The Chemistry of Baby Diapers

Introduction

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Many parents choose to use disposable baby diapers because they are convenient and easier than reusable cloth diapers. Disposable diapers are able to absorb a lot of urine but how? I chose my project because I am a mom of a busy toddler and I am curious what is in the diapers I put on my daughter. The chemistry of diapers affects my daily life because my daughter wears diapers every day.


Composition of ...

Sodium polyacrylate is the absorbent pad in a diaper. It is made from acrylic acid and it is a long and curly shaped molecule. Sodium polyacrylate’s molecular formula is C3H3NaO2.  On each side of The absorbent pad there is a nonwoven fabric such as nylon which keeps the absorbent pad in place.  Diapers also have elastic bands around the legs and at the top of the diaper to help the diaper fit well. At the top on both sides of the diaper there is adhesive strips which keep the diaper secured shut.

  • Acrylic Acid C3H4O2

  • Nylon  C12H22N2O2

  • Elastic Bands

  • Adhesive strips

Main Chemicals, Compounds, Components

Acrylic acid is a colorless liquid or colorless solid crystals depending on the temperature. It is used to make plastics, floor polish, paint and coatings, and many other things. It is made by the oxidation of propylene by the intercessor acrolein. Acrylic acid is also produced naturally by some species of algae. When acrylic acid is in its liquid state it is flammable and corrosive.  Acrylic acid is the parent compound of sodium polyacrylate. To make sodium polyacrylate, acrylic acid is frozen and mixed with water as well as cross-linking assistants and a ultraviolet provoker. This mixture is put into a reactor with series of strong ultraviolet lights which start the polymerization and cross-linking reaction. This process makes logs which are then shredded and dried. Once the sodium polyacrylate dries it is packed into sheets for diapers.

Nylon is a plastic resin and for it to be turned into a nonwoven fabric for a diaper they use the dry laid process. In the dry laid process the plastic resin is melted and pushed through small holes by air pressure. While the a fibers of the nylon are being cooled down by the air, the nylon fibers compress on a sheet. Then heat rollers are then used to squish and bind the nylon fibers together. Once the dry laid process is done you have the nonwoven fabric form of nylon that is used in diapers. The nylon that goes on the inside of the diaper is thin and not waterproof which allows urine to pass to the layer of sodium polyacrylate, but the nylon that goes on the outside of the diaper is waterproof.


Chemistry's Role

Acrylic acid is made in a lab through the oxidation of propylene by the intercessor acrolein. It is also produced naturally by some species of algae. Sodium polyacrylate is a daughter product of acrylic acid and is also made in a lab. Diapers are man made in a factory. Chemistry plays a role in how diapers are made because of the order in which materials are placed in the diaper when being assembled. If the absorbent layer of sodium polyacrylate was on the outside of the diaper, the diaper would not work properly. Diapers have nonwoven fabrics on both sides of the absorbent sheet of sodium polyacrylate. The nonwoven fabrics hold the absorbent sheet in place. Nonwoven fabrics can include nylon, polyester, or polyethylene. Urine is able to pass through the first layer of nonwoven fabric into the absorbent layer of sodium polyacrylate. Water has a positive and negative charge making it attracted to other molecules with a positive and negative charge. Sodium polyacrylate is a positive and negatively charged ion making it very attracted to water. When the water is attaches to the sodium polyacrylate it is absorbed and the sodium polyacrylate turns into a gel form. The curly sodium polyacrylate straightens out as it absorbs the urine. When the sodium polyacrylate straightens out it creates more surface area to attach to water. The water does not leak unless there is a high sodium content in the urine because sodium is not pure water so it is not as attracted to sodium polyacrylate as water is.

Background Research

Disposable baby diapers have become increasingly popular since World War II because there was a shortage of cotton and there were many mothers who worked so they did not have time to launder reusable diapers. These reasons created a demand for a disposable diaper instead of a cotton cloth diaper. However, disposable diapers did not have sodium polyacrylate in them until the early 1980’s. Sodium polyacrylate is a grainy powder chemical used in diapers and it is responsible for absorbing liquids. In fact sodium polyacrylate can absorb four hundred to six hundred times it’s own weight. When the sodium polyacrylate gets wet it turns into a gel, this process usually does not take more than ten seconds.


Resources

http://www.acs.org/content/acs/en/education/whatischemistry/adventures-in-chemistry/experiments/diapers.html

  • How sodium polyacrylate works to absorb liquids

  • What sodium polyacrylate molecules look like


https://www.sandiegofamily.com/for-the-kids/family-science/278-diaper-chemistry

  • How sodium affects sodium polyacrylate


http://chemistry.about.com/od/howthingsworkfaqs/f/diapers.htm

  • Why baby diapers sometimes leak

  • How sodium acrylate is made

  • Sodium Polyacrylate’s molecular formula and structure


http://imaginationstationtoledo.org/content/2011/03/how-do-diapers-work/

  • How super absorbers like sodium polyacrylate work


https://disposablediapers.wikispaces.com/The+Chemistry+of+Disposable+Diapers

  • Structure of sodium polyacrylate


http://disposablediaper.net/general-information/disposable-diaper-history/

  • History and background of diapers

  • Why there was a demand for disposable diapers


http://www.owletcare.com/blog/baby-diapers-are-they-safe/

  • When polyacrylate was introduced in diapers


http://www.encyclopedia.com/article-1G2-3441700192/sodium-polyacrylate.html

  • What sodium polyacrylate is composed of

https://pubchem.ncbi.nlm.nih.gov/compound/acrylic_acid#section=Experimental-Properties

  • Properties of acrylic acid

  • Properties of sodium polyacrylate


http://www.madehow.com/Volume-3/Disposable-Diaper.html

  • The components of a diaper

  • Nylon in diapers

  • How nylon is made

  • How a diaper is made

https://en.wikipedia.org/wiki/Nylon_66

  • Nylon’s molecular formula

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

  • How sodium polyacrylate is made from acrylic acid

About the Author
Taylor Tilzey is a senior at Billings Senior High School. She wondered how the diapers she uses on her daughter work and decided to learn the chemistry behind diapers. She is on honor roll and the dance team at Senior High. She is planning on going to college to study nursing or radiology.
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