{
  "spore": "profile",
  "id": "phb",
  "spore_version": "0.2",
  "family": "polyesters",
  "name": "Polyhydroxybutyrate (PHB), poly(3-hydroxybutyrate), with the PHB/PHV copolymer (PHBV) for comparison",
  "abbreviation": "PHB",
  "role": "Bacterial bioplastic polyester for moulded, extruded and printed parts",
  "category": "polymers",
  "type": "polyesters",
  "summary": "Polyhydroxybutyrate (PHB) is a biodegradable thermoplastic polyester that bacteria store inside their cells as an energy reserve. Its melting point is 151.2 °C for P(3HB) filament by DSC and 177 °C for pure PHB in another DSC result, and its second-heating glass transition is 2.4 °C. Unfilled P(3HB) is stiff but brittle, with a tensile strength of 34.2 MPa and an elongation at break of 3.8 %. Blends with PLA, copolymers with hydroxyvalerate (PHBV) and fillers are used to lower the melting point, widen the narrow processing window and reduce brittleness.\n",
  "best_for": "Bio-based, biodegradable thermoplastic parts and 3D-printed items where a fossil-free polyester is wanted and brittleness is acceptable or blended away.",
  "weakest_at": "Brittleness and a narrow processing window: unfilled P(3HB) breaks at 3.8 % elongation, and it degrades just above its melting point.",
  "identity": {
    "formula": "Poly(3-hydroxybutyric acid), P(3HB): a linear polyester of 3-hydroxybutyrate units, made by bacteria",
    "cas": "26063-00-3",
    "designations": [
      {
        "system": "Name",
        "code": "poly",
        "note": "3-hydroxybutyrate",
        "source": "wikipedia-phb",
        "where": "Lead and Biosynthesis sections: poly-3-hydroxybutyrate (P3HB) form of PHB"
      },
      {
        "system": "Name",
        "code": "P",
        "note": "3HB",
        "source": "pmc13119779",
        "where": "Materials section: poly-3-hydroxybutyrate (P(3HB)), Mw = 480,000"
      },
      {
        "system": "CAS",
        "code": "26063-00-3",
        "source": "pmc13119779",
        "where": "Materials section: CAS:26063-00-3 for P(3HB)"
      }
    ],
    "source": "wikipedia-phb",
    "where": "Biosynthesis section: Polyhydroxybutyrate (PHB) and poly-3-hydroxybutyrate (P3HB) naming"
  },
  "tags": {
    "environments": [],
    "stresses": [],
    "applications": [
      "structures",
      "in-space-manufacturing"
    ]
  },
  "properties": [
    {
      "benchmark": "density",
      "label": "Density, P(3HB) powder as listed by its supplier",
      "value": 1.23,
      "bound": "exact",
      "unit": "g/cm3",
      "scope": "material",
      "conditions": {
        "grade": "P(3HB), Mw 480,000, 98 % purity, powder",
        "test": "not printed",
        "temperature": "not printed"
      },
      "method": "Printed in the Materials section as the density of the supplier's P(3HB) powder. The authors did not measure it in the paper.",
      "status": "ground",
      "source": "pmc13119779",
      "where": "Materials section, first sentence on the P(3HB) supplier",
      "source_detail": {
        "title": "Structure-Property Relationships in PHB-Based Copolymers and PHB/PLA Biocomposites Modified with Hydroxyapatite and Chitosan (Polymers, 2026)",
        "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC13119779/",
        "kind": "paper",
        "license": "Open access (MDPI, cited, not reproduced)"
      }
    },
    {
      "benchmark": "density",
      "label": "Density, PHB produced by fermentation (review, citing a secondary study)",
      "value": 1.22,
      "bound": "exact",
      "unit": "g/cm3",
      "scope": "material",
      "conditions": {
        "material": "PHB produced by bacteria, purity 98.9 %, crystallinity 73 %",
        "test": "not printed",
        "temperature": "not printed"
      },
      "method": "Printed as a density of 1.22 g cm-3 in a sentence that cites reference 91. The review does not give the test method.",
      "status": "ground",
      "source": "pmc13413960",
      "where": "Full text, sentence citing reference 91 (purity, crystallinity and density)",
      "source_detail": {
        "title": "Polyhydroxybutyrate (PHB): Production, Properties, Modification Strategies, Additive Manufacturing, Biodegradation, and Applications (Materials, 2026)",
        "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC13413960/",
        "kind": "paper",
        "license": "Open access, CC BY (cited, not reproduced)"
      }
    },
    {
      "benchmark": "melting_point",
      "label": "Melting point, P(3HB) filament by DSC",
      "value": 151.2,
      "bound": "exact",
      "unit": "°C",
      "scope": "material",
      "conditions": {
        "material": "P(3HB) filament, as listed in the filament table",
