RoHS Audit Found Regrind in a Declared-Virgin PBT Part: Now What

A RoHS compliance audit of a glass-fiber reinforced polybutylene terephthalate connector housing has identified post-industrial regrind in a material lot declared as virgin. The finding is not, by itself, an Annex II exceedance of Directive 2011/65/EU because regrind is not a restricted substance. The nonconformance arises from the discontinuity between the declared material identity and the actual material placed on the market. Under EN IEC 63000:2018, the technical documentation must allow traceability between the restricted-substance assessment and the physical constituent under evaluation. A virgin-material declaration that is contradicted by regrind invalidates the conformity presumption even when X-ray fluorescence screening according to IEC 62321-3-1:2013 returns values below the Annex II maximum concentration values.

The immediate disposition is quarantine of the affected lot, physical segregation of candidate regrind streams, and review of the supplier’s material-specific RoHS file. Annex II maximum concentration values by weight in homogeneous materials are 0.1% for lead, mercury, hexavalent chromium, PBB, PBDE, DEHP, BBP, DBP, and DIBP, and 0.01% for cadmium. Screening by IEC 62321-3-1:2013 is a rapid first-tier check for lead, mercury, cadmium, total chromium, and total bromine, but it cannot confirm hexavalent chromium, specific brominated flame retardants, or phthalate plasticizers. Confirmatory analysis is required when the regrind source is unknown or when the screening result approaches the decision threshold.

Does the Regrind Finding Invalidate the PBT Part Under RoHS or Only the Declaration?

The part may remain compliant with the substance restrictions in Directive 2011/65/EU while the material disclosure is noncompliant with the conformity-assessment obligations in EN IEC 63000:2018. The audit must distinguish between a failed material and a failed declaration. If the regrind was generated from the same RoHS-assessed PBT compound, and if the regrind addition was controlled, the homogeneous material may still be below all Annex II maximum concentration values. The failure is then a documentation failure: the supplier declared virgin material when the batch record contained regrind. If the regrind source is unknown, the material must be treated as a new, unassessed material and subjected to full restricted-substance verification.

A PBT compound used in electrical and electronic equipment may contain glass fiber, flame retardants, nucleating agents, mold release agents, and colorants. A regrind stream can carry oxide-based pigments, antimony trioxide synergist, brominated epoxy flame retardant, or contaminants from co-mingled production scrap. Antimony trioxide is not restricted by RoHS, but it frequently co-occurs with brominated flame retardants. Total bromine detected by XRF above 1000 ppm is a common trigger for PBB and PBDE confirmation by IEC 62321-6:2015. If the regrind contains legacy cadmium red or lead chromate pigments, the material may exceed the cadmium limit of 0.01% or the lead limit of 0.1% even though the virgin PBT base resin was compliant.

Thermal and Hydrolytic Degradation Effects That Distinguish PBT Regrind From Virgin Feedstock

PBT is a semicrystalline thermoplastic polyester with a melting peak near 223 °C per ISO 11357-3:2018, a density of 1.31 g/cm³ per ISO 1183-1:2019, and tensile modulus near 2500 MPa per ISO 527-2:2012 for unreinforced grades. The melt-processing window is narrow. Barrel set points are normally 240 °C to 260 °C, and mold temperatures of 60 °C to 80 °C are used for glass-fiber reinforced PBT. At melt temperatures above 260 °C, chain scission accelerates and produces terminal carboxyl groups and volatile by-products. In the presence of residual moisture above 0.02%, ester hydrolysis becomes the dominant degradation route, and the reaction is acid-catalysed. PBT therefore requires closed-loop desiccant drying to a moisture content below 0.02% before melt processing; verification can be performed by ISO 15512:2019 Karl Fischer methods.

Production-scale experience on a 1200 kN injection molding machine with a 40 mm general-purpose screw has shown that dry blends of virgin PBT and post-industrial regrind with a fines fraction below 200 µm can segregate in the feed throat. Shot-mass variation of ±0.6 g to ±0.9 g and screw torque fluctuation are observed when regrind addition exceeds 20 wt%. In such cases, closed-loop transfer-pressure correction is required to prevent short shots in thin-walled connector geometries. The problem is exacerbated by melt-temperature overshoot above 265 °C, which reduces melt viscosity and changes the pressure-limited fill pattern.

