An adhesive is a substance that is used to fix or bond two surfaces together. They come from very small powered substances to incredibly strong. Adhesives can be natural or synthetic but more commonly are the latter, man made glues produced for anything from household repairs to industrial bonding.
The original adhesives were natural, plant resins or animal substances. Ancient Egyptians used animal glues and Native Americans used rendered buffalo hooves. Natural adhesives are usually classed together and are separate from synthetic ones which themselves come in a variety of forms. The cheapest and weakest are usually simple solvents that evaporate and leave a adhesive bond, basically drying out, like the white glue used by younger children in crafts that can be painted onto a surface.
A fairly common form of adhesive is reactive; the well known two part epoxy comes under this group. These are two chemicals that are not adhesive until they are mixed together; then they rapidly solidify into a chemical bond that is very difficult to separate on a flat surface.
Hot or ‘thermoplastic’ adhesives are the type often found in workshops and are what many of us used in school. They are often loaded in a solid state into a glue gun which heats the substance, letting it run onto the surface that needs it. The surface is pressed against the desired object and generally left under light pressure until the glue has cooled. Upon cooling the two surfaces should be very difficult to separate.
The glues used on masking tape are pressure sensitive and form a bond when pressed into place, but can be peeled away at a later date. They also come in more permanent forms that are used in safety labels and sound dampening seals among other things.
Many modern adhesives are advertised with wild tests of strength such as adhering a man to a vertical surface. They are used in a huge variety of things from repairing vases or plastics, to modelling and other crafts, to industrial strength bonds like some car parts.
