Overview
ISO 3858:2018 specifies a standardized laboratory method to determine the light transmittance of the toluene extract from carbon black used in the rubber industry. The measured transmittance provides an estimate of the degree of discolouration produced by toluene-extractable surface matter on carbon black. The method uses a spectrophotometric measurement at 425 nm and is intended for quality control and material characterization; it may not be suitable for carbon blacks with high extractable‑matter content.
Key topics and technical requirements
- Principle: A dried sample of carbon black is shaken with toluene, filtered, and the filtrate’s percent transmittance is measured against pure toluene at 425 nm.
- Instrumentation:
- Spectrophotometer: tungsten lamp, maximum 20 nm spectral passband (high‑resolution prism/grating recommended), read at 425 nm.
- Absorption cell: 10 mm optical path (polished parallel sides), or correction formula provided for other path lengths.
- Analytical balance, oven (125 °C), filtration equipment and chemically resistant glassware.
- Sample sizes and solvent ratio:
- Typical test portion: 2.00 g ± 0.01 g with 20 mL ± 0.5 mL toluene (special cases: N990/N991 use 5.0 g/50 mL; N907/N908 use 3.0 g/30 mL).
- Ratio may be maintained at 10 mL toluene per 1 g carbon black for scaled tests.
- Test conditions: ambient laboratory temperature 23 °C ± 2 °C (or 27 °C ± 2 °C); toluene handling in a fume hood; safety precautions against solvent exposure and potential PAHs in extracts.
- Precision: Annex A provides interlaboratory precision statistics (repeatability and reproducibility) based on multiple carbon black grades.
- Reporting: include reference to ISO 3858, sample identification, spectrophotometer passband, transmittance result (usually nearest 1 %) and test date.
Applications and users
- Quality control and incoming inspection at rubber manufacturers and compounding facilities.
- Materials testing laboratories and third‑party testing services evaluating carbon black surface extractables and visual discoloration potential.
- R&D teams comparing grades of carbon black or assessing processing effects on extractable matter.
- Suppliers documenting product specifications and conformity for customers in the tire, automotive, hose and general rubber goods sectors.
Related standards
- ISO 1124 - carbon black shipment sampling procedures (sample collection).
- ISO 1126:2015 - determination of loss on heating (drying procedures referenced).
- ISO/TR 9272 - referenced for interlaboratory precision program details.
Keywords: ISO 3858:2018, carbon black, toluene extract, light transmittance, spectrophotometer, rubber compounding, 425 nm, extractable matter, quality control.
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