The fascinating world of adhesion with hot-melt adhesives
Adhesion – a term that often comes up in the world of hot-melt adhesives and plays a crucial role there.
What is adhesion?
Adhesion describes the ability of two different materials to stick together. It is basically the sum of all the attractive forces acting between the surfaces of these materials. These attractive forces are mainly due to physical interactions, which include van der Waals forces and hydrogen bonds.
Reactive hot-melt adhesives and chemical bonds
With reactive hot-melt adhesives, adhesion goes one step further. Here, chemical bonds can occur between the adhesive and the material to be bonded. These chemical bonds are typically much stronger than the physical interactions that occur with non-reactive hot-melt adhesives. However, adhesion formation still depends on physical interactions between the adhesive and the substrate. The adhesive and the part to be joined must come closer than 1 nanometer within the so-called “open time” of the adhesive.
The challenge with hot-melt adhesives
One of the special challenges with hot-melt adhesives is the rapid increase in viscosity after application. This increased viscosity makes it more difficult to wet the surfaces and thus to bridge the small distance of less than 1 nanometer between the parts to be connected.
In addition to the time factor, pressure also plays a crucial role when bonding with hot-melt adhesives. Applying pressure on the substrates to be bonded improves adhesion.
Mechanical adhesion – an additional help
Another interesting aspect of adhesion is the so-called “mechanical adhesion” or mechanical anchoring. The assumption here is that the adhesive penetrated the tiny pores and unevenness in the material to be joined and thus adheres to it. This mechanism further contributes to the strength of the connection.
The complex world of adhesion
Adhesion is a fascinating and complex area, which is still being intensively researched. There are various theories to describe adhesion, because the interactions between the different adhesive systems and the surfaces of the materials to be bonded are extremely complex. Scientists are constantly working to better understand the fundamentals of adhesion, in order to develop more effective and reliable bonding processes.
In the world of hot-melt adhesives, adhesion is a crucial factor that determines the quality and durability of connections. The combination of physical interactions, chemical bonds, pressure and mechanical anchoring makes adhesion an impressive phenomenon that forms the basis of many modern adhesive technologies.
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