Super Absorber:
Sodium Polyacrylate
Jordan Waldorff
Honors Project
Chemistry 1045
For my honors project in chemistry 1045, I was asked to research sodium polyacrylate and find out why it is so absorbent. I also conducted an experiment to determine just how much water this polymer could absorb. Sodium polyacrylate is a super absorbent polymer; also sometimes called a super slurper. A polymer such as sodium polyacrylate is a large, usually chainlike molecule that is made up of chains of identical units known as monomers that repeat. The chemical structure of sodium polyacrylate is CH2-CH(COONa). It is easily found in disposable super absorbent diapers. I was also surprised to find many other uses for this polymer. Sodium polyacrylate can be put in soil to help it retain water. Sodium polyacrylate is also used by florists as a way to store water and keep cut flowers fresh for longer. Airplane and automobile fuels use this polymer in filtration units to remove water and keep the vehicles running smoothly. Another interesting place that one can find sodium polyacrylate is in children’s grow-creatures toys. These are small soft toys shaped like many different types of animals that expand when put in water. The magic of these toys is easily explained by the way sodium polyacrylate absorbs and holds on to water molecules.
Osmosis, which is the movement of water across a semi permeable membrane from areas of low solute concentration to areas of high solute concentration directly explains how sodium polyacrylate is able to absorb water. When the powder substance is placed in water there is a higher concentration of water outside the molecules. Water is drawn in toward the center of the molecule by the process of osmosis. Sodium polyacrylate is able to absorb between 200 and 300 times its weight in water due to osmotic pressure. The molecules will continue to absorb water until the water concentration on the inside and the outside of the polymer is in equilibrium; that is, there are equal amounts of water inside and outside the polymer.
In order to better understand the properties of the sodium polyacrylate polymer I conducted an experiment to find out just how much water a certain gram mass of the powder could absorb. To begin I took several pampers super absorbent diapers, cut them open, and exposed layers of cotton fibers embedded with the white sand-like sodium polyacrylate particles. I measured out 14.024g of the powder. Then, I took a 400mL beaker and proceeded to add water to the sodium polyacrylate in increments of 14 mL; about the same weight in water as the mass of sodium polyacrylate I began with. As I added the water, it was obvious that the polymers were absorbing all of it. At first the powder expanded when the water was absorbed. Then it began to transform from a white powder to a transparent gel. The more water I added, the more the molecules absorbed and expanded with all the particles taking on a gel-like feel and look. The sodium polyacrylate kept absorbing water with no signs of it reaching the maximum capacity. I had to transfer the particles to a 1000mL beaker in order to continue the experiment. There really was not much change in the particles besides the growth in size. It seemed as if they would just continue to expand and hold a limitless amount of water. When the 1000mL beaker became completely full, and I was about to transfer the sodium polyacrylate into a larger beaker, it seemed as if the sodium polyacrylate polymers had reached the maximum amount of water to which they could hold. When I totaled up the amount of water I had added to the particles, I found that I added 14 mL of water 89 times for a total of 1246 mL of water. These polymers began as 14.024g of powder; barely enough to cover the bottom of a 400 mL beaker. They expanded tremendously, and filled a 1000 mL beaker.
Many questions have been raised about this polymer and the overall safety of sodium polyacrylate because of its use in baby diapers. It does such a good job at absorbing liquids that it pulls all the moisture away from the baby’s skin. It is important that parents realize the safety concerns of using disposable diapers so that they do not leave their child in a “wet” diaper too long. It is obvious through my research and experiment that sodium polyacrylate is a very powerful polymer.
Sources
<http://home.howstuffworks.com/question207.htm>
<http://chemistry.about.com/od/moleculescompounds>