There are different types of gluebut all have an important feature in common: they must not glue and dry out within your container. But how do hill remain stable for months or years, before we use them and why does it sometimes happen to find a dry tube after months from the last use? The answer depends above all on the type of glue. Some hill, like those epoxy are formed by Two components held in separate packs And that “glue” only when they are mixed. The vinyl hill harden (and therefore glue) only when the water inside them evaporatefor this reason they do not harden or attack within the package; On the contrary, the hill cyanacrilicreact with water or with the humidity of the air, hardening, but inside the package they are liquid. It looks funny, but close the tube well It serves in the first case not to evaporate the water, in the second not to let it in.
Vinyl glue: avoid evaporation of the solvent
The famous vinyl glueadhesive par excellence in DIY and catchphrase of the famous program Art attackconsists of a watery solution in which Polivinil Acetate (PVA) molecules are dispersed, long carbon and hydrogen chains related to the so -called acetate groups (CH3Coo–).
Vinyl glue can be imagined as one emulsion (a “soup”) where the solvent (water) surrounds e makes PVA molecules mobile. Small mo molecules2Or prevent long pva chains from interacting with each other, reducing attractions Between molecules due to the forces of Van der Waals: in technical terms, rather than “soup”, this situation is called “latex“.
In contact with the air, vinyl glue begins to Losing water by evaporationhelped by the porosity of the materials to be glued: in this way, from the latex we quickly pass to one “Capping” of moleculeswhich in part also penetrate the surface of the glued pieces, and which are now free to interact with each other as much as possible Taking advantage of Van der Waals’s forces.
Within a very closed container, The water contained in the glue does not evaporateand the latex can remain long stable. However, this feature has negative implications: Very humid environments or direct contact with water can weaken the adhesive power of this glue, causing the detachment of the glued objects.
Cianoacrilati and bicomponent hill: chemical reactions to the right moment0
The rapid socket with such as the epoxy or basis of cyanacrililated, they glue thanks to chemical reactions leading to polymerizationthat is, the formation of larger molecules starting from smaller and reactive compounds. Obviously, for the conservation of glue it is essential that the reaction only begins Once the glue is applied And not in the starting container.
The epoxy are typically composed of two components, preserved in separate packs and that must be mixed before use. The first component It is a molecule containing the epoxy group (an oxygen linked to two adjacent carbon atoms, to form a cycle). The second component, also called hardening and often represented by Bisfenolo ais equipped with hydroxyil groups (-OH). When the two components come into contact, the epoxy group and the waterproof group react by creating a bond that leads to solidification of the mixture, ensuring strength and duration of the glue.
The discourse for the Colle Cianoacriliche: in this case, is the contact with thehumidity in the air or with water a trigger polymerization and the hardening of the adhesive. All the reactives are already in the same tube, and until we keep it closed, they do not come into contact with humidity or water and therefore cannot react and “glue” with each other or the package. A incorrect closure of the cap However, it can bring humidity and do dry easily the product, with a process unfortunately non -reversible.
