Overview
ISO 125:2020 specifies a standardized laboratory method for the determination of alkalinity in natural rubber latex concentrate (Hevea brasiliensis). The method measures the acid volume required to reach pH 6 in a stabilized test portion and expresses alkalinity as either ammonia (NH3) or potassium hydroxide (KOH) depending on the preservative used. The standard is aimed at quality control and laboratory testing within the rubber industry and includes procedural, reagent and reporting requirements.
Key topics and technical requirements
- Scope & limitations: Applies to natural rubber latex concentrate from Hevea brasiliensis; not necessarily suitable for synthetic latices, compounded or vulcanized latex, or artificial dispersions.
- Principle: Titrate a stabilized latex sample to pH 6.0 ± 0.05 and calculate alkalinity from the acid consumed.
- Reagents:
- 5% (w/w) non‑ionic stabilizer (alkyl phenol polyethylene oxide condensate), pH adjusted to 6.0 ± 0.05
- Standard volumetric acid solutions: H2SO4 c = 0.05 mol·dm‑3 or HCl c = 0.10 mol·dm‑3
- Methyl red and methyl orange indicators; Na2CO3 standard for acid standardization
- Methods: Two acceptable titration techniques:
- Potentiometric titration using a pH‑meter (combined electrode, readable to 0.02 pH units)
- Visual indicator titration using methyl red (colour change yellow → pink)
- Calculations: Alkalinity expressed as % NH3 or % KOH using prescribed factors (e.g., F = 1.7 or 3.4 for NH3 with HCl/H2SO4; F = 5.61 or 11.22 for KOH).
- Apparatus & sampling: Requires standard lab equipment, stirrer, balance (0.01 g readability), and sampling per ISO 123.
- Quality metrics: Precision data (repeatability and reproducibility) are provided in Annex A; typical repeatability r ≈ 0.01–0.02 and reproducibility R ≈ 0.03–0.06 (values depend on method/acid).
Applications and who uses it
- Latex producers: Routine quality control of concentrate alkalinity to ensure preservative effectiveness and product consistency.
- Testing laboratories: Accredited labs performing contract testing or compliance verification.
- Rubber product manufacturers: Incoming raw-material evaluation and supplier qualification.
- Regulatory and standards bodies: Method reference for specifications, conformity assessment and inter‑laboratory studies.
Related standards
- ISO 123 - Rubber latex - Sampling (referenced for sampling procedure)
- ISO 976 - pH measurement for polymer dispersions and rubber latices
- ISO 13773 - Alkalinity determination for polychloroprene latex (separate method)
ISO 125:2020 is a practical, reproducible test method for laboratories requiring reliable alkalinity determination in natural rubber latex concentrate, supporting quality control, supplier assessment and regulatory compliance.