ISO 8787:1986

Overview

ISO 8787:1986 - Paper and board: Determination of capillary rise (Klemm method) specifies a laboratory procedure to measure the capillary rise (water uptake by capillarity) of highly absorbent, unsized papers and boards (for example, blotting papers). The method suspends vertical strips with their lower ends immersed in water and measures the upward movement of the wetting front after a fixed time. It is not recommended for materials with capillary rise less than 5 mm; for such materials, tests like ISO 535 (Cobb) are more suitable.

Key topics and requirements

• Scope: Intended for unsized, high-absorbency papers and boards; avoid use if capillary rise < 5 mm.
• Sampling & conditioning: Sample preparation per ISO 186 (sampling) and conditioning per ISO 187 (standard atmosphere).
• Specimens: Cut 10 strips, at least 200 mm long and 15 ± 1 mm wide (machine and/or cross direction).
• Marking & immersion: Mark a line 15 mm from one end; suspend strips vertically and immerse the lower end to a depth of 10–15 mm. A paperclip or weight may be used to ensure immersion.
• Test liquid & temperature: Use distilled, deionized, or potable water shown comparable to ISO 3696 quality; water temperature 23 ± 1 °C. Change water frequently to avoid contamination from soluble paper components.
• Timing & measurement: Start timing when the mark aligns with the water surface and measure the capillary rise after 10 min ± 10 s. Read rise to 1 mm accuracy using a cathetometer or fixed scale. If meniscus is uneven, use the average level; with a cathetometer read the lowest point of the meniscus. Shorter times can be agreed for very absorbent materials but must be recorded.
• Reporting & precision: Report the mean of 10 results (machine and/or cross direction) and include test conditions and any deviations. Interlaboratory data cite repeatability ~10% and reproducibility ~20%.

Applications and users

• Quality control and acceptance testing for blotting papers, filter papers, medical absorbents, packaging, and specialty absorbent boards.
• Useful for paper manufacturers, converters, laboratory technicians, R&D in paper science, suppliers of absorbent goods, and conservation professionals assessing paper absorbency.
• Helps compare absorbency performance, control production, and validate material suitability for intended absorbent applications.

Related standards

• ISO 186 - Sampling for average quality
• ISO 187 - Conditioning of samples
• ISO 3696 - Water for laboratory use (quality)
• ISO 535 / Cobb methods - Alternative for materials with low capillary rise

Keywords: ISO 8787:1986, capillary rise, Klemm method, paper testing, absorbency, blotting paper, paper and board, ISO standard.