The Chemistry of Denim

Introduction

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  • Denim jeans are a very popular piece of clothing that have been in style for many years.  Denim is a strong twill fabric that is made out of cotton and dyed blue with indigo dye.  Denim is created by a weaving process.  In the weaving process, the “warp” is the term for the thread or yarn that runs lengthwise.  The “weft” is the thread or yarn that is drawn up through the warp.  When weaving denim, the warp threads are dyed, and the weft threads are left white.  As a result, blue jeans are blue on the outside and lighter or white on the inside.  This process creates denim’s unique fading characteristics and separates denim from other textiles.

  • I chose to examine the chemistry of denim for numerous reasons.  First, I love denim jeans.  I have always had a sense of style and I own many jeans in various styles and washes.  I wear jeans that are ”distressed,” jeans that have lighter washes, and I also wear the dark blue more formal looking jeans.  Second, denim jeans are an item that are universally popular.  People from all walks of life wear and enjoy jeans.  Finally, denim jeans provide a means of expression.  Denim jeans have always been a piece of clothing I wear to express myself and my style to the world.  The same is true for many individuals. Researching the chemistry of denim has given me even more appreciation for this piece of clothing.

  • Denim affects my life in many ways. Denim jeans are my go to piece of clothing.  I wear denim all year regardless of the weather.  Denim is usually a heavier fabric and so it does help keep a person warm when it is cold outside.  Denim impacts my life by allowing me to express myself through the style of my clothing. I feel great when I am wearing denim and it is comfortable.

Composition of ...

  • Cotton

    • cellulose(C6H10O5)n 91.00%

    • water(H2O) 7.85%

    • Protoplasm, pectins(HMDB03402) 0.55%

    • waxes, fatty substances 0.40%

    • mineral salts 0.20%


  • Indigo dye

    • properties

      • chemical formula - C16H10N2O2

      • dark blue crystalline powder

      • density- 1.199g/cm^3

      • melting 734-738 degrees f

      • boiling point - decomposes

Main Chemicals, Compounds, Components

  • Cotton = (cellulose(C6H10O5)n , water(H2O), Protoplasm, pectins(HMDB03402))

The soft and fluffy material called cotton grows from seeds of the genus Gossypium in the family of Malvaceae. The cotton seeds are grown in a “boll” which is a seed bearing capsule. Cotton is mainly grown in America, Africa, India, Mexico, and Australia. Cotton holds 2.5% of the world’s arable land. Cotton is almost pure cellulose. Although cotton is somewhat drought tolerant, it needs sunshine, warm climate, water, and a soil with nutrients in order to grow.  Cotton is often spun into yarn and used to make textile products.  Popular textile products include terrycloth towels, denim, shirts, and much more.

  • Indigo dye = C16H10N2O2

Indigo’s first major center of production was in India. Indigo was highly valued and mainly used as a dye. Indigo dye is one of the oldest used to dye textiles. Over the years, the production of indigo dye and the indigo dye itself has changed greatly.  Today, indigo dye is easier and less expensive to make. Indigo can be produced naturally or synthetically. Historically, indigo dye, which is an organic compound, was extracted from plants.  Today, most indigo dyes are synthetically made.  Indigo dye is mainly used to dye cotton that is then used to make denim.  The average amount of indigo used in a pair of jeans is 3-12g.


Chemistry's Role

The cotton in denim is naturally made. Although cotton grows naturally, it has become genetically modified. Genetically modified cotton withstands pesticides by introducing a what is called Bacillus Thuringiensis(Bt) to cotton. Bt is a naturally produced chemical that is only harmful to some pest insects.

The cellulose in cotton is a polymer of glucose and grown by special plants. Glucose molecules can attach to each other in many ways by different types of bonds. In cotton, glucose molecules are arranged so that the polymer is the most extended form possible.  Each glucose unit has three OH groups (hydroxyls) that can hydrogen bond to adjacent chains. The strong bond of chain, called intermolecular forces, makes cotton tough so that is can be strung into textiles for clothing.

