Correlation of melt viscosity of polyethylene terephthalate to solution intrinsic viscosity
Polyethylene terephthalate (PET) is a hygroscopic resin from the polyester family which absorbs moisture onto their molecular structure when they are exposed to the ambient air. This has a huge effect on the flow behavior and rheological parameters of the plastic melt. Normally, the moisture acts as a plasticizer and increases the flowability of the plastic melt. As a result, the melt flow rate (MFR) parameters of PET resins are strongly affected by their moisture level/drying condition and rarely provided by their suppliers. Intrinsic viscosity however; is commonly used among the PET manufactures as the specification of different resin grades.
Correlation of Melt Viscosity of Polyethylene Terephthalate to Solution Intrinsic Viscosity
Azadeh Farahanchi
01.14.2019
Correlation of melt viscosity of polyethylene terephthalate to solution intrinsic viscosity
Polyethylene terephthalate (PET) is a hygroscopic resin from the polyester family which absorbs moisture onto their molecular structure when they are exposed to the ambient air. This has a huge effect on the flow behavior and rheological parameters of the plastic melt. Normally, the moisture acts as a plasticizer and increases the flowability of the plastic melt. As a result, the melt flow rate (MFR) parameters of PET resins are strongly affected by their moisture level/drying condition and rarely provided by their suppliers. Intrinsic viscosity however; is commonly used among the PET manufactures as the specification of different resin grades. IV measurement is normally performed by dissolution of a small amount of the polymer in an appropriative solvent (e.g. phenol) at room temperature. As a result, IV parameter from dilute solution viscometer is not affected by the resin moisture content which removes the necessity of drying the samples before the tests. However; this characterization method involves with noxious solvents which may not be desirable.
Dynisco® LCR capillary rheometer series has a feature to provide correlation of shear viscosity data to the intrinsic viscosity of PET materials. The idea behind this correlation was that both zero-shear viscosity and intrinsic viscosity can be related to the molecular weight of the polymer. The reason is that, viscoelastic properties in polymer materials are dependent on molecular motion and chain entanglement. Polymers with higher molecular weight have higher chain entanglement and this can lead to the increasing of shear viscosity or intrinsic viscosity.
In polymers with high entanglement, the relationship between zero-shear viscosity and molecular weight is given by Fox-Flory equation as below [1]