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PCC 302 test 2
Terms in this set (39)
3 classes of bleach activators
Which class of bleach activator has the greatest affinity for cotton?
Why would a bleach activator be added to a bath containing H2O2+NaOH
Allow bleaching at a lower temp and shorter time.
Product generated at pH=11
Product generated at pH>11
Hydrolysis: Acid/Acid Salt
Product generated at pH<11
Why are FBAs applied to cotton? Why are they NOT applied to wool or silk?
To make cotton white and brighter.
Since FBAs absorb UV, would damage animal fibers
How does FBA work? Why does it emit a longer wavelength?
An electron absorbs energy in UV range, moves to an excited state then moves back down to ground state. Loses energy at a higher wavelength.
Explain sketch of reflectance curve
An FBA absorbs energy in UV range that we cant see (>100% reflectance). Releases energy in higher wavelength in UV range
Fibers used in mercerization
Chemical used in mercerization
Why is the process performed?
1) Improve color yield
2) appearance after dye
Mercerized vs non mercerized
mercerized are larger and swollen, non are like beans
How does mercerization work?
NaOH hits the cotton fibers and breaks existing hydrogen bonds between polymer chains and forms new h bonds, causing swelling and the internal fiber structure to open up
material imparting color unto another material
soluble in medium which applied, bonded on a molecular level inside of fiber
insoluble, requires binder to afix to fiber, lays on surface of fiber
Electron donating groups (2)
amino and hydroxyl
Electron withdrawing groups (2)
azo and nitro
Wavelength range of UV
Wavelength of Infa-red
Wavelength of visible
relationship between energy and wavelength
E up V up + wavelength down
How is light absorbed at 185nm/in organic materials
Through congegation: alternating between single and double bonds to enter the visible range, past the energy gap
1 or more azo group, auxochrome, and sulfuric acid
2 main structures and 2 or more reducible carbonyls. nonionic - no charges
fibers that can be dyed with direct dyes
How are direct dyes attracted to cotton?
shape of the dye molecule allows optimal hydrogen bonding with cellulose polymer
Adv of direct dye
easy to apply, range of shades
Dis of direct dye
poor chlorine fastness, limited brightness
Adv of Vat dye
excellent light/chlorine fastness, continuous dyeing
Dis of vat dye
limited shades (no bright or red), complicated application
Why is salt added to direct dye?
improves exhaustion, more soluble in water than the dye, pushes to fiber
vat dyes to cotton?
reduce to make soluble, go into fiber, oxidize to seal and revert back to original
Explain reduction of chromophore
reduces dye by interchanging single and double bonds with naoh and hydro (vatting) and creating a soluble leuco form
oxidize leuco form by using oxygen to make dye insoluble again
3 properties of indigo
smaller than other vat dyes
no affinity for cotton
poor lightfastness and washfastness
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