Polyethylene terephthalate is transferred between production plants and converter sites as amorphous chip, partially crystallized granules, or solid-state polymerized resin; the shipment origin file depends on the same intrinsic viscosity and carboxyl end-group records that govern downstream processing. Melt-phase esterification of purified terephthalic acid and monoethylene glycol yields a polyester with a typical intrinsic viscosity of 0.60–0.70 dL/g; bottle-grade solid-state polycondensation raises the value to 0.80–0.85 dL/g, while textile and film grades remain below 0.70 dL/g unless re-solidified. The viscosity number is determined in 60/40 w/w phenol/1,1,2,2-tetrachloroethane at 25 °C using ISO 1628-1:2021, and the same number controls harmonized system classification because heading 3907 draws a binding split at 78 mL/g for subheadings 3907.61 and 3907.69. A customs declaration that records the wrong subheading can invalidate a preferential duty claim even when the certificate of origin itself is correctly issued. The engineering context matters because PET pellets are hygroscopic; moisture above 50 ppm at the converter hopper leads to hydrolysis during melt processing, reducing intrinsic viscosity and generating acetaldehyde at a rate that affects food-contact compliance under FDA 21 CFR 177.1630 and EU Regulation No 10/2011. This interaction between resin thermal history and shipment documentation is the reason mill test certificates are retained as part of the origin evidence package.

How Is PTA-to-PET Polymerization Treated as Substantial Transformation?

Preferential origin treatment for polyethylene terephthalate is not determined solely by the tariff classification recorded on the commercial invoice; the competent authority tests whether the last substantial transformation occurred in the exporting country. Under the Harmonized System, purified terephthalic acid is classified in subheading 2917.36, monoethylene glycol in 2905.31, and the resulting primary-form PET in 3907.61 or 3907.69. A change from any other heading to heading 3907 is generally sufficient to confer origin under tariff-shift rules in several free trade agreements, because polymerization changes the chemical identity, molecular weight, and melt-phase behavior of the inputs. However, some preferential agreements require more than a tariff-shift sequence: they apply a regional value content test, in which the invoice value of non-originating PTA, MEG, and additives is compared with the ex-works price of the resin under Incoterms 2020 EXW. If the regional value content is below the agreement-specific threshold, the resin is not preferential even though the HS 2022 classification is correct. Documentation of input origins therefore includes supplier declarations for each monomer or co-monomer lot, and the purchaser must be able to trace a specific batch number from the silo backward through the continuous polycondensation line to the incoming raw-material tank.

Operations that do not confer origin for PET include sifting, screening, sorting, grading, blending, pressing, labeling, and placing the resin in bags or bulk containers. These operations appear throughout secondary distribution channels, especially when imported chip is toll-processed into smaller packages before import. A regional distribution hub that re-bags bulk PET from a non-qualifying source into 1,000 kg FIBCs cannot claim preferential origin on the basis of the re-bagging. The same limitation applies when a converter blends bottle-grade chip with post-industrial regrind without changing the tariff heading and without meeting the regional value content test.

Bulk continuous polymerization and solid-state polycondensation do not affect origin to the same degree as the transition from monomers to polymer, but they alter the analytical release profile that customs reviewers compare against the mill test certificate. A continuous melt-phase line discharging at 0.62 dL/g intrinsic viscosity will typically feed a solid-state reactor operating at 205–225 °C under vacuum or inert gas, which removes acetaldehyde and raises intrinsic viscosity by chain extension. The resulting pellet is partially crystallized to prevent blocking during bulk loading into hopper railcars or ISO tank containers. Bulk shipment requires heated or insulated vessels only during summer transits in high-temperature corridors; PET pellet surface temperatures above 80 °C during long dwell can initiate sticking and increase the proportion of fines, which must be reported on the packing list if the buyer’s incoming resin specification includes a fines threshold below 100 ppm larger than 0.5 mm. These physical changes do not create a new origin because the resin remains under the same 3907 heading; however, the certificate of analysis must match the production lot’s measured values, and any discrepancy between the declared intrinsic viscosity and the value on the mill test certificate can lead to a customs laboratory referral.

When Regional Cumulation Applies to Post-Consumer Recyclate Blends

Recycled polyethylene terephthalate flake and pellet introduce a separate origin question because the input is waste that may be collected, washed, sorted, and extruded across more than one customs territory. Preferential rules often permit regional cumulation, meaning that flake originating in a partner country may be used without losing preference when it is compounded or pelletized in the exporting country. The operator must retain mass-balance records from collection through pelletization, including the weight of collected bottles, the yield after hot caustic washing, the fraction removed by near-infrared sorting, and the pelletized output. A typical wash line producing 2,000 kg/h of clean flake may lose 15–25 wt% as caps, labels, fines, and sorting rejects; the surviving PET flake is then extruded with a melt filter rated at 40–60 µm to remove metal and incompatible polymers. The melt filter pressure buildup above 90–120 bar indicates excessive contamination from polyolefins, polyvinyl chloride, or aluminum and is a process signal that the claimed recyclate content cannot be met without rework. Under several agreements, waste collection, washing, and grinding are not enough to confer origin because they do not create a new product; pelletizing recycled flake through a vented twin-screw extruder with L/D 40:1 and vacuum degassing can qualify only when the specific rule of origin accepts a change from waste or scrap classification to 3907.