Indigo dye can be made naturally and synthetically. Most natural indigo dye comes from the genus of indigofera plants. There are several steps to making natural indigo because the dye itself does not actually exist in nature.  Initially a chemical called indican is extracted from the natural plant leaves. The indican is put through a series of tanks. The upper tank contains the fermentation vessel where the freshly cut plants are put through fermentation. In this process, indimulsin is added to hydrolyze or break down the indican into indoxyl and glucose. Carbon dioxide is given off and the broth in the tank turns into a dark yellow color. After approximately fourteen hours, the remaining liquid is drained into tank number two. In this tank, an indoxyl-rich mixture is stirred with paddles to mix with the surrounding air. Air is mixed in with the indoxyl-rich mixture allowing the indoxyl mixture to oxidize and form into indigotin. The product of this step settles to the bottom of the tank. After removing the the top layer of liquid, the pigment that settles at the bottom of the tank is now transferred to the third and final tank. To stop the fermentation process the pigment is heated. The final mixture of the third tank is filtered to remove impurities and dried producing a thick paste that can be used to dye.

Indigo dye can be synthetically produced as well. The many different processes in making the synthetic dye all involve combining a series of chemical reactions under controlled conditions. These reactants undergo many reactions that result in formating indigo molecules. Many byproducts are produced during the reaction. These procedures are all done inside a stainless steel or glass reaction vessel. These vessels have jackets which allow steam or cold water to flow around the batch as the reaction is occurring. The complexity of this product usually forces many producers of indigo to make the synthetic indigo in large batches. Chemicals used in producing synthetic indigo pigment, and throughout the manufacturing process include aniline, sulfur, sodium hydroxide, hydrosulfate, and formaldehyde. For indigo to actually attach itself to yarn it must become water soluble. The indigo dye needs to be mixed with a reducing agent, sodium hydrogen sulfite, turning the dye yellow in color. Although the dye is yellow, it can attach to the cotton yarn. The yarn will appear yellow at first but the dye will react with the oxygen in the air.  After exposure to oxygen, the dyed yarn will soon appear indigo blue.


Background Research

The name “blue jeans” for denim originated from a swiss banker by the name of Jean-Gabriel Eynard in 1795. The swiss banker furnished uniforms to Massena’s troops which were cut from blue cloth called “Bleu De Genes” otherwise known as blue jeans. The first official denim “trousers” were made in Genoa, Italy. These denim trousers were introduced to the United States in the mid 19th century by Levi Strauss. Strauss imported denim fabric from France during the California Gold Rush in 1853. The denim trousers were made of strong sturdy fabric and used as work clothes. On May 20, 1873, Levi Strauss partnered with Jacob Davis forming Levi Strauss & Co. The company originally designed work clothes for cowboys, ranchers, and miners.  The denim trouser quickly became a desired clothing item.

The infamous blue jeans grew in popularity among teenagers in the 1950s with the “greaser” subculture. In the 1960s, denim was in demand with the “hippie” subculture. Next, in the 1970s and 1980s youth subcultures of punk rock and heavy metal made denim trendy.  Today denim remains a very popular and fashionable clothing item.  One reason that denim jeans remain crowd-pleasing is because they come in numerous types of fits so they can be worn by virtually anyone regardless of shape or size.  Denim jeans come in various cuts and styles.  A few include: skinny, tapered, slim, straight, bootcut, cigarette bottom, narrow bottom, low waist, anti-fit, and flare.  One of the great things about denim is that there are so many styles that really anyone can find the style that they love and that they feel good wearing.

Four hundred million pairs of denim jeans are sold every year. The worldwide market for denim is valued at forty billion dollars. While the history of the popularity of jeans is interesting, how jeans are made is fascinating as well.  First, cotton is picked in the fields to be used to make the yarn for the textile known as denim.  After the cotton is picked, it is transported to a cotton gin that separates the cotton fiber from seeds, leaves, and other plant parts that are mixed in with the raw cotton.  Later, after cleaning and drying the cotton, the cotton is sent to be spun into yarn.

