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D5247-92 – Standard Test Method Technical Guide
ASTM D5247-92 is a standard test method for determining the aerobic biodegradability of degradable plastics using specific microorganisms in submerged culture. Degradation is evaluated through weight loss, tensile strength loss, percent-elongation loss, and changes in molecular-weight distribution. This method supports regulatory compliance in regions mandating degradable plastics.
📐 Method Summary and Specimen Preparation
Plastic samples are cut into lengths suitable for tensile testing per ASTM D 882 and sized for a 250-mL Erlenmeyer shake-flask. The strips are chemically disinfected, aseptically dried, and initial weights are recorded. They are then added to growth medium and incubated with shaking for 24 hours at 125 r/min. If the medium remains clear (uncontaminated), it is inoculated with a pure culture of the target microorganism.
| 🟦 Measurement Parameter | 📏 Relevant Standard | 🎯 Assessment Criteria |
|---|---|---|
| Tensile Strength | ASTM D 638 / D 882 | Loss of strength |
| Elongation | ASTM D 638 / D 882 | Percent elongation reduction |
| Molecular Weight | ASTM D 3536 (GPC) | Distribution changes |
| Weight Loss | Direct measurement | Mass reduction |
⚙️ Test Procedure and Incubation Conditions
After inoculation, test and uninoculated control flasks are incubated with shaking for a specified period at a temperature optimal for the specific microorganism. A minimum of four replicates per condition is required. Residual plastic strips are washed in 70% ethanol for 30 minutes and dried. Significant differences between inoculated and control films are determined via analysis of variance (p < 0.05).
| 🟦 Sample Type | 📋 Description | ⚡ Function |
|---|---|---|
| Test Samples | Inoculated with microorganism | Measure biodegradation |
| Uninoculated Control | Disinfected, incubated without microbes | Account for abiotic changes |
| Zero Control | Starting material, no treatment | Baseline reference |
📊 Key Measured Properties and Significance
The test method assesses biodegradation through multiple metrics: weight loss, tensile strength loss, percent-elongation loss, and average-molecular-weight distribution changes. This comprehensive evaluation ensures reliable detection of degradation. The standard is significant for regulatory applications where degradable plastics in disposable products are required.
⚠️ Important: Contamination can invalidate results. After the 24-hour pre-incubation, check the medium for cloudiness and only inoculate if it remains clear.
💡 Tip: Use four or more replicates per condition to achieve statistically significant results, as recommended by the standard.
❓ Frequently Asked Questions
🔍 What is the uninoculated control used for?
The uninoculated control is chemically disinfected and incubated without microorganisms to account for abiotic degradation, ensuring that changes in test samples are due to microbial activity.
💡 How are plastic samples prepared for the test?
Samples are cut to lengths suitable for tensile testing per ASTM D 882 and sized for a 250-mL Erlenmeyer shake-flask. They are chemically disinfected, aseptically dried, and initial weights are recorded.
⚡ What measurements indicate biodegradation in this test?
Biodegradation is indicated by weight loss, loss in tensile strength, reduction in percent elongation, and changes in molecular-weight distribution compared to uninoculated controls.
📌 Why is temperature control important in incubation?
The incubation temperature must be appropriate for the specific microorganism used to ensure optimal activity and reliable biodegradation data.