Establishing Rheological Dispersity Limits to Prevent Strain Hardening Failure in Regrind Blends
Establishing Trouton ratio floors via capillary extensional rheology prevents catastrophic web tear and parison sag in regrind polyolefin blends.
Rheotens Melt Strength
Meaning
Polymer elasticity during extensional flow defines the rheotens melt strength. This metric captures the force required to stretch a molten polymer filament until fracture occurs under controlled conditions. Higher values indicate a material that maintains structural integrity when drawn, which prevents sagging in blow moulding or film drawing processes.
Processing Resistance
Extrusion lines rely on high polymer cohesion to maintain parison shape before the mould closes. If the force drops below a specific threshold, the molten plastic stretches unevenly and creates thin spots on the finished part wall. Moulders check this property to confirm that virgin resin batches perform consistently during production cycles.
Lower resistance forces often signal degradation in regrind material that reduces the quality of the final output.
Material Geometry
Molecular weight distribution and long chain branching exert control over the filament stability throughout the drawing operation. Straight chain polymers usually snap earlier than branched versions because they lack the entangled network needed to withstand high tension. Researchers measure this behaviour by pulling the strand at a constant acceleration while recording the peak load before rupture.
The resulting curve plots the relationship between drawing speed and tension to reveal how the material responds to sudden shifts in stress.
Operational Utility
Tooling engineers adjust the die gap and draw down ratio to compensate for low material tension during high speed extrusion. A stable melt allows for faster line speeds without risking catastrophic breakage of the continuous product. Deviations from target ranges usually correlate with fluctuations in resin temperature or excessive contamination in the feed.
Accurate measurement confirms the capability of a polymer to sustain its shape under the weight of its own mass.