PCC 302 Test One

 

 

 

Describe the 3 main stages of wet processing of textiles. 

 

Preparation

Coloration

Finishing

 

 

 

Describe the primary goals of wet processing. 

 

Preparation

Dyeing

Finishing

 

 

 

Describe what batch processes and continuous processes are. 

 

Batch= entire batch of dry fabric contacts the entire amount of the solution

 

Continuous= Process where the dry fabric only contacts a portion of the solution

 

 

 

Describe the objective of slashing, which yarns are treated, and list three main properties of a well sized yarn. 

 

To improve the weaving efficiency of the yarn by making the yarn stronger.

 

Warp yarns are treated

 

Higher tensile strength, Lower Elongation, Higher abrasion resistance, more rigid, less flexible

 

 

 

 

 

Recognize a diagram of a slashing machine. 

 

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Describe at least three requirements of a good warp size. 

 

Inexpensive, Recyclable, Water Soluble, good adhesion, form strong, flexible, and abrasion resistant films

 

 

 

Draw the structure of amylose, a component of starch. 

 

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Recognize amylopectin and describe the different properties between amylose and amylopectin. 

 

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INSOLUBLE IN WATER

 

 

 

Compare the differences in structure between amylose and cellulose. 

 

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The second half is flipped in Cellulose (shown is carboxymethylcellulose, which just has some added stuff to the cellulose)

 

 

 

 

Recognize the repeat unit for PVA, and describe it’s properties. 

 

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Water SOLUBLE

More expensive than starch

Recyclable

 

 

 

Describe what BOD is, and why it is important in textile wet processing. 

 

BIOLOGICAL OXYGEN DEMAND

For a given material, the amount of oxygen that will be consumed by biological processes

 

It is important because too much BOD can cause pollution

 

 

 

Describe what chemicals can be used to remove starch size. 

 

*Alpha Amylase enzyme, mineral acids, or oxidizing agents

 

 

 

Sketch a desizing range, and explain how a J box works. 

 

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THE J-BOX provides a dwelling time for the reaction to take place

 

 

 

Describe how PVA can be removed from warp yarns and how it can be recycled. 

 

It can be dissolved using hot water

It has a low BOD and therefore can be recycled

-by- using ultrafiltration

 

 

 

Describe how ultrafiltration works. 

 

[image]

 

 

 

Describe the purpose of scouring. 

 

Process to remove impurities from fibers, yarns, fabrics, or garments

 

 

 

List at least three impurities in cotton that should be removed during scouring. 

 

Cellulose

Proteins and Pectins

Minerals

Waxes

 

 

 

Describe the three main chemicals used in a scouring bath and explain why they are used. 

 

NaOH (Caustic Soda) — Swell Motes(seed coat fragments), dissolve pectins and degrade proteins

 

Surfactant — Reduces surface tension, disperse insoluble particles

 

Chelate — form water-soluble complexes with metal ions

 

 

 

Define saponification and emulsification. 

 

Chemical process that converts insoluble fatty esters to soluble alcohols and fatty acid salts

 

Physical process that disperses water insoluble waxes and oils in water

 

 

 

Explain in detail, and with the aid of diagrams, what a surfactant is and how it can form a micelle 

 

molecules with both hydrophobic and hydrophilic characteristics

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Draw the structure of sodium lauryl sulfate. 

 

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Define what a chelate does. 

 

solubilize the metal ions and prevent interactions with other chemical species

 

 

 

List at least three impurities present in wool, and explain why NaOH cannot be used to scour this fiber. 

 

Keratin, Dirt, Grease

NaOH will destroy wool

 

 

 

Explain why synthetic fibers should be scoured. 

 

Removes processing oils and waxes, residual warp sizes

 

 

 

 

Explain, with the aid of sketches, the concept of cloud point of solutions of non-ionic surfactants 

 

The temperature at which a 1% solution of a nonionicsurfactant becomes insoluble

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Explain why bleaching is sometimes performed on natural fibers. 

 

because it remove natural color bodies from fibers, yarns, fabrics, or garments

 

 

 

Draw the structure of hydrogen peroxide. 

 

 

H2O2

lines divided underneath

 

 

 

 

List the three main components of a peroxide bleach bath. 

 

Sodium Hydroxide (activates peroxide)

Hydrogen Peroxide (bleaching agent)

Stabilizer (controls rate of bleaching reaction)

 

 

 

Why are FBAs applied to cotton? Why are they NOT applied to wool or silk? 

 

Increase whiteness in cotton by emitting in the blue range to offset the yellow

 

They will damage wool and silk through uv absorption

 

 

 

Using sketches of absorption in the UV and emission in the visible spectrum, explain how an FBA works. 

 

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Using labels, sketch a reflectance curve for greige cotton, bleached cotton and bleached cotton treated with FBA. 

 

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State what chemical is used in mercerization and why the process is performed. 

