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Polymers | Intrinsic Viscosity Measurements for Quality Control of PET

PET is one of the most important polymers used for packaging materials in the world. Different grades of PET are classified using the Intrinsic Viscosity, a parameter to calculate the polymer’s molar mass. Lovis 2000 M with its implemented polymer software measures and calculates polymer parameters automatically at the touch of a button.

Intrinsic viscosity for quality control of PET

PET(Polyethylene terephthalate) is a linear thermoplastic with a wide range of use including fibers, textiles and of course as a packaging material.

The main indicator for the quality and the most important characteristic of PET is the value of its Intrinsic Viscosity. The Intrinsic Viscosity is related to the polymer’s molar mass and therefore reflects the material’s melting point, crystallinity and tensile strength. The Intrinsic Viscosity is dependent upon the length of the polymer chains. The longer the polymer chains are, the more entanglements between chains occur and therefore the viscosity value is higher. The desired Intrinsic Viscosity of PET is dependent on its application and classified in different grades (see Table 1).

PET gradeIntrinsic Viscosity [dL/g]
Fiber grade 0.40 – 0.70
Film grade 0.70 – 1.00
Bottle grade 0.70 – 0.78
Water and soft drink bottle grade 0.78 – 0.85

Table 1: Typical Intrinsic Viscosity values of different PET grades.

The demand for reliable Intrinsic Viscosity measurements is high as PET has to be characterized in various fields:

  • Research & Development, where new polymers are synthesized and characterized
  • PET suppliers, who want to control the quality of their products
  • Process plants, who want to optimize their conditions for constant production
  • Recycling facilities, that need to control the properties of recycled PET

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