The cotton goes through a machine called a DK760. This machine puts the cotton through the process of carving. The machine untangles the raw cotton fiber by pulling and combing the cotton. The cotton becomes stretched and forms into a thick strand known as a sliver. The cotton slivers are then spun into threads of yarn.  The yarn is then ready for dyeing. The yarn goes through a continuous running machine called the range. The cotton yarn feeds into the dyeing section of the range, dipping in and out of the colorful yellow dye. The dye is yellow because the blue indigo dye is not water soluble, so it needs to be mixed with a reducing agent, sodium hydrogen sulfite, which turns it yellow.

At first, the rope will appear yellow after dipping it into the liquid, but the rope will eventually turn the famous indigo blue as the dye reacts to the oxygen in the air.  The range also washes the threads in warm water and neutralizes the threads with mild acids such as acetic or citric.  Lastly, the yarn is strengthened with cornstarch before it goes off to get woven into denim.  Weaving denim is the combination of white and indigo blue thread.  Cotton is fed into a loom and is blended with one white thread to every three blue threads. The typical pair of pants with five pockets uses 15 pieces of cloth.  Each pair of jeans needs 1.6 meters of denim, several hundred meters of thread, 6 rivets, and one zipper.  To make the jeans look distressed, the jeans are sanded to create worn looks.  Some blue jeans are frayed on the edges and stained with sprays.  Using a laser gun and tossing the jeans into a giant washing machine with rocks are also ways that are used to create the distressed look.  After all of these processes, the jeans are then pressed and ready to be shipped off to the stores.


Resources

https://en.wikipedia.org/wiki/Denim#Etymology_and_origin

How denim is made

History of denim

Jean-Gabriel Eynard

Levi Strauss

styles of denim

fits

color

Dyeing denim

https://en.wikipedia.org/wiki/Cotton

how cotton is grown

history of cotton

Genetically modified cotton (Bt cotton)

cotton’s chemical composition

cotton is 2.5% of the world’s arable land

what cotton needs to survive

https://en.wikipedia.org/wiki/Indigo_dye

properties of indigo

chemical formula - C16H10N2O2

dark blue crystalline powder

density- 1.199g/cm^3

melting 734-738 degree f

boiling point - decomposes

plants indigo is extracted from (Indigofera genus plants)

indigo is not soluble to water

direct printing of indigo

Chemical synthesis of indigo

http://www.madehow.com/Volume-6/Indigo.html

Manufacturing process of indigo

natural extraction of indigo

synthetic production of indigo

https://pubs.acs.org/cen/science/89/8943sci3.html

Indigo rope dyeing

Forms of indigo

https://en.wiktionary.org/wiki/boll

boll is a seed-bearing capsule

http://pslc.ws/macrog/proposal/dreyfus/outcome/plascot/cellace.htm

cotton is mostly cellulose

what cotton is made of

chemistry behind cotton

https://www.youtube.com/watch?v=kfvaCQwRfiI

                    the process and manufacturing of denim video


About the Author
Dawson LaRance is a junior at Senior High School in Billings, Montana.  Dawson loves to run track and cross country. Dawson placed third in the 800 and sixth in the mile during the 2015 track season.  Dawson earned all state honors for cross country in 2015.  Dawson has high aspirations for track times during the 2016 season.  Dawson’s goal is to achieve times needed to compete for a Division I college. Dawson has lettered, gone to state, and competed varsity in cross country and track since his freshman year at Senior High. Dawson has received academic all-state for track and cross country and is continuing to work hard in the classroom to maintain his high GPA.  Dawson is in the Billings Senior Varsity Singers as well as Senior’s extracurricular choir, Expressions. Dawson has also received a letter in choir each year.  Dawson has participated in two All-state choir festivals and he will be singing in the All-Northwest choir in the spring of 2016.  Dawson will be graduating from Billings Senior High in 2017. Dawson chose to do his “Chemistry is Life” project on denim. He chose to research the chemistry of denim because he likes clothes and denim plays a big part in his style.
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