        "test": "DSC, from -50 to 200 °C (Materials section of the paper)",
        "temperature": "column Tm2 as printed"
      },
      "method": "Read from the Tm2 column of the filament DSC table. The table gives an uncertainty of plus or minus 0.3 °C, which is not entered.",
      "status": "ground",
      "source": "pmc13119779",
      "where": "Filament table, P(3HB) row, Tm2 column",
      "source_detail": {
        "title": "Structure-Property Relationships in PHB-Based Copolymers and PHB/PLA Biocomposites Modified with Hydroxyapatite and Chitosan (Polymers, 2026)",
        "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC13119779/",
        "kind": "paper",
        "license": "Open access (MDPI, cited, not reproduced)"
      }
    },
    {
      "benchmark": "melting_point",
      "label": "Melting point, pure PHB by DSC (review)",
      "value": 177,
      "bound": "exact",
      "unit": "°C",
      "scope": "material",
      "conditions": {
        "material": "pure PHB",
        "test": "not printed in the sentence",
        "temperature": "not printed in the sentence"
      },
      "method": "Printed as DSC results show that pure PHB had a melting temperature of about 177 °C.",
      "status": "ground",
      "source": "pmc13413960",
      "where": "Full text, DSC sentence on the 3D-printable PHB filament",
      "source_detail": {
        "title": "Polyhydroxybutyrate (PHB): Production, Properties, Modification Strategies, Additive Manufacturing, Biodegradation, and Applications (Materials, 2026)",
        "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC13413960/",
        "kind": "paper",
        "license": "Open access, CC BY (cited, not reproduced)"
      }
    },
    {
      "benchmark": "melting_point",
      "label": "Melting point, PHB 3D-printable filament after extrusion (review)",
      "value": 167,
      "bound": "exact",
      "unit": "°C",
      "scope": "material",
      "conditions": {
        "material": "PHB 3D-printable filament, after extrusion",
        "test": "not printed in the sentence",
        "temperature": "not printed in the sentence"
      },
      "method": "Printed as about 167 °C, lower than pure PHB, which the review attributes to heat exposure during extrusion.",
      "status": "ground",
      "source": "pmc13413960",
      "where": "Full text, DSC sentence on the 3D-printable PHB filament",
      "source_detail": {
        "title": "Polyhydroxybutyrate (PHB): Production, Properties, Modification Strategies, Additive Manufacturing, Biodegradation, and Applications (Materials, 2026)",
        "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC13413960/",
        "kind": "paper",
        "license": "Open access, CC BY (cited, not reproduced)"
      }
    },
    {
      "benchmark": "glass_transition_temperature",
      "label": "Glass transition temperature, P(3HB) filament, second heating",
      "value": 2.4,
      "bound": "exact",
      "unit": "°C",
      "scope": "material",
      "conditions": {
        "material": "P(3HB) filament",
        "test": "DSC, second heating cycle (Tg2 column)",
        "temperature": "not printed"
      },
      "method": "Read from the Tg2 column of the filament table, which gives plus or minus 0.2 °C. The first heating cycle printed 57.9 °C and is not entered, because the paper reports Tg2 as the value after melting and controlled cooling.",
      "status": "ground",
      "source": "pmc13119779",
      "where": "Filament table, P(3HB) row, Tg2 column",
      "source_detail": {
        "title": "Structure-Property Relationships in PHB-Based Copolymers and PHB/PLA Biocomposites Modified with Hydroxyapatite and Chitosan (Polymers, 2026)",
        "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC13119779/",
        "kind": "paper",
        "license": "Open access (MDPI, cited, not reproduced)"
      }
    },
    {
      "benchmark": "decomposition_temperature",
      "label": "Decomposition temperature, P(3HB) filament (Tdeg)",
      "value": 282,
      "bound": "exact",
      "unit": "°C",
      "scope": "material",
      "conditions": {
        "material": "P(3HB) filament",
        "test": "not printed in the table",
        "temperature": "not printed in the table"
      },
      "method": "Read from the Tdeg column of the filament table, which gives plus or minus 0.2 °C. The test method is not given in the table.",
      "status": "ground",
      "source": "pmc13119779",
      "where": "Filament table, P(3HB) row, Tdeg column",
      "source_detail": {
        "title": "Structure-Property Relationships in PHB-Based Copolymers and PHB/PLA Biocomposites Modified with Hydroxyapatite and Chitosan (Polymers, 2026)",
