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D2842-19 – Standard Test Method Technical Guide
📐 Scope and Standard Overview
ASTM D2842-19 specifies the standard test method for determining water absorption of rigid cellular plastics. The procedure measures the change in buoyant force resulting from immersion under a precise 5.1 cm (2 in.) head of water for a standard period of 96 hours. The method distinguishes between two procedures based on material behavior, and alternative immersion periods may be agreed upon by the involved parties.
⚠️ Procedure Selection Required: Materials experiencing rapid water absorption or volume increase during exposure must be evaluated using Procedure A. Selecting the wrong procedure can lead to significant inaccuracies in the reported water absorption values.
⚙️ Test Procedures: Procedure A vs. Procedure B
The standard provides two distinct procedures (Section 1.2). Procedure A is designed for materials with dynamic properties such as rapid absorption or swelling. Procedure B is intended for stable materials that do not exhibit these characteristics. The correctness of the procedure selection is paramount to the validity of the test.
| 🟦 Feature | 📏 Procedure A | 🎯 Procedure B |
|---|---|---|
| Material Behavior | Rapid absorption / Volume increase | Stable, no rapid absorption |
| Buoyant Force | Direct final measurement required | May be calculated from dry weight/volume |
| Sample Handling | Specific procedures for unstable foams | Standard procedure for stable foams |
📊 Key Principle and Interpretation
The test relies on the fundamental buoyant force principle. Water absorbed into the specimen increases its weight, thereby lowering the net buoyant force when submerged. The initial buoyant force is determined from the dry weight and volume. The final buoyant force is measured via an underwater weighing assembly. The difference between these values directly represents the weight of water absorbed per unit volume of specimen. This standard is equivalent to ISO 2896.
✅ International Equivalence: As stated in Note 1 of the standard, this test method is equivalent to ISO 2896, ensuring global consistency in test results.
| ⚡ Parameter | 📐 Specification |
|---|---|
| Immersion Head | 5.1 cm (2 in.) |
| Standard Duration | 96 hours |
| Governing Units | SI |
| Related ISO Standard | ISO 2896 |
❓ Frequently Asked Questions
🔍 What is the basic principle of ASTM D2842?
The test measures water absorption by calculating the change in buoyant force of a submerged specimen. Water uptake increases the specimen’s weight, reducing its buoyancy, and this change is measured.
© 2026 TNLab — This article is a technical interpretation for reference only. The original standard as published by ASTM International takes precedence.