PET Resin Price per kg: Why Bottle, Film and Flake Quotes Differ

Polyethylene terephthalate (PET) is an aromatic polyester produced from purified terephthalic acid (PTA) and ethylene glycol (MEG) through continuous esterification and melt-phase polycondensation. The stoichiometric consumption is approximately 0.86 t PTA and 0.34 t MEG per 1.00 t PET, with the balance released as water and process losses. The commercial phrase PET Resin Price per kg: Why Bottle, Film and Flake Quotes Differ describes a market in which the same repeat unit is traded as bottle-grade amorphous pellet, film-grade pellet, and washed post-consumer flake. A single price-per-kilogram figure is not technically comparable across these forms unless intrinsic viscosity, acetaldehyde ceiling, comonomer chemistry, contamination potential, and solid-state conversion history are held constant.

Virgin PET contracts are typically built on a PTA and MEG formula plus a conversion margin. Spot paraxylene-linked PTA and ethylene-linked MEG dominate the variable cost. Polymer-grade marginal cost does not, however, explain differences between bottle and film quotes. Bottle-grade resin requires solid-state polycondensation after melt-phase finishing to raise intrinsic viscosity from roughly 0.60–0.65 dL/g to 0.80–0.84 dL/g. That additional processing step introduces nitrogen circulation, heating energy, longer reactor residence time, and lower throughput compared with direct melt-phase transfer. Film-grade pellet and flake quotes do not always include that solid-state burden, which is a primary structural reason for quote divergence.

What Distinguishes Bottle-Grade Pellet, Film-Grade Pellet and Washed Flake on a per kg Basis?

Bottle-grade PET is specified by intrinsic viscosity, acetaldehyde, crystallinity, color, and moisture. Intrinsic viscosity is measured by dilute-solution viscometry according to ASTM D4603-18 or ISO 1628-1. For carbonated soft drink and water bottle preforms, the typical contract window is 0.80–0.84 dL/g, with a delivered-lot tolerance commonly near ±0.01 dL/g. Acetaldehyde is controlled because it migrates into packaged beverages and creates off-taste; ASTM F2013-10 headspace gas chromatography is widely used to enforce a ceiling of ≤3 ppm in bottle-grade preforms. These specifications are operational, not commercial: they determine preform molecular weight distribution, melt strength during injection stretch blow molding, and carbonation-pressure sidewall stability.

Film-grade PET is sold into a lower intrinsic viscosity window, commonly 0.58–0.65 dL/g, because biaxial orientation during tenter-frame stretching supplies orientation-induced strength without a high starting molecular weight. Film buyers emphasize gel count, surface flatness, haze, coefficient of friction, and thickness uniformity rather than beverage-contact acetaldehyde. Some food-contact film contracts may set acetaldehyde at ≤10 ppm, but this is not a universal film-grade release limit. Consequently, film-grade quotes can be numerically lower per kilogram even though the PTA and MEG inputs are identical, because the specification burden shifts from solid-state polycondensation and acetaldehyde to filtration quality and dimensional control.

The tabulated values are representative order-level ranges, not universal specifications; actual contracts vary by end-use, region, and supplier. The table illustrates why a price-per-kilogram quotation cannot be moved directly from bottle to film or flake without a specification sheet and a normalized yield calculation.

Bottle-grade amorphous pellets are converted on injection molding machines with reciprocating screws, typically 22:1 to 25:1 L/D, feeding hot-runner preform molds with 8–96 cavities. Pre-drying at 160–170 °C to a residual moisture of ≤50 ppm is mandatory because hydrolytic degradation during plasticizing reduces molecular weight. At a melt temperature near 280 °C, residual moisture above 100 ppm produces measurable intrinsic viscosity loss within normal residence time; this can shift preform burst pressure and acetaldehyde levels. The preform is reheated and stretch-blow-molded at a blow-up ratio above 6:1 to induce strain-hardening. Bottle resin with intrinsic viscosity below 0.76 dL/g can reduce sidewall burst resistance in carbonation-pressure applications. This processing relationship is embedded in the bottle-grade quote through tighter molecular-weight control and more demanding packaging validation.

Continuous solid-state polycondensation for bottle resin operates at 200–220 °C under vacuum or hot nitrogen, with pre-crystallization to prevent pellet agglomeration. During this step, acetaldehyde is stripped below the required ceiling and low-molecular-weight oligomer content is reduced. The product is then cooled and packaged under dry-air or nitrogen purge. These unit operations are absent from direct melt-phase film pellet production and from simple hot-washed flake. The capital cost of continuous solid-state reactors, nitrogen purification, and post-reactor handling adds fixed cost per kilogram, which appears as a premium over film-grade quotes in most regional markets.

Comonomer chemistry further separates quotes. Bottle-grade resins may incorporate isophthalic acid at low levels to disrupt chain packing, lower crystallization rate during quenching, and widen injection stretch-blow-molding latitude. The effect is visible in the melting temperature reported by ISO 11357-3:2018 and in preform cooling behavior. Film-grade PET may contain different comonomer or additive packages for dimensional stability and windability; these packages are not automatically interchangeable with bottle resin. Washed flake is a blend of historical bottle and packaging resins with less uniform comonomer distribution, so its melting and crystallization behavior can vary beyond a single-pellet specification. That variability is reflected in a separate pricing mechanism based on sorting, washing yield, and downstream dilution.

