Rheological Character
Shear-thinning fluid behavior wherein apparent viscosity drops as the shear rate increases governs the movement of polymer solutions used throughout wet flax processing. This non-Newtonian flow characterizes dissolved flax pectins, warp yarn sizing formulations, and concentrated finishing emulsions. The classification applies strictly to fluids whose shear stress to shear rate ratio deviates from a constant value across varying shear regimes.
The scope ceases when shear-independent Newtonian behavior takes over at low solids concentrations or when shear rates approach infinite-shear limiting viscosity plateaus.
Flow Mechanics
Pectin dissolution products that enter the wet spinning bath impart pseudoplastic shear-thinning properties to the circulating water. At the high shear conditions present inside drafting roller nips, non-Newtonian flow ensures that the lubricating fluid film maintains low resistance to bundle attenuation. In stagnant corners of the spinning trough where low shear rates prevail, fluid viscosity rises, hindering natural particulate settling and encouraging scum accumulation.
In the weaving preparatory section, modified starch and polyvinyl alcohol size mixtures display identical pseudoplasticity. Under high roller pressure inside the size box nip, size viscosity drops sharply to saturate the internal bundle, whereas low shear outside the nip causes rapid thickening that holds the protective coating on the yarn surface. Mill technical staff measure fluid behavior at three shear rates on laboratory viscometers, calculating the flow behavior index recorded on size preparation logs.
Process Bounds
Divergence from standard shear-thinning curves disrupts sizing pick-up rates, generating uneven yarn friction that triggers warp breakage on high-speed air-jet looms. Sizing chemical suppliers must furnish rheological flow profiles to verify paste viscosity stability over eight-hour production shifts. Non-Newtonian flow profiles govern fluid transport inside drafting roll contact points.
