Coating Rupture
Displacement or tearing of the protective layer on a yarn occurs when the mechanical force of the loom exceeds the bond strength of the size. Sizing film shear exposes the underlying flax fibres to direct friction from the reed and the healds. Once this shield is broken, the yarn quickly loses its resistance to fraying and breaking.
Abrasive Resistance
Testing the ability of the size to remain intact under sliding pressure helps in selecting the right binder for linen. If sizing film shear occurs too easily, the loom will experience frequent stops and the fabric will show signs of surface fuzziness. The toughness of the film is determined by the ratio of starch to synthetic polymers in the size mix.
Laboratory tests use weighted rollers to slide against the sized yarn to simulate the action of the weaving reed. A failure of the film is noted when the first flax filament becomes visible through the coating.
Fibre Protection
Maintaining a continuous coating is essential for the high-speed weaving of coarse natural fibres. Preventing sizing film shear ensures that the yarn remains smooth and compact as it moves through the weaving shed. This stability is the primary goal of the yarn preparation department.
