What is the intrinsic viscosity IV value?
The intrinsic viscosity IV value is an important indicator to measure the length and degree of polymerization of PET molecular chain, and the unit is dL/g. It directly reflects the molecular weight, melt strength and mechanical properties of the final product of PET resin.
Ordinary preform grade PET resin: IV value is usually 0.70-0.85 dL/g.
IV=0.72-0.78 dL/g: Suitable for mineral water bottles and ordinary beverage bottles.
IV=0.78-0.85 dL/g: Suitable for carbonated beverage bottles that require higher pressure resistance.
High IV value PET (≥0.85 dL/g): Used for high-strength packaging, such as large-capacity edible oil bottles and medical bottles.
The impact of too low IV value:
The preform strength is insufficient and it is easy to break when blowing the bottle.
The bottle body has poor pressure resistance and carbonated beverages are easy to deform.
Effects of too high IV value:
Poor melt fluidity, difficult injection molding.
Increased energy consumption, rising production costs.
Impact of IV value on injection molding
Low IV value (0.65~0.75 dL/g): Good melt fluidity, easy injection molding, suitable for thin-walled preforms. However, the molecular chain is short, which may lead to insufficient strength of the preform.
High IV value (0.80~0.90 dL/g): High melt viscosity, poor fluidity, requiring higher injection temperature and pressure. However, the molecular chain is longer, the tensile strength and pressure resistance of the preform are better.
Effect of IV value on bottle blowing process
Stretch blow molding performance
Low IV value: The preform is easy to stretch, but the molecular chain is short. After blowing, the bottle body strength is low, and problems such as uneven bottle wall and bottom concave may occur.
High IV value: Large stretch resistance, requiring higher blowing pressure (such as 40~45 bar vs. ordinary 30~35 bar). However, after blowing, the bottle body is more uniform and has better anti-explosion performance.
Preform wall thickness control
High IV value: The preform wall thickness can be thinner because the molecular chain is long and the strength is still maintained after stretching.
Low IV value: The wall thickness needs to be increased, otherwise the bottle will easily break after blowing.
Effect of IV value on preform quality
Mechanical properties
| Performance index | Low IV value（0.72） | High IV value（0.82） |
| Bursting pressure（500ml bottle） | 1.2Mpa | 1.8Mpa |
| Pass rate of drop test（2m） | 85% | 97% |
| Longitudinal shrinkage ratio | 2.5% | 1.2% |
Transparency and surface gloss
Low IV value: Slow crystallization, high transparency, suitable for mineral water bottles.
High IV value: High crystallinity, may slightly affect transparency, cooling process needs to be optimized.
Acetaldehyde content
High intrinsic viscosity IV value PET resin is more likely to produce acetaldehyde during high temperature processing, affecting the taste of beverages.
The impact of intrinsic viscosity IV value on production cost
Raw material cost
PET with high IV value is more expensive. For every 0.01 increase in IV value, the cost increases by $5~8/ton.
But it can reduce the weight of the preform. Lightweighting saves raw materials.
How to choose the right IV value
| Applications | Recommend IV value | Why choose | Recommend models |
| Mineral water bottles | 0.72-0.75 | Low cost, high transparency | WK-801, CZ-302, YS-W01, CR-8816, TH102, BG80 |
| Carbonated beverage bottles | 0.78-0.82 | High pressure resistance，CO2 resistance | WK-851, WK-881, CZ-318, CZ-328, CR-8828, YS-C01, TH104, BG85 |
| Hot-filling bottles | 0.80-0.85 | High temperature resistance | WK-811, CR-8839, TH105, BG801 |
| Oil bottles | ≥0.85 | Ultra-high strength, leak-proof | WK-821, TH102C, CR-8863, BG802 |
| Medical packaging | 0.80-0.90 | High purity, low precipitates | / |