Pseudoplasticity

Shear Rate Response

Polymer chains align rapidly along the flow direction when subjected to high velocity gradients inside injection barrels and runner channels. Molecular orientation drops the apparent viscosity significantly below the static zero shear baseline established in capillary rheometer tests. Screw rotational speed and injection velocity dictate the magnitude of this structural alignment during the plastication phase.

Operators adjust barrel temperature profiles to complement this mechanical thinning effect without inducing thermal degradation in sensitive engineering resins.

Processing Limits

Datasheet values measured under standard laboratory conditions rarely match the actual rheological behaviour observed inside commercial production tooling. Moulders face severe flash or short shots when lot to lot molecular weight distribution shifts alter the melt flow index unexpectedly. Virgin polymer exhibits predictable shear thinning curves while regrind material often shows reduced pseudoplasticity due to thermal history damage accumulated during previous reprocessing cycles.

Adjusting injection pressure profiles compensates for minor viscosity variations but cannot fully restore the molecular chain integrity lost from excessive shear heating.

Part Quality

Molecular orientation frozen during rapid cooling determines the final mechanical strength and dimensional stability of moulded components. Excessive shear rates near gate locations induce high residual stresses that trigger warping or premature structural failure under load. Wall thickness uniformity depends heavily on how evenly the resin maintains its reduced viscosity throughout the cavity filling stage.

Controlling melt temperature and injection speed prevents localized jetting defects from compromising the structural integrity of finished plastic parts.