Analytical Rheology and Thermal Methods for Polymer Lot Acceptance
High shear capillary rheology and thermal analysis prevent polymer lot failures that low shear melt index testing and supplier certificates miss entirely.
Zero Shear Viscosity
Meaning
Polymer melt properties define the flow resistance of a thermoplastic material when the shearing forces acting upon it approach zero. This parameter is highly sensitive to the molecular weight and molecular weight distribution of the polymer chains. Measuring zero shear viscosity enables processors to evaluate the starting structure and melt strength of a resin before it undergoes high-shear moulding.
This property applies to polymer melts and dense solutions but does not describe the flow behavior of low-viscosity fluids.
Molecular Information
Chain length and polymer entanglement dictate the resistance to flow under minimal deformation. High values of this metric indicate longer polymer chains and a higher average molecular weight. Quality control laboratories in China use rotational rheometers to measure this property during incoming resin inspections.
This metric provides a reliable way to detect molecular degradation and resin blending before processing begins.
Processing Application
Flow behavior during processes like blow moulding or film extrusion depends heavily on the polymer melt strength at low shear. High zero shear viscosity prevents the parison from sagging or the film bubble from collapsing during the cooling phase. Technical supervisors select resins with high low-shear viscosity to maintain wall-thickness uniformity in blow-molded bottles.
This choice reduces defect rates and increases production efficiency.
Quality Verification
Rheological measurements provide a precise fingerprint of the molecular structure of the raw material. This testing confirms that the polymer has not suffered degradation during compounding or storage before being fed into the molding machine.