Overview
ISO 1628-3:2010 - Plastics: Determination of the viscosity of polymers in dilute solution using capillary viscometers - Part 3 covers standardized laboratory procedures for measuring reduced viscosity (viscosity number) and intrinsic viscosity of polyethylenes and polypropylenes. Measurements are performed in dilute solution at 135 °C using capillary (Ubbelohde) viscometers. The standard identifies solvents, apparatus, sample preparation and calculation methods, and notes limitations when additives or fillers are present.
Key topics and technical requirements
- Test temperature and principle: Measure solvent and solution efflux times at 135 °C; calculate reduced viscosity and intrinsic viscosity from efflux times and solution concentration.
- Solvent: Use analytical-grade decahydronaphthalene, redistilled (≤65 °C at ≈500 Pa) and stabilized with 0.2% antioxidant to prevent peroxidation. Examples of acceptable antioxidants are listed in the standard.
- Apparatus: Preferably Ubbelohde viscometers (type 0B or 0a) with a nominal viscometer constant of 0.005; other capillary viscometers per ISO 3105 may be used if equivalent results are obtained.
- Concentration selection: Choose polymer concentration so the ratio t/t0 (solution efflux time / solvent efflux time) is between 1.2 and 2.0. If unknown, start with 0.001 g·ml⁻¹ and adjust per guidance.
- Sample dissolution: Dissolve sample in solvent by shaking at 150 °C (recommended heating/shaker procedure: 1 h vigorous + 1 h slow; may extend up to 2 h with notation in report).
- Calculation: Reduced viscosity I = (t − t0) / (t0 · c). Intrinsic viscosity [η] calculated with [η] = I / (1 + k·c·I) where an approximate k = 0.27 can be used for estimates.
- Limitations & precautions:
- Additives and fillers can alter measured viscosity - values may be unreliable for filled or additive-rich samples.
- Polyethylene and isotactic polypropylene are not soluble at room temperature - avoid precipitation during handling and filling.
- Filtration can reduce measured viscosity for ultra-high-molecular-weight polyethylene (PE-UHMW).
Applications and users
- Quality control and acceptance testing of polyethylene and polypropylene grades.
- Polymer R&D and materials characterization to estimate molecular weight-related parameters.
- Processing and formulation development where flow-related properties are relevant.
- Contract and independent testing laboratories performing standardized viscosity measurements.
Keywords: ISO 1628-3:2010, intrinsic viscosity, reduced viscosity, capillary viscometer, Ubbelohde, polyethylene viscosity, polypropylene viscosity.
Related standards
- ISO 1628-1:2009 - General principles for dilute-solution viscosity measurement.
- ISO 3105:1994 - Glass capillary kinematic viscometers - specifications and operating instructions.
- Other parts of ISO 1628 (PVC, polycarbonate, polyesters, MMA polymers) for different polymer classes.
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