Overview
ISO 506:2020 specifies a laboratory method to determine the volatile fatty acid (VFA) number of natural rubber latex concentrate. The VFA number expresses the grams of potassium hydroxide equivalent to volatile fatty acids in a latex concentrate containing 100 g of total solids. The standard applies to natural Hevea brasiliensis latex concentrates and is not intended for compounded or vulcanized latices, artificial dispersions or synthetic rubber latices.
Keywords: ISO 506:2020, volatile fatty acid number, natural rubber latex concentrate, VFA, rubber latex testing, Hevea brasiliensis.
Key topics and technical requirements
- Principle: Coagulate a test portion with ammonium sulfate, separate and acidify the serum, steam‑distill the volatile acids and titrate the distillate with a standard barium hydroxide solution.
- Reagents: ammonium sulfate solution, sulfuric acid, standardized barium hydroxide, indicator (bromothymol blue or phenolphthalein), silicone antifoam, calcium hydroxide solution, distilled water.
- Apparatus: steam‑jacketed distillation apparatus (Markham still) or equivalent, steam bath, 70 °C water bath, pipettes, burette, qualitative filter paper, air pump for CO2 removal.
- Procedure highlights: typical test portion ≈ 50 g latex concentrate; coagulate with ~50 cm3 ammonium sulfate, filter serum, acidify, steam‑distill a measured aliquot and titrate the collected distillate. Duplicate determinations are required and repeatability/reproducibility criteria are specified.
- Expression of results: calculation formula provided to convert titration volume and sample parameters (dry rubber content, total solids, serum density) into VFA number.
- Precision: Annex A contains interlaboratory precision data (repeatability and reproducibility) based on an ITP.
Keywords: Markham still, steam distillation, barium hydroxide titration, VFA calculation.
Applications and users
- Quality control laboratories in latex manufacturing - monitor volatile acid levels during concentrate production, preservation and storage.
- Raw material suppliers and buyers - verify latex concentrate quality for processing, pricing and acceptance criteria.
- Rubber processing and R&D teams - assess effects of preservation (e.g., ammonia) and chemical treatments on volatile acid formation.
- Third‑party testing laboratories and regulatory bodies - provide standardized VFA measurements for compliance and specifications.
Practical benefits include early detection of acid generation (spoilage or additive reactions), consistent product quality, and data to guide preservation or processing adjustments.
Related standards
- ISO 123 - Rubber latex - Sampling
- ISO 124 - Latex, rubber - Determination of total solids content
- ISO 126 - Natural rubber latex concentrate - Determination of dry rubber content
- ISO 19983 - Precision of test methods (used for ISO 506 precision evaluation)
Using ISO 506:2020 ensures reproducible, internationally recognized measurement of volatile fatty acids in natural rubber latex concentrate for reliable quality control and trade.
