Why modern glues sticks
Until a century ago, glues were either gums from plants or boiled-down hides and bones of animals. These gums and glues took a long time to stick and they formed a joint that was not particularly strong. They were used mainly for woodworking. The liquid glue flowed into the pores of the wood and then dried, bonding the pieces of wood together.
Today, however, most glues are wholly synthetic. They dry quickly and form very strong bonds. The fastest-acting ones are called superglues or instant glues, and they set in seconds. There are also epoxy resins which are sold as two ingredients that have to be mixed together and then set in 10 to 30 minutes.
Superglue is an acrylic resin made from petroleum chemicals. When it is exposed to the slightest trace of moisture its small molecules join together to form longer ones – a chemical process called polymerisation.
In its tube, the glue is prevented from polymerising by an acidic stabiliser. When it is applied to a surface the most minute amount of moisture overcomes the action of the stabiliser, and the resin polymerises instantly. It is the presence of water ions groups of atoms that have an electric charge – that triggers off the polymerisation process. The ions are present on practically any surface that is exposed to the air, because the air always contains some moisture.
Superglues stick well to skin because it is moist. There have been many cases of people becoming stuck to all sorts of objects, from teacups to door handles. They can be freed by soaking the stuck part in warm water and gently prising it away.
This skin-bonding property is not always a bad thing. Superglues have been used in surgery as an aerosol spray to seal wounds and reduce bleeding.