Polymers: Linking things together!
Today students had a fun chemistry lesson on polymers. The students learned how important polymers are in their lives, since polymers include starches (pasta, potatoes), cellulose (wood, plants), plastics, fabrics both natural (cotton, wool) and manufactured (rayon, nylon), and proteins. But exactly what is a polymer, you might ask? Polymers are a type of molecule made of linked chains of individual units, called monomers. Students learned that monomers form chains to create polymers, and that chains of polymers can be cross-linked together to make materials with different properties, like density, tensile strength, and elasticity.
After learning about the polymers that are all around us, students were then able to experiment with some cross-linking polymers themselves. We took an existing polymer (white school glue, which is polyvinyl acetate) and mixed it with a cross-link solution, tetrahydroxyborate (Borax) in water. The result was dramatic! The slimy, sticky glue changed into a rubbery, dry substance that could be stretched, formed into a ball, broken sharply apart, and bounced. Your students should be able to tell you why cross-linking the polymer had this effect!
We then tested the effect that different amounts of cornstarch (a highly branched polymer that does not cross-link) had on the elasticity of the polymer gel by measuring the bounce height of the gel balls when dropped.