Epoxy Resin Crystallisation
What is epoxy resin crystallisation?
Epoxy resin crystallisation is a common problem. It is a transition from the liquid to the natural solid state of epoxy. Epoxy resin is a “super-cooled” liquid, which means it remains liquid even when its temperature drops below freezing point. If enough “seeds” are formed, super-cooled liquids have a natural tendency to form crystals at lower temperatures. These tiny seeds grow over time and can eventually prevent the product from functioning properly.
Epoxy crystallisation is more common in two-part systems (usually the resin side, labelled as part A). It can, however, also occur in one-part heat cure epoxy. In rare cases, crystallisation occurs in curing agents as well (usually labelled as Part B). Because crystallisation occurs naturally, it cannot be completely avoided, but the effects can be easily reversed with modest amounts of heat. So, while it can be inconvenient, crystallisation is a simple problem to solve.
How to recognise epoxy resin crystallisation.
Crystals typically appear as small floating lumps, and because they are heavier than liquid resin, they sink to the bottoms of containers. The presence of cloudy, hazy, or foggy resin usually indicates the start of crystallisation. Small crystals will grow and spread from the bottom and side walls of containers, and if left undetected and untreated for an extended period of time, they can form a single solid mass.
It is critical to note that if crystallisation occurs, the resin is not defective and can still be used. It only needs to be reconstituted to work properly.
Causes of epoxy crystallisation and how to avoid them.
Crystallisation is unpredictable and difficult to completely avoid. Epoxy crystallisation is caused by temperature fluctuations, prolonged exposure to extreme cold, high moisture content, high resin purity, low viscosity, and product contamination. The following simple tips will help to reduce the likelihood of crystallisation:
- Thoroughly clean container lids and edges after use.
- Use only clean hardware and tools to avoid resin contamination.
- Keep temperatures above 25°C during storage and transportation.
How to reconstitute a crystallised epoxy resin kit.
An epoxy resin kit should be inspected for crystallisation before use. If crystallisation has occurred, reconstitute the product by heating to between 55°C and 65°C until it is fully liquified. To ensure even heat circulation and crystal melting, the resin must be thoroughly stirred and scraped from the sides and bottom of the container. The amount of time required is determined by the size of the container, the amount of product, and the state of crystallisation. A small kit with a small number of crystals may only take a few minutes to reconstitute, but a large drum with severe crystallisation could require overnight heating. Once all crystals have been liquified, the product should be allowed to cool to room temperature, before mixing, to prevent flash curing. When the resin has cooled, it will function as if crystallisation had never occurred.
It should be noted that this method will not work for one-part heat cure epoxy systems, where heating the material will initiate curing.
This simple and inexpensive procedure is usually all that is required to control crystallisation, which can be bothersome for unprepared users, particularly when it occurs unexpectedly.