Epoxy adhesive and crystallization
What is crystallization?
When working with 2-component epoxy, it is not unusual for one component to crystallize.
This is manifested when one component (epoxy resin) visually becomes milky or cloudy, grainy, and may even appear partially cured.
In reality, it is just the resin changing form from liquid to solid, similar to water freezing into ice. Just as water has a melting point of 0°C, epoxy resin has a melting point around +50°C.
Crystallization is not a problem, but it can be inconvenient because it can prevent the two components (resin and hardener) from mixing optimally, which affects curing.
The solution is simple:
To reach the melting point of the epoxy resin, heat the epoxy to 40–50°C for about 60–120 minutes (depending on the container size), then allow it to cool slowly to normal room temperature.
This will cause the crystals to melt, and the epoxy will become uniform and clear. Store the epoxy afterward at a stable and consistent temperature as recommended.
The process does not affect the properties of the epoxy.
Why does resin crystallize?
Many types of plastic resin, including epoxy resin, are “supercooled,” meaning a material has not solidified even though its temperature is below the normal solidification point.
The reason it does not solidify is that crystallization is a slow process, or the molecules are positioned in a way that prevents crystal formation.
Therefore, it is natural for these “supercooled” liquids to crystallize when exposed to cold or temperature fluctuations.
It can be difficult to predict if a material (in this case epoxy resin) will crystallize and when. It depends on the resin’s viscosity, additives, and temperature.
Which types of epoxy are most likely to crystallize?
Properties of epoxy resin that can contribute to crystallization:
- Purity: The purer and more uniform the resin, the higher the chance of crystallization.
- Viscosity: Lower viscosity increases the chance of crystallization, and the crystallization rate is faster for low-viscosity epoxy resin.
- Temperature: Low temperatures influence crystallization.
- Temperature fluctuations: When the resin is exposed to increased temperature, molecules can shift position more easily. This increases the likelihood of crystallization when the temperature drops again (not necessarily below 0°C).
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