ADHESIVES, GLUES AND SEALANTS
What is an adhesive?
We define adhesive or glue as a non-metallic material which is able to join 2 substrates using adhesion mechanisms (developed between the adhesive and substrate) and cohesive mechanism (developed within the adhesive itself).
As it is set out in the above definition, an adhesive is a non-metallic material, we usually refer to adhesives as the materials which are composed by organic polymers in a liquid state when applied and become a solid state after further curing or hardening.
Following the definition of adhesive in any bonding joint we find the following scheme:
Based on the previous figure and the definition of adhesive, we need to define three important concepts:
Definition of substrate – Corresponds to the material we wish to adhesive or join, for example:
If we bond 2 aluminum plates, each of the aluminum plates will be the substrate, in this example both the substrate 1 and substrate 2 are equal.
If you want to bond a glass front of a painted aluminum frame, we will have the substratum of glass and painted aluminum substrate in this example the substrate 1 is different from the substrate 2.
Definition of adhesion – adhesion are all the forces or mechanisms that keep the adhesive with each substrate, the term refers to all adhesion mechanisms or forces located in a thin layer (boundary layer) between the substrate and the adhesive itself.
Definition of cohesion - cohesion forces are all the forces or mechanisms that hold the adhesive itself.
The adhesive and cohesive definition refers to the forces that keep together the adhesive with the substrate (adhesion) and the adhesive itself (cohesion), these forces correspond to :
The chemical bonds.
Covalent chemical bonds are developed between atoms, enabling the creation of molecules and polymers, also chemical bonds allow to join different polymer chains creating compact and highly crosslinked structures (thermosets).
Intermolecular forces between molecules occur allowing the creation of amorphous structures with excellent elasticity and deformability.
The chemical bonds and intermolecular forces are the anchoring elements that holds together the adhesive with the substrate (adhesion) and the adhesive itself (cohesion).
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