 

Treatment of cotton, or cotton blends, with a high concentration of NaOH prior to dyeing

 

  • Improved color yield in cotton
  • Improved appearance after dyeing
  • Improved strength
  • Improved luster
  • Increased absorbency

 

 

 

 

Sketch the cross-sectional appearance of mercerized and non mercerized cotton 

 

non-mercerized

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mercerized

Large circles, like theyre swollen

 

 

 

Explain how mercerization works (i.e. via breaking and reforming H-bonding….) 

 

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The bottom part is then taken out (the OHs)

 

 

 

Recognize a mercerizing range. 

 

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Using a sketch define nanometer (nm) 

 

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Define the wavelength ranges of UV, visible and infra-red light, and explain the relationship of energy and wavelength. 

 

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Define the terms colorant, dye and pigment. 

 

Colorant — any material imparting color to another material

Dye — soluble in the medium in which it is applied

Pigment — insoluble, particulate: fixed by a binder, or mechanically entrapped in the fiber

 

 

 

List at least five factors that are considered when designing dyes for textiles 

 

HUE

COLOR STRENGTH

LIGHT FASTNESS

WASH FASTNESS

TOXICITY

COST: inexpensive starting materials, inexpensive synthesis 

 

 

 

Using sketches and formaldehyde as an example explain how light is absorbed at 185 nm (UV region) 

 

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Using chemical structures as examples, explain how we get organic molecules to absorb light in the visible region (hint: Increasing the number of alternating single and double bonds) 

 

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Give two examples of electron donating groups 

 

NH2 (amino)

N(CH3)  (dimethylamino)

OH (hydroxy)

 

 

 

Give two examples of electron withdrawing groups 

 

NO2 (nitro)

CN (cyano)

 

 

 

Define the term: auxochromes and give a structural example of electron donating auxochromes. 

 

Auxochromes (color intensifier)

 

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Recognize the structure of a direct dye 

 

[image]

 

 

 

 

Explain what fiber can be dyed with direct dyes 

 

Cotton, because the direct dyes form hydrogen bonds with the cellulose polymer

 

With the aid of a sketch explain how direct dyes are attracted to cotton
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With the aid of a sketch, explain how direct dyes are attracted to cotton 

 

[image]

 

 

 

Provide at least two advantages AND disadvantages to direct dyes 

 

Economical process

Easy to apply

wide range of shades available

 

poor chlorine fastness

limited brightness

must be aftertreated with fixatives to achieve acceptable wetfastness properties

 

 

 

Describe a typical dyeing procedure for direct dyes on cotton. 

 

Load well prepared fabric into dyeing machine; fill to proper running level

 

Add wetting agent and diluted dye at room temperature

 

Heat to dyeing temperature: hold 20 minutes

 

add salt in three increments over 45 minutes, run additional 10 minutes

 

cool and rinse several times with salt solution

 

aftertreat with cationic fixative if required

 

 

 

Be able to recognize a typical structure of an azo based fiber reactive dye, and an anthraquinone based fiber reactive dye. 

 

[image]6 member brain, chlorine

 

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Show how a covalent bond can be formed between a fiber- reactive dye and an OH group in cellulose 

 

[image]

 

 

 

Explain why alkali (OH) is needed to fix the dye to the fibre, and why a precise amount of alkali is needed (typically, to give pH 11) (slide 7) 

 

Alkali is used to get a desired pH around 11

Too much OH- gives greater hydrolysis of dye

Too little OH- gives lower fixation rate to fiber

 

 

 

Describe which fibers can be dyed with disperse dyes 

 

Polyester, acetate, and nylon

because it has no affinity for cellulose

 

 

 

Be able to recognize the structures of the three main chemical classes of dyes: azo, anthraquinone and nitrodiphenylamine 

 

[image]

 

 

 

Explain, with the aid of sketches, how disperse dyeing of fibers occurs 

 

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List at least two benefits and disadvantages of using disperse dyes 

 

+Good fastness properties

+Wide range of shades available

+unique application properties

 

-thermal migration to fiber surface during drying can cause crocking or staining problems

-Polyester dyeing requires carriers or high temperature

 

 

 

Explain why high temperature (130 oC) is required to dye PET with disperse dyes without a carrier. 

 

Provides energy for diffusion

 

Increases polymer chain mobility

 

 

 

Explain why a reduction clear is sometimes necessary, and explain how it is performed (what chemicals, temp. and time). 

 

Removes surface dyes to improve crockfastness

Chemically reduces the chromophores to water-soluble material

 

  1. Pad on disperse dye and antimigrant
  2. Predry; dry
  3. Heat to 400c for 45 seconds
  4. Cool on Cans
  5. Pad on caustic and hydro

 

 

 

 

Explain what polyester trimer. 

 

Polyester oligomer

Controlled with auxiliaries and procedures

 

 

 

Describe, with the aid of a diagram, a typical continuous dyeing process of polyester (e.g. the Thermosol® process) 

 

pad on disperse dye and antimigrant

predry; dry

heat to 400c for 45seconds

 

draw a circle with dots around it, and then dots in it

 

 

 

 

Explain the difference between low, medium and high energy disperse dyes and explain why the different energy classes should not be used in the same dyebath. 

 

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