Repeated heat history reduces intrinsic viscosity. A virgin PBT lot with a viscosity number of 105 cm³/g to 110 cm³/g measured per ISO 1628-5:2018 in phenol/tetrachloroethane may drop by 5 cm³/g to 12 cm³/g after one additional extrusion cycle. The melt volume-flow rate measured at 250 °C with 2.16 kg per ISO 1133-1:2022 may rise from 15 cm³/10 min to 22 cm³/10 min or higher, depending on moisture and residence time. These shifts alter weld-line strength, long-term hydrolytic stability, and dimensional consistency, but they may not be visible in RoHS elemental screening.

Analytical verification of regrind content in PBT must be treated as a material-identity problem rather than a simple RoHS elemental problem. The first measurement layer should compare the suspect lot against a retained virgin sample using differential scanning calorimetry per ISO 11357-3:2018, melt volume-flow rate per ISO 1133-1:2022, and intrinsic viscosity per ISO 1628-5:2018. A second layer should identify inorganic fillers and flame-retardant packages by thermogravimetric analysis and Fourier-transform infrared spectroscopy. The third layer is confirmatory RoHS testing. If the regrind is suspected to contain a different flame-retarded PBT grade, bromine-positive XRF screening does not distinguish PBB and PBDE from non-restricted brominated epoxy or brominated polyacrylate. Only IEC 62321-6:2015 gas chromatography–mass spectrometry can discriminate. The audit outcome therefore depends on whether the supplier can demonstrate that the regrind originated from the same RoHS-assessed compound and that the substance profile has not been diluted or enriched by foreign material.

Supplier Corrective Action and Material Traceability Records

Corrective action begins with lot quarantine and sample retention. The supplier must provide the original production record for the declared virgin PBT compound: resin grade, glass-fiber content, flame-retardant package, lubricant system, extrusion batch number, drying parameters, and regrind ratio. Under EN IEC 63000:2018, Clause 4, the technical documentation must enable the market surveillance authority to identify the material and its conformity status. A declaration that does not match the physical material is a documentation nonconformance even if the part remains below Annex II limits. If the regrind was generated from the same compound and controlled to a maximum addition of 20 wt% with documented drying to 0.02% moisture, the material can be re-declared with the actual regrind content. If the source is unknown, the lot requires restricted-substance testing and a risk assessment for REACH SVHCs and other legacy additives.

The audit should also examine whether the original declaration omitted a regrind allowance that the supplier’s internal specification actually permitted. In such cases, the corrective action is a disclosure correction rather than a material change. That correction must still be supported by batch traceability, retained samples, and, if required by the customer contract, production part approval process documentation. A material-identity correction is not an exemption from Annex II testing; it is a change to the conformity file that must be maintained for the period specified in Directive 2011/65/EU, Article 7(b).

When the Audit Finding Demands Full RoHS Re-Testing Instead of Paper Correction

The decision to re-test is triggered by four conditions: the regrind source is unknown; the regrind is suspected to contain a different colorant or flame-retardant package; the XRF screen indicates total bromine above 1000 ppm or cadmium above 100 ppm; or the regrind includes post-consumer material. In these cases, the original conformity file no longer describes the actual substance profile. Sample preparation must follow IEC 62321-2:2013, with cryomilling to a particle size near 200 µm and multiple aliquot analysis because a heterogeneous regrind-containing material can produce localised false-negative or false-positive screening results. Confirmatory testing is then required for lead and cadmium by IEC 62321-5:2013, mercury by IEC 62321-4:2013, hexavalent chromium by IEC 62321-7-2:2017, PBB and PBDE by IEC 62321-6:2015, and phthalates by IEC 62321-8:2017.

If the re-tested material passes all Annex II limits, the part can be re-declared with the correct regrind content. If the material fails any confirmatory test, the affected lot cannot be placed on the European Union market, and the noncompliant homogeneous material must be segregated from compliant production. The audit finding then expands from a supplier corrective action to a product-conformity hold, with the technical file updated to identify the failed lot, the test report, and the disposition.

Process validation of regrind-containing PBT should include tensile testing of dry-as-molded specimens per ISO 527-2:2012, Charpy impact per ISO 179-1:2010, and melt volume-flow rate per ISO 1133-1:2022. For a 30% glass-fiber reinforced PBT connector housing, typical production targets are tensile strength above 110 MPa, notched Charpy impact above 7 kJ/m², and MVR below 25 cm³/10 min at 250 °C/2.16 kg. These values are material-grade specific, and published data for other glass loadings and flame-retardant packages may differ. A robust corrective action closes only when the re-declared material has a matched RoHS file, a controlled regrind stream, and verified processing stability under the actual molding conditions.