ISO 1628-1:2021

Overview

ISO 1628-1:2021 - "Plastics - Determination of the viscosity of polymers in dilute solution using capillary viscometers - Part 1: General principles" defines the general principles and conditions for measuring reduced viscosity, intrinsic viscosity and K‑value of organic polymers in dilute solution. It sets standard parameters for viscosity measurement using capillary (Ubbelohde-type) viscometers and provides the basis for developing polymer-specific viscosity test standards or for measuring solution viscosities where no separate standard exists.

Key topics and technical requirements

• Scope and definitions: Clear terms for viscosity, kinematic viscosity, relative viscosity, reduced viscosity, inherent viscosity, intrinsic viscosity and K‑value.
• Measurement principle: Use of capillary-tube viscometers; efflux time measurement of solvent and polymer solution; Poiseuille-based relations reducing to the efflux-time ratio under defined conditions.
• Apparatus requirements:
  • Capillary viscometer (suspended‑level Ubbelohde recommended); choice of size guided by solvent viscosity/density.
  • Thermostatic bath ensuring temperature uniformity (±0.05 K between 25 °C and 100 °C; ±0.2 °C above 100 °C).
  • Temperature probe (readable to 0.02 °C) and timing device (readable to 0.1 s, speed stable to 0.1 % over 15 min).
• Sample and solution handling: Preparation and concentration guidance for dilute polymer solutions; solvent/solution density differences should be ≤0.5 % for the efflux-time ratio approximation.
• Procedure and results: Steps for viscometer charging, efflux time measurement, expression of results (reduced/inherent/intrinsic viscosity) and calculation of K‑value by the Fikentscher relation.
• Quality & error control: Annexes cover apparatus cleaning and common sources of error (e.g., kinetic energy corrections, density effects).

Applications and users

ISO 1628-1 is used by:

• Polymer testing and quality control laboratories performing dilute-solution viscosity measurements.
• R&D teams characterizing polymer molar mass trends via intrinsic viscosity.
• Manufacturers validating batch-to-batch consistency of plastics raw materials.
• Standards developers creating polymer-specific viscosity methods where no existing standard applies. Practical uses include estimating degree of polymerization (K‑value), comparative viscosity reporting, and providing a harmonized method for regulatory or commercial specifications.

Related standards

• ISO 3105 (glass capillary kinematic viscometers - specifications and operating instructions)
• ISO 80000-1 and ISO 80000-4 (quantities and units) These referenced standards provide equipment specifications and unit definitions that complement ISO 1628-1:2021.

Keywords: ISO 1628-1:2021, polymer intrinsic viscosity, reduced viscosity, K‑value, capillary viscometer, Ubbelohde, dilute solution viscosity, viscometer procedure.