Meaning
Fraction of a polymer distribution consisting of exceptionally long molecular chains influences the melt strength and elasticity. The high mass tail occupies the far right of the molecular weight distribution curve and usually represents only a few percent of the total material. Despite its small volume, this fraction dominates the slow relaxation processes and the non-linear rheology of the melt.
Rheological Impact
Viscosity at very low shear rates is determined almost entirely by the longest chains in the resin. The high mass tail increases the zero-shear viscosity and the elasticity of the melt, making it more resistant to sag.
Processing Challenge
Melt fracture and surface roughness often occur when the longest chains cannot relax quickly enough as they exit the die. While the high mass tail is beneficial for blow molding, it can limit the maximum line speed in high-speed film extrusion. This fraction can also lead to increased pressure in the extruder barrel, requiring more energy to maintain the flow rate.
Material Sourcing
Resin buyers specify the presence of these long chains to ensure that the material can handle demanding forming steps. Because the high mass tail is sensitive to catalyst conditions and reactor fouling, its consistency is a major indicator of supplier quality. Batches that lack this fraction may process easily but fail to meet the mechanical requirements of the finished part.
