Chapter 3: Activity 7 Dyes What are they?
Dyes • Dyes are organic compounds that can be used to impart bright, permanent colors to fabrics. • Organic compounds are compounds that contain carbon. • Ex: C6H12O6 C12H22O11
History of Dyes The earliest records of dyeing processes are from the Chinese, dating back to approximately 2600 BC.
History of Dyes Until the mid 19th century, all dyes were obtained from living materials, usually plants. Processing of cochineal dye (made from beetles) Certain plants are harvested and dried for their natural color
La Cochinilla Starbucks
The insect produces carminic acid that deters predation by other insects. Carminic acid, which occurs as 17-24% of the weight of the dry insects, can be extracted from the insect's body and eggs and mixed with aluminum or calcium salts to make carmine dye (also known as cochineal). Carmine is today primarily used as a food colouring and for cosmetics.
History of Dyes Modern dyeing now takes advantage of synthetic dyes that can be specifically made according to the colors that are desired The first synthetic dye -- 1856
History of Dyes-Food Coloring -Dyes aren't just for fabrics. Colorants have been added to food for centuries to enhance its appearance. -Synthetic colorants are currently approved for use in foods.
History of Dyes-Food Coloring -Color is a big factor in what foods we choose and how much we enjoy a food. -Many food dyes have been banned through the years because they were shown to cause cancer. -Currently only 7 FD&C dyes are approved in the US. -While some food colorings are natural, 95% of those used today are artificial.
Fabrics • Cotton & Wool: • Natural fibers • Polymer-Cotton (Cellulose) & Wool (Keratin) • Polyester, Acrylic, & Nylon: • Synthetic fibers • Polymers
Chemistry of Dyes • The affinity of a dye for a fabric depends on the chemical structure of the dye • and fabric molecules and on the interactions between them. • Chemical bonding plays an important role in how and why dyes work.
Chemistry of Dyes • Some dyes require an additional substance (usually a metallic salt) to assist in the binding of the dye to the fabric. This substance is called a MORDANT. • It prevents the dye from washing out of the fabric.
Chemistry of Dyes A dye molecule has to include a part that is responsible for the color that you see. This is called a CHROMOPHORE
White light is made up of ROY G BIV. • The chromophore will absorb some of the colors of light and reflect the rest. The reflected color(s) will be seen as the color of the item. • So, if the chromophore absorbs ROY BIV, then you will see the dye as green!
Color • We see what is reflected. EX: A leaf is green because it absorbs all the colors but green
White vs Black • White is created when all colors are reflected • TVs add color • Black is created when all colors areabsorbed and no color is reflected
Chemistry of Dyes A Second component of a dye is called the AUXOCHROME. It affects the chromophore’s ability to absorb light energy and thereby affects the color and intensity of the dye.
Colorfastness Some dyes have better colorfastness, • the ability to not run or fade after wearing or washing
Stains • A stain is a discoloration that can be clearly distinguished from the surface, material, or medium it is found upon • Intentional stains (wood stains or paint), • Indicative stains (food coloring or adding a substance to make bacteria visible under a microscope) • Natural stains (such as rust on iron or a patina on bronze) • Accidental stains (like spilling ketchup on your shirt).
Detergents • Soap molecules contain a hydrophilic (polar) head and a hydrophobic (nonpolar) tail
Why do we add detergent? • The hydrophobic tail embeds itself in the stain. (agitation cycle) • The hydrophilic head dissolves in the water and washes the stain away (rinse cycle)
Like Dissolves Like • Hydrophilic substances like other hydrophilic substances Hydrophilic (Polar) likes Hydrophilic (Polar)Hydrophobic (Nonpolar) likes Hydrophobic (Nonpolar) • Dyes and the fabric need to “like” each other
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Paper Marbling • Patterns are floated on a liquid and then transferred to an absorbent surface (paper) • Originated in Japan