2100 3A-Prep - Chapter 3, Part I: Wet Preparation for...

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Unformatted text preview: Chapter 3, Part I: Wet Preparation for Dyeing and Finishing TXMI 2100 Outline Desizing Scouring Beaching Mercering Optical Brightener (1) Desizing Sizing agents applied to warp yarn before weaving to improve abrasion resistance Sizing agents must be remove before dyeing/finishing to improve absorbency Modified starch: sizing agents for cotton Synthetic polymers: sizing agents for cotton and synthetic fibers Desizing Starch: hot water + enzyme Synthetic sizing agents: alkaline wash (2) Scouring: A Cleaning Procedure Removing hydrophobic cuticle and impurities from cotton and cotton blend Cotton scouring: high concentration NaOH solution Removing lubricants (spinning finishes) from synthetic fibers Synthetic fibers scouring: detergent washing Scouring Using A Detergent (3) Bleaching Process Bleaching removes any color from nature fibers and improves fabric whiteness Cotton bleaching follows desizing and scouring and before dyeing/printing Oxidative bleaches for cotton: chlorine-based bleach and hydrogen peroxide (pH 10.5) Wool bleaching: hydrogen peroxide only Reductive bleaches: less effective Any residual bleaches needs be washed after the process. Bleaches for Consumers Chlorine-based bleach (sodium hypochlorite) Hydrogen peroxide ("Clorox2") Reductive bleaches: less effective (4) Mercerization Process A optional process for cotton only Changing cotton crystal structure Changing cotton's cross-section to a fully rounded shape Changing cotton physical properties Method of Mercerization Immersion of fabric under tension in a strong NaOH solution at 15 25 C for a short time (<4 min) Rinsing to remove NaOH Residual NaOH neutralized Applied to cotton yarns or cotton fabric or both (double mercerization) Effects of Mercerization on Cotton Fabric Properties Increasing strength (up to 20%) Increasing absorbency/swellability Increasing cotton reactivity Increasing luster Mercerization Increases Y arn luster Textile Processing Sequence Weaving Desizing Scouring Bleaching Merceriztion (optional) Final Fabric Products Dying/Finishing (5) Optical Brighteners Applied to fabrics of natural as well as manemade fibers Organic compounds absorbing UV and emitting visible (blue) light Increasing whiteness for bleached fabrics Increasing brightness of dyed fabrics Reducing UV radiation penetrating to human body Not a bleaching agent ...
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