        "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC13119779/",
        "kind": "paper",
        "license": "Open access (MDPI, cited, not reproduced)"
      }
    },
    {
      "benchmark": "ultimate_tensile_strength",
      "label": "Tensile strength, unfilled P(3HB)",
      "value": 34.2,
      "bound": "exact",
      "unit": "MPa",
      "scope": "material",
      "conditions": {
        "material": "unfilled P(3HB), matrix of the copolymer and biocomposite study",
        "test": "not printed in the sentence",
        "temperature": "not printed in the sentence"
      },
      "method": "Printed in the Results sentence on unfilled P(3HB), which describes predominantly brittle fracture.",
      "status": "ground",
      "source": "pmc13119779",
      "where": "Results, sentence on unfilled P(3HB) mechanical behaviour",
      "source_detail": {
        "title": "Structure-Property Relationships in PHB-Based Copolymers and PHB/PLA Biocomposites Modified with Hydroxyapatite and Chitosan (Polymers, 2026)",
        "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC13119779/",
        "kind": "paper",
        "license": "Open access (MDPI, cited, not reproduced)"
      }
    },
    {
      "benchmark": "elongation",
      "label": "Elongation at break, unfilled P(3HB)",
      "value": 3.8,
      "bound": "exact",
      "unit": "%",
      "scope": "material",
      "conditions": {
        "material": "unfilled P(3HB), matrix of the copolymer and biocomposite study",
        "test": "not printed in the sentence",
        "temperature": "not printed in the sentence"
      },
      "method": "Printed in the same Results sentence as the 34.2 MPa tensile strength.",
      "status": "ground",
      "source": "pmc13119779",
      "where": "Results, sentence on unfilled P(3HB) mechanical behaviour",
      "source_detail": {
        "title": "Structure-Property Relationships in PHB-Based Copolymers and PHB/PLA Biocomposites Modified with Hydroxyapatite and Chitosan (Polymers, 2026)",
        "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC13119779/",
        "kind": "paper",
        "license": "Open access (MDPI, cited, not reproduced)"
      }
    },
    {
      "benchmark": "ultimate_tensile_strength",
      "label": "Tensile strength, PHB produced by fermentation (review, citing a secondary study)",
      "value": 30,
      "bound": "exact",
      "unit": "MPa",
      "scope": "material",
      "conditions": {
        "material": "PHB produced by bacteria, purity 98.9 %, crystallinity 73 %",
        "test": "not printed",
        "temperature": "not printed"
      },
      "method": "Printed in the same sentence as the 1.22 g cm-3 density, which cites reference 91.",
      "status": "ground",
      "source": "pmc13413960",
      "where": "Full text, sentence citing reference 91",
      "source_detail": {
        "title": "Polyhydroxybutyrate (PHB): Production, Properties, Modification Strategies, Additive Manufacturing, Biodegradation, and Applications (Materials, 2026)",
        "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC13413960/",
        "kind": "paper",
        "license": "Open access, CC BY (cited, not reproduced)"
      }
    },
    {
      "benchmark": "elongation",
      "label": "Elongation at break, PHB produced by fermentation (review, citing a secondary study)",
      "value": 4.5,
      "bound": "exact",
      "unit": "%",
      "scope": "material",
      "conditions": {
        "material": "PHB produced by bacteria, purity 98.9 %, crystallinity 73 %",
        "test": "not printed",
        "temperature": "not printed"
      },
      "method": "Printed in the same sentence as the 30 MPa tensile strength, which cites reference 91.",
      "status": "ground",
      "source": "pmc13413960",
      "where": "Full text, sentence citing reference 91",
      "source_detail": {
        "title": "Polyhydroxybutyrate (PHB): Production, Properties, Modification Strategies, Additive Manufacturing, Biodegradation, and Applications (Materials, 2026)",
        "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC13413960/",
        "kind": "paper",
        "license": "Open access, CC BY (cited, not reproduced)"
      }
    },
    {
      "benchmark": "elastic_modulus",
      "label": "Tensile modulus, T-PHBV compound (value quoted from the producer's datasheet)",
      "value": 3300,
      "bound": "exact",
      "unit": "MPa",
      "scope": "material",
      "conditions": {
        "material": "T-PHBV compound, poly(3-hydroxybutyrate-co-3-hydroxyvalerate)",
        "test": "not printed in the sentence",
        "temperature": "not printed in the sentence"
      },
