Density Testing Protocols under ISO 1183 for Customs Classification
ISO 1183 density testing determines customs tariff lines under Chapter 39; accurate classification demands exact fluid temperature control and plaque molding.
Immersion Fluid
Meaning
A liquid medium provides the buoyancy needed to measure the volume and density of a polymer specimen through displacement. Selecting the correct immersion fluid ensures that the liquid does not react with the plastic or cause it to swell during the test. Distilled water is the most common choice, though alcohols are used for materials that are less dense than water.
Surface Wetting
The ability of the liquid to cover the entire sample without trapping air is a primary requirement. An immersion fluid with high surface tension might leave small bubbles on the specimen, leading to an inaccurate volume measurement. Surfactants are frequently added to water to improve wetting and ensure the precision of the density data.
Liquid Selection
The choice of medium depends on the expected density of the resin being tested. If the immersion fluid is more dense than the polymer, the sample will float, making it impossible to weigh while submerged without a sinker. Choosing ethanol or an oil with a lower density allows the technician to submerge lightweight foams and polyolefins effectively.
Temperature Sensitivity
The density of the liquid changes as the laboratory environment warms or cools. Every immersion fluid must have its temperature recorded during the test so that a correction factor can be applied to the final calculation. High precision density measurements are only possible when the properties of the liquid are known to four decimal places.
Monitoring the purity of the fluid is also necessary to prevent contaminants from altering the buoyancy of the bath.