The first use of glue dates back to the two hundredth millennium BC, the first user of glue soaked the thread connecting the stone with the wooden handle and, judging by the fact that the tool survived in the ground to this day, this Neanderthal deserves the honorary title of "engineer of the two hundredth millennium"!
By the word "glue" we mean any substance that binds two surfaces, therefore wax or resin in general, they are also adhesives.
What are the adhesives
At school, in labor lessons and for everyday tasks, we used PVA glue, white, with a faint smell,
it glues paper and cardboard well. Dries up not immediately, there is time to correct the incorrectly applied piece
paper for the application.
If you need to glue something more serious, like a wooden frame or a laptop cover, another one is used
glue - instant action. The instructions say to quickly and firmly squeeze and hold for about a minute
and then you can use it immediately. Fast and hard!
The epoxy adhesive consists of two flasks, in one resin, in the other a hardener. The contents are mixed
immediately before gluing and then you need to act quickly, otherwise the glue will dry up, and for correction
there are no time errors at all.
There are many other types: for tiles, for shoes, for rubber, glass, even for human skin!
How does bonding work
There are several basic bonding processes: drying, pressure, heating and exposure to radiation.
Drying
Drying the glue is the simplest mechanism, the glue consists of an adhesive and a solvent. Being in a closed container, the glue does not dry, because it is in a closed space. Getting to the surface the solvent begins to evaporate and as a result, only the adhesive composition remains, which freezes, penetrating into the surfaces to be bonded and forming a rigid joint. The thicker the glue layer, the slower the glue dries, therefore, when applying this type of glue, it is necessary to follow the technology and wait for complete drying.
Examples of glue drying glue - PVA, rubber glue.
Pressure
Some types of glue require the application of force to start the bonding process. In such an adhesive material the molecules are far from each other and as a result of the pressure, the molecules approach each other, triggering reactions between them.
As an example, tape or blocks of notes. The adhesive tape will hold well if you put enough pressure on it. In the shoe business, nairit glue is used - it begins to glue after compression.
Thermosetting adhesive
The bonding mechanism is similar to the previous type of pressure bonding. When heated in thermosetting glue reactions occur between the molecules and the mass freezes.
Thermoplastic adhesive
A separate type of adhesive is thermoplastic, at room temperature it is in a solid state and can melt repeatedly to glue surfaces.
