Presented at the 8th International Conference on Polyolefin Characterization (ICPC), 2023, Valencia, Spain.
By Alba Cárdenas, Pilar del Hierro, Alberto Ortín, Benjamín Monrabal. Polymer Char, Valencia, Spain.
The measurement of the intrinsic viscosity in materials like PET is extremely important for the control of the final product in the manufacturing process. The intrinsic viscosity is not only measured in the raw material, but also in the different stages of the production.
The viscosity can be measured directly or by indirect means, using different methods, in the melt and in solution. Depending on the accuracy needed in the measurement a method will be chosen.
The intrinsic viscosity in solution has been measured traditionally using glass Ubbelohde viscometers (1-2) of different capillary diameter, depending on the resin measured. An optimized equipment for low temperature analysis is proposed as an alternative method using a differential 2-capillary viscometer. The measurement is fully automated, and the combination of capillaries and pressure transducers covers a wide range of different resins with the same hardware.
The measurement can be performed with two different approaches, “plateau height” and “peak area”, giving both similar results. Three PET resins covering an intrinsic viscosity range from 0.4 to 1.0 dL/g have been analyzed using two different mixtures of solvents (50:50 oDCB:phenol and 60:40 phenol:TCE).
The results obtained have a direct correlation with the glass capillary method, and the reproducibility and analysis time are also comparable.