Moving a PBT part to a new supplier without losing its certification requires more than a resin grade match. The existing part qualification normally rests on three separate documentation layers: the resin compound’s UL 94 Recognized Component listing under category QMFZ2, the molder’s production approval under ISO 9001:2015 or IATF 16949, and the part-level regulatory statement under REACH Regulation (EC) No 1907/2006, RoHS Directive 2011/65/EU, and food-contact obligations where applicable under 21 CFR 177.1660. The qualification is not transferable by default: a new supplier may process the same compound on different equipment and alter the crystallinity, fiber orientation, and flame-retardant distribution that the original part approval assumed. Field observation from production-scale injection molding indicates that switching a 30% glass-fiber PBT from a reciprocating-screw machine with a 20:1 L/D barrel to a 24:1 L/D machine can change tensile elongation at break by a measurable amount under ISO 527-2, even when the compound lot is unchanged.

When a PBT Component Crosses Supplier Boundaries, Certification Is Not Automatically Transferred

The UL Yellow Card for a PBT compound is issued for a specific grade identifier, thickness, color range, and maximum regrind fraction. A part molded from that compound is not automatically covered by the original listing when the molder changes. Under UL 746A, short-term properties are evaluated on standardized specimens; under UL 746B, long-term thermal aging generates relative thermal index values; under UL 746D, fabricated parts may require additional evaluation if molding conditions change the end-product’s performance. The minimum thickness at which a UL 94 V-0 rating applies must be read from the Yellow Card. A color concentrate added by the new supplier can reduce flammability performance because pigments and dispersants modify char formation; the resulting part cannot be assumed to retain the original UL 94 class at the same thickness. The same condition applies to regrind fraction: a listing that allows a maximum regrind level of 25% does not grant permission to exceed that level on a new production line.

Does the New Supplier’s Base Resin and Glass-Fiber Package Replicate the Original UL Yellow Card Conditions?

The equivalence assessment starts with the compound’s base polymer and filler package. Intrinsic viscosity measured by ISO 1628-1 in 60:40 phenol/tetrachloroethane is used to compare molecular weight; unreinforced PBT typically falls between 0.70 dL/g and 1.20 dL/g. Melt mass-flow rate determined at 250 °C under a 2.16 kg load per ISO 1133-1:2022 can expose differences in stabilizer or chain extender packages. Glass-fiber content is confirmed by ash testing per ISO 3451-1. A 30% glass-fiber grade should not be qualified by nominal filler content alone; fiber diameter, sizing chemistry, and retained fiber length after molding all influence tensile modulus and notched impact. The melting peak determined by differential scanning calorimetry per ISO 11357-3 should remain in the typical PBT range of 223 °C to 225 °C, and crystallization temperature should be compared with the original grade to anticipate differences in mold cycle time. Published data for the effect of proprietary fiber sizings on certification-specific outcomes is limited; therefore, comparative molded-part testing remains necessary.

Before comparative molding trials are performed, the new supplier’s drying system must be verified. PBT hydrolyzes in the presence of moisture above 0.02%; desiccant dryers with a supply-air dew point of −40 °C to −30 °C and a hopper residence time of 4 h at 120 °C are standard for glass-filled grades. Moisture content should be confirmed by ISO 15512. The melt-temperature window for glass-filled PBT is typically 250 °C to 270 °C, with mold temperatures of 80 °C to 120 °C. Barrel residence time should be limited to avoid molecular weight loss; field data on production machines with 25 mm to 40 mm screw diameters show that residence times beyond 10 min at 270 °C can reduce tensile elongation at break. The new supplier’s process audit should record screw L/D ratio, compression ratio, back pressure, injection velocity, and hold pressure because these parameters influence the glass-fiber orientation and weld-line strength measured on production parts. Regrind use must be limited to the percentage stated in the Yellow Card; common PBT listings permit up to 25%, but each grade must be verified individually.

Melt Viscosity and Shrinkage Boundaries That Can Invalidate Part Qualification

Melt viscosity differences are not fully captured by a single melt mass-flow rate value. A capillary rheometer test per ISO 11443 at 260 °C and shear rates from 100 s⁻¹ to 10,000 s⁻¹ is required to compare the new compound’s shear-thinning behavior with the original grade. A higher-viscosity PBT may require lower nozzle temperatures or faster injection speeds, shifting cavity pressure curves. Mold-flow simulation inputs—melt density, specific heat, thermal conductivity, and viscosity model coefficients—must be updated from the new supplier’s data rather than reused from the original molder. Mold shrinkage measured per ISO 294-4 can differ between suppliers even at equal glass-fiber content because nucleating agents and mold-release packages influence crystallization rate. For a 30% glass-fiber PBT, parallel shrinkage often falls near 0.3% to 0.5% and perpendicular shrinkage near 0.8% to 1.2%. A shift of 0.2 percentage points may move a bearing journal outside the dimensional specification on a glass-filled housing. Therefore, shrinkage validation must use the production tool and production coolers, not a prototype mold.

