Crystallization of Liquid Epoxy Resins Crystallization Epoxy resins, under certain conditions, can become solid or have a slush like appearance. This is called crystallization and it is where some component parts of the epoxy resin form a crystal like structure. The crystallization of an epoxy is very similar to water freezing in that it goes from a liquid state to become a solid. And like water once warmed it will revert back to it liquid state without any change or damage to the properties of the resin. But unlike water which melts at approximately 0°C the melting point of the Epoxy is 50°C. How to tell if your resin is affected. The first signs of crystallization are that the resin becomes cloudy, hazy or milky which are more easily seen in clear resin systems like the Ampreg 21. This opacity is generated by small crystals free floating in the resin. But as the size of the crystals increases the resin becomes more like a slush in that the material will still flow but sluggishly. As this crystallization of the resin increases the slush forms larger lumps. As the density of the crystallized resin is higher than the material surrounding it sinks to the bottom of the container, building in thickness until the whole container becomes solid. Why has this happened? First, it will not always happen but some things make it more likely to occur. Viscosity Lower viscosity systems are more likely to crystallize as the material can flow into the matrix patterns required for crystallization. Purity The higher the purity of the resin increases the possibility as there are less additives to disrupt the crystalline matrix forming.

Temperature fluctuations But the main cause of this effect is repeated changes in temperature; the resin being warmed and cooled repeatedly. The thermal cycling helps to orientate the material into the right chemical structure for the material to form crystals. But this should be greatly lessened if the material is stored as directed in the data sheets which normally are between 10°C to 25°C. The temperature fluctuations that occur between night and day start or enhance the crystal growth process. Dust & Contamination The introduction of dust particles into the resin can accelerate the process...