      "method": "The paper quotes the producer's datasheet (TDS) as giving a tensile elastic modulus (Et) of 3300 MPa, and says its own tensile results agree fairly well with it. The datasheet value is entered, not the paper's measurement.",
      "status": "ground",
      "source": "pmc10844030",
      "where": "Mechanical testing section, sentence comparing results with the TDS",
      "source_detail": {
        "title": "Degradation of a PHBV compound in different environments (Heliyon, 2024)",
        "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC10844030/",
        "kind": "paper",
        "license": "Open access (cited, not reproduced)"
      }
    },
    {
      "benchmark": "ultimate_tensile_strength",
      "label": "Tensile strength at break, T-PHBV compound (value quoted from the producer's datasheet)",
      "value": 38,
      "bound": "exact",
      "unit": "MPa",
      "scope": "material",
      "conditions": {
        "material": "T-PHBV compound, poly(3-hydroxybutyrate-co-3-hydroxyvalerate)",
        "test": "not printed in the sentence",
        "temperature": "not printed in the sentence"
      },
      "method": "The paper quotes the datasheet stress at break (sigma B) of 38 MPa in the same sentence as the 3300 MPa modulus.",
      "status": "ground",
      "source": "pmc10844030",
      "where": "Mechanical testing section, sentence comparing results with the TDS",
      "source_detail": {
        "title": "Degradation of a PHBV compound in different environments (Heliyon, 2024)",
        "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC10844030/",
        "kind": "paper",
        "license": "Open access (cited, not reproduced)"
      }
    },
    {
      "benchmark": "elongation",
      "label": "Strain at break, T-PHBV compound (value quoted from the producer's datasheet)",
      "value": 3.7,
      "bound": "exact",
      "unit": "%",
      "scope": "material",
      "conditions": {
        "material": "T-PHBV compound, poly(3-hydroxybutyrate-co-3-hydroxyvalerate)",
        "test": "not printed in the sentence",
        "temperature": "not printed in the sentence"
      },
      "method": "The paper quotes the datasheet strain at break (epsilon B) of 3.7 % in the same sentence as the 3300 MPa modulus.",
      "status": "ground",
      "source": "pmc10844030",
      "where": "Mechanical testing section, sentence comparing results with the TDS",
      "source_detail": {
        "title": "Degradation of a PHBV compound in different environments (Heliyon, 2024)",
        "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC10844030/",
        "kind": "paper",
        "license": "Open access (cited, not reproduced)"
      }
    }
  ],
  "corrosion": [
    {
      "environment": "Accelerated UVA-340 weathering of plasticised PHBV/rapeseed biocomposites (QUV, ISO 4892-3)",
      "headline": "Under accelerated UV weathering, stiffness rose and elongation at break fell below 1.5 % by 500 h.",
      "effect": "The tensile modulus rose up to two times by 500 h. The ultimate strength rose only until 250 h. Samples ruptured at ultimate elongations even lower than 1.5 %. The authors link the rise in crystallinity partly to hydrolytic degradation of the matrix. These are plasticised PHBV composites, not neat PHB.",
      "rating": "moderate",
      "conditions": {
        "irradiance": "0.75 W/m2",
        "cycle": "8 h UV at black panel temperature 50 +/- 3 °C, 15 min spray, 3 h 45 min condensation at 50 °C",
        "exposure": "250 h and 500 h",
        "standard": "ISO 4892-3:2016"
      },
      "source": "pmc10934408",
      "where": "Section 2.5 (weathering conditions), Section 3.1.3 (tensile modulus and elongation)"
    },
    {
      "environment": "Melt above the melting point (processing)",
      "headline": "Degradation starts just above the melting point, so the processing window is narrow.",
      "effect": "Above the melting point, beta-elimination causes chain scission, which forms crotonic acid or crotonate and other volatile products. Processing close to the melting point can also cause thermal ageing during processing.",
      "rating": "moderate",
      "conditions": {
        "reference_melting_point": "151.2 °C (P(3HB) filament, DSC)",
        "reference_decomposition": "282.0 °C (P(3HB) filament, Tdeg)"
      },
      "source": "pmc13413960",
      "where": "Full text, paragraphs on the narrow processing window and beta-elimination"
    },
    {
      "environment": "Immersion in Mediterranean seawater for 12 months (dumbbell bars of a PHBV compound)",
      "headline": "Surface chemistry changed little after 12 months of seawater immersion.",
