Sizing Agent Selection for Fine Spun Bast Yarns
Optimal fine bast yarn sizing requires balancing PVA and CMC polymers to achieve eleven percent dry add-on without causing warp brittleness.
Shear Thinning Rheology
Fluid Flow Characteristic
Non-Newtonian flow properties where a fluid’s viscosity decreases as the rate of shear stress increases optimize the application of sizing agents. Utilizing size mixes with shear thinning rheology allows for easy pumping and uniform distribution of the sizing liquid on yarn sheets. This behavior ensures that the liquid flows readily under mechanical agitation but thickens once the agitation stops.
Sizing Application
High shear forces encountered in the squeeze rollers of the sizing machine reduce the viscosity of the liquor, allowing deep penetration into the yarn core. During this fast passage, the shear thinning rheology ensures that the polymer or starch flows smoothly between the individual flax fibres. Once the yarn exits the nip zone, the shear rate drops, and the viscosity quickly rises again, keeping the sizing agent on the surface to form a protective jacket.
This rapid transition prevented the sizing from migrating or dripping off the yarn before drying. Controlling this fluid property is essential for maintaining uniform pick-up across the entire width of the yarn sheet.
Coating Benefit
Uniform film distribution prevents the occurrence of patchy spots and weak areas along the warp yarn. Exploiting shear thinning rheology results in a smooth, non-sticky coating that enhances the yarn’s glide through loom components. This reduces mechanical friction and lowers the rate of yarn breakages.