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.
ISO 1183-2
Meaning
Density gradient column testing standardizes the measurement of non-cellular plastic mass per unit volume using liquid columns of varying density. Applying iso 1183-2 permits laboratory technicians to determine resin density with exceptional precision down to four decimal places. Polymer crystallinity directly correlates with measured density, allowing quality teams to evaluate specimen cooling rates and annealing states.
Datasheet density values established via this standard assist raw material incoming inspection and compound verification. Variations in regrind content cause measurable density shifts that signal contamination or thermal degradation.
Test Procedure
Glass columns filled with two miscible liquids create a continuous, calibrated vertical density gradient at controlled ambient temperature. Conducting tests according to iso 1183-2 involves dropping small, bubble-free plastic specimens into the column and recording their equilibrium floating position. Glass float standards calibrated by national metrology institutes establish the column height-to-density curve.
Temperature fluctuations inside the gradient column distort density readings, requiring strict thermal bath regulation within hundredths of a degree.
Crystallinity Determination
Semi-crystalline polymers exhibit density changes proportional to their crystalline fraction. Measuring specimen density under iso 1183-2 enables precise calculation of relative crystallinity in moulded parts. Higher crystallinity increases tensile strength and chemical resistance while reducing impact toughness.
Mold cooling rate variations produce localized density gradients across thick part cross-sections.
Quality Control
Incoming resin verification prevents off-spec polymer lots from entering processing extruders or injection presses. Utilizing iso 1183-2 ensures regulatory compliance when verifying density specifications for medical and packaging compounds. Discrepancies between virgin resin datasheets and lot samples indicate filler settlement or incorrect monomer stoichiometry.
Consistent density monitoring guarantees stable part weight and uniform volumetric shrinkage across moulding runs.
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.