: Zylon",
        "id": "Zylon",
        "url": "https://en.wikipedia.org/wiki/Zylon",
        "kind": "web",
        "license": "CC BY-SA 4.0 (cited, not reproduced)"
      }
    },
    {
      "benchmark": "elastic_modulus",
      "label": "Young's modulus, secondary summary",
      "value": 270,
      "bound": "exact",
      "unit": "GPa",
      "scope": "material",
      "conditions": {
        "basis": "secondary figure quoted in Wikipedia for the PBO fibre, no test conditions given; NIST virgin yarn gave 147.11 GPa"
      },
      "method": "Figure printed in Wikipedia; not a test result and not used for design",
      "status": "ground",
      "source": "wiki-zylon",
      "where": "Mechanical properties list, Young's modulus line",
      "source_detail": {
        "title": "Wikipedia: Zylon",
        "id": "Zylon",
        "url": "https://en.wikipedia.org/wiki/Zylon",
        "kind": "web",
        "license": "CC BY-SA 4.0 (cited, not reproduced)"
      }
    }
  ],
  "corrosion": [
    {
      "environment": "Ultraviolet light and sunlight",
      "headline": "UV is PBO's main weakness: NIST cites a loss of more than 90 percent of tensile strength after 450 hours at 340 nm.",
      "effect": "NIST cites one study in which PBO lost more than 90 percent of its tensile strength after 450 hours of 340 nm radiation (that study is NASA 1995, cited by NIST). Wikipedia says PBO is degraded by UV light. A Chinese study reports that UV ageing of PBO has an early physical stage that creates surface flaws and a later chemical chain-scission stage, and that copolymerising or adding rutile TiO2 improves UV resistance (abstract only read).",
      "rating": "severe",
      "conditions": {
        "wavelength": "340 nm",
        "exposure": "450 hours, unprotected"
      },
      "source": "nist-7237",
      "where": "Introduction, paragraph on hydrolytic and UV-visible light stability (citing NASA 1995)"
    },
    {
      "environment": "Heat and moisture",
      "headline": "Heat and moisture reduce strength: a vest yarn used in service lost 30 percent of its tensile strength.",
      "effect": "NIST reports that the manufacturer has documented tensile strength degradation after heat and moisture exposure. In the NIST body-armour study, yarn from a penetrated vest had a mean tensile strength of 3.22 GPa against 4.78 GPa for new yarn, a 30 percent decrease.",
      "rating": "moderate",
      "conditions": {
        "basis": "field-worn vest yarn compared with new yarn, both as printed in the NIST table"
      },
      "source": "nist-7237",
      "where": "Introduction, officer vest paragraph; Table 1"
    },
    {
      "environment": "Acids, water and hypochlorite",
      "headline": "Hot methanesulfonic acid cleaves PBO bonds; NASA in 1995 reported strength losses after immersion in several acids and water.",
      "effect": "NIST cites a 1995 NASA study that found significant tensile losses after immersion in water, hydrochloric acid, nitric acid, sulfuric acid, sodium chloride and sodium hypochlorite. So et al. observed bond cleavage when PBO was dissolved in hot methanesulfonic acid, but no change in relative molecular mass after sulfuric acid, poly(phosphoric acid) or sodium hydroxide.",
      "rating": "moderate",
      "conditions": {
        "basis": "qualitative findings as summarised by NIST; no numbers given"
      },
      "source": "nist-7237",
      "where": "Introduction, paragraphs on hydrolytic stability"
    },
    {
      "environment": "Heat in air (thermal ageing and decomposition)",
      "headline": "PBO does not melt; in air its 5 percent mass-loss temperature is about 634 degC for virgin yarn.",
      "effect": "Thermogravimetric analysis gives 5 percent mass loss at 633.6 degC in air and 699.4 degC in nitrogen for virgin yarn. Mass loss at 110 degC is small, from 0.26 to 0.48 percent. Wikipedia names PBO among the high-strength fibres that resist heat, and the NIST data show no large difference between vest yarns in air.",
