Meaning
Glass capillary instruments measure the kinematic viscosity of dilute polymer solutions by timing the gravity flow of the liquid through a calibrated capillary tube. The Ubbelohde viscomometer is widely used to determine the intrinsic viscosity and molecular weight of polymers like polyethylene terephthalate and polyamide. This measurement is independent of the exact volume of liquid filled into the bulb.
Measurement Method
Solvents dissolve the polymer to a specified concentration before the solution is drawn into the capillary. Operation of the Ubbelohde viscometer involves measuring the time it takes for the liquid meniscus to pass between two printed lines. This time is compared to the flow time of the pure solvent.
Degradation Tracking
Resin degradation can be tracked by measuring the decline in molecular weight after compounding or moulding. A decrease in viscosity indicates that the polymer chains have broken. This tracking confirms polymer stability.
Quality Assurance
Sourcing resin for high-performance applications requires verifying that the molecular weight has not been degraded during the drying or melting phases of production. The test methodology ensures that incoming resin matches the structural specifications of the material datasheet. By using this capillary device, laboratory personnel can detect the presence of thermal or hydrolytic damage in regrind material before it is used in production.
