Melt Characterization
Polymer analysis requires heavy machinery designed to force molten feedstock through a precision die at a controlled temperature. A capillary rheometer executes this extrusion by driving a piston down a heated barrel containing the plastic sample. Operators use a capillary rheometer to measure shear viscosity across high rates common during extrusion coating and high speed film blowing.
Extrusion laboratories rely upon the capillary rheometer to generate flow curves needed for predicting how polymer melts behave under extreme mechanical stress. Viscous resistance depends heavily upon molecular weight distribution and branching architecture within the resin matrix.
Pressure Drop
Force sensors register the pressure drop developed along the die length during extrusion. Pressure transducer calibration dictates data accuracy during long production runs involving specialty packaging resins. High molecular weight polymers generate massive friction against the capillary wall, forcing the piston motor to exert substantial force.
Die swell phenomena occur immediately after the extrudate leaves the orifice, creating dimensional deviations that affect subsequent film thickness uniformity. Pressure oscillations indicate melt fracture limits beyond which smooth output becomes impossible.
Shear Limit
Shear rate calculations define the operational boundary for specific converting machinery configurations. Excessive throughput speeds cause polymer chains to degrade thermally inside the heated barrel, ruining mechanical properties in the final converted web. Rheological data obtained from high pressure testing allows engineers to optimize processing temperatures without inducing melt fracture defects.
Molecular relaxation times dictate how fast extruded polymer chains recover normal conformation after exiting the narrow die geometry. Precise viscosity profiles prevent high speed coating failures on commercial paper laminators.
