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.
Crystalline Volume Fraction
Meaning
The structural composition of semi-crystalline polymers is characterized by the coexistence of highly ordered crystalline domains and disordered amorphous regions. The crystalline volume fraction represents the ratio of the volume of these crystalline regions to the total volume of the polymer specimen. This parameter governs the density, stiffness, and barrier properties of moulded components.
The applicability of this measurement is confined to materials capable of forming ordered lattices, excluding fully amorphous polymers like polystyrene.
Material Performance
Component stiffness and thermal resistance increase directly as the ordered phase grows within the polymer matrix. A high crystalline volume fraction provides excellent resistance to chemical solvents and mechanical creep under constant load. However, this high degree of order also reduces impact strength and increases post-moulding shrinkage.
Processing Factor
Slower cooling of the melt allows polymer chains more time to organize and fold into lamellar structures.
Measurement Practice
Differential scanning calorimetry determines this property by measuring the heat of fusion as the crystalline regions melt. A moulder can hold this value consistent across a production run by maintaining uniform cycle times and precise mould temperature control. Variations in this value often indicate inconsistent polymer resin quality or irregular cooling rates.