Traceability for recycled content in PET shipments should be based on EN 15343:2007 or an equivalent audited chain-of-custody system, because customs authorities may dismiss a recycled-origin claim that lacks lot-level sorting yields and extruder throughput records. The documentation must separate post-consumer PET from post-industrial regrind; reverse osmosis bottles, glycol-modified PET, and polyester fiber waste may not be treated as identical feedstocks for origin or for the final resin quality.

A preferential duty claim for a cross-border PET shipment rests on a small set of documents that must be mutually consistent. The commercial invoice records the harmonized system code, the origin criterion code, the gross and net mass of the resin, and the agreed Incoterms 2020 term; a mismatch between the invoice subheading and the mill test certificate viscosity number is a standard customs audit flag. The bill of lading identifies the vessel or railcar, container number, seal number, port of loading, and port of discharge, which must align with the transport document submitted for the origin claim. The packing list links the shipper’s lot number to pallet or bulk hopper-level identification and gives the tare and net weight in kilograms. The certificate of origin records the preferential origin criterion under the applicable trade arrangement, such as tariff shift, wholly obtained, regional value content, or cumulation. When the certificate is replaced by a supplier’s declaration or origin statement, the exporter’s authorized signatory must remain the same legal entity named on the commercial invoice. Additional records include raw-material supplier declarations, production records, and the mill test certificate.

A 78 mL/g Viscosity Number Splits the Tariff Heading, Not the Origin Claim

The distinction between HS 3907.61 and HS 3907.69 is measurement-driven, not process-driven. Subheading 3907.61 covers primary-form PET with a viscosity number of 78 mL/g or higher; subheading 3907.69 covers the remaining primary-form PET. This boundary is not an origin rule, but an incorrect classification may nullify a preferential entry because the certificate of origin must state the subheading that corresponds to the shipped material. For bottle-grade resin, the mill test certificate reports viscosity number from ISO 1628-1:2021; if the reported intrinsic viscosity is 0.78 dL/g or above, the corresponding viscosity number is approximately 78 mL/g, but the conversion between intrinsic viscosity and viscosity number must be performed with the specified solvent and concentration because numerical conversion errors are a recurring source of customs disputes. Customs laboratories may apply ISO 1628-1:2021 with 0.5000 g of resin dissolved in 100 mL of solvent, reporting viscosity number in milliliters per gram. A shipment that tests at 77.5 mL/g falls under 3907.69 even if the commercial invoice states 3907.61; the origin claim is then reopened because the tariff shift analysis may depend on the subheading.

Mill Test Certificate Parameters and Evidentiary Thresholds

The mill test certificate serves two functions in a preferential shipment: it confirms the tariff classification value and it demonstrates batch consistency. Typical release parameters for bottle-grade PET resin are set out below; each value must be read against the test method listed because identical numerical limits cannot be compared across different solvent systems or sample preparation histories.

Acetaldehyde is the most shipment-sensitive release parameter for bottle-grade resin. A value above 1.0 µg/g may fail the downstream converter’s water-contact specification, especially when the resin is intended for still water under FDA 21 CFR 177.1630 or EU Regulation No 10/2011. Acetaldehyde can be regenerated during melt processing if the resin is not dried to below 0.005 wt% moisture; the drying system should supply air at -40 °C dew point and 160–170 °C for 4–6 h in closed-loop desiccant beds. Hoppers with extended residence beyond 6 h at 170 °C may increase thermal degradation and shift colour; the specification for the b* colour coordinate should not exceed the supplier limit, commonly -0.5 to 0.5 for bottle resin measured on crystallized chip.

Diethylene glycol content is controlled because it depresses melting point and crystallinity; levels above 1.4 wt% reduce the hot-fill performance of blow-molded containers. The melting temperature determined by ISO 11357-3:2018 should typically fall in the 246–251 °C range for a bottle-grade copolymer with 1.0–2.0 mol% isophthalic acid. A lower melting range combined with a wider crystallization exotherm can indicate excessive comonomer or uncontrolled thermal degradation, and customs authorities may request the production log if the release data cannot be reconciled with the declared grade.

The customs record-keeping obligation for preferential origin evidence extends to the mill test certificate and raw-material supplier declarations; in many jurisdictions the retention period is 3–5 years from the date of import, and the resin lot number is the primary key linking the certificate of analysis to the bill of lading and the origin statement.