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D644-99 – Standard Test Method Technical Guide
📐 Specimen Requirements and Preparation
The test method defines specific specimen weights based on the application. For chemical analysis, specimens must weigh no less than 1 gram, with a preferred weight of 2 grams, and must be in moisture equilibrium with the sample being analyzed. For determining moisture in a shipment, specimens of at least 50 grams are required, obtained per Practice D585. For combined board or containers, approximately 50-gram specimens are used.
| 🟦 Purpose | 📏 Minimum Weight | 🎯 Preferred Weight |
|---|---|---|
| Chemical analysis | 1 g | 2 g |
| Shipment moisture | 50 g | — |
| Combined board tests | Approximately 50 g | — |
⚠️ Always ensure specimens are in moisture equilibrium before initial weighing to guarantee accurate moisture content results.
⚙️ Apparatus and Test Conditions
The required apparatus includes an airtight weighing container, such as a glass weighing bottle with ground stopper for small specimens or a metal container with wire basket for larger ones. A thermometer covering 100–110°C with 1° divisions monitors the oven. The drying oven must be constant-temperature with air circulation and separated heating coils. A chemical balance sensitive to 1 mg for specimens ≤2 g and to 0.05% of weight for larger specimens is essential. After drying, specimens are cooled in a desiccator using anhydrous alumina desiccant.
| 🟦 Apparatus | 📏 Specification | 🎯 Requirement |
|---|---|---|
| Thermometer | Range | 100–110°C |
| Scale division | 1° intervals | |
| Chemical balance | Sensitivity (≤2 g) | 1 mg |
| Sensitivity (>2 g) | 0.05% of weight | |
| Drying oven | Temperature control | Constant with circulation |
| Desiccator | Desiccant | Anhydrous alumina |
💡 Use indicator-grade anhydrous alumina as the desiccant to visually confirm its effectiveness through color change.
📊 Significance and Use
Moisture content directly influences the purchase cost and performance of paper and paperboard. It affects critical properties such as tensile strength, tearing resistance, dimensional stability, permanence, printability, flexibility, and runability on processing equipment. Accurate moisture measurement is also necessary to convert analytical results to a dry basis from specimens weighed at ambient or conditioned moisture levels. This test method is technically equivalent to TAPPI T 412 – 83.
❓ Frequently Asked Questions
🔍 What is the drying temperature specified in ASTM D644?
The standard specifies drying at 105°C in a constant-temperature oven with adequate air circulation.
💡 How should specimens be handled before drying?
Specimens should be in moisture equilibrium with the samples being analyzed and weighed in an airtight container immediately before drying.
⚡ What are the balance sensitivity requirements?
For specimens of 2 grams or under, a balance sensitive to 1 mg is required. For larger specimens, the sensitivity must be 0.05% of the original weight.
📌 Why is moisture content important for paper and paperboard?
Moisture content affects purchase cost and key properties like tensile strength, tearing resistance, dimensional stability, and printability, making it critical for quality and performance.