Overview
ISO 489:2022 - Plastics - Determination of refractive index specifies two standard test methods for measuring the refractive index of plastics. The standard defines:
- Method A: a refractometric procedure (e.g., Abbe refractometer) for moulded parts, cast or extruded sheets and films, suitable for isotropic and anisotropic, transparent, translucent, coloured or opaque plastics.
- Method B: an immersion (Becke line) method using a microscope for powdered or granulated transparent materials, typically with monochromatic light to avoid dispersion (sodium D line, 589 nm).
The refractive index is a fundamental optical property used for material identification, composition and purity checks, optical design and for detecting temperature-related transitions.
Key topics and requirements
- Apparatus
- Method A: Abbe or equivalent refractometer accurate to 0.001; measurement range ~1.300–1.700; temperature control to (23 ± 0.5) °C for prisms and specimen.
- Method B: Microscope ≥200× total magnification with suitable condenser; monochromatic light (commonly sodium D line, 589 nm); a set of immersion liquids with known refractive indices.
- Contacting / immersion liquids
- Lists of recommended liquids (examples: 1‑bromonaphthalene, methylene iodide, methyl salicylate, zinc chloride solutions, silicone oils) and guidance that liquids must not attack or swell the plastic. Users must observe safety and disposal regulations for potentially hazardous liquids.
- Specimen preparation
- Sheets: recommended thickness 3–5 mm; optically flat, polished measurement face.
- Films: actual film thickness, not less than 2 µm; specific mounting technique using a glass plate is described.
- Powders/granules: particles small enough to compare sample area and surrounding field.
- Number of measurements: generally five specimens or five measurements.
- Conditioning and environment
- Condition per ISO 291 at (23 ± 2) °C and (50 ± 5) % RH for at least 88 h unless otherwise specified.
- Precision & reporting
- Precision information is provided (moved to Annex A in the 2022 edition); test report requirements are specified in Clause 9.
Applications and users
ISO 489:2022 is used by:
- Polymer testing and quality control laboratories (material verification, batch control).
- R&D and product development teams designing optical plastics or transparent components.
- Forensic and identification labs comparing unknown plastics to reference materials.
- Manufacturers checking composition, purity and temperature-dependent optical behavior.
Practical applications include material identification, optical part design, quality assurance and investigation of thermal transitions via refractive index changes.
Related standards
- ISO 291 - Plastics: standard atmospheres for conditioning and testing (referenced for specimen conditioning).
Keywords: ISO 489:2022, refractive index, plastics, refractometric method, immersion method, Abbe refractometer, Becke line, sodium D line, contacting liquids, specimen conditioning.
