Plot of shear viscosity versus shear rate for different PET samples and their resulted values of intrinsic viscosity. The intrinsic viscosity measurements were performed using a dilute solution viscometer at room temperature (25 ☌) and the condition of 60/40 phenol/TCE.įigure 1. The Zero-shear viscosity values were obtained using a capillary rheometer at temperature of 285 ☌. shows this relationship for a PET sample with various moisture contents. įigure 2 which has been obtained by Reilly et. Combining these equations yields a relationship between zero-shear viscosity and intrinsic viscosity independent of molecular weight value as belowĪs it can be seen, for a high entangled, linear and monodisperse polymer with narrow molecular weight distribution, the plot of logarithm of intrinsic viscosity versus logarithm of zero-shear viscosity gives a straight line with the slope of □/3.4. So, melt viscosity and intrinsic viscosity can be related to each other as well. It is clear that, the changes in molecular weight of a polymer with high entanglement, affect melt viscosity more than intrinsic viscosity.īoth equations (2) and (4) are related to the molecular weight. For most polymers the value of □ is within 0.5-0.8. Where □ is the intrinsic viscosity, and □՛ and □ are Mark-Houwink parameters and depend on a particular polymer-solvent system. On the other hand, Mark-Houwink equation defines the relationship between intrinsic viscosity of the polymer and its molecular weight as below Where □0 is zero-shear viscosity, and □ is a constant dependent on the polymer type. In a log form, the equation can be shown as In polymers with high entanglement, the relationship between zero-shear viscosity and molecular weight is given by Fox-Flory equation as below Polymers with higher molecular weight have higher chain entanglement and this can lead to the increasing of shear viscosity or intrinsic viscosity. The reason is that, viscoelastic properties in polymer materials are dependent on molecular motion and chain entanglement. The idea behind this correlation was that both zero-shear viscosity and intrinsic viscosity can be related to the molecular weight of the polymer. However this characterization method involves with noxious solvents which may not be desirable.ĭynisco® LCR capillary rheometer series has a feature to provide correlation of shear viscosity data to the intrinsic viscosity of PET materials. 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. IV measurement is normally performed by dissolution of a small amount of the polymer in an appropriative solvent (e.g. Intrinsic viscosity however is commonly used among the PET manufactures as the specification of different resin grades. 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. Normally, the moisture acts as a plasticizer and increases the flowability of the plastic melt. This has a huge effect on the flow behavior and rheological parameters of the plastic melt. 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. Correlation of Melt Viscosity of Polyethylene Terephthalate to Solution Intrinsic Viscosity Azadeh Farahanchi Ĭorrelation of melt viscosity of polyethylene terephthalate to solution intrinsic viscosity
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