      "rating": "low",
      "conditions": {
        "atmosphere": "air and nitrogen, thermogravimetry"
      },
      "source": "nist-7237",
      "where": "Table 2; text after Table 2"
    }
  ],
  "risks": {
    "hazards": [
      {
        "text": "PubChem GHS for terephthalic acid (a PBO monomer, CID 7489): H302 harmful if swallowed; H315 causes skin irritation (17.4 percent of reports); H319 causes serious eye irritation (17.1 percent); H335 may cause respiratory irritation (15.1 percent); H361 suspected of damaging fertility or the unborn child; H372 causes damage to organs through prolonged or repeated exposure; H373 may cause damage to organs through prolonged or repeated exposure.",
        "ghs": [
          "H302",
          "H315",
          "H319",
          "H335",
          "H361",
          "H372",
          "H373"
        ],
        "source": "pubchem-terephthalic",
        "where": "Safety and Hazards, GHS Classification (CID 7489)"
      },
      {
        "text": "Fibre dust: PBO yarn is a textile, and cutting or abrading it can release fibre fragments. No PBO-specific safety data sheet was read in this run, so no fibre-dust limit is given.",
        "ghs": [],
        "source": "nist-7237",
        "where": "Materials description (no hazard statement read)"
      }
    ],
    "failure_risks": [
      {
        "mode": "UV-driven loss of strength",
        "trigger": "Unprotected sunlight or UV exposure",
        "consequence": "Surface damage and chain scission, with more than 90 percent strength loss after 450 hours at 340 nm",
        "severity": "critical",
        "source": "nist-7237",
        "where": "Introduction, UV stability paragraph"
      },
      {
        "mode": "Strength loss after heat and moisture",
        "trigger": "Heat and moisture in service",
        "consequence": "About a 30 percent loss of tensile strength in a field-worn vest yarn",
        "severity": "moderate",
        "source": "nist-7237",
        "where": "Introduction, officer vest paragraph; Table 1"
      },
      {
        "mode": "Low compressive strength",
        "trigger": "Axial compression, which causes slippage of fibrils",
        "consequence": "Compressive strength is about 10 to 15 percent of tensile strength (NIST)",
        "severity": "moderate",
        "source": "nist-7237",
        "where": "Introduction, paragraph on PBO structure"
      }
    ],
    "side_effects": [],
    "handling": [
      {
        "text": "Shield PBO from sunlight and UV; NIST documents severe loss of strength under 340 nm radiation.",
        "source": "nist-7237",
        "where": "Introduction, UV stability paragraph"
      },
      {
        "text": "Keep PBO dry and away from strong acids, which cleave the benzoxazole bonds (So et al., as summarised by NIST).",
        "source": "nist-7237",
        "where": "Introduction, hydrolytic stability paragraph"
      }
    ],
    "mitigations": [
      {
        "text": "Blend rutile nano-TiO2 into the fibre or copolymerise it with 2,5-dihydroxyterephthalic acid; the Acta Chimica Sinica abstract reports that both improve UV resistance over unmodified PBO.",
        "source": "sioc-uv",
        "where": "Abstract (no numbers read)"
      }
    ]
  },
  "uses": [
    {
      "application": "habitats-and-suits",
      "device": "Ballistic body armour",
      "example": "PBO vests were issued to police from 1998; after recalls and decertification by the National Institute of Justice the use ended.",
      "source": "wiki-zylon",
      "where": "Applications section (ballistic)"
    },
    {
      "application": "structures",
      "device": "Parachute suspension lines",
      "example": "SpaceX uses Zylon suspension lines on Mk3 parachutes for Crew Dragon.",
      "source": "wiki-zylon",
      "where": "Applications section (space)"
