Overview
ISO 127:2018 specifies a laboratory method to determine the KOH number (potassium hydroxide equivalent) of natural rubber latex concentrate preserved wholly or in part with ammonia. The method covers ammonia‑preserved Hevea brasiliensis latex concentrates and is applicable when boric acid is present. It is not applicable to latex preserved with potassium hydroxide, to many non‑Hevea natural sources, or to synthetic, compounded, vulcanized or artificial rubber dispersions.
Keywords: ISO 127:2018, KOH number, natural rubber latex concentrate, KOH number determination, ammonia‑preserved latex, boric acid.
Key topics and requirements
- Scope and limits: Method restricted to ammonia‑preserved natural latex concentrates; excludes KOH‑preserved and many synthetic/compounded latices.
- Sampling & pre‑tests: Sampling per ISO 123; total solids and alkalinity determined per ISO 124 and ISO 125 respectively; boric acid content per ISO 1802 when present.
- Reagents: Uses analytical‑grade reagents and CO2‑free water. Recommended titrants include carbonate‑free KOH standard solutions (nominally 0.1 and 0.5 mol·dm‑3) and a defined formaldehyde solution for adjusting alkalinity.
- Apparatus: pH‑meter (readable to 0.01 pH), suitable glass electrode (pH up to 12.0), mechanical or magnetic stirrer; automatic titrators allowed if validated against the manual method.
- Procedure: Dilute a test portion to ~30% total solids, adjust alkalinity with formaldehyde if needed, then titrate with 0.5 mol·dm‑3 KOH while recording pH. The end‑point is determined from the titration curve as the point of inflection (maximal first derivative / change of sign of second derivative). Determinations are carried out in duplicate.
- Calculation: KOH number is calculated from the volume and concentration of KOH titrant, the test portion mass and total solids; a correction is applied if boric acid is present.
- Quality and reporting: Duplicate results must agree within 5% (mass). Test reports must reference ISO 127:2018 and include sample ID, pH‑meter details, results, boric acid correction and any deviations from the standard method.
Applications and users
- Quality control and acceptance testing in latex processing plants and rubber manufacturers.
- Analytical and compliance testing in industrial laboratories and third‑party testing services.
- R&D and formulation labs monitoring latice alkalinity and residual acid radicals combined with ammonia.
- Useful for suppliers and buyers specifying latex quality, and for auditors enforcing standards‑based testing.
Keywords: latex testing, titration pH end‑point, quality control, rubber industry.
Related standards
- ISO 123 - Rubber latex - Sampling
- ISO 124 - Latex - Determination of total solids
- ISO 125 - Natural rubber latex concentrate - Determination of alkalinity
- ISO 976 - pH measurement for polymer dispersions and latices
- ISO 1802 - Determination of boric acid in latex
For implementation, laboratories should follow normal safety and good laboratory practice and consult ISO 127:2018 for full procedural details and annexes (formaldehyde determination, titration examples, precision data).
