Verifying Polyethylene Hydrostatic Balance Test Calibration for Entry
Polyethylene hydrostatic testing requires degassed, temperature-corrected fluid baths and void-free plaques to prevent false 0.002 g/cm³ receiving rejections.
Immersion Fluid Density
Meaning
Hydrostatic weighing methods for determining the density of solid polymer samples rely on the displacement of a liquid of known mass per unit volume. The immersion fluid density is the specific mass-to-volume ratio of the test liquid, usually deionized water or silicon oil, at the precise temperature of the measurement. This value governs the buoyancy calculation from which the polymer’s density is derived.
The applicability of this parameter is restricted to the duration of the weighing run, during which the fluid must remain stable and uncontaminated.
Temperature Sensitivity
Liquids expand and contract with changing thermal conditions, which alters their volumetric mass. A minor fluctuation in the testing room temperature will shift the immersion fluid density, which can distort the calculated density of the polymer sample. High-precision laboratories use recirculating water baths to lock the fluid temperature to within a fraction of a degree.
Calibration Metric
Measuring the fluid density before and after the sample runs ensures data integrity.
Experimental Precision
Small errors in this baseline value propagate directly into incorrect calculations of the polymer’s crystalline volume fraction. This issue is particularly critical when distinguishing between high-density and linear low-density polyethylene grades, where the density difference is minute but determines the physical properties of the moulded part. Accurate documentation of this density is therefore a necessity for quality assurance.