High Load Melt Index

Viscous Behavior

High molecular weight polymers exhibit severe shear thinning under the high shear rates encountered during processing. While standard tests would show almost zero flow, the high load melt index provides a measurable value that correlates with shear thinning behavior in the extruder. This measurement helps the processor select the right temperature profile to prevent melt fracture in the extruded product.

Molecular Structure

Long polymer chains and broad molecular weight distributions increase melt strength while reducing standard melt flow rates. Measuring the high load melt index alongside the standard index reveals the shear sensitivity of the polymer. This ratio is used by resin manufacturers to control the polymerization process and ensure consistency in high density polyethylene grades.

Extrusion Processing

Extruders processing high molecular weight resins require high motor torque. An incorrect high load melt index can overload the drive system or cause severe wall thickness variations. Virgin resin batches must match these limits.