The PBT Food-Contact Migration Test: Simulants, Time-Temperature and What Labs Report defines the compliance workflow for polybutylene terephthalate food-contact articles under European Union and ISO/IEC 17025:2017 analytical frameworks. PBT is produced by melt-phase polycondensation of 1,4-butanediol with terephthalic acid or dimethyl terephthalate; the semicrystalline ester backbone gives a melting point near 223 °C, a density between 1.31 g cm⁻³ and 1.35 g cm⁻³, and a water absorption at 23 °C and 50 % RH below 0.1 %. These thermal and barrier properties place PBT in injection-moulded reusable coffee filter bodies, kettle windows, dairy gaskets, and dry-food dispenser parts. A compliance dossier for such articles cannot rely on formulation data: Regulation (EU) No 10/2011 assigns food simulants in Annex III, establishes migration test conditions in Annex IV, and sets the overall migration limit at 10 mg dm⁻² for most articles and 60 mg kg⁻¹ for infant products. Specific migration limits for the two monomers dominate the analytical report: 7.5 mg kg⁻¹ for terephthalic acid and 5.0 mg kg⁻¹ for 1,4-butanediol. Gravimetric procedures are drawn from the EN 1186 series; specific migration methods are drawn from EN 13130-1:2004 and validated laboratory methods.

What Simulants Are Assigned to PBT Articles Under EU 10/2011?

Simulant selection is driven by the food category, not by PBT itself. Because the ester linkage is hydrolytically sensitive, simulant B, composed of 3 % w/v acetic acid, often yields the worst-case specific migration for acid-contact articles and must not be omitted from a PBT test plan even if the end food is neutral in sensory trials. Aqueous foods with pH above 4.5 are represented by simulant A, 10 % v/v ethanol. Alcoholic beverages up to 20 % alcohol and some dairy products are represented by simulant C, 20 % v/v ethanol. Higher-alcohol beverages and oil-in-water emulsions are represented by simulant D1, 50 % v/v ethanol. Fatty foods require simulant D2, normally vegetable oil, with isooctane or 95 % v/v ethanol as substitute overall-migration media under EN 1186-14:2002. Dry foods require Tenax MPO as simulant E. For a PBT coffee-machine filter holder, the assigned simulant set is usually simulant B for acidic coffee extraction and simulant C for milk-based beverages; if the same part is used in a dispenser containing fatty roasted-coffee oils, simulant D2 or its permitted alternative is added.

Time-Temperature Pairings That Drive Overall Migration into Liquid Simulants

Test laboratories select time-temperature pairs from Annex IV of Regulation (EU) No 10/2011 and EN 1186-1:2002. For PBT articles intended for prolonged ambient storage, the standard overall migration condition is 10 days at 40 °C; for refrigerated or frozen contact, the condition is 10 days at 20 °C. Short hot-fill contact is represented by 2 h at 70 °C, and coffee extraction or similar hot liquid contact is often assessed at 1 h at 100 °C. Retortable PBT candidates require 30 min at 121 °C only when the part retains dimensional stability; semicrystalline PBT may be acceptable, but the laboratory must report whether deformation, sink marks, or haze were observed. The gravimetric overall-migration test under EN 1186-14:2002 uses a standard liquid volume of 100 mL per dm² of contact surface for aqueous and oil simulants; the result is expressed in mg dm⁻². Specific migration data are converted to mg kg⁻¹ using the conventional EU surface-to-mass ratio of 6 dm² per kg food. In acidic simulants at 70 °C and above, PBT may undergo surface hydrolysis; if the laboratory observes a rise in 1,4-butanediol between the first and third exposure, the data are reported as a repeated-use trend rather than as a single-point pass/fail.