      "effect": "ATR-FTIR spectra of the bars showed no substantial change, except a slow rise in the 3100 to 3600 cm-1 band and a broad band near 1600 cm-1, which the authors read as increasing hydroxyl and carboxyl groups. The authors describe environmental degradation as slow, which depends on natural enzymes, UV resistance and low water absorption.",
      "rating": "low",
      "conditions": {
        "medium": "Mediterranean seawater",
        "time": "12 months"
      },
      "source": "pmc10844030",
      "where": "Results, seawater immersion paragraph, and Discussion"
    }
  ],
  "risks": {
    "hazards": [
      {
        "text": "PubChem lists 3-hydroxybutyric acid, the monomer, with skin irritation (H315, 100 %), serious eye irritation (H319, 100 %) and respiratory irritation (H335, 100 %), signal word Warning, aggregated from 44 company reports in 4 ECHA C&L notifications. This describes the monomer, not the polymer.",
        "ghs": [
          "H315",
          "H319",
          "H335"
        ],
        "source": "pubchem-3hba",
        "where": "GHS Classification, aggregated ECHA C&L notifications (CID 441)"
      }
    ],
    "failure_risks": [
      {
        "mode": "Brittle fracture of unfilled P(3HB)",
        "trigger": "Tensile loading of unfilled P(3HB)",
        "consequence": "Tensile strength 34.2 MPa with elongation at break 3.8 %, described as predominantly brittle fracture",
        "severity": "moderate",
        "source": "pmc13119779",
        "where": "Results, sentence on unfilled P(3HB) mechanical behaviour"
      },
      {
        "mode": "Thermal degradation during melt processing",
        "trigger": "Melt processing close to or just above the melting point (151 to 177 °C in the sources)",
        "consequence": "Chain scission, molecular weight loss and volatile products such as crotonic acid",
        "severity": "moderate",
        "source": "pmc13413960",
        "where": "Full text, narrow processing window and beta-elimination paragraphs"
      },
      {
        "mode": "UV-induced stiffening and embrittlement of a PHBV composite",
        "trigger": "500 h of accelerated UVA-340 exposure at 0.75 W/m2 (QUV)",
        "consequence": "Modulus up to two times the starting value, and rupture at elongations below 1.5 %",
        "severity": "moderate",
        "source": "pmc10934408",
        "where": "Section 3.1.3, tensile modulus and elongation results"
      }
    ],
    "side_effects": [
      {
        "text": "Chain scission above the melting point can release crotonic acid or crotonate and other volatile degradation products.",
        "affects": "Operators and equipment during melt processing",
        "source": "pmc13413960",
        "where": "Full text, beta-elimination paragraph"
      }
    ],
    "handling": [
      {
        "text": "Keep the melt close to the melting point but no hotter than needed, because PHB degrades just above it.",
        "source": "pmc13413960",
        "where": "Full text, narrow processing window paragraph"
      }
    ],
    "mitigations": [
      {
        "text": "A 50:50 P(3HB)/PLA blend lowers the P(3HB) melting point from 151.2 to 147.7 °C and reduces its melting enthalpy from 57.6 to 26.9 J/g. The paper presents blending with lower-melting polymers as a route to a lower processing temperature.",
        "source": "pmc13119779",
        "where": "Thermal analysis of the P(3HB)/PLA blend section"
      },
      {
        "text": "The copolymer study proposes P(3HB-co-4HB), P(3HB-co-3HV) and P(3HB-co-3HHx) as partners that improve processability of P(3HB) filament.",
        "source": "pmc13119779",
        "where": "Introduction, paragraph on processability"
      }
    ]
  },
  "uses": [
    {
      "application": "in-space-manufacturing",
      "device": "Engineered microbes producing PHA for in-space manufacturing (research, not flown)",
      "example": "NASA's record Enhanced Polyhydroxybutyrate Production for Long-Term Spaceflight Applications describes a secretion route that exports PHA from engineered E. coli, to avoid downstream extraction during spaceflight. It is a development record, not a flight result.",
      "source": "nasa-ntrs-20160008913",
      "where": "Abstract"
    },
    {
      "application": "structures",
      "device": "3D-printed PHB parts (fused deposition modelling)",
      "example": "The review names additive manufacturing as a growing use of PHB and reports that a 3D-printable filament had a DSC melting point of about 167 °C after extrusion, below the 177 °C of pure PHB.",
      "source": "pmc13413960",
      "where": "Full text, additive manufacturing sections and DSC sentence"
    }
  ],
  "supply": [
    {
      "subject": "PHB production by fermentation",
