ISO 483:2005

Overview

ISO 483:2005 - "Plastics - Small enclosures for conditioning and testing using aqueous solutions to maintain the humidity at a constant value" - provides guidelines for constructing and using small enclosures (volumes < 200 dm³) to obtain atmospheres of constant relative humidity for conditioning and testing plastics. The standard covers methods using saturated salt solutions, glycerol/water solutions, and sulfuric acid/water solutions to generate reproducible humidity levels at controlled temperatures (0 °C to 70 °C). It is intended for conditioning small quantities of material and tests that can be performed entirely inside a sealed enclosure (for example electrical tests). Enclosures that require frequent opening are excluded.

Key topics and requirements

• Scope and principle
  • Enclosures under 200 dm³ using aqueous solutions to establish equilibrium relative humidities.
  • Atmospheres produced by saturated salts (Method A), glycerol solutions (Method B) or sulfuric acid solutions (Method C).
• Materials
  • Use analytical/reagent-grade chemicals (salts, glycerol, sulfuric acid) and water meeting ISO 3696 Grade 3.
• Apparatus & environmental control
  • Temperature control: ovens, baths or conditioned rooms able to maintain ±1 °C.
  • Thermometry: internal thermometers readable to ±0.1 °C; record 1 hour after closing and at least every 24 h.
  • For Method B: refractometer (range ~1.330–1.470, 0.001 resolution). For Method C: hydrometer accurate to ±0.001 g/ml.
  • Air circulation (fans) recommended for hygroscopic materials to ensure uniform RH.
• Procedures
  • Precondition enclosure (e.g., place saturated solution 24 h before specimens unless proven faster).
  • Maintain excess undissolved salt to keep solutions saturated.
  • Limits on specimen load relative to solution surface area (V/S considerations); different allowances with/without air circulation.
  • Cleaning/replacement schedule: keep solution and interior surfaces clean; replace solution weekly if conditioning >1 week.
• Tolerances, precision and reporting