In this “trash-to-treasure” activity, polystyrene clamshell containers (#6 plastic) are used to make hard plastic art pieces. When polystyrene clamshell containers are produced, the material is heated and stretched into a mold, thus locking the material in an extended state. When this material is heated again, it returns to its unstretched size and shape. This property can be utilized to create a range of crafts, including buttons, key chains, luggage tags and jewelry. If students mass their plastic before and after, this could also be tied to the Law of Conservation of Mass.
In this demo, a skewer is pierced through a balloon without popping it. The balloon is made from a rubber polymer. The polymer is made of many long, elastic, overlapping chains, very similar to spaghetti. When a skewer pierces the balloon, these chains are stretched and pushed open to make a hole for the skewer and the balloon does not pop. It is important to pierce the balloon near the bottom & top, where the rubber has the least amount of stress. The polymer is more able to stretch and rearrange, allowing the skewer to pass through.
This demo uses sodium polyacrylate, a super absorbing polymer found in diapers, to turn water into a gel. The sodium polyacrylate has carboxylate anion portions and sodium cation portions. Water is attracted to the sodium ions, thus it enters the polymer through osmosis and the polymer swells and the sodium carboxylate is ionized. The anionic carboxylates on the polymer repel each other, causing the polymer to swell, trap the water, and form a gel. When NaCl is added the increase of electrolytes (ions) in the water shield the repulsion of the carboxylates, thus contracting the polymer and expelling the liquid water.