Overview
ISO 9944:1990 defines a laboratory method for determining the electrical conductivity of phenolic resin extracts. The procedure is particularly important where phenolic resins are used as impregnating materials. The test is based on adding an acetone/deionized-water mixture to a resin solution or dissolved resin, allowing a precipitate to form and settle, then measuring the conductance of the supernatant suspension. Results are reported in microsiemens per centimetre.
Key Topics
- Principle: Addition of an acetone/water mixture produces a milky suspension; after settling the conductance of the liquid above the resin is measured and converted to conductivity.
- Reagents & conditions:
- Reagent-grade acetone and deionized water (low conductivity) are specified.
- The acetone/deionized-water mixture in the procedure uses an acetone:water volumetric ratio described in the standard.
- Measurements are carried out at 23 °C ± 2 °C.
- Apparatus:
- Conductivity cell with known cell constant and a conductance-measuring instrument capable of appropriate precision in the specified frequency range.
- Magnetic stirrer, beakers (250 ml), balance with 1 mg scale interval.
- Procedure highlights:
- Test portions of resin solution or dissolved powdered resin are prepared to the specified mass tolerance.
- Acetone is added, the mixture stirred, then an acetone/deionized-water mixture is added dropwise to avoid coagulation.
- After a short settling period the milky suspension above the resin is transferred to the conductivity cell, temperature-equilibrated, and measured within the time window defined by the standard.
- A blank test (without resin) is run under the same conditions for correction.
- Expression of results & precision:
- Conductivity is calculated from measured conductances and the cell constant and reported in microsiemens per centimetre (rounded to one decimal place).
- Precision figures in the standard indicate repeatability and reproducibility values (both cited as 10 % in the document).
- Practical notes:
- The conductivity cell must be cleaned and recalibrated regularly to avoid contamination; the standard provides cleaning guidance.
Applications
- Quality control of phenolic resins intended for impregnation processes (electrical insulation, laminates, and composite manufacture).
- Material acceptance testing and batch-to-batch comparison to detect ionic contamination or extractable conductive species.
- Supporting material selection where low extractable conductivity is critical for electrical performance.
Related Standards
- ISO/TC 61 committee publications on plastics and thermosetting resins.
- Standards and guidance on conductivity measurement and laboratory calibration practices (conductivity cell calibration, instrument precision, and sample handling).
Keywords: phenolic resins, electrical conductivity, resin extracts, acetone/water extraction, conductance measurement, impregnating materials, quality control, microsiemens per centimetre.
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