Dyes
Chapter 3: Activity 7
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.
China Indigo
India Indigo
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
Dried cochineal beetle eggs
La Cochinilla
Starbucks
Products that contain cochineal beetle extract dye
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.
The Chemistry of Synthetic Dyes
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 are
absorbed and no color is
reflected
Color wheel
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
link
• link
Paper Marbling
• Patterns are floated on
a liquid and then
transferred to an
absorbent surface
(paper)
• Originated in Japan