    },
    {
      "application": "structures",
      "device": "Tether and high-altitude balloon structures",
      "example": "A University of British Columbia team used a tether made from Zylon fibres in a 2006 Tether Challenge, and NASA uses Zylon in high-altitude balloon structures.",
      "source": "wiki-zylon",
      "where": "Applications section (space)"
    }
  ],
  "supply": [
    {
      "subject": "PBO (Zylon) fibre production",
      "abundance": "Not sourced. Feedstock is terephthalic acid and a diamine monomer; terephthalic acid is made by catalytic oxidation of p-xylene (Amoco process).",
      "producers": [
        {
          "country": "Japan"
        }
      ],
      "critical_lists": [],
      "recycling": "Not sourced.",
      "substitutes": [],
      "source": "wiki-zylon",
      "where": "Lead and history paragraphs; Toyobo headquarters from wiki-toyobo"
    }
  ],
  "media": [],
  "documents": [
    {
      "title": "NASA/TM-2008-215490: Atomic Oxygen Erosion Yield Predictive Tool for Spacecraft Polymers in Low Earth Orbit",
      "type": "report",
      "url": "https://ntrs.nasa.gov/citations/20090011780",
      "year": 2008
    },
    {
      "title": "NISTIR 7237: Chemical and Physical Characterization of Poly(p-phenylene-2,6-benzobisoxazole) Fibers Used in Body Armor",
      "type": "report",
      "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/IR/nistir7237.pdf",
      "year": 2005
    }
  ],
  "gaps": [
    "Molar mass of the repeat unit: NASA Table IV gives 258.2356 g/mol; Wikipedia gives a monomer molar mass of 234.214 g/mol with formula C14H6N2O2. The two do not match; NASA is used.",
    "No PBO-specific safety data sheet or PubChem record for the polymer was read; hazards use terephthalic acid only.",
    "Moisture regain, vacuum outgassing and total radiation dose for PBO were not read, though the passport lists those stresses.",
    "Thermal ageing numbers (strength retained after heating at 500 degC for 60 seconds, and 30 weeks in argon) were seen only in search snippets and are not used.",
    "The Acta Chimica Sinica 2010 UV paper and the NCSU thesis (Gupta 2005, Zylon and Vectran UV loss) could not be read in full; neither gives numbers used here.",
    "The MDPI Polymers 2019 TiO2 UV-ageing paper was blocked (HTTP 403); its loading figures are not used.",
    "The DTIC report AD1031722 was blocked (HTTP 403) and the Toyobo product page returned 404; no Toyobo datasheet values were read.",
    "No critical-mineral or producer-volume data were read; supply is limited to the Toyobo headquarters and the terephthalic acid route.",
    "Secondary Wikipedia figures (5.8 GPa and 270 GPa) conflict with NIST virgin-yarn values and are labelled as secondary.",
    "The ash mass fraction and decomposition-temperature names are not in property-canon.yaml; they are used as short snake_case names.",
    "Compressive strength (about 10 to 15 percent of tensile) is in the failure risks as a ratio, not as a property value."
  ],
  "story": {
    "why": "PBO is a rigid-rod polymer whose chains are aligned in the fibre, which gives very high tensile strength and modulus. NIST measured virgin yarn at 5.34 GPa and 147.11 GPa. The trade is UV sensitivity and low compressive strength. In the MISSE 2 flight test it eroded at 1.36e-24 cm3 per oxygen atom, which is why it was included in the passport.",
    "uses": [
      {
        "where": "Ballistic body armour",
        "line": "PBO vests were issued to police from 1998; recalls and decertification ended their use (Wikipedia)."
      },
      {
        "where": "Parachute lines",
        "line": "SpaceX uses Zylon suspension lines on Mk3 parachutes for Crew Dragon (Wikipedia)."
      },
      {
        "where": "Tethers and balloons",
        "line": "A 2006 Tether Challenge entry used a Zylon tether, and NASA uses Zylon in high-altitude balloon structures (Wikipedia)."