What Mechanical and Thermal Test Program Must Be Applied to Confirm Equivalence?

The qualification batch should be tested at 23 °C and 50% relative humidity after conditioning per ISO 291. Tensile properties are measured per ISO 527-2; flexural properties per ISO 178; Charpy notched impact per ISO 179-1/1eA; Izod impact per ISO 180/A when required by the original print. Heat deflection temperature under 1.8 MPa is measured per ISO 75-2 method A; Vicat softening temperature per ISO 306. For electrical enclosures, comparative tracking index is tested per IEC 60112 and dielectric strength per IEC 60243-1. Long-term thermal aging data from the original grade’s UL 746B relative thermal index cannot be transferred automatically if the new supplier’s stabilizer package differs. When the part is exposed to automotive under-hood temperatures, additional heat aging at 150 °C for 1,000 h followed by tensile strength and impact testing is common but must be specified by the customer because no universal pass criterion exists. Acceptance windows must be derived from the original PPAP control limits, not from datasheet ranges alone. A 30% glass-fiber PBT may show tensile strength of 130 MPa to 145 MPa, flexural modulus of 9,000 MPa to 11,000 MPa, and Charpy notched impact of 8 kJ/m² to 10 kJ/m² at 23 °C.

Regulatory and Food-Contact Compliance Documentation in a Supplier Migration

Moving a PBT part to a new supplier without losing its certification also requires documentation continuity for RoHS, REACH, and food-contact compliance. Under RoHS Directive 2011/65/EU, the new supplier’s materials must be screened by IEC 62321-3-1 X-ray fluorescence and, if necessary, confirmed by wet methods such as IEC 62321-4 for mercury, IEC 62321-5 for cadmium, IEC 62321-6 for lead, and IEC 62321-7-2 for hexavalent chromium. A brominated flame-retardant PBT must be checked against RoHS restrictions on polybrominated biphenyls and polybrominated diphenyl ethers; not all brominated systems are restricted, but the supplier must document the specific flame-retardant chemistry. Under REACH Regulation (EC) No 1907/2006, the new supplier must provide an Article 33 substances of very high concern declaration for the finished article when applicable. For food-contact use, 21 CFR 177.1660 covers poly(tetramethylene terephthalate); the new supplier must maintain composition within the specified reactant and additive limits. A change in heat stabilizer, mold-release agent, or colorant may require a new food-contact evaluation because end-test requirements are composition-specific.

The Certification Audit Does Not End with a Resin Certificate

Test reports used to support the supplier-change qualification must be issued under ISO/IEC 17025:2017 accreditation when the customer or certification body requires third-party evidence. Internal batch release data are not a substitute for external confirmation of flammability or regulatory substances. The new supplier’s ERP system should preserve lot-level traceability for base resin, glass fiber, flame retardant, colorant, and regrind fraction from incoming raw material to finished part. Under ISO 9001:2015 clause 8.5.2, this traceability must allow the batch genealogy to be reconstructed. The certificate of analysis for each PBT compound batch should report melt mass-flow rate per ISO 1133-1:2022, density per ISO 1183-1, filler content per ISO 3451-1, moisture content per ISO 15512, and UL-relevant color or regrind data. If the new supplier uses a different laboratory for UL 94 verification, the laboratory must be able to maintain sample traceability and test-equipment records required by ISO/IEC 17025:2017 clause 7.8.

Production-scale validation on the target mold remains mandatory after material equivalence, processing trials, and documentary review are complete. The run should use the new supplier’s production press, auxiliary equipment, and operators, with cavity-pressure sensors recording the filling, packing, and holding phases. A customer-specific PPAP may require a 300-piece consecutive production run with dimensional capability studies; critical dimensions are often required to demonstrate Cpk ≥ 1.33 and safety-related features Cpk ≥ 1.67. The PPAP record should include the qualifying material lot, processing sheet, mold temperature, screw recovery time, cushion, peak cavity pressure, and cycle time. Dimensional data from first shot, middle shot, and last shot are used to detect process drift across the run. Parts from the validation run should be retained for the period specified in the customer’s quality agreement. If the new supplier’s process is capable but the material lot changes after approval, subsequent lots must be covered by the same certificate of analysis and change-management procedure; otherwise the original certification basis may be invalidated.