ISO 23508:2021 - Overview
ISO 23508:2021 defines standardized methods for evaluating the viscoelastic properties of compounds based on solution‑polymerized styrene‑butadiene rubber (S‑SBR), including functionalized S‑SBR. The standard provides a single test formulation, a detailed mixing procedure (three‑stage laboratory mixing), sample preparation and test methods for measuring uncured mix viscosity, vulcanization behavior and dynamic viscoelastic characteristics used to predict tire and rubber performance.
Key topics and technical requirements
- Standard test formulations: Two model formulations are specified (Formulation A - oil‑extended S‑SBR; Formulation B - non oil‑extended). Typical ingredients and pphr values are listed (e.g., S‑SBR 70 pphr, BR 30 pphr, silica 70 pphr, TESPD silane ~5.6 pphr, TDAE oil, ZnO, antioxidants, curatives).
- Mixing procedure: A three‑stage laboratory internal‑mixer procedure is prescribed, with target starting/discharge temperatures and rotor speeds. Example targets include discharge temperatures ~155–165 °C after stages 1–2 and final sheeting to ~2.2 mm thickness after stage 3.
- Uncured mix testing: Viscosity at 100 °C is measured with a shearing‑disc viscometer per ISO 289‑1.
- Vulcanization evaluation: Use of oscillating‑disc or rotorless curemeters (ISO 6502‑2 / ISO 6502‑3) to determine scorch and cure parameters (e.g., ML, MH, t′(10), t′(50), t′(90)) under specified conditions (oscillation frequency and die temperature guidance provided).
- Dynamic viscoelastic testing: Procedures for assessing strain dependency (Payne effect) and temperature dependency of viscoelastic properties. Sample preparation, deformation modes and expression of results are specified to ensure comparable data.
- Quality and reporting: Precision, data reliability guidance and a required test report format are included. Informative annexes cover filler dispersibility, examples of measurements, Payne effect and precision data.
Applications and users
ISO 23508:2021 is valuable for:
- Rubber compound developers and R&D laboratories optimizing rolling resistance, wet grip and filler interactions for tire treads.
- Quality control and incoming‑inspection teams verifying S‑SBR batches and supplier claims.
- Test laboratories performing comparative viscoelastic assessments for material selection and regulatory/contractual testing.
- Material scientists studying functionalized S‑SBR interactions with silica and coupling agents.
Practical benefits include reproducible comparisons of S‑SBR grades, improved formulation development, and consistent input data for tire performance modelling.
Related standards
Keywords: ISO 23508:2021, solution‑polymerized SBR, S‑SBR, viscoelastic properties, test formulation, mixing procedure, vulcanization, dynamic viscoelastic testing, Payne effect, tire compound testing.