PET resin: Characteristics
How viscosity decides which drink a bottle can hold
What this tab covers The physical and chemical properties that set its grade, price and uses, with the commercial grades and the standards that define them.Bottle-grade PET is specified by intrinsic viscosity (IV), acetaldehyde, colour and comonomer content. IV sets strength and the drink it can hold; acetaldehyde affects taste in water; colour (b*) matters for clear bottles. For rPET the key issues are contamination, colour and food-contact approval.
Properties that matter commercially
| Property | Value / specification | Why it matters | Source |
|---|---|---|---|
| Intrinsic viscosity | about 0.74-0.78 dl/g for water bottles; 0.80-0.85 for carbonated drinks; about 0.62-0.64 for fibre (indicative) | Higher IV gives strength and pressure resistance. | industry standard (indicative) |
| Acetaldehyde | typically under 1 ppm in bottle chips (indicative) | Gives off-taste in mineral water. | industry standard (indicative) |
| Moisture before moulding | under about 50 ppm (indicative) | Moisture hydrolyses PET in the melt and drops IV. | industry standard (indicative) |
| Glass transition and melting point | Tg about 75°C; Tm about 250-255°C | Limits hot-fill unless heat-set grades are used. | standard polymer data |
| Carbon content | about 62.5% by mass | About 2.3 t CO2 per t if incinerated. | stoichiometric |
Commercial grades
- Water bottle grade (IV about 0.76)
- CSD bottle grade (IV about 0.84)
- Hot-fill and heat-set grades
- Sheet and thermoforming grade (APET, CPET)
- Film grade (BOPET)
- Food-grade rPET pellets
- Bio-PET (bio-MEG) and PEF (emerging)