ISO 15671:2023

Overview

ISO 15671:2023 - "Rubber and rubber products - Determination of total sulfur content using an automatic analyser" specifies an instrumental method for measuring total sulfur in solid rubber and latex using an automatic analyser. The method converts sulfur-containing material to sulfur dioxide (SO2) and quantifies SO2 by one of three detection schemes, providing a rapid, repeatable laboratory procedure for quality control, formulation verification, batch release and research.

Key topics and technical requirements

• Principle: Sulfur is converted to SO2 in an oxygen stream; SO2 is then measured to determine total sulfur.
• Detection options:
  • Hydrogen peroxide absorption → conversion to sulfuric acid → titration with alkali.
  • Iodine solution absorption → reduction of iodine to iodide → measurement via a polarized dual platinum electrode.
  • Direct SO2 detection using an infrared (IR) absorption detector, thermal conductivity detector (TCD) or equivalent detector calibrated with SO2 standards.
• Apparatus: No single system design mandated; instruments must ensure complete combustion (sufficient oxidant, temperature and time) and provide appropriate detector readout and, where needed, nonlinear response correction.
• Reagents: Use reagent-grade chemicals and those specified by the instrument manufacturer; oxygen per manufacturer specification.
• Instrument preparation & calibration:
  • Assemble and condition the analyser per manufacturer instructions.
  • Perform drift adjustment and calibrate with at least three certified sulfur calibrating agents across the expected concentration range.
  • Verify periodically with a control sample; out-of-limit checks require recalibration and rejection of intervening results.
• Sampling & test piece preparation:
  • Follow ISO 1795 (solid rubber) and ISO 123 / ISO 124 (latex) for sampling and dry test-piece preparation.
• Procedure & calculation:
  • Analyse test pieces (duplicate analyses recommended).
  • Percent sulfur S is calculated using instrument detector response B, calibration factor C, and test-piece mass m: S = (B × C / m) × 100%.
• Precision: Annex A reports repeatability (r) and reproducibility (R) from an interlaboratory study (examples: for samples R2 and R3 average results 1.34% and 1.95% with reproducibility R ≈ 0.20% and 0.44% respectively).

Applications and users

• Who uses it: rubber manufacturers, contract testing laboratories, quality control teams, instrument manufacturers and regulatory bodies.
• Practical uses:
  • Routine QC and acceptance testing of rubber compounds and products.
  • Verification of sulfur-based curing systems and formulation control.
  • Comparative testing during material development and failure analysis.
  • Regulatory and compliance reporting where total sulfur content is required.

Related standards

• ISO 1795 - sampling/preparation for solid rubber
• ISO 123 and ISO 124 - latex sampling and total solids preparation
• ISO 19983 - determination of precision for test methods

ISO 15671:2023 provides a standardized, instrument-based route to consistent, traceable sulfur analysis in rubber products-critical for product performance, safety and regulatory compliance.