      }
    ],
    "can_do": [
      {
        "label": "Strength",
        "line": "Virgin PBO yarn breaks at 5.34 GPa (NIST Table 1); yarn from a new vest at 4.78 GPa.",
        "benchmark": "ultimate_tensile_strength",
        "scope": "material"
      },
      {
        "label": "Stiffness",
        "line": "Virgin PBO yarn has a modulus at break of 147.11 GPa (NIST Table 1).",
        "benchmark": "elastic_modulus",
        "scope": "material"
      },
      {
        "label": "Flight exposure",
        "line": "In low Earth orbit on MISSE 2, PBO eroded by 1.36e-24 cm3 per atomic oxygen atom (NASA Table I).",
        "scope": "material",
        "value": "1.36e-24 cm3/atom"
      }
    ],
    "compare": "PBO is stronger and stiffer than most polymers in these sources, but it is far weaker in UV and has poor compressive strength. Its atomic oxygen erosion yield of 1.36e-24 cm3 per atom sits in the middle of the NASA table, below polyoxymethylene and polybutylene terephthalate and close to polypropylene. It is a credible structural fibre for space use shielded from sunlight.",
    "compare_rows": [
      {
        "label": "Strength",
        "benchmark": "ultimate_tensile_strength",
        "scope": "material"
      },
      {
        "label": "Stiffness",
        "benchmark": "elastic_modulus",
        "scope": "material"
      },
      {
        "label": "Atomic oxygen erosion",
        "benchmark": "atomic_oxygen_erosion_yield",
        "scope": "material"
      }
    ],
    "handling": [
      "Keep it out of sunlight and UV, or cover it with a UV blocker.",
      "Avoid compressive loading; its compressive strength is low.",
      "Keep it away from strong acids and hot alkalis."
    ],
    "good_for": [
      "Very high tensile strength and stiffness for weight in armour and tensile lines.",
      "Low atomic oxygen erosion in LEO, measured on MISSE 2."
    ],
    "watch_out": [
      "UV cuts strength sharply, about 90 percent after 450 hours at 340 nm (NIST).",
      "Low compressive strength (about 10 to 15 percent of tensile).",
      "Vest yarn lost about 30 percent of its strength in service (NIST)."
    ],
    "verdict": "PBO is one of the strongest and stiffest fibres in these sources, and its erosion yield in LEO is moderate. Its weak point is sunlight: shield it from UV, and it performs well in orbit and in armour.",
    "recipe": {
      "line": "PBO is made by condensation of a diamine monomer with terephthalic acid, followed by liquid-crystalline spinning and drawing (process details not sourced). The repeat unit is C14H6N2O2 with molar mass 258.2356 g/mol (NASA Table IV). Wikipedia calls PBO a thermoset liquid-crystalline polyoxazole.",
      "parts": [
        {
          "name": "Terephthalic acid (monomer)",
          "symbol": "C8H6O4",
          "role": "Diacid monomer that forms the terephthalyl part of each repeat unit",
          "share_note": "molar mass as printed in Wikipedia"
        },
        {
          "name": "Diamine monomer (2,5-diamino-1,4-benzenediol)",
          "symbol": "C6H8N2O2",
          "role": "Diamine that forms the benzobisoxazole rings with the diacid (named as a PBO monomer in the standard PBO description; no source read for its role in the synthesis)"
        },
        {
          "name": "Repeat unit",
          "symbol": "C14H6N2O2",
          "role": "The polymer unit that repeats along the chain; carbon, hydrogen, nitrogen and oxygen only",
          "share_note": "molar mass 258.2356 g/mol (NASA Table IV)"
        }
      ]
    },
    "risk_groups": [
      {
        "title": "For people",
        "lead": "No PBO-specific safety data sheet was read. The PubChem record for terephthalic acid lists skin and eye irritation and possible organ and fertility effects.",
        "points": [
          {
            "label": "Monomer",
            "line": "Terephthalic acid, a PBO monomer, is classed H315 and H319 (about 17 percent of reports each) and H372 and H373 for organ damage with repeated exposure (PubChem CID 7489)."
          },
          {
            "label": "Fibre",
            "line": "PBO yarn is handled as a textile; cutting or abrading may release fibre fragments, and no limit was read."
