Dye & Pigments Flashcards

1
Q

What is the primary difference between dyes and pigments?

A

Dyes are soluble substances that impart color through absorption, while pigments are insoluble and rely on dispersion within a binder to provide color.
- Dyes are colored substances that can be applied in solution or dispersion to a substrate, giving it colour appearance.

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2
Q

What distinguishes natural dyes from synthetic dyes?

A

Natural dyes are derived from organic or inorganic materials, such as plants and minerals.
Synthetic dyes are man-made, created using chemical processes, offering a broader color range and lower costs.

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3
Q

What is the defining characteristic of reactive dyes?

A

Reactive dyes chemically bond with fibers to form covalent bonds, ensuring good fastness due to direct reaction eith fibres..

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4
Q

On which types of fibers are reactive dyes primarily used?

A

Reactive dyes are commonly used for cellulosic fibers such as wool, silk and rayon.

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5
Q

What are the advantages of using reactive dyes?

A

A complete color range.
Good fastness properties, especially wash and light fastness.
Simple application.
Cheapest

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6
Q

What challenges are associated with reactive dyes?

A

They have a low affinity for cellulose, requiring large amounts of salt to aid absorption.
They cannot be used on synthetic fibers or fabrics treated with resin or drip-dry finishes.

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7
Q

What are direct dyes, and why are they widely used?

A

Direct dyes are water-soluble anionic dyes that are easily applied to cellulosic fibers like cotton and rayon. They are widely used because of their economical cost and simple application process

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8
Q

What materials are suitable for dyeing with direct dyes?

A

Direct dyes are primarily used for cellulosic fibers such as cotton and rayon but can also be applied to wool, silk, and nylon.

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9
Q

What are the advantages of direct dyes?

A

Simpler application
They are cost-effective
provide a full color range.
Moderate color fastness can be improved with post-treatment, such as using cationic fixing agents or copper salts.

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10
Q

What are the weaknesses of direct dyes?

A

Some shades have poor fastness, especially medium and heavy colors.
They are not suitable for applications requiring high durability or exposure to extreme conditions.

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11
Q

What makes direct dyes unique compared to reactive dyes?

A

Unlike reactive dyes, direct dyes do not form covalent bonds with fibers. They rely on adsorption and have a simpler application process.

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12
Q

What are vat dyes, and why are they unique?

A

Vat dyes are insoluble dyes that must be chemically reduced to a soluble form before application. They are known for their excellent fastness properties and are commonly used for high-quality cotton goods like denim.

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13
Q

Which dye type offers the best all-around fastness?

A

Vat dyes provide the best all-around fastness, especially for wash, light, and chlorine resistance.

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14
Q

Why are mordant dyes less commonly used today?

A

Mordant dyes require complex application processes involving pre-treatment with a mordant, making them less practical compared to modern dyes like reactive and direct dyes.

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