Elongation Threshold
Deforming under mechanical tension without fracturing protects sizing materials on warp yarns from premature degradation during high-speed loom operation. The measurement known as film rupture strain quantifies the exact percentage extension at which a dried size film fractures under axial loading. High-grade flax yarns require formulation coatings that match or exceed warp tensile extension during shed opening.
Laboratory tensile testers measure this parameter on cast size films prior to slasher sizing trials.
Size Coating
Formulations combining modified starches and synthetic binders establish protective films over hairy flax spun yarns. When slasher speed or drying temperature varies, film rupture strain changes significantly due to residual moisture content and polymer retrogradation inside the sizing bath. Higher plasticizer ratios increase maximum elongation, protecting fine linen warp threads against shed opening stress.
A low failure elongation leads to shed foul and loom stoppages during high-density weaving. Mill laboratories adjust chemical additives until test specimens achieve the required strain value for targeted yarn counts.
Tension Boundary
Tensile stress on warp yarns during weaving must never exceed the strain limit of the protective film. If operational warp elongation exceeds the film rupture strain, microscopic cracks form along the sizing shell, exposing raw flax fibers to abrasive reed contact. Breakage rates rise immediately upon film failure.
