ISO 22088-5:2006

Overview

ISO 22088-5:2006 specifies a laboratory method for assessing the environmental stress cracking (ESC) behaviour of thermoplastics using the constant tensile deformation method. The standard describes how to hold molded or machined specimens at a constant deformation while immersed in a chemical medium and to monitor stress relaxation over time. ISO 22088-5 is intended as a ranking test to compare materials or environments and is not designed to provide data for engineering design or performance prediction.

Key Topics and Requirements

• Test principle: Apply an initial tensile deformation (below yield or breaking stress) and record stress relaxation while the specimen is exposed to the chosen chemical medium. Compare stress relaxation curves and the critical stress in the medium with those obtained in air.
• Specimens: ISO 527-2 type 1BA geometry (half-size). Preferred thickness (2 ± 0.2) mm; finished-product thickness allowed. Ten specimens per condition (5 in medium, 5 in air). Preparation per ISO 293 / ISO 294-1 / ISO 294-5 or machined per ISO 2818.
• Apparatus: Device to maintain constant tensile deformation (e.g., worm-gear clamp and load cell or strain gauge ±1%); materials in contact with the medium must be inert (stainless steel, PTFE, etc.). Temperature-controlled bath/oven to ±2 °C.
• Conditioning & temperature: Precondition specimens at (23 ± 2) °C, (50 ± 10)% RH for ≥24 h. Preferred test temperatures: (23 ± 2) °C and (55 ± 2) °C; other options include 40, 70, 85, 100 °C (±2 °C) or as agreed.
• Test stress & calculation: Initial stress recommended ≈ half yield stress (or half breaking stress if no yield). Force computed as F = σA using the specimen’s minimum cross-sectional area. Record force up to 200 h and plot stress relaxation curves to find the critical stress where curves become invariant with further strain reduction.
• Results & limitations: Report critical stress difference between medium and air. Method precision is not established across laboratories; test serves for ranking and material comparison rather than design data.

Applications and Users

• Material selection and comparative screening of thermoplastics for chemical resistance.
• R&D and formulation teams validating polymer additives or grades against specific environments.
• Quality control and independent testing laboratories performing ESC screening.
• Chemical compatibility assessment for products exposed to solvents, detergents or industrial chemicals. Note: Product designers may use results to inform material choice but should not use ISO 22088-5 data alone for final design decisions.

Related Standards

• ISO 22088-1 (General guidance)
• ISO 22088-2 (Constant tensile load)
• ISO 22088-3 / 22088-4 (Other constant-strain methods)
• ISO 22088-6 (Slow strain rate method)
• Specimen preparation and tensile test refs: ISO 293, ISO 294-1, ISO 294-5, ISO 527-2, ISO 2818

Keywords: ISO 22088-5, environmental stress cracking, ESC, thermoplastics, constant tensile deformation method, stress relaxation, critical stress, chemical compatibility.