Overview
ISO 2930:2017 - "Rubber, raw natural - Determination of plasticity retention index (PRI)" specifies a laboratory method to measure the plasticity retention index (PRI) of raw natural rubber. PRI quantifies a material’s resistance to thermal oxidation by comparing the rapid plasticity number before and after controlled oven ageing. A higher PRI indicates greater resistance to thermal oxidative degradation. The standard provides the test principle, apparatus, procedure, expression of results and precision information.
Key topics and requirements
- Scope: PRI is a relative index and not an absolute classifier of post‑oxidation plasticity.
- Test principle: Determine rapid plasticity numbers of unaged and oven‑aged test pieces using a parallel‑plate plastimeter (10 mm platen). PRI = (plasticity after ageing / plasticity before ageing) × 100.
- Ageing conditions: Oven ageing at 140 °C for 30 minutes (air‑oven), with oven temperature control to ±0.5 °C and recommended air change of 10 changes per hour (or semi‑open air‑flap alternative per Annex A).
- Apparatus: Parallel‑plate plastimeter (10 mm platen), punch for test discs, thickness gauge (0.01 mm divisions), laboratory mixing mill (specified roll sizes/speeds), lightweight aluminium tray/dishes and tissue/cigarette paper as described.
- Sample preparation: Homogenize and sheet raw rubber, cut test pieces of ~3.4 mm thickness, divide into triplicate sets for unaged and aged determinations.
- Measurement & reporting: Use median of three rapid plasticity readings for each condition; round PRI to nearest whole number. Test report must reference ISO 2930 and include sample ID, median plasticities, PRI, date and any deviations.
- Precision and validation: Annex B summarizes interlaboratory precision data and Annex A addresses oven air‑change considerations.
Applications and users
ISO 2930:2017 is used for:
- Quality control and incoming raw material inspection by rubber manufacturers, compounders and tyre producers.
- R&D and formulation development to assess antioxidant effectiveness and thermal stability of raw natural rubber.
- Supplier verification and comparative assessment of batch stability under thermal oxidative stress.
- Test laboratories performing standardized rubber property testing.
Typical users: material scientists, QA/QC laboratories, rubber technologists, procurement teams, and certification bodies.
Related standards
- ISO 2007 - Determination of plasticity (rapid‑plastimeter method)
- ISO 1795 - Sampling and preparative procedures for raw rubber
- ISO 2393 - Preparation, mixing and vulcanization equipment/procedures
- ISO 23529 - Preparing and conditioning test pieces for physical tests
Keywords: ISO 2930:2017, plasticity retention index, PRI, raw natural rubber, thermal oxidation, rapid plastimeter, oven ageing, rubber testing, quality control.
