What is adhesion?

Adhesion refers to the interaction at the boundary layer between two different materials to enable mechanical force transmission. In elastomer technology, the term primarily describes the adhesion between materials such as rubber and metal, plastic or fabric. It plays a central role in the production of composite components, as reliable adhesion has a significant influence on the mechanical load-bearing capacity and service life of the component.

 

Mechanisms of adhesion

  • Adhesion is caused by a variety of physical and chemical mechanisms, some of which are not yet fully understood
  • Mechanical adhesion to a rough surface
  • physical interactions through van der Waals or dipole-dipole forces between the molecules
  • chemical (covalent) bonds between atoms of both phases (e.g. Silane coating between glass and polymer)

 

Factors influencing adhesion

The strength of adhesion depends on several factors:

  • Surface quality: Roughness, cleanliness and surface energy that ensure good wettability
  • Chemical compatibility: Interactions between the material surfaces
  • Pre-treatment: Use of Adhesion promoters, Primers or surface treatments such as roughening and Degreasing
  • Curing or Vulcanisation conditionsTemperature, pressure and time influence molecular cross-linking at the interface

 

Adhesion in rubber processing

With elastomers, adhesion is often achieved through special Adhesion promoter systems which form the chemical bridge between the rubber and the substrate material. For example. NBR- or EPDM-Seals reliably on metal surfaces if the surface has previously been treated with a suitable adhesion promoter. During the Vulcanisation different processes take place simultaneously in the substrate, the adhesion promoter, the elastomer and in the boundary layers between them. The materials and bonding system must therefore be harmonised with each other on the basis of their respective reaction kinetics.

Good adhesion prevents detachment under mechanical load, temperature fluctuations or media contact. Insufficient adhesion can lead to premature component failure, leaks or functional failure and is therefore particularly critical for safety-relevant components. In quality assurance, adhesion is often tested by means of peel or tensile tests. The damage should always be cohesive within the elastomer phase, i.e. the elastomer should be stronger than the boundary layer.