Determining Intrinsic Viscosity Loss in Polyethylene Terephthalate Processing
Intrinsic viscosity loss in PET processing is determined by measuring dilute solution flow time or capillary melt viscosity to quantify polymer chain cleavage.
Dilute Solution Viscometry
Meaning
Capillary flow measurement of a polymer dissolved in a solvent provides the baseline data needed to calculate molecular size. Utilizing dilute solution viscometry allows researchers to determine the intrinsic viscosity of a polymer by measuring how much the dissolved chains increase the flow resistance of the solvent. This technique is highly sensitive to the length of the polymer chains, making it a reliable way to monitor degradative changes in the resin.
Characterization Method
Comparing the flow times of a pure solvent and a dilute polymer solution yields the relative viscosity of the mixture. In dilute solution viscometry, the measurements are conducted at very low concentrations to ensure that individual polymer molecules do not entangle with each other. This isolate state allows for the precise calculation of molecular weight using established mathematical relationships.
Laboratory Protocol
Precise temperature control is essential because viscosity changes significantly with even minor thermal fluctuations. Analysts performing dilute solution viscometry use automated glass capillary viscometers suspended in constant-temperature water baths. They must also choose compatible solvents that can fully dissolve the specific polymer without degrading it during the test.
Solid particulates must be filtered out before the solution is introduced to the capillary to prevent blockages that would invalidate the flow time measurements.
Molecular Weight
Moulders use these laboratory results to verify that incoming virgin resins meet the required specifications. Changes in the values obtained from dilute solution viscometry can indicate that a resin has suffered thermal degradation during compounding or that too much regrind has been blended into the batch.