Overview
ISO 699:2015 specifies a laboratory method for determining the alkali-insoluble fraction (alkali resistance) of pulps using fixed-concentration sodium hydroxide solutions. The standard is applicable to all kinds of pulp and defines how to prepare samples, treat them with NaOH (commonly 18%, 10% or 5% (m/m)), filter, acidify, wash, dry and weigh the insoluble residue to calculate the R‑value (alkali resistance) expressed as a percentage by mass.
Key topics and technical requirements
- Scope and principle: Gravimetric determination of the alkali‑insoluble fraction after controlled defibering in NaOH solution.
- Reagents: Sodium hydroxide solutions of known concentration (examples and densities given for 18.0%, 10.0% and 5.0% m/m) and acetic acid 1.7 mol/L for neutralization. Use analytical‑grade reagents and carbon dioxide‑free water.
- Apparatus: Alkali‑resistant beaker (250 ml), non‑brittle stirring rod, sintered glass filtering device (porosity grade P250 per ISO 4793), weighing bottles, and a constant temperature bath capable of maintaining (20 ± 0.2) °C (note: 18% NaOH can be at (20 ± 2) °C).
- Procedure (high level): Condition and weigh test portion (~2.5 g oven‑dry basis), swell pulp in NaOH, defiber mechanically, dilute and incubate at controlled temperature, filter and wash the insoluble fraction, acidify with acetic acid, wash free of acid, dry (105 ± 2 °C) to constant mass and weigh. Perform at least two parallel determinations.
- Calculation and precision: R = (m1 / m0) × 100, where m0 is oven‑dry test portion and m1 is oven‑dry mass of alkali‑insoluble fraction. Parallel results should agree within 0.3%; report mean R to one decimal place.
- Safety note: The method uses hazardous chemicals (strong alkali); follow appropriate precautions and waste disposal.
Applications and users
- Quality control and specification testing in the pulp and paper industry to characterize pulp behavior in alkaline environments.
- Research and development groups evaluating pulping processes, bleach stability or chemical composition of pulps.
- Laboratory service providers and certification bodies performing standardized pulp testing.
- Useful for manufacturers of specialty pulps (e.g., straw, wood, recycled fibres) where alkali resistance affects downstream processing or product performance.
Related standards
- ISO 692 - Pulps: Determination of alkali solubility (complements ISO 699 by measuring the alkali‑soluble fraction).
- ISO 638 - Determination of dry matter content (oven‑drying), referenced for test portion basis.
- ISO 4793 - Laboratory sintered (fritted) filters (porosity grading) for required filter specifications.
Keywords: ISO 699:2015, alkali resistance, pulps, sodium hydroxide, R‑value, alkali‑insoluble fraction, pulp testing, pulp industry, laboratory method, ISO 692.