      "abundance": "Bacteria such as Cupriavidus necator, Methylobacterium rhodesianum and Bacillus megaterium produce PHB as a stored carbon reserve, mainly under nutrient-limited conditions.",
      "producers": [],
      "critical_lists": [],
      "substitutes": [],
      "source": "wikipedia-phb",
      "where": "Biosynthesis section"
    },
    {
      "subject": "PHB feedstock: sugars, glycerol and waste streams",
      "abundance": "PHB bacteria can grow on glucose, sucrose, starch, vegetable oils, glycerol, dairy and food residues. The review says feedstock strongly affects production cost, and that at larger scale glycerol cut production costs by 10 to 20 % compared with glucose. No mineral is involved, so no critical-mineral entry applies.",
      "producers": [],
      "critical_lists": [],
      "substitutes": [],
      "source": "pmc13413960",
      "where": "Full text, feedstock and production-cost paragraphs"
    }
  ],
  "media": [],
  "documents": [
    {
      "title": "Polyhydroxybutyrate (PHB): Production, Properties, Modification Strategies, Additive Manufacturing, Biodegradation, and Applications (Materials, 2026, doi 10.3390/ma19143115)",
      "type": "paper",
      "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC13413960/",
      "year": 2026
    },
    {
      "title": "Structure-Property Relationships in PHB-Based Copolymers and PHB/PLA Biocomposites Modified with Hydroxyapatite and Chitosan (Polymers, 2026, doi 10.3390/polym18080913)",
      "type": "paper",
      "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC13119779/",
      "year": 2026
    },
    {
      "title": "Accelerated Weathering Testing (AWT) and Bacterial Biodegradation Effects on PHBV/Rapeseed Microfiber Biocomposites (Polymers, 2024, doi 10.3390/polym16050622)",
      "type": "paper",
      "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC10934408/",
      "year": 2024
    },
    {
      "title": "Degradation of a PHBV compound in different environments (Heliyon, 2024, doi 10.1016/j.heliyon.2024.e24770)",
      "type": "paper",
      "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC10844030/",
      "year": 2024
    },
    {
      "title": "NASA: Enhanced Polyhydroxybutyrate Production for Long-Term Spaceflight Applications (NTRS 20160008913)",
      "type": "report",
      "url": "https://ntrs.nasa.gov/citations/20160008913",
      "year": 2016
    },
    {
      "title": "PubChem CID 441, 3-Hydroxybutyric acid: GHS classification",
      "type": "database",
      "url": "https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/441/JSON?heading=GHS+Classification"
    }
  ],
  "gaps": [
    "No moisture absorption (equilibrium water uptake, % by weight) value for PHB was found in any fetched page.",
    "No hydrolysis rate, molecular-weight loss or humidity-ageing data for neat PHB was found. The seawater result is for a PHBV compound and is qualitative.",
    "UV ageing data are for plasticised PHBV/rapeseed composites only. No UV result for neat PHB was found.",
    "No heat deflection temperature, Vicat softening temperature, specific heat, thermal conductivity or coefficient of thermal expansion for PHB was found in the fetched pages.",
    "No solvent, acid or alkali resistance number was found. Wikipedia says PHB is soluble in chloroform, but it is not entered because Wikipedia is used here for composition and history only.",
    "No flight, outgassing (ASTM E595) or atomic-oxygen data for PHB was found. The NASA record is a development paper, so no environment tag is set.",
    "Producer country shares and capacity volumes were not found. The supply entries cite production sites and feedstocks, not shares.",
    "No PubChem record for the PHB polymer was found, and no safety data sheet for PHB powder was read. The GHS entry is for the monomer, 3-hydroxybutyric acid.",
    "Tensile values for PHB disagree across sources (34.2 MPa in the copolymer study, 30 MPa in the review). They are not reconciled, and each is entered with its own conditions.",
    "Test standards and temperatures are not printed for the 34.2 MPa, 151.2 °C, 177 °C and 282.0 °C rows.",
    "Non-canonical property names are used: decomposition_temperature. It is not in spores/property-canon.yaml.",
    "The 1.23 g/cm3 density is the supplier's listed value, not a measurement in the paper.",
    "The Biomer P300 datasheet could not be retrieved, so its density, glass transition and tensile values are not entered.",
    "Atomic counts and atomic weights are not given in the recipe, because no formula with atom counts was found in a fetched source.",
    "No photographs or diagrams were added to media, and no image licence was read in this run."
