A Customer Sends a PET Carbon-Footprint Questionnaire: Answering With Numbers requires a unit-process inventory, an explicit system boundary, and an allocation rule for recycled or bio-based flows. Bottle-grade polyethylene terephthalate is not a single-carbon-footprint material; the declared value shifts with resin intrinsic viscosity, PTA and MEG feedstock routes, electricity grid mix, and the treatment of post-consumer recycling credit. A cradle-to-gate value of 2.15 kg CO₂e/kg is frequently reported for European amorphous PET pellet, but that number is valid only when accompanied by the reference year, plant location, database version, and allocation assumptions required by ISO 14067:2018.

For the customer questionnaire to yield comparable numbers, the resin grade should be identified by intrinsic viscosity. Still-water preforms typically use 0.70–0.78 dL/g; carbonated soft drink bottles use 0.80–0.85 dL/g; sheet and fiber grades fall below 0.65 dL/g. The test method is ASTM D4603-18 or ISO 1628-5:1998. This distinction matters because the carbon footprint of solid-state polymerization to raise IV from 0.60 dL/g to 0.80 dL/g adds thermal energy and nitrogen consumption not present in amorphous resin.

The thermal inputs required for PET conversion are governed by the resin enthalpy and crystallisation behaviour. The glass transition temperature is 76–80 °C, the cold crystallisation peak is 130–140 °C, and the melting point is 245–265 °C by differential scanning calorimetry per ISO 11357-3:2018. Preform molding requires the melt to remain above 270 °C to avoid premature crystallisation in the hot runner, while mold cooling must quench the preform below 10–15 °C to limit haze development. These values are typically requested in a material property sheet, but they also inform the energy calculation because the sensible heat required to raise 1 kg of PET from 20 °C to 280 °C is 0.35–0.42 MJ at a heat capacity of 1.3–1.5 kJ/(kg·K). Actual process energy is higher due to barrel losses and hot-runner maintenance heating.

Which Unit Processes Control the Cradle-to-Gate Inventory?

The cradle-to-gate inventory for bottle-grade PET is dominated by the two monomers. Purified terephthalic acid is produced by air oxidation of p-xylene in acetic acid with a Co/Mn/Br catalyst; published gate-to-gate GWP values for PTA range from 0.8 to 1.7 kg CO₂e/kg PTA. Monoethylene glycol from ethylene oxide hydrolysis contributes 0.9 to 2.1 kg CO₂e/kg MEG. The repeating unit mass balance shows that 1.0 kg PTA plus 0.37 kg MEG yields 1.16 kg of PET repeat unit and 0.22 kg water; commercial melt-phase polycondensation with losses consumes about 0.86 kg PTA and 0.32 kg MEG per kg bottle resin. Thus upstream monomer production contributes roughly 1.2–1.8 kg CO₂e/kg PET depending on plant technology and feedstock supply.

Melt-phase polycondensation is operated at 270–285 °C under vacuum down to 10 mbar, followed by solid-state polymerization under nitrogen at 200–220 °C. Electricity and thermal energy for polymerization and drying typically add 0.30–0.60 kg CO₂e/kg PET. Transport of PTA, MEG, and pellet adds 0.03–0.08 kg CO₂e/kg for regional truck and ship movements. The full cradle-to-gate result is therefore a range, commonly 1.8–2.8 kg CO₂e/kg, with the 2.15 kg CO₂e/kg European average sitting near the lower-middle of that range. If a supplier cannot provide primary PTA and MEG data, the questionnaire response must state that secondary data from ecoinvent 3.10 or an equivalent LCA database were used.

When the questionnaire includes converter-level Scope 2, the processing columns require machine-specific data rather than resin default factors. A 48-cavity PET preform injection system with a 24:1 L/D reciprocating screw and compression ratio of 2.5:1 runs barrel zones at 270–295 °C, hot runner at 275–290 °C, and mold cooling water at 8–12 °C. The specific energy consumption for preform injection molding is 0.35–0.60 kWh/kg; stretch blow molding adds 0.25–0.50 kWh/kg. With a grid emission factor of 0.40 kg CO₂e/kWh, these two operations contribute 0.24–0.44 kg CO₂e/kg converted article. Pre-drying at 155–170 °C for 4–6 h in desiccant-dried air with a dew point below -40 °C is mandatory when moisture exceeds 50 ppm by ASTM D6869-03 Karl Fischer titration. Drying energy is commonly 0.15–0.25 kWh/kg but may be excluded from Scope 2 if already accounted in resin production, so the questionnaire must state the boundary.

