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.
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:
  - scope: material
    status: ground
    benchmark: density
    label: Density, P(3HB) powder as listed by its supplier
    value: 1.23
    unit: g/cm3
    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.
    source: pmc13119779
    where: Materials section, first sentence on the P(3HB) supplier
  - scope: material
    status: ground
    benchmark: density
    label: Density, PHB produced by fermentation (review, citing a secondary study)
    value: 1.22
    unit: g/cm3
    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.
    source: pmc13413960
    where: Full text, sentence citing reference 91 (purity, crystallinity and density)
  - scope: material
    status: ground
    benchmark: melting_point
    label: Melting point, P(3HB) filament by DSC
    value: 151.2
    unit: °C
    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.
    source: pmc13119779
    where: Filament table, P(3HB) row, Tm2 column
  - scope: material
    status: ground
    benchmark: melting_point
    label: Melting point, pure PHB by DSC (review)
    value: 177
    unit: °C
    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.
    source: pmc13413960
    where: Full text, DSC sentence on the 3D-printable PHB filament
  - scope: material
    status: ground
    benchmark: melting_point
    label: Melting point, PHB 3D-printable filament after extrusion (review)
    value: 167
    unit: °C
    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.
    source: pmc13413960
    where: Full text, DSC sentence on the 3D-printable PHB filament
  - scope: material
    status: ground
    benchmark: glass_transition_temperature
    label: Glass transition temperature, P(3HB) filament, second heating
    value: 2.4
    unit: °C
    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.
    source: pmc13119779
    where: Filament table, P(3HB) row, Tg2 column
  - scope: material
    status: ground
    benchmark: decomposition_temperature
    label: Decomposition temperature, P(3HB) filament (Tdeg)
    value: 282
    unit: °C
    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.
    source: pmc13119779
    where: Filament table, P(3HB) row, Tdeg column
  - scope: material
    status: ground
    benchmark: ultimate_tensile_strength
    label: Tensile strength, unfilled P(3HB)
    value: 34.2
    unit: MPa
    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.
    source: pmc13119779
    where: Results, sentence on unfilled P(3HB) mechanical behaviour
  - scope: material
    status: ground
    benchmark: elongation
    label: Elongation at break, unfilled P(3HB)
    value: 3.8
    unit: '%'
    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.
    source: pmc13119779
    where: Results, sentence on unfilled P(3HB) mechanical behaviour
  - scope: material
    status: ground
    benchmark: ultimate_tensile_strength
    label: Tensile strength, PHB produced by fermentation (review, citing a secondary study)
    value: 30
    unit: MPa
    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.
    source: pmc13413960
    where: Full text, sentence citing reference 91
  - scope: material
    status: ground
    benchmark: elongation
    label: Elongation at break, PHB produced by fermentation (review, citing a secondary study)
    value: 4.5
    unit: '%'
    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.
    source: pmc13413960
    where: Full text, sentence citing reference 91
  - scope: material
    status: ground
    benchmark: elastic_modulus
    label: Tensile modulus, T-PHBV compound (value quoted from the producer's datasheet)
    value: 3300
    unit: MPa
    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.
    source: pmc10844030
    where: Mechanical testing section, sentence comparing results with the TDS
  - scope: material
    status: ground
    benchmark: ultimate_tensile_strength
    label: Tensile strength at break, T-PHBV compound (value quoted from the producer's datasheet)
    value: 38
    unit: MPa
    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.
    source: pmc10844030
    where: Mechanical testing section, sentence comparing results with the TDS
  - scope: material
    status: ground
    benchmark: elongation
    label: Strain at break, T-PHBV compound (value quoted from the producer's datasheet)
    value: 3.7
    unit: '%'
    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.
    source: pmc10844030
    where: Mechanical testing section, sentence comparing results with the TDS
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.
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
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 14
  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.
story:
  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
        glycerol or other carbon source: null
        role: Feedstock. Glucose, sucrose, starch, vegetable oils, glycerol and food residues can all feed the fermentation (review).
  risk_groups:
    - title: For people
      level: 0
      verdict: Monomer irritates skin, eyes and airways
      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.
    - 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.
  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
      benchmark: ultimate_tensile_strength
      value: 30 MPa to 34.2 MPa
      line: Tensile strength is 34.2 MPa for unfilled P(3HB), and 30 MPa for a PHB sample quoted in the review.
    - label: Heat
      benchmark: melting_point
      value: 167 °C to 177 °C
      line: Pure PHB melts at about 177 °C by DSC, and a 3D-printable filament at about 167 °C after extrusion.
    - label: Glass transition
      benchmark: glass_transition_temperature
      value: 2.4 °C
      line: The second-heating glass transition of the P(3HB) filament is 2.4 °C.
    - label: Ductility
      benchmark: elongation
      value: 3.8 %
      line: Unfilled P(3HB) breaks at 3.8 % elongation, and the paper describes its fracture as predominantly brittle.
  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.