  ],
  "story": {
    "why": "PHB is a thermoplastic polyester made by bacteria. It is the simplest and most studied member of the polyhydroxyalkanoate family (review). Its melting point is close to that of polypropylene, and it is biodegradable and made from renewable carbon. What holds it back is brittleness, high crystallinity, low thermal stability and a narrow processing window, which the review lists as the main barriers to wider use.",
    "uses": [
      {
        "where": "Additive manufacturing",
        "line": "The review names 3D printing as a growing use of PHB. It reports that a 3D-printable PHB filament had a DSC melting point of about 167 °C after extrusion, below the 177 °C of pure PHB."
      },
      {
        "where": "In-space manufacturing research",
        "line": "A NASA record describes a secretion route that exports PHA from engineered E. coli, so that product recovery is simpler during spaceflight. It is a development paper, not a flight result."
      }
    ],
    "can_do": [
      {
        "label": "Stiff",
        "line": "Tensile strength is 34.2 MPa for unfilled P(3HB), and 30 MPa for a PHB sample quoted in the review.",
        "benchmark": "ultimate_tensile_strength",
        "scope": "material",
        "value": "30 MPa to 34.2 MPa"
      },
      {
        "label": "Heat",
        "line": "Pure PHB melts at about 177 °C by DSC, and a 3D-printable filament at about 167 °C after extrusion.",
        "benchmark": "melting_point",
        "scope": "material",
        "value": "167 °C to 177 °C"
      },
      {
        "label": "Glass transition",
        "line": "The second-heating glass transition of the P(3HB) filament is 2.4 °C.",
        "benchmark": "glass_transition_temperature",
        "scope": "material",
        "value": "2.4 °C"
      },
      {
        "label": "Ductility",
        "line": "Unfilled P(3HB) breaks at 3.8 % elongation, and the paper describes its fracture as predominantly brittle.",
        "benchmark": "elongation",
        "scope": "material",
        "value": "3.8 %"
      }
    ],
    "compare": "According to the review, PHB's melting point is close to that of polypropylene. Its elongation at break is small: 3.8 % for unfilled P(3HB), 4.5 % for a second PHB sample in the review, and 3.7 % for the PHBV compound quoted from its datasheet. The sources agree that PHB-family polymers are stiff and brittle without blends.",
    "compare_rows": [
      {
        "label": "Melting point",
        "benchmark": "melting_point",
        "scope": "material"
      },
      {
        "label": "Tensile strength",
        "benchmark": "ultimate_tensile_strength",
        "scope": "material"
      },
      {
        "label": "Elongation at break",
        "benchmark": "elongation",
        "scope": "material"
      }
    ],
    "handling": [
      "Process close to the melting point but do not overheat it, because PHB degrades just above it (review).",
      "Expect brittleness in unfilled PHB. Use a blend or copolymer where impact or elongation matters.",
      "Plan for UV exposure. Accelerated UV stiffened a PHBV composite and cut its elongation below 1.5 % by 500 h."
    ],
    "good_for": [
      "Bio-based, biodegradable stiff parts where the service temperature stays well below the 151 to 177 °C melting range and brittleness is acceptable.",
      "3D-printing research, where the review cites printed PHB parts and a printable filament with a melting point of about 167 °C."
    ],
    "watch_out": [
      "Brittleness: unfilled P(3HB) breaks at 3.8 % elongation.",
      "Narrow processing window: degradation starts just above the melting point.",
      "UV ageing: a PHBV composite stiffened and broke below 1.5 % elongation after 500 h of accelerated UVA-340 exposure.",
      "Gaps: no moisture, hydrolysis, heat-ageing or space data was found for neat PHB."
    ],
    "verdict": "PHB is a bio-based, biodegradable polyester with a melting point of 151 to 177 °C and a glass transition of 2.4 °C for the filament sample. Unfilled, it is stiff but brittle, at 3.8 % elongation at break. Its processing window is narrow, and accelerated UV ageing of a PHBV composite stiffened it and cut its elongation below 1.5 % by 500 h. No flight, moisture or heat-ageing data for neat PHB was found, so PHB is not verified for space use.",
    "recipe": {
      "line": "PHB is a bacterial polyester. Bacteria join 3-hydroxybutyric acid units head to tail into a linear chain and store it as granules inside the cell. The sources read describe fermentation as the production route, and no fossil chemical route is described.",
      "parts": [
        {
          "name": "3-hydroxybutyric acid",
          "role": "Monomer. Each unit links to the next through an ester bond, forming the polyester backbone."
        },
        {
          "name": "Sugar",
          "role": "Feedstock. Glucose, sucrose, starch, vegetable oils, glycerol and food residues can all feed the fermentation (review)."
