Gluep - Solid or Liquid?

Plastics are all around us. There are many different kinds, with a wide range of properties. Some are hard, others are soft. Some are transparent, others are opaque. Most plastics are made in factories, but here’s one you can make at home.

For this experiment you will need:

Here's what to do:

  1. In one of the cups, dissolve 1 teaspoon of laundry borax in 5 tablespoons (75 mL) of water. You will need to stir this for a while to get it to dissolve. (If a tiny bit does not dissolve, that is OK.)
     
  2. In the other cup, combine 1 tablespoon of water and 1 tablespoon of white glue. If you wish, you may color the mixture with a couple drops of food coloring. With a clean spoon, stir the mixture thoroughly until it is uniform.
     
  3. Put 2 teaspoons of the borax solution from the first cup into the glue mixture in the second cup. Stir the mixture.
     
  4. As you stir the mixture, it will stiffen into a soft lump. After the lump has formed, take it from the cup and knead it in your hand for a couple minutes.

The material you have made is called Gluep, and it is ready for you to examine.


The materials we call plastics are all composed of large molecules whose structure is like a chain. These molecules are composed of many small repeating units, like the links in a chain. Like a chain, the molecules of a polymer are long and narrow. The name plastic is applied to a wide variety of substances, some of them soft and others very hard. Originally, plastic referred to something shapeable or bendable. However, as new polymer materials were made that were hard and stiff, the name plastic was applied to them, too.

White glue is a mixture of water with a polymer. The polymer molecules are shaped like very tiny pieces of spaghetti. The tangled molecules make glue thick and viscous rather than thin and runny. When glue is exposed to air, the water evaporates, leaving the tangled polymer molecules. The tangled molecules stick to the surfaces on which they dried, and hold the surfaces together.

Borax solution contains borate ions. These ions can form links between the long, thin polymer molecules in the glue, turning it into a 3-dimensional network. This network makes Gluep more like a solid than the plain liquid glue. The network holds its shape for a short time, and as long as it is not strained. When Gluep rests, the flexible network gradually relaxes, and the Gluep flattens. When Gluep is stretched quickly, the links between molecules break, and the Gluep snaps apart into pieces.

The polymer molecules in white glue are called polyvinyl acetate. These molecules are composed of long chains of carbon atoms, with an acetate group attached to every other one. Acetate comes from acetic acid, the compound that gives vinegar its odor and flavor. This is why white glue smells a bit like vinegar. When borax is mixed with white glue, each borax ion replaces two acetate groups, forming a borate link between two polymer molecules.

Gluep contains a lot of water trapped in the network of linked polymer molecules. This water contributes to the liquid-like properties to Gluep. If the Gluep is left exposed to open air, the water will evaporate, and the Gluep will gradually stiffen. To preserve the Gluep, store it in an air-tight plastic bag.

A material similar to Gluep can be made using a gel glue in place of white glue. Fluid gel glue contains polyvinyl alcohol in place of polyvinyl acetate. Borate ions form links between these molecules, too. In this case, the alcohol groups are displaced, forming water.

 


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