Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D4250-92 – Standard Test Method Technical Guide
📐 Apparatus and Setup
The test apparatus is precisely defined in ASTM D4250. A flat-bottomed tray with inside dimensions of 200 by 300 by 50 mm (8 by 12 by 2 in.) is used, typically a borosilicate glass baking dish. A small circular spirit level ensures the tray is level, and a pin and bar elevation indicator set for 5 mm is used to calibrate the suction head. Distilled water at 23 ± 1°C (73 ± 2°F) is supplied continuously via a siphon at two to three drops per second.
Other key items include the excess water extractor (Fig. 2), specimen catcher made from 0.12 mm thick aluminum, and a specimen holder with polystyrene foam backup (13 mm thick, 50 mm wide, 100 mm long).
| 🟦 Component | 📏 Dimension | 🎯 Material |
|---|---|---|
| Tray | 200 × 300 × 50 mm | Borosilicate glass |
| Specimen Catcher | 100 × 125 mm, 0.12 mm thick | Aluminum |
| Specimen Holder Foam | 13 × 50 × 100 mm | Polystyrene |
⚙️ Test Procedure and Conditions
After conditioning per Practice D 685, the dry specimen is weighed. It is then soaked by laying it gently on distilled water for 1 minute. The wetted specimen is transferred to the excess water extractor for 15 seconds, where a 5-mm suction head removes excess water. After this, the specimen is weighed again.
| 🟦 Phase | 📏 Time | 📐 Condition |
|---|---|---|
| Soaking | 1 minute | Distilled water at 23°C |
| Suction Drainage | 15 seconds | 5 mm head difference |
| Reweighing | Immediate | Record wet weight |
📊 Key Measured Properties
The water-holding capacity (Cwh) is calculated from the weight gain. It is expressed as mass per area (g H₂O/m²) and as a water-to-fiber ratio (g H₂O/g conditioned fiber). This ratio provides a normalized measure of absorbency, enabling comparison across products such as tissues, towels, and nonwovens.
For instance, weight gain divided by specimen area yields g/m², while weight gain divided by initial dry weight yields the water/fiber ratio. The method discriminates well among different absorbing products per Section 4.2.
💡 Tip: Always use the specified aluminum for the specimen catcher (Section 5.3). Plastic can alter the capillary action and bias results.
⚠️ Ensure water temperature is strictly maintained at 23 ± 1°C to avoid deviations in measured capacity.
❓ Frequently Asked Questions
🔍 What is the soaking time specified?
The standard requires a soaking time of exactly 1 minute (Section 3.1).
💡 What water quality is needed?
Use distilled water at room temperature (23 ± 1°C) as per Section 5.5.
⚡ How is water-holding capacity reported?
It is reported in grams per square metre (g H₂O/m²) and as grams of water per gram of conditioned product (g H₂O/g conditioned fiber) according to Section 3.1.
📌 Why is the 5 mm suction head used?
The 5 mm head difference provides a controlled low suction to remove excess water without dewatering the specimen, as described in Section 3.1 and Fig. 2.