Goal: Scouts will synthesize an example of a first plastic (casein) and understand the role plastics play in today's society.
Supplies: milk, vinegar, food coloring*, popsicle stick, heat resistance cup, slotted spoon, large container (or sink) that will fit the strainer, paper towels, examples of colorful plastics (toys, buttons, kitchen items, colorful packaging e.g., laundry detergent bottles). *These items are in the Wonders of Polymer Science kit found at the scout store.
Casein recipe: watch video to 5:32 minutes. Make casein with adult supervision only.
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, or 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 different molecules that they are made of. Plastics are similar because they are all made up of molecules, called monomers, that are repeated over and over again in a chain. The chain-like structures of monomers linked together are called polymers and all plastics are made from polymers. Sometimes polymers are chains of just one type of molecule. In other cases polymers are chains of different types of molecules that link together in a regular pattern.
Milk contains many molecules of a protein called casein (pronounced “kay-seen”). 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 casein monomers hooked together in a repeating pattern. The polymer can be scooped up and molded, which is why it is a plastic.
The plastic you make will be a bit more crumbly and fragile than Erinoid plastic. 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. Try shaping it, molding it, or dyeing it to make beads, figures, or ornaments.