Film-grade PET is extruded through a flat die onto a chilled quench drum, then oriented in machine and transverse directions. Film lines use extruders with L/D ratios of 28:1–33:1 and screen changers with filtration ratings down to 20–40 µm to remove gel bodies and agglomerates. Melt volume-flow rate may be controlled as a secondary release property under ISO 1133-1:2022 at 280 °C and 2.16 kg load. A film-grade resin with 0.62 dL/g intrinsic viscosity can run at higher throughput than a 0.82 dL/g bottle resin on the same extruder because lower melt viscosity reduces melt pressure and drive current. The price per kilogram therefore includes lower molecular weight but higher melt smoothness; film suppliers may add antiblock silica at 500–2,000 ppm and antistatic agents. The additive package and surface quality are part of the film quote, not the base PET matrix cost.

Flake Quotes and the Contamination Discount Structure

Washed post-consumer PET flake is priced after sorting, grinding, washing, and density separation. A flake quote per kilogram reflects input bale cost, yield loss, and contamination control rather than virgin monomer arithmetic. Mixed bales may contain PVC, polyolefin caps and labels, adhesives, metals, polylactic acid, and residual beverage content. PVC is particularly destructive because it degrades at PET melt-processing temperatures and generates hydrochloric acid, accelerating hydrolysis and producing black specks. Recyclers therefore use near-infrared sorting, metal detection, and density flotation or hydrocyclone arrays to reduce PVC to ≤50 ppm for food-grade applications.

Hot caustic washing is standard for label-adhesive removal and decontamination. Typical conditions use 2–4 wt% sodium hydroxide solution at 80–90 °C in agitated immersion washers, followed by friction washers and dewatering. After washing, flake moisture is brought below 100 ppm before extrusion or solid-state upgrading. Because the incoming bale mix is heterogeneous, batch-to-batch intrinsic viscosity can vary by ±0.02 dL/g or more. Converters often blend washed flake with virgin bottle resin at 20–30 wt% to stabilize melt viscosity, dilute metals and black specks, and maintain preform reject rates within process control limits.

Flake quotations are also structured around yield. The clean-flake cost is the bale price divided by yield plus processing cost. At a 70 wt% yield, 1.0 kg of clean flake requires 1.43 kg of bale input. This arithmetic explains part of the discount to virgin pellet: a low-yield bale source can erase an apparently attractive per-kilogram flake quotation after washing losses, label removal, and fines generation are accounted for. The flake price must therefore be normalized to dry, washed, contaminant-controlled flake before comparison with bottle or film pellet.

To upgrade washed flake to bottle-grade recycled PET, recyclers use vacuum solid-state polycondensation at 200–220 °C to raise intrinsic viscosity from 0.68–0.72 dL/g to greater than 0.78 dL/g. The solid-state step also reduces acetaldehyde and may reduce volatile contaminants. This processing step narrows the quote difference between flake and virgin bottle resin but adds energy, nitrogen, and capital. The resulting recycled pellet may trade close to virgin bottle-grade resin when demand for food-grade recycled content is high. Published data for specific regional delivered prices is limited because recycled PET contracts are often indexed, bale-linked, and subject to seasonal collection variation.

Food-contact recycled PET flake requires a process-specific decontamination evaluation. In the United States, recycled PET producers rely on FDA letters of no objection for recycling processes producing food-contact material under 21 CFR 177.1630. In the European Union, the material must comply with EU Regulation 10/2011 and the process must be assessed by EFSA. These regulatory steps add cost, batch reporting, traceability, and change-control discipline that virgin film and bottle quotes may not carry to the same depth.

When Bottle-Grade Pellet, Film-Grade Pellet and Flake Compete in a Single Contract

When the three forms are quoted side-by-side for the same downstream line, the procurement comparison cannot stop at price per kilogram. A bottle preform operation must normalize quotes to delivered intrinsic viscosity, acetaldehyde, color, and drying burden. A film operation must normalize to gel count, haze, melt uniformity, and surface-scrap potential. A recycling compounder must normalize to flake intrinsic viscosity loss after extrusion, washing yield, filtration load, and contamination-related filter replacement. The same nominal mass can produce different scrappage rates, throughput rates, and reject rates depending on specification compliance.

For bottle-grade resin, the preform melt-temperature window is narrow. At melt temperatures above 285 °C, acetaldehyde regeneration increases; below 270 °C, screw recovery time lengthens and melt homogeneity can degrade. Operators therefore monitor hot-runner nozzle temperatures and barrel zones to preserve the ≤3 ppm acetaldehyde target. A lower-IV flake substitution opens the processing window slightly but reduces mechanical strength; a higher-IV bottle resin raises melt pressure and energy draw. This trade-off is not visible in a per-kilogram purchase price but appears as re-normalized scrap and cycle time.

For film-grade substitution, haze and gel formation are the limiting constraints. Haze is measured under ASTM D1003-21 on oriented film samples; gel counts are inspected by optical scanners on the cast web. Flake-derived contaminants above the screen-changer rating of 20–40 µm can increase back pressure and force more frequent screen changes. The throughput loss from a screen change and the associated edge-trim waste are operating costs that must be added to any flake-based film feedstock evaluation. Published data for post-consumer film-grade PET in high-barrier food packaging is limited; converters therefore validate each flake source against EU Regulation 10/2011 and 21 CFR 177.1630 before commercial substitution.