Specific migration determinations for PBT are not automated; they require separate chromatographic methods that tolerate acidic and ethanolic simulant matrices. Terephthalic acid is determined by reversed-phase LC-MS/MS or LC-UV with negative electrospray ionization and weak anion-exchange cleanup, because simulant B can suppress ionization in direct injection. 1,4-butanediol is poorly retained in reversed-phase systems; laboratories often acetylate the diol and analyze the acetate ester by GC-FID, or use HILIC-LC-MS/MS if the method has been validated from 0.5 mg kg⁻¹ to at least 10 mg kg⁻¹. PBT cyclic oligomers migrating into simulant D2 or 95 % v/v ethanol are monitored by UHPLC-QTOF/MS; because no specific migration limit is assigned to the cyclic dimer and trimer in Regulation (EU) No 10/2011, the laboratory reports them as overall migration contributors and as NIAS under Article 19 of the regulation. Published isotope dilution and certified reference data for PBT oligomers in food simulants are limited; therefore the report should state whether calibration was based on external standards or on a terephthalate-equivalent UV response.

In practice, migration variability across a PBT moulding batch is seldom below 10–15 % when the article has hot-runner gate vestiges or weld lines. A laboratory sample set should therefore include three replicate parts per simulant, not three aliquots from a single part. Production equipment with a hot runner held at 260 °C for more than 5 min of residence time can generate measurable cyclic oligomers at the gate vicinity; migration from this zone into 50 % v/v ethanol may be higher than from the flat wall. These positional effects are reported as “gate area” versus “bulk area” and are part of an ISO/IEC 17025:2017 certificate when the sample is injection-moulded.

How Surface Crystallinity and Drying History Affect Migration Results

Surface crystallinity is a critical process variable. PBT pellets pre-dried at 120 °C for 4 h in a desiccant dryer to a dew point of −40 °C reduce hydrolysis during moulding. Mould temperature below 60 °C produces a quenched amorphous skin that can release more low-molecular-mass ester species into simulants; mould temperatures above 80 °C produce greater crystallinity and lower diffusion. A PBT article intended for reusable food contact should not be moulded at moisture above 0.02 %, because residual moisture hydrolyzes the polymer in the barrel and shortens the ester chain, increasing later 1,4-butanediol availability. Drying history should be recorded in the certificate because it is an operational boundary for compliance interpretation.

Analytical Determinands, LOQs, and Report Fields in an ISO/IEC 17025 Certificate

An ISO/IEC 17025:2017 clause 7.8.3.1-compliant report separates overall migration from specific migration and does not use a single PBT pass statement. The certificate includes the sample geometry, gate and weld-line location for injection-moulded parts, the applied simulant lot and expiry, the contact mode, the time-temperature condition, the surface-to-volume ratio, the analytical finish, the blank-corrected result in mg dm⁻² or mg kg⁻¹, and the expanded uncertainty at k = 2. Compliance is assessed by comparing the upper limit of the expanded uncertainty interval with the migration limit; if the interval straddles 10 mg dm⁻², the laboratory reports “not conclusively compliant.” For specific migration, recovery in the spiked simulant should be within the method’s validated range; if matrix suppression reduces recovery below 70 %, the result must be reported as non-quantified or corrected by isotope dilution.

When PBT Re-usable Articles Require Third-Migration Verification

For repeated-use PBT articles, the migration test requires three successive exposures using the same test specimen under the same conditions. The first exposure removes surface oligomers and soluble lower-molecular-mass fractions; the third exposure measures whether depolymerization under aqueous or acidic simulants continues. If the third migration result is lower than the first, the laboratory reports the first value as the worst case; if the third result increases, the article is not considered compliant for that repeated-use condition without additional exposure data. This is particularly relevant for simulant B at 70 °C, where ester hydrolysis can generate additional 1,4-butanediol after repeated contact. The report records the three exposures, the intermediate drying or conditioning step, and the analytical value for each replicate. A missing third-migration value is a non-conformity in a PBT reusable-food-contact certificate, regardless of the first-migration result.

Laboratory data for PBT food-contact migration are limited outside the monomer SML framework; therefore gravimetric overall migration and the principal monomer limits remain the primary compliance endpoints. The report must state any deviations from Regulation (EU) No 10/2011 Annex III or Annex IV, especially when the actual intended contact time is shorter than the selected test condition. Migration into simulant D2 is considered high variability because oil absorption by PBT requires extraction correction; if the laboratory does not perform correction, the data are unsuitable for legal comparison with the 10 mg dm⁻² limit.