Meaning
A rheological parameter comparing melt flow resistance between continuous and dispersed polymer phases dictates morphological domain size during composite blending operations. Calculating viscosity ratio involves dividing the dynamic viscosity of a dispersed additive or regrind polymer by that of the host virgin matrix under matching shear and thermal conditions. Compounding engineers target numerical values near unity to maximize phase breakup and achieve uniform distribution across the melt stream.
Morphological Control
Values deviating significantly from one create large dispersed droplets that weaken mechanical interfaces. High matrix viscosity elongates minor phase domains into thin threads before breakup occurs.
Processing Dynamics
Shear rate dependence in non-Newtonian polymer melts causes dynamic changes in phase viscosity across extruder die geometry. Adjusting barrel temperature profiles modifies the local viscosity ratio, controlling domain size in immiscible polymer blends. Precise viscosity matching reduces interfacial tension, improving impact strength in toughened engineering thermoplastics.
Scrap Incorporation
Thermal degradation lowers the molecular weight of recycled polymer streams, creating rheological mismatches when blended into virgin resin. Unmatched viscosity ratio values during extrusion cause melt instability, phase separation and surface roughness on extruded profiles. Processing plants monitor lot-to-lot melt flow variations to adjust blending ratios and maintain consistent product dimensions.