The temperature dependence of PET melt viscosity creates an operational boundary for energy-reduction programmes. At 280 °C and 1,000 s⁻¹, melt viscosity for 0.80 dL/g bottle-grade PET is typically 120–250 Pa·s. Published data for a given preform geometry and hot-runner shear profile is limited, but an apparent activation energy near 50 kJ/mol predicts a roughly 20–25% viscosity increase for a 10 °C reduction in melt temperature. Reducing barrel temperatures to lower Scope 2 can therefore increase hydraulic injection pressure, extend cycle time, or require higher clamp force, and the carbon saving from heaters may be partly offset in the hydraulic drive measurement.

Crystallinity changes the material density and gas barrier performance but has only a second-order effect on cradle-to-gate carbon footprint. Oriented PET bottle sidewalls crystallise to 25–35% during stretch blow molding at draw ratios of 2.5–3.5 axial and 2.5–4.0 hoop, depending on preform geometry. Density increases from 1.37 g/cm³ amorphous to 1.40 g/cm³ oriented. Carbon footprint questionnaires for finished bottles should use final bottle mass, not pellet mass, because wall thickness distribution changes the declared unit.

When the Questionnaire Requests Recycled Content Allocation

The recycled-content field cannot be answered with a single number unless the allocation method is fixed. ISO 14044:2006 section 4.3.4.5 requires the respondent to state whether the cut-off or avoided-burden method is used. For mechanically recycled bottle flake, gate-to-gate GWP values reported in European recycling LCAs range from 0.45 to 1.0 kg CO₂e/kg. The process includes bale opening, size reduction, hot washing in 2% NaOH at 85–90 °C, float separation, and optional solid-state polycondensation. A 100% rPET bottle pellet can reduce cradle-to-gate fossil GWP by 50–80% relative to 2.15 kg CO₂e/kg virgin resin, but the actual declared reduction depends on bale quality, washing energy, and end-of-life allocation.

If the customer requests food-contact recycled PET, the recycling process must be covered by an EU recycling process authorisation under Regulation (EC) No 282/2008 or a US FDA letter of no objection for 21 CFR 177.1630 PET. These authorisations are process-specific, not resin-generic. Published data for a specific commercial recycler configuration is limited unless primary bale composition, washing line electricity, and flake-to-pellet conversion data are available. The questionnaire should separate post-consumer recycled content from post-industrial scrap because their carbon footprints and traceability requirements differ under ISO 22095:2020 chain-of-custody systems.

Biogenic carbon reporting requires a separate column. Fossil-based PET contains essentially 0% modern carbon, while partially bio-based PET grades using renewable MEG or renewable PTA have a biogenic carbon fraction quantified by ASTM D6866-21. ISO 14067:2018 requires fossil GWP and biogenic CO₂ removals to be reported separately, so a questionnaire that combines them into a single value is not compliant. Published cradle-to-gate data for 30% bio-MEG PET are limited; a supplier-specific LCA with primary biomass cultivation data is required before using published values from unrelated supply chains.

Data Completeness Fields for a Defensible Response

A complete PET carbon-footprint questionnaire response includes the declared unit, reference year, plant location, coproduct allocation, cut-off criteria, database version, and GWP characterisation factors. Under ISO 14067:2018, GWP100 should be reported with the chosen IPCC assessment report, typically IPCC AR5 2013 without climate-carbon feedback unless the programme operator requests otherwise. Electricity data may be supplier-specific or grid-average; the choice can shift resin carbon footprint by 0.3–0.5 kg CO₂e/kg when a high-carbon grid emission factor is replaced by a low-carbon supplier contract. The following fields form a minimum compliance matrix.

For production-scale data validation, the response should attach the measured power log rather than nominal machine nameplate values. A 2,500 kN clamp force preform injection machine operated over 72 h with 15-min sampling intervals provides a defensible basis for Scope 2 conversion energy. Published declarable values for this specific configuration are limited; primary measurement is therefore the only method that avoids double counting and meets the data-quality requirements of ISO 14044:2006.