Testing Adhesives for Resistance to Ethanol

Many Master Bond epoxy systems are formulated with superior chemical resistance. In the lab, we continually test our materials by exposing them to specific chemicals over a long period of time. A common way of testing the chemical resistance of an epoxy is immersing a sample in a chemical and measuring its change in weight over time. A significant loss or gain in weight would indicate a decreased ability of a material to stand up to chemical exposure. These tests allow us to more accurately recommend the right adhesive based on specific application requirements.

In this experiment, we’ve focused on testing our epoxies for their resistance to ethanol. The compounds we used for testing are two component epoxies and one component UV curing systems with good overall chemical resistance: EP41S-5, EP62-1HT, UV25, and EP46HT-2AO Black. A few thin castings, roughly 2 inches in diameter and around 0.125 inches thick, were made for each product and cured in accordance to their specifications. Once the cured samples were created and initial weight was recorded, we submerged them in ethanol. Then we continued recording weekly weight measurements. Although we plan to carry on with these weekly weight recordings over a longer period of time, below you will see the results from the first 37 weeks of testing, demonstrating the percentage of weight change over time.

To put these numbers into comparison, a casting of a standard epoxy that hasn’t been formulated for chemical resistance was also tested under these same conditions. As you can see in the graphs, the standard epoxy was not as resistant to the ethanol as the other epoxies tested, considering that it demonstrated a significantly higher weight gain over time. In general, a swelling of less than 1% can be considered excellent, especially since this test may be more rigorous compared to actual service conditions. It is also worth noting that in the context of a bonded joint or a potted assembly the exposure to fuels might not be as severe or direct, as in the above test conditions.

Please note, when choosing an epoxy for an application where the resistance to fuels is critical, many other factors must be considered in addition to the chemical resistance. Each of the epoxies in the chart above offers a distinct set of performance properties. For example, if thermal conductivity is needed, EP46HT-2AO Black may be a good option. If a fast cure is required and there is full access to a light source, UV25 can be considered.

Disclaimer: The findings in this article are not meant to be used for specification purposes.