Material Property
The flow resistance of a fluid when it is at rest or subjected to extremely low shear forces characterizes its structural stability. In textile chemical formulation, zero-shear viscosity determines how well the pad bath resists dripping or flowing when the fabric is stationary or under very low tension. This property is crucial for maintaining a uniform distribution of chemicals before the drying process begins.
System Mechanism
When a thickened pad liquor is applied to the fabric, it undergoes high shear in the pad mangle nip, which lowers its viscosity to allow deep penetration. As the fabric leaves the nip and the mechanical force drops to zero, the liquid must quickly recover its viscosity. A high zero-shear viscosity creates a dense, structured network that prevents the liquid from running or pooling on the fabric surface.
This rapid recovery of viscosity stops the capillary movement of dye particles before the fabric enters the drying zone.
Operational Control
Technicians measure this parameter on a rotational rheometer by applying very low shear rates and plotting the viscosity plateau. To increase the zero-shear viscosity, formulators add high-molecular-weight polymers that form strong physical networks in the bath. Operators monitor the temperature of the storage tanks because rising temperatures can break these networks and reduce the viscosity.
Regular chemical analysis ensures that other bath additives do not disrupt the polymer structure.
Process Constraint
A high viscosity at rest can make the chemical mixture difficult to stir or pump from the preparation tanks to the pad trough. This constraint requires the use of specialized pumps that can handle highly structured fluids.
