ISO 1628-1:2024

Overview

ISO 1628-1:2024 defines the general principles for determining the viscosity of organic polymers in dilute solution using capillary viscometers. The standard covers measurement and reporting of reduced viscosity, intrinsic viscosity and K‑value, and specifies the standard parameters, apparatus and procedural conditions to obtain reproducible viscosity data. It applies both to development of polymer-specific measurement standards and to routine viscosity reporting when no dedicated standard exists.

Keywords: ISO 1628-1, viscosity of polymers, capillary viscometers, intrinsic viscosity, reduced viscosity, K-value.

Key Topics

• Measurement methods
  • Method A - Efflux time method: uses a capillary-tube viscometer to compare efflux times of solvent and polymer solution. The standard notes the Poiseuille/Hagenbach relation and treats kinetic-energy corrections as negligible when below 3% of solvent viscosity.
  • Method B - Differential pressure method: a two-capillary relative viscometer measures differential pressures for solvent and solution under forced flow; designed for easier automation and reduced solvent use.
• Apparatus and preparation
  • Specifications for viscometers and supporting instrumentation for both efflux-time and differential-pressure approaches.
  • Guidance on solution preparation and recommended concentration ranges for dilute-solution measurements.
• Measurement conditions
  • Controlled temperature of measurement, attention to solvent and solution densities (document notes limits such as density differences < 0.5% for certain approximations).
• Results and reporting
  • Calculation and expression of reduced viscosity, inherent viscosity, intrinsic viscosity and K‑value.
  • Test report requirements and normative/ informative annexes on sources of error and cleaning procedures.

Applications

• Quality control and lot release testing in polymer manufacturing.
• R&D and polymer characterization (molar mass estimation via K‑value relationships).
• Instrument manufacturers and laboratories validating capillary viscometer methods.
• Regulatory and standards bodies developing polymer-specific viscosity methods.
• Useful when no polymer-specific ISO/CEN method exists, providing a harmonized general procedure.

Practical benefits include consistent intrinsic viscosity data for estimating viscosity-average molecular mass, improved repeatability through defined measurement parameters, and, with the differential-pressure method, potential for automation, higher throughput and lower solvent consumption.

Related Standards

• ISO 80000-1 and ISO 80000-4 (quantities and units referenced by ISO 1628-1).
• Other parts of the ISO 1628 series (for specific polymer types and solvents). Check the ISO catalogue for the complete series.