        }
      ]
    },
    "risk_groups": [
      {
        "title": "For people",
        "lead": "No GHS classification was found for the PHB polymer. PubChem classifies its monomer, 3-hydroxybutyric acid, as an irritant.",
        "points": [
          {
            "label": "The monomer",
            "line": "PubChem lists skin, eye and respiratory irritation (H315, H319, H335) for 3-hydroxybutyric acid, from 44 company reports. This describes the monomer, not the polymer."
          },
          {
            "label": "Dust",
            "line": "No safety data sheet for PHB powder was found, so dust hazards are not stated here."
          },
          {
            "label": "Decomposition",
            "line": "Above the melting point, chain scission gives crotonic acid or crotonate and other volatile products."
          }
        ],
        "level": 0,
        "verdict": "Monomer irritates skin, eyes and airways"
      },
      {
        "title": "Heat during processing",
        "lead": "PHB degrades just above its melting point, so melt temperature is the main control.",
        "points": [
          {
            "label": "Melting range",
            "line": "The sources give a melting point of 151.2 °C for P(3HB) filament by DSC and 177 °C for pure PHB. Degradation starts just above the melting point."
          },
          {
            "label": "Blends",
            "line": "A 50:50 PHB/PLA blend lowers the P(3HB) melting point to 147.7 °C, which the paper presents as a route to lower processing temperatures."
          }
        ]
      },
      {
        "title": "Ageing in service",
        "lead": "The only ageing data come from PHBV composites, not neat PHB.",
        "points": [
          {
            "label": "UV",
            "line": "Under accelerated UVA-340 weathering, a PHBV/rapeseed composite stiffened and ruptured below 1.5 % elongation by 500 h."
          },
          {
            "label": "Seawater",
            "line": "After 12 months of immersion in Mediterranean seawater, a PHBV compound's surface chemistry changed little."
          }
        ]
      }
    ]
  },
  "updated": "2026-10-26",
  "review": {
    "status": "draft",
    "method": "assistant",
    "checked_values": 14,
    "unreachable": 0,
    "caveats": 0,
    "note": "Written by an AI assistant on 2026-10-26 from pages read in this run. verify-values found all 14 values and all 3 designations in their cited source pages."
  },
  "sources": {
    "pmc13413960": {
      "title": "Polyhydroxybutyrate (PHB): Production, Properties, Modification Strategies, Additive Manufacturing, Biodegradation, and Applications (Materials, 2026)",
      "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC13413960/",
      "kind": "paper",
      "license": "Open access, CC BY (cited, not reproduced)"
    },
    "pmc13119779": {
      "title": "Structure-Property Relationships in PHB-Based Copolymers and PHB/PLA Biocomposites Modified with Hydroxyapatite and Chitosan (Polymers, 2026)",
      "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC13119779/",
      "kind": "paper",
      "license": "Open access (MDPI, cited, not reproduced)"
    },
    "pmc10934408": {
      "title": "Accelerated Weathering Testing (AWT) and Bacterial Biodegradation Effects on PHBV/Rapeseed Microfiber Biocomposites (Polymers, 2024)",
      "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC10934408/",
      "kind": "paper",
      "license": "Open access (MDPI, cited, not reproduced)"
    },
    "pmc10844030": {
      "title": "Degradation of a PHBV compound in different environments (Heliyon, 2024)",
      "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC10844030/",
      "kind": "paper",
      "license": "Open access (cited, not reproduced)"
    },
    "nasa-ntrs-20160008913": {
      "title": "NASA NTRS 20160008913: Enhanced Polyhydroxybutyrate Production for Long-Term Spaceflight Applications (2016)",
      "url": "https://ntrs.nasa.gov/citations/20160008913",
      "kind": "report",
      "license": "NASA public technical report (cited, not reproduced)"
    },
    "pubchem-3hba": {
      "title": "PubChem CID 441, 3-Hydroxybutyric acid: GHS classification (aggregated ECHA C&L notifications)",
      "url": "https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/441/JSON?heading=GHS+Classification",
      "kind": "database",
      "license": "PubChem record (cited)"
    },
    "wikipedia-phb": {
      "title": "Wikipedia: Polyhydroxybutyrate (used for composition, biosynthesis and history only)",
      "url": "https://en.wikipedia.org/wiki/Polyhydroxybutyrate",
      "kind": "web",
      "license": "CC BY-SA 4.0 (cited, not reproduced)"
    }
  },
  "license": "CC-BY-4.0",
  "url": "https://spacemushroom.com/profiles/phb/"
}