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.
Intrinsic Viscosity Correlation
Meaning
Conversion formula that translates flow time into molecular structure. An intrinsic viscosity correlation allows a laboratory to estimate polymer chain length by measuring the time taken for a liquid to pass through a capillary tube. This calculation bridges the gap between raw physical measurements and the structural properties defined on a material datasheet.
Producers use these values to ensure that a batch of resin meets the specifications required for processing.
Analytical Mechanism
Empirical equations like the Mark Houwink form provide the basis for these conversions. Because the intrinsic viscosity correlation depends on specific constants for each polymer and solvent pair, the temperature of the test must remain strictly controlled. A slight variation in thermal conditions during the test alters the resulting molecular weight estimate.
The data point indicates the inherent resistance to flow when the polymer chains are fully extended in a solvent.
Process Control
Performance of the resin during injection moulding is influenced by the length of the molecular chains. When a moulder identifies a drift in part strength, they might look at the intrinsic viscosity correlation to see if the virgin material or the regrind ratio has shifted. Lower values usually suggest shorter chains and reduced impact resistance in the finished part.
Monitoring these shifts allows the production team to adjust cycle times or temperatures to compensate for material variations.
Value Deviation
Measurements taken at the resin plant often differ from those taken after the material has passed through an extruder screw. Thermal degradation during the heating process breaks polymer chains, which is visible in a changed intrinsic viscosity correlation. This drop in viscosity is a result of the shearing forces and heat exposure during the moulding cycle.