Determining Polyethylene Specific Gravity Thresholds for Tariff Entry
Polyethylene tariff entry requires density testing per ISO 1183-1 Method A on annealed plaques, where crossing 0.940 g/cm³ shifts classification from 3901.10 to 3901.20.
Sample Degassing
Meaning
Test preparation steps remove dissolved or trapped gases from a specimen to ensure the accuracy of subsequent measurements. The process of sample degassing is performed before density testing of polymers to eliminate micro-bubbles on the specimen’s surface. This process is essential for obtaining precise density values.
Degassing Mechanism
Vacuum chambers are used to draw out air from the specimen and the surrounding liquid. During sample degassing, the specimen is placed in a vacuum desiccator filled with a wetting solution. The vacuum reduces the pressure, causing trapped air bubbles to expand and detach from the polymer.
This step is critical for hydrophobic resins like polyethylene, which naturally attract air bubbles.
Specific Gravity
Density measurements are altered if the air bubbles are not completely removed. Without sample degassing, the measured specific gravity of the polymer will be lower than the true density. This error can lead to a resin batch being rejected because it appears to fall outside the specification limits.
Accurate degassing is therefore necessary to avoid false alarms in quality control.
Industrial Control
Molded part production relies on these accurate laboratory tests to maintain high quality. When a compounder runs a density test, sample degassing ensures that the test results are reliable and reproducible. This reliability allows the factory to monitor the compounding process and make adjustments when the density drifts.
By preventing measurement errors, the compounder can maintain a consistent product and reduce waste.