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Inorganic filler content and the mechanical values of an Epoxy or Polyurethane system


The correlation between the chemical composition of the inorganic filler content and the mechanical values of an epoxy system

There are three main factors that would be considered when formulating an epoxy or urethane system for adhesives, potting and encapsulation applications.


The chemical structure

The more opportunity for chemical bonding between the epoxy resin and the filler (Van Der Waals forces), the better the mechanical strength at the interface of the epoxy and the filler. The chemistry of the filler will determine the quality of the bonding with the epoxy resin. In other words, the better the surface bond of the resin to the inorganic particles, the better the mechanical properties of the cured system in adhesive and potting applications.


The shape of the particles of the filler

  • The aspect ratio is a property of the shape of the filler particle. A round particle would have a lower aspect ratio than a pancake shape or a rod shaped particle. The greater the aspect ratio, the better the mechanical properties would be (i.e. talc has a higher aspect ratio than calcium carbonate an would have better overall mechanical properties as an additive filler). Adhesives and potting applications do realize benefits when particle shape is taken into account in epoxy and urethane formulations.
  • The surface of the filler will also impact the adhesive quality of the bond between the resin and the filler. A more jagged shape surface will have better properties than a more smooth and regular shaped particle.


The Mohs hardness of the filler

Typically, the higher the hardness, the better the mechanical properties. This would seem to be intuitive, as the higher hardness of the filler would provide stronger mechanical strength to the adhesive or potted formulation.


Additional Notes

  • These factors should be taken into consideration as an aggregate, and the individual properties should not be taken individually out of context. Formulating adhesives and potting materials does require the formulator to take into account many variables.
  • Most epoxy and urethane formulations will incorporate more than one filler to aid in satisfying the requirements of the epoxy or urethane system.
  • This discussion only dealt with the issue of mechanical properties. Fillers, will impact on a number of other properties such as viscosity, thermal conductivity etc.
  • There is a whole science of other surface additives that are integrated in the formulations that enhance the use of fillers that has not been addressed in this article.



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