ISO 4645:2022

Overview

ISO 4645:2022 - Rubber and rubber products - Identification of antidegradants - Thin layer chromatographic methods describes standardized thin‑layer chromatography (TLC) procedures for identifying antidegradants (antioxidants, antiozonants and stabilizers) in raw rubber, unvulcanized compounded rubber, and finished rubber products. The document specifies two complementary TLC methods: Method A (simplified check for expected/known antidegradants) and Method B (higher‑resolution separation for detecting/identifying unknown antidegradants). The standard covers principle, reagents, apparatus, plate preparation, extraction, development, colour visualization and interpretation (including calculation of spot ratio/shift R).

Key topics and requirements

• Scope and principle: Extraction of antidegradants from rubber, deposition as spots on silica gel plates, separation by TLC and identification by comparison with standard chromatograms.
• Two methods:
  • Method A - simplified, for routine presence/absence checks of known antidegradants.
  • Method B - detailed, for better separation and identification of unknowns.
• Applicable antidegradant classes: phosphited polyalkyl phenols, substituted bisphenols, secondary amines, substituted cresols, substituted p‑phenylenediamines; other types may be examined if a standard chromatogram exists.
• Reagents and developing solvents: specifies analytical‑grade solvents and mixtures (e.g., n‑heptane/ethyl acetate, toluene/ethyl acetate, diethylamine/cyclohexane) and colour reagents (2,6‑dichloroquinone chlorimide, diazotised sulphanilic acid, Tollen’s reagent, etc.).
• Apparatus and plate prep: silica gel plates (pre‑coated or lab‑made), developing tanks, micropipettes, extraction apparatus, optional short columns and rotary evaporators.
• Oil handling: procedures for removing extender oils (column chromatography of extract or pre‑development in light petroleum) prior to normal development.
• Safety & quality: use analytical‑grade reagents, fume hoods for volatile solvents, and fresh spray reagents where indicated; follow ISO reporting and standard chromatogram comparison.

Applications and who uses it

• Quality control: routine verification of antioxidant/antiozonant additions in compounding and finished goods.
• R&D and formulation: identifying stabilizers in new formulations or in cross‑checking suppliers’ claims.
• Failure analysis and field investigation: detecting absence/degradation of protective additives in aged or failed rubber components.
• Compliance and lab testing: standardized method for labs performing rubber chemical analysis, contract testing laboratories, manufacturers, and regulatory bodies.

Keywords: ISO 4645:2022, antidegradants, thin layer chromatography, TLC, rubber testing, antioxidants, antiozonants, stabilizers, silica gel plates.

Related standards

• ISO 1407 - Rubber - Determination of solvent extract (referenced for extraction).
• ISO 4661‑2 - Rubber, vulcanized - Preparation of samples and test pieces - Part 2: Chemical tests.