ISO 22088-6:2006

Overview

ISO 22088-6:2006 - Plastics: Determination of resistance to environmental stress cracking (ESC) - Part 6: Slow strain rate method describes a standardized, rapid procedure to assess the ESC susceptibility of polymeric materials by applying a slowly increasing tensile strain to a specimen while it is exposed to a chemical environment. The test is intended as a ranking/screening method, not as a source of design data, and is valued for quickly comparing material/environment combinations.

Key topics and technical requirements

• Test principle: apply a constant, low strain rate to a tensile specimen immersed in the test medium and compare its stress–strain response with the same specimen tested in air. ESC onset is identified as the point where the tangent modulus in the test medium drops to 75% of that in air (the “departure” point).
• Specimens: generally use ISO 527-2 type 1BA specimens; moulded or machined specimens are acceptable. Surface finish and measurement procedures (width/thickness minimums) are specified.
• Conditioning and environment:
  • Conditioning: (23 ± 2) °C and (50 ± 10) % RH for ≥24 h unless agreed otherwise.
  • Test temperature: (23 ± 2) °C (unless specified).
  • Test medium: representative of service or analytical reagent grade.
• Apparatus and accuracy:
  • Tensile machine capable of constant displacement rate repeatable to ±2%.
  • Typical initial strain rate commonly used: 9 × 10^‑6 s‑1.
  • Load cell accuracy ≈ 1%, displacement transducer ≈ 0.4%.
  • Data logging of load and displacement at intervals ≤ 10 min.
  • Inert environmental chamber and non‑slipping grips.
• Procedure highlights:
  • Calculate crosshead speed as CHS = ε̇ × l0 (effective gauge length).
  • Immerse specimen and run until fracture or necking; record stress–strain data.
  • Fit stress–strain curves (usually third‑order polynomial to peak; R² ≥ 0.99 or higher order if needed), differentiate to obtain tangent modulus, and determine departure stress.
• Results:
  • Report departure stress, polynomial coefficients and derived tangent moduli.
  • Compute an ESC index by normalizing departure stress to the maximum stress in air for comparative ranking.

Practical applications

• Rapid screening of plastics vs. chemicals to identify ESC-prone polymer/environment combinations.
• Comparing relative aggressiveness of fluids on a polymer (ESC index).
• Material selection and qualification in industries where chemical exposure and mechanical stress coincide (e.g., packaging, piping, consumer goods, automotive components).
• R&D and quality-control labs for material ranking and formulation evaluation.

Who should use this standard

• Materials and polymer engineers
• Plastics R&D and formulation teams
• Independent test laboratories and QA/QC departments
• Product designers and specification writers seeking comparative ESC data (note: not for deriving design stress values)

Related standards

• ISO 22088-1: General guidance on ESC testing
• ISO 527-2: Tensile properties - test conditions for moulding and extrusion plastics

Keywords: ISO 22088-6:2006, environmental stress cracking, ESC, slow strain rate method, plastics testing, departure stress, ESC index, tensile specimen, strain rate.