Adhesion - essential in the production of composite parts
What is adhesion?
Adhesion describes the interaction at the boundary layer between two different materials in order to enable mechanical force transmission. In elastomer technology, the term primarily describes the adhesion between materials such as Rubber-metal compounds, Rubber-plastic compounds or Rubber-fabric connections. It plays a central role in the manufacture of composite components, as reliable adhesion has a significant influence on the mechanical strength and service life of the component.
What are the 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)
What factors influence 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
What role does adhesion play 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 contact with media. Insufficient adhesion can lead to premature component failure, leaks, or functional impairments and is therefore particularly critical for safety-relevant components. In quality assurance, adhesion is often tested using peel or tensile tests. In these tests, damage should always occur cohesively within the elastomer phase, meaning the elastomer should be stronger than the interface.
