Dyes and Fibers Carol LeBaron Chemistry and Art February 15-17, 2004

Dyes and FibersCarol LeBaron Chemistry and Art

February 15-17, 2004

Nasca Wari textile, 400 CE Resist dyed

Light is made up of bands pf varying wavelengths

Reflection

• White can only be broken up by prisms or by colorants such as pigments and dyes

• This surface has no colorant so the light is reflected

It can be fully absorbed by the surface

Or a transparent surface may let all of the light pass through or a colored surface

may absorb part of the spectrum

Bands of light mix together to produce lighter colors

A “blue” surface absorbs red, orange, and yellow light

A “yellow” surface absorbs blue and violet light

The pigment primaries absorb and reflect different combinations of colored light

Interference: the kind of surface light hits can affect the way light waves behave

Structural Color

• Iridescence• Luminescence• Refraction• Diffraction• Fluorescence• Phosphorescence

• Materials that light hits can cause a multitude of effects

The nature of fiber affects the way light appears

Fiber reflects, refracts, absorbs and diffuses

The unique color properties of fiber depend on the interaction of fabric structure, dye application, and light

“Humidity” (2002)

Pigments and Dyes

• A dye is a colorant that goes into solution or dissolves. Dye particles break apart into single molecules

• Pigment particles remain clustered together in suspension

• Dyes have a chemical affinity for fiber but pigments do not

Pigmentparticles

Dyemolecules

Pigments and Dyes

• Pigment molecules carry their own color

• They do not unite with fiber molecules chemically and must be fixed to the fibers with bonding agents

• In man made fibers pigments can be mixed into the fiber solution before it is formed

• Dyes migrate out of the solution, are absorbed into the fiber, and diffuse from the surface of the fiber toward its center. There they either:– Bond chemically with fiber

moleculesOR

– React chemically with fiber molecules to produce permanent, enlarged colored fiber molecules

• Both situations are permanent

Dye molecules must be firmly fixed to fiber

Chain fiber molecule

Dye molecules

A negative dye molecule links with a positive fiber molecule at a dye site. The process is affected by surface charge, temperature, and agitation. Different fibers have different numbers of dye sites. Wool fiber has 1000 dye sites, silk has 100, and cotton has less than 10

Assembly of dye molecules at the fiber surface

• When soaked in water all fibers acquire an electric potential or surface charge

• Cellulosic fibers acquire negative charges• Protein fibers acquire both positive and negative

charges, depending on the pH of the water• Acid solutions help break down protein fibers to

allow dye sites access to the dye• Cellulose fibers must be soaked in alkaline

solution• Salt is used to set up electrical movement that

initiates the movement of dye molecules in search of a resting place on the fiber

Once the dye molecule enters the fiber, it has a a chemical reaction with it. It is

enlarged, which prevents its exit.

Color is produced when a divided molecule is united.

Acid Dyes

• Used mainly on wool, silk, and nylon*• They have acid chemical groups in their dye

molecules• They use an acid dye bath to produce the

chemical reaction• Reaction involves acid, salt, heat, agitation, and

time– Amount of acid and rate at which it is added affects the

rate at which the dye bonds– Salt slows the bonding process, helping the dye color

the fiber evenly. It attaches to the dye first.

Gradually, dye replaces the salt and bonds with the fiber. Leveling is achieved

when this happens at an even rate.

• Heat affects the leveling of the dye bath by speeding up the chemical reaction

• Generally the dye bonds slowly until 160° F

• Agitation helps keep both chemicals and heat evenly distributed

• The full immersion time is necessary to allow the dye to be light fast and wash fast

Structural Orientation

• Structural orientation is the arrangement of parts relative to one another within a fiber piece– Molecules in a fiber– Fibers in a piece of yarn– Yarn in a piece of fabric

• It affects moisture and dye absorption• Textile polymers are chains with a monomer for

each link• Fiber polymers have the same structure that fibers

do

Chromophores and auxochromes

• The ability of dye to create color comes from chromophores in the dye molecules

• Auxochromes regulate the intensity of color. They are chemical groups that make dyes water soluble. They also provide chemical groups that form bonds between the dye and fiber

• A dye bath must contain both chromophores and auxochromes, either from the dyestuff alone or a mixture of dye and other added chemicals

The structural orientation of the polymers within a fiber varies, It affects dye results

and other fiber properties

Dye and molecular orientation

• Amorphous areas of a fiber take more dye than highly oriented areas

• They will be darker in the dye bath

• A fiber’s character depends on the color changes that take place from amorphous areas to crystalline or oriented areas

• All fibers contain all three areas in different degrees

Fibers

• Fiber molecules are arranged in fiber filaments

• Loose arrangement of fibers allows good penetration

• Fibers are often dyed before they are made into yarn for this reason

• Fibers are combed before they are made into yarn

Cotton fiber

Different fibers have different surfaces

Yarn staples

Lightly combed = good penetration

Carded and combed= fairly good penetration

Tightly packed = poor penetration

The shape of the fiber filament affects appearance

Wool fibers are crimped and create an absorbent surface

Structure of a wool fiber

The size of the yarn and the way it is plied will affect the finished material

Weave structure affects color and appearance of the dyed piece

Wool fiber comes in different colors from the animal

Heat, agitation and moisture cause wool fiber to felt: wool fiber after it is felted

Wool fabric after fulling

Before

After: the fibersHave locked together

Resist Dyeing

Two Examples of Clamp Resist with Folding

Chemistry Lab

Removing the Dyed Piece

Placing in the Rinse Tank

“Larkspur”