Acidic Extraction
Acid treatment provides an effective method for removing mineral salts and metallic deposits from retted flax yarns prior to bleaching. Wet treatment mills use demineralization to dissolve calcium carbonate and iron compounds that accumulate during the retting and washing cycles. This prevention of salt accumulation is necessary to maintain the activity of enzymes used in subsequent bio-polishing steps.
Failure to extract these minerals results in harsh yarn texture and uneven bleach distribution.
Fibre Cleaning
Boiling flax yarn in dilute organic acids under pressure decomposes insoluble salts into soluble compounds. The demineralization process breaks down the mineral-rich ash content of raw flax by replacing bound metal ions with hydrogen ions. This reaction leaves the cellulose structure clean and ready for peroxide treatment.
Process Control
The washing temperature must remain below the degradation point of flax cellulose to avoid strength loss. Acidic treatments carried out at elevated temperatures can hydrolyze the glucosidic bonds in flax, reducing the yarn’s tensile strength and increase the fraction of short fibres. Operatives must maintain the pH of the demineralization bath between two and three to balance mineral removal against fibre preservation.
Consistent monitoring ensures that the yarn retains its natural lustre after the process.
