ISO 6209:2009

Overview

ISO 6209:2009 - Rubber compounding ingredients - Carbon black - Determination of solvent-extractable material specifies a standardized gravimetric method to quantify solvent-extractable material in carbon black used in the rubber industry. Applicable to all types of carbon black, the method prescribes sampling, extraction, solvent removal and weighing procedures to report extractable content as a percentage by mass. The 2009 fourth edition reduced extraction time to 8 h (from 16 h) and adds precision data.

Key topics and technical requirements

• Scope: Quantitative determination of solvent-extractable material in carbon black for rubber compounding.
• Principle: Soxhlet-style extraction of a prepared test portion, solvent evaporation, drying and gravimetric weighing of the extract.
• Extraction solvent: Analytical grade solvent; toluene recommended (widely accepted for food-contact legislation).
• Sample preparation:
  • Follow ISO 1124 for shipment sampling.
  • Dry ~20 g sample at 125 °C ± 5 °C for 1 h (ISO 1126 method referenced).
  • Use duplicate test portions (typically 10 g; increase to 20 g for very low extracts).
• Apparatus:
  • Type 1: Jacketed Soxhlet with 150 cm³ receiver flask.
  • Type 2: Suspended extraction cup with 500 cm³ receiver flask.
  • Extraction thimbles (15–30 cm³), analytical balance accurate to 0.1 mg, oven (70 °C ± 5 °C and 125 °C ± 5 °C), rotary evaporator or distillation head.
• Procedure highlights:
  • Fill receiver flask with ~100 cm³ solvent, adjust reflux ~10 fills/hour.
  • Extract for 8–8.5 h.
  • Remove bulk solvent, dry concentrate at 70 °C ± 5 °C for 2 h, cool in desiccator and weigh.
  • Run a blank and perform two determinations.
• Results & precision:
  • Results expressed as percentage by mass (gravimetric calculation with blank correction).
  • Annex A provides repeatability and reproducibility data; note that values <0.02% may need more rigorous extraction.

Practical applications & who uses it

• Quality control labs in tyre, automotive and general rubber product manufacturing - to verify carbon black purity and consistency.
• Suppliers and purchasers of carbon black - for specification compliance and acceptance testing.
• Regulatory and food-contact compliance teams - to demonstrate suitability for regulated applications (toluene recommended for food-contact relevance).
• Research & development - assessing effect of extractables on compound performance or safety (e.g., PAH-related concerns).
• Independent testing laboratories performing standardized contract testing.

Related standards

• ISO 1124 - Carbon black shipment sampling procedures
• ISO 1126:2006 - Carbon black - Determination of loss on heating
• ISO 383 - Laboratory glassware - Interchangeable conical ground joints

Safety note: solvent extracts can contain polycyclic aromatic hydrocarbons (PAHs). Handle extracts and solvents with appropriate laboratory safety measures.