Overview
ISO 5794-2:2014 provides standardized procedures for evaluating precipitated hydrated silica in a styrene-butadiene rubber (SBR) mix. The document specifies the test formulation, sampling, laboratory mixing, conditioning and the test methods required to determine key physical properties such as viscosity, cure behaviour and stress‑strain performance. The standard is intended to deliver reproducible results for rubber compounding, quality control and comparative material assessment.
Key Topics
- Scope and purpose: Defines test formulation, equipment, procedure and test methods for precipitated hydrated silica in SBR.
- Sampling: Sampling to be performed in accordance with ISO 15528 to ensure representative material for testing.
- Test formulations: Two standard formulations are provided (Formulation 1 and Formulation 2) that differ in activator content; high specific surface area silica requires more activator.
- Mill mixing procedure: Laboratory mill batch mass and roll temperatures are specified (per ISO 2393). Mixing steps, sequence of ingredient additions, roll openings and pass/run counts are prescribed. Sheets of specified thickness are to be prepared (6 mm for cure tests and 2.2 mm for tensile specimens) and conditioned for 18–24 hours where possible.
- Uncured mix testing: Determine Mooney viscosity at 100 °C using a shearing‑disc viscometer per ISO 289-1.
- Vulcanization and cure evaluation: Two curemeter methods are referenced:
- Oscillating disc curemeter (ISO 3417) - measure parameters such as minimum and maximum torque and cure times (M_L, M_H, t_s1, t_c, t′(50), t′(90)) under defined test conditions.
- Rotorless curemeter (ISO 6502) - measure torque and cure times (F_L, F_max, t_s1, t_c, t′(50), t′(90)) under defined test conditions.
- Post‑cure physical tests: Tensile stress‑strain properties according to ISO 37 (type 2 test pieces) and hardness testing per ISO 48 after vulcanization (e.g., 160 °C for 15 min as indicated in the standard).
- Reporting and precision: Test reports must cite ISO 5794-2:2014 and include sample identification, formulation used, uncured viscosity, cure characteristics, stress‑strain results, hardness and any deviations or optional operations.
Applications
- Quality control for silica suppliers and rubber compounders to compare batch‑to‑batch performance.
- R&D and formulation optimisation when changing silica grades or activator levels.
- Comparative evaluation of silica effects on processing viscosity, cure kinetics and final mechanical properties in SBR-based products (tires, technical rubber goods, seals).
- Establishing consistent test data for supplier specifications and material acceptance criteria.
Related Standards
- ISO 5794-1:2010 - Non‑rubber tests for precipitated hydrated silica (chemical and physical characterization).
- ISO 5794-3 - Evaluation procedures for silica in blends of S‑SBR and BR.
- ISO 2393 - Rubber test mixes: preparation, mixing and vulcanization equipment and procedures.
- ISO 289-1, ISO 3417, ISO 6502, ISO 37, ISO 48 - Referenced methods for viscosity, curemeter measurements, tensile and hardness testing.
By applying ISO 5794-2:2014, laboratories and compounders can achieve repeatable, comparable evaluations of precipitated hydrated silica in SBR formulations, improving formulation control and material selection decisions.
Open preview (PDF)Rubber compounding ingredients — Silica, precipitated, hydrated — Part 2: Evaluation procedures in styrene-butadiene rubber