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D5071-06 – Standard Test Method Technical Guide
📐 Scope and Application of D5071
ASTM D5071 −06 (Reapproved 2021) is the Standard Practice for Exposure of Photodegradable Plastics in a Xenon Arc Apparatus. This practice outlines specific procedures and test conditions tailored for photodegradable plastics, conducted meticulously in accordance with Practices G151 and G155. It covers the preparation of test specimens, the specific test conditions best suited for photodegradable plastics, and the evaluation of the test results.
The standard is technically equivalent to ISO 4892-2 and Practice D2565. However, a critical distinction exists: D2565 covers xenon arc exposures for plastics intended for long-term use in outdoor applications, whereas D5071 focuses on materials engineered to degrade. This difference dictates the specific exposure cycles, endpoints, and evaluation criteria employed, primarily defined by tensile property retention according to D3826 and D5870.
⚙️ Test Methodology and Exposure Conditions
The practice mandates the use of a xenon arc lamp apparatus operated per Practice G155. The specific conditions are selected to simulate the spectral power distribution of natural daylight while accelerating the degradation mechanism. Typically, daylight filters (e.g., Type S borosilicate inner and soda lime outer) are used to achieve the appropriate spectrum for photodegradation.
⚠️ Important Note on Irradiance Control: Maintaining precise irradiance control at 340 nm or 420 nm is critical for reproducibility. The specific level should be agreed upon between interested parties, but typical values follow G155’s standard cycles for harsh or outdoor environments, such as the widely used 0.35 W/m²/nm at 340 nm.
| 🟦 Parameter | 📏 Typical Condition (G155 Reference) |
|---|---|
| Light Source | Xenon Arc Lamp (Per G155) |
| Filters | Daylight (e.g., Type S Borosilicate / Soda Lime) |
| Irradiance (Typical) | 0.35 W/m²/nm at 340 nm |
| Black Panel Temperature | 63 ± 3°C (Light Cycle) |
| Chamber Temperature | 38 ± 3°C (Light Cycle) |
| Relative Humidity | 50 ± 5% (Light Cycle) |
| Dark Cycle / Water Spray | Optional, per specific G155 Cycle (e.g., Cycle 1 or 4) |
📊 Evaluation of Degradation Mechanisms
Evaluating the end point of degradation is a cornerstone of this practice. The standard heavily relies on mechanical property testing to determine the material’s embrittlement or loss of structural integrity. The overall framework for addressing variability in exposure testing of nonmetallic materials is provided by Guide G141.
The primary evaluation methods referenced include Tensile Testing (D882) and the specific Practice for Determining Degradation End Point in Degradable Polyethylene and Polypropylene Using a Tensile Test (D3826). Property retention is calculated following Practice D5870.
| 📊 Property Measured | ⚡ Standard Method | 🎯 Typical Metric |
|---|---|---|
| Tensile Elongation at Break | D882 / D3826 | % Elongation Retained (End Point: 5% or 50% of initial) |
| Tensile Strength | D882 | % Strength Retained |
| Property Retention Index | D5870 | Ratio of After Exposure / Initial Value |
| Molecular Weight (Optional) | D3593 (GPC) | Reduction in Mw, Mn |
💡 Pro Tip: For photodegradable plastics, the Degradation End Point is most commonly defined by a specific retained tensile elongation (e.g., a 50% or 80% reduction from the original value), as defined by D3826. Always specify the end point criterion clearly in your report according to G141 to ensure valid comparison of results across interlaboratory studies (E691).
❓ Frequently Asked Questions
🔍 What is the primary difference between D5071 and D2565?
D5071 is specifically designed for photodegradable plastics intended to break down under environmental exposure. D2565 targets plastics formulated for long-term outdoor durability. While both use a xenon arc apparatus, the test conditions and evaluation criteria (especially the degradation end point in tensile elongation defined in D3826) are tailored to their respective material goals and failure mechanisms.
💡 Which referenced standard is used to determine the degradation end point?
The end point is determined using ASTM D3826 (Practice for Determining Degradation End Point in Degradable Polyethylene and Polypropylene Using a Tensile Test). This standard helps define the exposure time required for the material to reach a specific level of embrittlement or loss of mechanical properties, typically an 80% reduction in a mechanical property like elongation.
⚡ What are the typical light exposure conditions for xenon arc in D5071?
The practice operates in accordance with G151 and G155. A widely used cycle employs a xenon arc lamp with daylight filters, an irradiance of 0.35 W/m²/nm at 340 nm, and a black panel temperature of 63 ± 3°C during the light cycle. Specific dark cycles and water spray can be incorporated based on the intended environmental simulation detailed in G155.
📌 How should property retention be reported for these tests?
Property retention should be calculated and reported following the guidelines in ASTM D5870 (Practice for Calculating Property Retention Index of Plastics). It is typically expressed as a percentage of the original (unexposed) value. Guidance on handling variability in these results is covered in ASTM G141, and the application of basic statistical methods is outlined in G169.