ISO 17278:2020

Overview

ISO 17278:2020 specifies a laboratory test method for measuring the gel content of technically specified rubber (TSR) - raw natural rubber processed from Hevea brasiliensis. The method determines the insoluble (gel) fraction by dissolving TSR in toluene, separating the insoluble material by centrifugation, drying and weighing the residue. Results are reported as a percentage gel content (rounded to one decimal place).

Key topics and requirements

• Principle: dissolve a defined mass of TSR in toluene, allow extraction, centrifuge to separate insoluble gel, remove solvent, dry precipitate and calculate gel content as a percentage of the original sample mass.
• Reagents: analytical-grade toluene (primary solvent) and acetone (for rinsing precipitate).
• Apparatus & accuracy:
  • Laboratory centrifuge: 14 000 r/min (recommended) or minimum 8 000 r/min with extended time.
  • Screw-cap centrifuge tubes (≥30 cm3) able to withstand >110 °C.
  • Balance accurate to ±0.1 mg and weighing containers to ±1 mg.
  • Oven capable of 110 °C ±10 °C and a desiccator.
• Test conditions & procedure:
  • Sample ratio: typically 0.1 g TSR per 30 cm3 toluene.
  • Extraction: stand 16–20 h at (25 ± 2) °C in the dark.
  • Centrifugation: 14 000 r/min for 2 h (or 8 000 r/min for 6 h).
  • Drying: precipitate dried at 110 °C for 1 h; repeat weighings until mass change <0.2 mg.
• Calculation: Gel content G (%) = (m2 − m1) / m0 × 100, where m0 = original test piece mass, m1 = empty container mass, m2 = container + dry precipitate mass.
• Precision: Annex A reports interlaboratory repeatability and reproducibility values across low, medium and high gel levels; precision depends on gel content level.
• Safety & lab practice: warns about solvent handling and standard laboratory safety; conditioning per ISO 23529.

Applications and users

ISO 17278:2020 is intended for:

• Quality control laboratories in natural rubber production and processing.
• Third‑party testing services validating TSR batches for suppliers and purchasers.
• R&D and product development teams assessing rubber processing effects (mixing, storage, coagulation) on gel formation.
• Procurement/specification engineers who require documented gel-content results for acceptance criteria.

Practical uses include batch acceptance testing, supplier quality verification, and comparative studies of processing methods that influence gel formation in TSR.

Related standards

• ISO 2000:2014 - Guidelines for specification of technically specified rubber (TSR).
• ISO 23529 - Conditioning and general procedures for rubber test pieces.
• Precision methodology reference: ISO/TR 9272 (withdrawn; now superseded by ISO 19983) is cited for precision evaluation.