In relation to adhesion, there are six theories, namely (physical adsorption, chemical adsorption, penetration, electrostatic, internal mechanical bonding and weak boundary layer), which we are going to explain each one separately and briefly so that you can get familiar with them.
Physical absorption theory
Physical attraction includes van der Waals forces between surfaces. which includes attractions between permanent dipoles and induced dipoles and Landen forces.
Chemical adsorption theory
In the case of adhesion, it is based on the formation of covalent, ionic and hydrogen bonds between the theory of chemical bonding with silane coupling agents to form the surface. There is evidence that covalent bonds are formed. It is possible that adhesives contain hydroxy or amine groups, which are active hydrogen forming atoms, such as hydroxyl groups. If wood or paper are used, hydrogen bonds are formed.
Penetration theory suggests that polymers may penetrate each other when in contact. Therefore, the internal boundary is finally removed and the penetration of polymers occurs if the chains are mobile and compatible. In other words, the temperature should be higher than the glass temperature.
Electrostatics originates from this idea that when two metals are in contact with each other, electrons are formed, which are transferred from one to the other, thus showing an electrical double layer. Because polymers are non-conductive. It seems difficult to apply this theory to adhesives.
Theory of internal mechanical linkage
If the surface on which we want to stick something has an irregular surface. The glue may get into the unevenness of the surface before it hardens. This idea led to the emergence of this theory that was extended to adhesive joints with porous materials such as wood and textiles. An example of this is the use of iron in the adhesive layer and in clothes. The adhesive layer contains hot melt adhesives that penetrate the fabric after melting.
Weak boundary layer theory
Clean surfaces create stronger bonds with the adhesive. But the weak boundary layer theory, some pollutions such as oil rust or greases create a layer that has poor adhesion. All contaminants create a weak boundary layer, because in some cases they will be dissolved by the adhesive. In this range, acrylic construction adhesives are superior to epoxides, and this is because of their ability to dissolve oils and greases.
Need an adhesive with special features?
Persia Production Group, relying on its production capacity and outstanding engineers, can meet your needs in supplying all kinds of industrial, automotive and construction adhesives.