          }
        ],
        "level": 0,
        "verdict": "Hazards from monomer only"
      },
      {
        "title": "In the environment",
        "lead": "UV is the main route to loss of strength.",
        "points": [
          {
            "label": "UV",
            "line": "NIST cites more than 90 percent tensile loss after 450 hours at 340 nm."
          },
          {
            "label": "Heat and moisture",
            "line": "A field-worn vest yarn lost about 30 percent of its tensile strength (NIST)."
          }
        ],
        "level": 1,
        "verdict": "Sunlight is the watch point"
      }
    ]
  },
  "updated": "2026-10-20",
  "review": {
    "status": "draft",
    "method": "assistant",
    "checked_values": 15,
    "unreachable": 4,
    "caveats": 4,
    "note": "Written by an AI assistant on 2026-10-20 from the NASA TM Tables I, II and IV (PDF), the NIST NISTIR 7237 Tables 1 and 2, the Wikipedia Zylon and terephthalic acid pages, Wikipedia Toyobo, the PubChem terephthalic acid record and the Acta Chimica Sinica abstract. Seven sources, short of the eight requested; the NCSU thesis, DTIC report, MDPI paper and Toyobo datasheet could not be reached."
  },
  "sources": {
    "nasa-tm": {
      "title": "Atomic Oxygen Erosion Yield Predictive Tool for Spacecraft Polymers in Low Earth Orbit",
      "id": "NASA/TM-2008-215490 (Banks, Backus and de Groh, December 2008)",
      "url": "https://ntrs.nasa.gov/citations/20090011780",
      "year": 2008,
      "kind": "report",
      "license": "public domain (NASA)"
    },
    "nist-7237": {
      "title": "NISTIR 7237: Chemical and Physical Characterization of Poly(p-phenylene-2,6-benzobisoxazole) Fibers Used in Body Armor",
      "id": "NIST NISTIR 7237 (Chin, Byrd, Forster et al.)",
      "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/IR/nistir7237.pdf",
      "year": 2005,
      "kind": "report",
      "license": "NIST public domain"
    },
    "wiki-zylon": {
      "title": "Wikipedia: Zylon",
      "id": "Zylon",
      "url": "https://en.wikipedia.org/wiki/Zylon",
      "kind": "web",
      "license": "CC BY-SA 4.0 (cited, not reproduced)"
    },
    "pubchem-terephthalic": {
      "title": "PubChem GHS classification: Terephthalic acid (CID 7489)",
      "id": "PubChem CID 7489, read via the PUG View JSON API",
      "url": "https://pubchem.ncbi.nlm.nih.gov/compound/7489",
      "kind": "database",
      "license": "PubChem, cited not reproduced"
    },
    "wiki-terephthalic": {
      "title": "Wikipedia: Terephthalic acid",
      "id": "Terephthalic_acid",
      "url": "https://en.wikipedia.org/wiki/Terephthalic_acid",
      "kind": "web",
      "license": "CC BY-SA 4.0 (cited, not reproduced)"
    },
    "wiki-toyobo": {
      "title": "Wikipedia: Toyobo",
      "id": "Toyobo",
      "url": "https://en.wikipedia.org/wiki/Toyobo",
      "kind": "web",
      "license": "CC BY-SA 4.0 (cited, not reproduced)"
    },
    "sioc-uv": {
      "title": "Preparation and Characterization of Poly(p-phenylene benzobisoxazole) (PBO) Fiber with Anti-ultraviolet Aging, Acta Chimica Sinica 68(2), 2010",
      "id": "Acta Chimica Sinica 2010, vol 68, issue 2, pp 199-204",
      "url": "https://sioc-journal.cn/Jwk_hxxb/EN/Y2010/V68/I02/199",
      "year": 2010,
      "kind": "paper",
      "license": "cited, not reproduced"
    }
  },
  "license": "CC-BY-4.0",
  "url": "https://spacemushroom.com/profiles/pbo-zylon/"
}