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D1434-23 – Standard Test Method Technical Guide
📐 Scope and Core Terminology
The D1434‑23 standard utilizes a manometric method to determine the steady‑state rate of transmission of a gas through plastics in the form of film, sheeting, laminates, and plastic‑coated papers or fabrics. It provides for the determination of (1) gas transmission rate (GTR), (2) permeance, and, in the case of homogeneous materials, (3) permeability.
The standard defines gas transmission rate (GTR) as the quantity of a given gas passing through a unit of the parallel surfaces of a plastic film in unit time under the conditions of test. A commonly used unit for GTR is mL (STP)/(m²·d) at a pressure differential of one atmosphere. Permeance (P) is the ratio of the gas transmission rate to the difference in partial pressure of the gas on the two sides of the film. For homogeneous materials, Permeability (P′) is the product of the permeance and the thickness of a film. The standard emphasizes that this quantity should not be used unless the constancy of the permeability has been verified using several different thicknesses of the material.
💡 Tip: The test conditions—including temperature, partial pressure of the gas on both sides of the film, relative humidity, and hydrostatic pressure—that influence the transport of the gas must always be stated alongside the reported values.
⚙️ Test Method and Procedure Overview
The sample is mounted in a gas transmission cell so as to form a sealed semi‑barrier between two chambers. One chamber contains the test gas at a specific high pressure, and the other chamber, at a lower pressure, receives the permeating gas. The lower pressure chamber is initially evacuated. Following the evacuation, the low‑pressure chamber is allowed to accumulate the permeating test gas. The transmission of the gas through the test specimen is determined from monitoring the slope of the increasing pressure in the low‑pressure chamber over time.
The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. Material conditioning should follow the guidance of Practice D618.
📊 Key Measured Properties and Unit Conversions
The standard mandates SI units but provides critical conversion factors in Note 1 for users transitioning from common inch‑pound values. These conversions are essential for accurate reporting and comparison of gas barrier properties.
| 🟦 Property | 📏 Definition | 📐 SI Unit | ⚡ Conversion Factor |
|---|---|---|---|
| Gas Transmission Rate (GTR) | Quantity of gas passing through unit area in unit time | mol/(m²·s) | Multiply inch‑pound units by 5.160 × 10⁻¹⁰ |
| Permeance (P) | Ratio of GTR to partial pressure difference | mol/(m²·s·Pa) | 1 atm = 0.1013 MPa |
| Permeability (P′) | Product of permeance and film thickness | mol/(m·s·Pa) | 1 mL (STP) = 44.62 µmol |
⚠️ Critical Requirement for Permeability: Permeability (P′) is meaningful only for homogeneous materials and should not be used unless the constancy of the value has been verified using several different thicknesses of the material. The steady state is defined as the state attained when the amount of gas absorbed in the film is in equilibrium with the flux of gas through the film.
❓ Frequently Asked Questions
🔍 What is the primary purpose of ASTM D1434‑23?
It determines the steady‑state rate of transmission of a gas through plastics in the form of film, sheeting, laminates, and plastic‑coated papers or fabrics using a manometric method.
💡 What is the difference between Gas Transmission Rate (GTR) and Permeance?
GTR is the quantity of gas passing through a unit area in unit time. Permeance is the ratio of the GTR to the partial pressure difference across the film. Test conditions must be stated for both.
⚡ When should the Permeability (P′) value be used?
Permeability should only be used for homogeneous materials, and only after verifying the constancy of the value using several different thicknesses of the material.
📌 What are the standard SI units for GTR, Permeance, and Permeability?
GTR is in mol/(m²·s). Permeance is in mol/(m²·s·Pa). Permeability is in mol/(m·s·Pa).