ISO 23673:2021

Overview

ISO 23673:2021 specifies a standardized procedure to determine an elasticity index (EI) for plastic melts and viscoelastic materials. The EI is defined from the shear storage modulus G' measured with an oscillatory rheometer at a fixed angular frequency, strain/stress and temperature. The standard provides general principles, measurement guidelines, and reporting requirements for thermoplastics and other materials where melt elasticity is a critical property.

Key topics and technical requirements

• Principle: EI is based on G' measured using parallel-plate or cone-and-plate oscillatory rheometry (cone angle < 5°).
• Reference methods: Measurement and apparatus requirements follow ISO 6721-10 and ISO 6721-1 for dynamic mechanical testing.
• Apparatus & specimen:
  • Parallel plates typical diameter: 20–50 mm; specimen thickness 0.5–3 mm.
  • Cone-and-plate allowed with < 5° cone angle and tight concentricity (separation variation < ±0.01 mm).
• Procedure essentials:
  • Measure G' at a fixed angular frequency (example: 1.0 rad·s⁻¹), with stress/strain and temperature selected for the material.
  • Determine thermal stability and the linear-viscoelastic region by strain or stress sweeps. Use the largest strain/torque below the threshold where G' deviates by 5% from linear behaviour.
  • Average EI from five repeated measurements.
• Expression of results: Report EI with its measurement conditions, e.g. EI (ω, ε, σ, T) - EXAMPLE: EI (1.0 rad·s⁻¹, 10.0%, 22.2 MPa, 210.0 °C).
• Test report: Must include reference to ISO 23673:2021, material ID, rheometer details, plate geometry, preheating/equilibration times, thermal-stability time, test duration, corrections, and visual observations (melt fracture, air entrapment).

Practical applications and users

Who uses ISO 23673:2021:

• Polymer rheologists and materials scientists evaluating melt elasticity.
• Quality control and R&D teams in plastics manufacturing and compounding.
• Product designers and process engineers optimizing extrusion, injection moulding and film/blow molding where elastic behaviour affects processing and final properties.

Why it’s useful:

• Provides a single, comparable elasticity index (analogous to MFR/MVR for viscosity) to differentiate materials with similar viscosity but different elastic response.
• Supports material selection, formulation tuning, and process parameter optimization where elastic behaviour impacts melt fracture, die swell, or dimensional stability.

Related standards

• ISO 6721-1: General principles for dynamic mechanical properties
• ISO 6721-10: Complex shear viscosity using parallel-plate oscillatory rheometer
• ISO 1133-1 / ISO 1133-2: Melt flow rate (MFR/MVR) methods (contextual reference)

ISO 23673:2021 helps quantify melt elasticity with a reproducible EI metric for better material comparison, process control, and product development in plastics and viscoelastic materials.