Meaning
Fluid deformation properties dictate that the viscosity of a polymer melt decreases as the rate of flow or shear rises. This shear-thinning behavior is a critical property of thermoplastic resins that enables them to be injected into complex moulds at reasonable pressures. The mechanism relies on the disentanglement of polymer chains under the influence of high shear forces.
Flow Behavior
At rest, polymer chains are random coils. When a force is applied, these coils untangle and align with the direction of flow, reducing their resistance.
Processing Utility
Molders exploit this behavior by using high injection speeds to fill thin-walled sections of a cavity. The high speed generates a high shear rate, which drops the melt viscosity and lets the plastic flow further. This behavior reduces the required clamping force and injection pressure, saving energy and allowing the use of smaller machines.
Material Selection
Different polymers exhibit varying degrees of this thinning effect, which influences their suitability for specific moulding applications. Sourcing managers check this property on material datasheets to select resins that can fill difficult cavities without flashing. Resins with strong shear-thinning behavior are preferred for complex, thin-walled electronics enclosures.
By selecting the correct grade, companies minimize the need for mold modifications and reduce the setup times for new production lines.
