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D3079-94 – Standard Test Method Technical Guide
📋 Test Overview and Conditions
This test method, designated D3079‑94 (Reapproved 2009)´1, determines the water vapor transmission rate (WVTR) of flexible heat‑sealed packages intended for dry products. The standard quantifies the amount of water vapor that permeates through a package under controlled exposure conditions. It is essential for evaluating barrier performance and selecting materials that provide the desired product shelf‑life. The test involves exposing packages filled with desiccant to a humid environment of 90 ± 2 % relative humidity at 37.8 ± 1.1 °C for at least one month. Periodic mass measurements are taken to calculate the average rate of water vapor transmission.
Adequate heat‑seal efficiency should be assessed prior to testing (see Note 1). The values stated in SI units are regarded as standard, and all measurements are based on mass change under the assumption that the increase is solely due to water vapor ingress from the chamber to the desiccant.
⚙️ Apparatus and Materials
Apparatus: An analytical balance accurate to ±1 mg is required for weighing. The test chamber must maintain 37.8 ± 1.1 °C and 90 ± 2 % RH with continuous air circulation to prevent condensation on the specimens.
Desiccant: Anhydrous calcium chloride in small lumps is recommended. It shall pass a No. 8 (2.36‑mm) sieve and be free of fines that pass a No. 30 (600‑µm) sieve. The desiccant must be dried for at least 24 h at 200 °C prior to use.
Test Specimens: Packages shall be representative and closed in the normal manner. Each specimen is filled half‑full with desiccant up to 100 g. Generally, three to five samples are sufficient, but the precision and bias statement should be reviewed for specific requirements.
| 🟦 Parameter | 📏 Specification |
|---|---|
| Exposure Temperature | 37.8 ± 1.1 °C |
| Relative Humidity | 90 ± 2 % |
| Balance Accuracy | ±1 mg |
| Desiccant Type | Anhydrous CaCl₂ |
| Desiccant Sieve Size | Pass No. 8 (2.36 mm), Retain on No. 30 (600 µm) |
| Desiccant Drying | ≥24 h at 200 °C |
📊 Test Procedure and Key Measured Properties
Packages are prepared, sealed with desiccant, and placed in the conditioned chamber. Mass readings are taken at intervals over the exposure period (minimum one month) to establish a rate of mass change. The water vapor transmission (WVT) is expressed as grams per 30 days (or another time unit) and represents the average barrier performance of the package materials.
Reproducibility requires proper precautions and background experience. Results aid in selecting materials for shelf‑life targets and can be used to establish performance specifications. Ensure that no condensation occurs on the specimens and that the seal integrity is consistent throughout the test.
🔍 Tip: Perform preliminary heat‑seal checks and use preconditioned desiccant to minimize variability. Monitor control packages to account for any mass gain from the packaging films themselves.
⚡ Warning: Refer to ASTM E691 for precision and bias guidance. The number of specimens (typically three to five) should be validated based on the desired statistical confidence. Always follow applicable safety and regulatory practices.
❓ Frequently Asked Questions
🔍 How does the desiccant indicate water vapor transmission?
The anhydrous calcium chloride absorbs water vapor permeating through the package; the measured mass increase is directly attributed to water vapor ingress. This allows the WVTR to be calculated reliably when the desiccant is properly dried and sieved.
💡 Why are 37.8 °C and 90 % RH specified?
These conditions accelerate water vapor permeation without causing condensation or damaging typical packaging materials. They provide a controlled, accelerated environment for comparing barrier properties and predicting shelf‑life under humid conditions.
⚡ Can the test be run for less than one month?
The method specifies a minimum of one month to ensure measurable and stable mass gain. For materials with very high WVTR, shorter intervals may be acceptable, but the standard recommends following the prescribed duration for consistency.
📌 How many samples are required for valid results?
For most applications, three to five specimens are sufficient. However, consult the precision and bias statement referenced in the standard (ASTM E691) to determine the appropriate sample size for the desired statistical reliability.