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Abstract"Plastic made from milk" —that certainly sounds like something made-up. If you agree, you may be surprised to learn that in the early 20th century, milk was used to make many different plastic ornaments —including jewelry for Queen Mary of England! In this chemistry science project, you can figure out the best recipe to make your own milk plastic (usually called casein plastic) and use it to make beads, ornaments, or other items.
In this chemistry science project, you will investigate which is the best recipe for making plastic out of milk.
What can you make out of milk? Cheese, butter, whipped cream, sour cream, yogurt, ice cream, and...plastic! Are you surprised by plastic? It is true. In fact, from the early 1900s until about 1945, plastic made from milk was quite common. This plastic, known as casein plastic or by the trade names Galalith and Erinoid, was used to manufacture buttons, decorative buckles, beads, and other jewelry, as well as fountain pens and hand-held mirrors and fancy comb-and-brush sets. Figure 1 below shows examples of belt buckles made from casein plastic in the 1930s and '40s; more examples can be found in the references in the Bibliography.
But how can milk be changed into plastic? To answer that we need to think first about what plastic is. The word plastic is used to describe a material that can be molded into many shapes. Plastics do not all look or feel the same. Think of a plastic grocery bag, a plastic doll or action figure, a plastic lunch box, and a disposable plastic water bottle. They are all made of plastic, but they look and feel different. Why? Their similarities and differences come from the molecules that they, like everything else, are made of. Molecules are the smallest units (way too small to see with your eye!) of any given thing. Plastics are similar because they are all made up of molecules that are repeated over and over again in a chain. These are called polymers, and all plastics are polymers. Sometimes polymers are chains of just one type of molecule, as in the top half of Figure 2 below. In other cases polymers are chains of different types of molecules, as in the bottom half of Figure 2, that link together in a regular pattern. A single repeat of the pattern of molecules in a polymer (even if the polymer uses only one type of molecule) is called a monomer.
Milk contains many molecules of a protein called casein. When you heat milk and add an acid (in our case vinegar), the casein molecules unfold and reorganize into a long chain. Each casein molecule is a monomer and the polymer you make is made up of many of those casein monomers hooked together in a repeating pattern like the top (all pink) example in Figure 2.. The polymer can be scooped up and molded, which is why it is a plastic.
In this chemistry science project, you will investigate what is the best recipe for making casein plastic by making batches of heated milk with different amounts of vinegar. How much vinegar is needed to give you the most plastic? Without enough vinegar the casein molecules do not unfold well, making it difficult for them to link together into a polymer. Of course, if you were manufacturing you would be thinking about both the amount of plastic you can make and the cost. The more of any ingredient you use the more expensive the end product is. The "best" recipe will have the highest yield (make the most plastic) for the smallest amount of vinegar.
The plastic you make will be a bit more crumbly and fragile than Galalith or Erinoid. That is because the companies that made those casein plastics included a second step. They washed the plastic in a harsh chemical called formaldehyde. The formaldehyde helped harden the plastic. Although you will not use formaldehyde because it is too dangerous to work with at home, you will still be able to mold the unwashed casein plastic you make. Once you have a recipe, with the best ratio of vinegar to milk, for your casein plastic, you can have fun with it. Try shaping it, molding it, or dyeing it to make beads, figures, or ornaments, such as those shown in Figure 3 below.
Terms, Concepts, and Questions to Start Background Research
These resources have more information about, and photos of, casein plastic:
This website is a fun introduction to polymers:
For help creating graphs, try this website:
Materials and Equipment
The materials listed below are for doing the experimental procedure exactly as written. However, you can make changes to the experimental procedure in order to use a different size measuring cup and/or a stovetop rather than a microwave.
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Making Casein Plastic
This experiment uses hot liquids, so an adult's help will be needed throughout.
Analyzing Your Data
Ideas for Fun with Your Casein Plastic
Try making beads, ornaments, or figurines out of your casein plastic. You should do the molding and coloring steps (except for paint and/or marker) within the first hour of making the plastic or it will start drying out.
Sandra Slutz, PhD, Science Buddies
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