ISO 29681:2009 PDF

Overview

ISO 29681:2009 specifies a standardized method for the determination of pH of salted water extracts of paper, board and pulps. The method uses a 0.100 M KCl (salted water) extract to reduce Donnan ion‑exchange effects and provide pH values that better reflect real mill/process conditions-especially for bleached pulps from virgin fibres and other samples with low ionic strength. Results can differ notably from those obtained with ISO 6588-1 / ISO 6588-2.

Key topics and technical requirements

• Salted water: potassium chloride solution c(KCl) = 0.100 M (7.45 g KCl per 1 000 ml).
• Test portion: air-dry, cut to small pieces; weigh 2.0–2.2 g into a flask.
• Extraction/soaking: add 100 ml salted water and soak 1 hour; soak at 20–25 °C (cold) or (90 ± 5) °C (hot), shaking at least once during the period.
• Filtration: filter the suspension (fritted glass or low-ash filter paper) before measurement.
• pH measurement:
  • Calibrate pH-meter with at least two buffer solutions (e.g. pH ≈ 4, 7, 9) at 20–25 °C.
  • Measurement at 20–25 °C; electrode system must allow measurement error