PCC 302 - Exam 1 Study Guide

What is Textile Wet Processing?

Wet Processing transforms greige fabric to a fabric that is ready for cutting and sewing.

Goals of Textile Wet Processing

Preparation (remove impurities, prepare yarns), Coloration (improve appearance & functionality), and Finishing (Alter appearance)

Sizing (Slashing)

Applied to warp yarns prior to weaving to protect them.

Purpose of Sizing

To reduce friction and improve weaving efficiency, protect yarn from damage at high speeds

Goals of Sizing

Increases yarn abrasion resistance and strength, controls yarn hairiness, maintains yarn flexibility and elongation

Starch as a Warp Size

Cheap and widely available, long cooking times, hard to remove.

Structure of Cellulose

Cellulose contains β-1,4 linkages, Amylase breaks down the α-1,4 linkages found in starch

Methods to desizing starch

Enzyme (a-amylase) , Acid (Uses H3O+), and Oxidative (hydrogen peroxide)

Desizing Starch with Amylase

Main process for desizing starch

PVA as a Warp Size

removable using water, recyclable, more expensive, higher cost

CMC as a Warp Size

Solution can be made to room temp, No cooking step, More expensive than starch

Singeing

A process where loose fiber and fuzz are removed from the surface of fabric to give a smooth appearance (fabric with staple fibers)

Singeing Process

row of gas burners arranged for material passing through an open flame

Singeing Precautions

Fabrics like PET can form hard melt balls, passed into quench bath of desizing chemicals to douse fuzz balls that may have been ignited

What is Bleaching

Process used to remove colored impurities from fibers, yarns, fabrics, or garments (batch or continuous)

Bleaching

Colored impurities are converted into colorless, involving destruction of the chromophore

Steps for bleaching

1) Application

2) Reaction (during swelling)

3) Washing

Types of bleaching agents

Oxidative: hydrogen peroxide, Sodium hypochlorite and Reductive: Sodium chlorite, sodium hydrosulfite

Hydrogen Peroxide (H2O2)

Must be activated before it can perform a bleaching action, needs sodium hydroxide, stabilizer, and sequestrate/chelating agent

Adv and Disadvantage of H2O2 Bleaching

Adv: suitable for continuous process, widely used, does not yellow wool, safe for colors. Disadvantage: degrades cotton, skin irritant, explosive if heated to dryness

Sodium Hypochlorite Bleaching

Oxidative bleaching agent, it is alkaline in solution, used in low temperatures in batch process. Needs sodium carbonate, and Antichlor agent to destroy excess hypochlorite

Adv and Disadvantahes for Hypochlorite Bleaching

Adv: cheap, powerful Disadvantages: Degrades cotton, skin irritant, not for continuous, corrosive, yellows wool, can release hazardous gas

Hydrosulfite bleaching

reductive bleaching agent, also called hydro, not used as much (leaves harsh touch), reduction clear

Bleaching wool and silk

with Sodium peroxide under controlled conditions to prevent alkali damage

Scour/Bleach combination

Often combined into one step, especially for cotton knits

Sequestering Agents (chelating)

Solubilize the metal ions and prevent interaction with other chemical species, used to soften water, acids, EDTA or TSPP

Optical Brightening Agents

OBA, used to obtain white without overbleaching/damaging goods, used on natural/synthetic fibers, NOT substitute for bleaching

Scouring

Process to remove hydrophobic impurities such as waxes, fats, solids, and dirt. Surface goes from phobic to philic, can be batch or continuous.

Reasons for Scouring

Increase absorbency, improve uniformity of dyeing, improve appearance (remove motes)

Components of Scouring

Sodium Hydroxide - swell motes, dissolve pectins, degrades proteins, saponify waxes/oils

Surfactant - emulsify non-saponifiable waxes/oils, reduce surface tension of water

Chelating Agent - form water dispersible complexes with metal ions

Saponification

Chemical process that converts insoluble fatty esters to soluble alcohols, requires hot alkaline conditions, high pH

Emulsification

Physical process that disperses water-insoluble waxes and oils in water, process of mixing liquids to create a semi-stable mixture

Surfactants

Molecules with both phobic (tail) and philic (head) characteristics, surface active agents

Formation of Micelles

When a high enough concentration of surfactant, micelles will form CMC (critical micelle concentration)

Dispersing Agents

Compound added to a suspension of solid or liquid particles to improve separation of particles and to prevent setting/clumping

Cloud Point of Nonionic Sufactants

three types of surfactants: cationic, anionic, nonionic

ionic: charge of philic head allows to interact with water

nonionic: interact with water through hydrogen bonds

Cloud point = temp at with 1% solution of nonionic surfactant becomes insoluble

Mercerization

application of sodium hydroxide to cellulose fibers to improve luster, water absorbance, dye yield, and fiber strength

Mercerization Process

cotton swells during treatment (kidney to round)

Effects of Mercerization Swelling

1) Lumen disappears

2) Fiber starts to untwist

3) Fiber becomes round, smooth, and uniform

4) Fiber becomes more amorphous rather than crystalline

5) reflects light easily

Advantages of Mercerizing cotton

Improved strength, appearance, color yield, absorbance, fabric smoothness, and luster (under tension)

Tension and Cotton Shrinkage

Without tension, cotton shrinks during mercerization, becomes denser.

Tenter Frame

Stenter (tenter) makes sure fabric maintains final dimensions throughout process.

Carbonization

Application of acid treatment to remove vegetable matter and cellulose impurities from wool, impurities are degraded from sulfuric acid, wool isn’t.

Heat setting

Application of heat treatment to fabrics containing thermoplastic synthetic fibers to stabilize. (Nylon and Polyester)

Performance of Heat Setting

Performed above the glass transition temperature of the polymer but below the melting temperature to reset fibers structural memory

Heat Setting After Scouring

Adv: Color uniformity is enhanced Disadvantage: creases/wrinkles are permanent, dye yield decreased

Heat Setting After Dyeing

Adv: One less process needed, Higher die yield Disadvantage: Dye used must be stable to high temperatures

Heat Setting Process

Involves passing fabric through heating zone for time + temp that resets fiber’s structural memory

Heat Setting Disadvantages

Reduces PET’s dye up take, heat must be controlled and uniform, fabric may become flatter and develop unwanted gloss, hand may be stiff