How does contact adhesive work?

Answer

Dear Vic,

any glue must meet a few conditions in order to function as glue:

– the fabric must be able to wet the surfaces, so there must be sufficient attractive interactions between the adhesive and the surface to be bonded;

– the substance must be allowed to cure to a certain extent (think of epoxy glue as an example of a 2-component glue: adding the 2nd component ensures that the polymer chains in the 1st component form a strong network with many connections between the different polymer chains, leading to a hard bond);

– and the fabric must also be able to transfer the load between the two objects to be glued.

Exactly how the interactions between the various adhesive components and between the adhesive and the surfaces to be bonded depend on the type of adhesive.

Contact adhesive typically consists of a solvent or solvent mixture, and polymers that readily bond with themselves. When they are diluted in this solvent, this only happens to a limited extent – the solvent actually ensures that you can apply the polymers in a thin layer. If you apply the glue to the two surfaces, a large part of the solvent will evaporate from both surfaces and the concentration of ‘glue polymers’ in the glue layer left behind will increase. The glue has already dried to a great extent. Once the relatively dry surfaces are brought into contact with each other, the polymers immediately form a strong network. If you don’t let the surfaces dry first, the solvent will have a hard time getting rid of and you won’t get a strong bond.

Exactly which polymers these are depends on the adhesive itself: typically neoprene or more natural rubbers are used.