Overview
ISO 11235:2023 - Rubber compounding ingredients - Sulfenamide accelerators - Test methods defines standardized test methods for evaluating commercial sulfenamide accelerators used in rubber compounding. The third edition (2023) replaces ISO 11235:2016 and covers sampling, physical and chemical property determination, and a suite of analytical procedures to assess purity and quality of accelerators such as CBS, TBBS, DIBS, DCBS, MBS and MBTS (MBTS being the principal decomposition product). The document emphasizes HPLC as the preferred purity method and includes informative Annex A (classification and key properties) and Annex B (precision).
Key topics and technical requirements
- Scope and sampling: Procedures for representative sampling and limits of acceptance for commercial batches.
- Purity testing:
- Method 5.1 - reduction with MBT and titration (chemical titrimetric approach).
- Method 5.2 (preferred) - high performance liquid chromatography (HPLC) for quantitative purity analysis and detection of MBTS and related impurities.
- Physical/chemical tests: Determination of melting range (capillary tube and DSC), volatile matter, insoluble material, wet sieve analysis, and ash content.
- Analytical performance: Precision data, calibration and standardization guidance, and expression of results.
- Practical lab options: Use of auto-titrators with electrodes is accommodated; interferences and limitations for methods (e.g., DSC vs capillary melting range) are discussed.
- Classification: Sulfenamides grouped by amine type (type I - primary amines, type II - unhindered secondary, type III - hindered secondary).
- Safety & compliance notes: Standard advises normal laboratory practice and highlights potential patent considerations.
Applications and who uses it
ISO 11235:2023 is intended for:
- Rubber compounders and tyre manufacturers - to verify accelerator quality for consistent vulcanization and process control.
- Raw material suppliers and procurement - to set acceptance criteria and supplier specifications.
- Quality control and analytical laboratories - for batch release testing, stability monitoring (MBTS formation), and R&D comparison of accelerator grades.
- Standards bodies and regulatory agencies - to harmonize test protocols and reporting of chemical/physical properties.
Practical benefits include improved reproducibility of purity results (HPLC preferred), consistent classification of accelerators, and reliable detection of insoluble and volatile contaminants that affect cure performance.
Related standards
- Developed by ISO/TC 45 (Rubber and rubber products), Subcommittee SC 3 (Raw materials).
- Use alongside other ISO test methods for rubber raw materials and general chromatographic/DSC guidance. For implementation, consult national standards bodies for any complementary or region-specific test protocols.