Chemical Transition
Starch paste transformations affect the performance of weaving sizes by altering the solubility and flexibility of the protective film over time. Retrogradation involves the recrystallization of amylose molecules as the sizing mixture cools, causing the gel to become rigid and expel water. This transition occurs within the size box of the warp treatment machine, reducing the adhesion of the starch to the flax yarn.
In linen weaving mills, this phenomenon is managed by keeping the sizing mix at an elevated temperature.
Molecular Alignment
Understanding the behaviour of amylose during cooling is critical for maintaining consistent sizing quality. As the cooked starch paste cools below its gelation point, the dispersed polymer chains begin to align and form hydrogen bonds, transitioning from a disordered state to a crystalline structure. This realignment decreases the water-holding capacity of the gel and causes it to separate into a polymer-rich phase and a water-rich phase.
If this occurs in the size storage tank, the paste becomes lumpy and fails to coat the warp yarns evenly. To prevent this separation, sizing recipes often incorporate modified starches or synthetic binders like polyvinyl alcohol. These additives disrupt the alignment of the amylose chains, maintaining a stable viscosity during long production runs.
Sizing Consistency
Preventing the formation of insoluble starch aggregates ensures that the sizing film remains flexible on the yarn surface. When starch reverts to its crystalline state, the resulting film becomes brittle, causing it to flake off the warp during weaving. This loss of protective coating exposes the flax fibres to intense friction, leading to high yarn breakage rates.
