Intrinsic Viscosity (IV), measured in dl/g by solution viscometry in phenol/TCE mixture, directly reflects PET molecular weight and determines how the resin processes (melt viscosity, preform stretching behaviour) and performs in service (mechanical strength, barrier performance). Higher IV = higher molecular weight = better mechanical properties but higher melt viscosity (more demanding processing, higher barrel temperatures). Specifying IV to the required range for your application is the single most important PET grade selection decision.
| Application | Target IV (dl/g) | Key Additional Requirement |
|---|---|---|
| Carbonated soft drinks (CSD) | 0.78–0.82 | CO2 barrier, creep resistance under internal pressure |
| Still water bottles (standard) | 0.74–0.78 | Low acetaldehyde (<3 ppm preform), clarity |
| Edible oil bottles | 0.72–0.76 | Oil resistance, option for amber colour (UV barrier) |
| Hot-fill juices (pasteurised at 85–93°C) | 0.78–0.82 + heat-set process | Heat resistance, maintained geometry at fill temperature |
| Beer bottles | 0.80–0.84 (often with barrier coating) | O2 barrier, CO2 pressure resistance, low light transmission |
| Large water dispensers (20L) | 0.80–0.85 | Load-bearing wall thickness, UV resistance |
| Stretch blow for personal care | 0.72–0.78 | Clarity, surface finish, compatibility with product |
Acetaldehyde (AA) is a natural by-product of PET thermal degradation, formed whenever PET is melted. Even at trace concentrations (20–40 ppb in the filled product), AA imparts a distinct fruity off-taste detectable in water and mild beverages — a quality failure that drives consumer complaints and brand damage. AA content in the finished preform is the critical specification: below 5 ppm for premium still water, below 10 ppm for CSD and juices (where flavour masks trace AA).
AA is controlled through: Low-AA resin grades — contain AA scavengers (isophthalic acid copolymers or commercial AA scavenger additives like anthranilamide) incorporated by the resin producer; minimum melt temperature in the injection barrel — every 10°C increase roughly doubles AA generation rate; short residence time — AA accumulates with dwell time; well-maintained tooling — hot spots in manifold or gates generate AA disproportionately. The converting process contributes as much AA as the resin grade — specifying low-AA resin while operating with poorly controlled barrel temperatures defeats the purpose.
Bottle-grade PET in India is produced by Reliance Industries (Recron PET — dominant market position), JBF Industries (multiple plants), and Pearl Engineering Polymers. PET pricing tracks the combined cost of PTA (purified terephthalic acid, ~65–70% of raw material) and MEG (monoethylene glycol, ~30–35%). Both are petrochemical derivatives — PTA from para-xylene (PX), MEG from ethylene. Global PX and ethylene markets thus ultimately drive PET pricing. For current PET market pricing, see our raw material price trends report.
India’s EPR recycled content mandates are pushing PET bottle manufacturers toward rPET inclusion. For food contact rPET, the recycling process must be approved — EFSA (EU) or equivalent CPCB guidance (India, still developing). Key technical considerations when blending rPET with virgin: rPET typically has IV 0.68–0.76 dl/g after mechanical recycling — blend proportion must be calibrated to meet final bottle IV target; rPET has higher colour values (slight yellow or grey tint) — manage with opaque or lightly coloured bottles, or premium super-clean rPET from dedicated bottle-to-bottle processes; rPET may have higher residual AA from reprocessing — monitor finished preform AA carefully. See our EPR and sustainability guide for the regulatory framework around recycled content.
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