Recently, we received a complaint from a customer,
“ Why the resin (Part A) of this batch is cured before mixing, has it gone bad? “
Actually this is epoxy resin crystallization.
It is normal occurrence in epoxies which have been exposed to low temperatures either in storage or during transit when being delivered.
Please don’t worry, the material has not gone bad. Once you return the epoxy to its normal state, it is perfectly usable and still has the same performance properties.
What is epoxy crystallization?
As the epoxies start to crystallize you will see little white granules, or the epoxy may look foggy and milky, or it may have solidified.
The epoxy crystallization is very similar to water freezing in that it goes from a liquid.
As well like water, once warmed it will revert back to liquid state without any change or damage to the properties of the resin. But water which melts at approximately 0°C, and the melting point of the Epoxy is 50°C.
Crystallization cannot be prevented completely since it is naturally occurring, but the effects can be resolved easily with proper heat, crystallization is not a difficult issue to overcome.
Why has crystallization happened?
Crystallization is unpredictable.
Data sheets will often tell you how to store resins and hardeners at a certain range temperature. But the epoxy may still be exposed to low temperatures, or temperature fluctuations during transit which is beyond anyone’s control.
There are some factors which epoxy crystallize easier :
Low viscosity.
High purity of material.
Temperature fluctuations.
Extreme cold temperatures.
Dust & Contamination.
How to return crystallized epoxy back to its normal state?
1. Heat crystallized epoxy between 50 to 60 °C (122°F to 140°F).
2. Stir epoxy including container sides and bottom thoroughly to ensure all crystals have been melted and that heat has been evenly distributed.
3. Check the epoxy at 10 minutes, at 20 minutes, at 30 minutes, and at 1 hour until there is no evidence of crystals.
(P.S. container size will affect the length of time needed for decrystallization.)
4. Let the epoxy to cool to room temperature, then proceed to use normally.
(Note: The treatment of low-temperature heat doesn’t damage the epoxy or impact its properties. As well, since you haven’t mixed the material, the epoxy won’t cure.
The treatment is not workable for one-part heat cure epoxy systems, where heating of material will initiate curing.)