Testing Adhesives for Resistance to DMSO

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 compatibility 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 product based on specific application requirements.

In this experiment, we focused on testing our epoxies for their resistance to DMSO (Dimethyl sulfoxide). The compounds Master Bond used for testing are a variety of two component epoxies and one component UV curing systems with good overall chemical resistance. For the first round of testing the products tested were EP46HT-2AO Black, UV22DC80-1, UV26, EP41S-5LV and EP41S-1HT. For the second round of testing the products tested were EP125 and UV25. For the final round the products tested were EP41S-5, EP62-1HT and EP62-1. These were compared against the resistance of a generic or standard non-chemically resistant epoxy. 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 DMSO. Then we continued recording frequent weight measurements. We carried on these tests with weight recording for varying lengths of time based on the products performance. Below you will see the results of soaking for 10 months in the first batch, 2 years for the next batch, and greater than 2.5 years for the third batch of products. The castings were weighed periodically and the graphs shown below demonstrate the percentage of weight change over time.

For the purpose of comparison, please notice that for each testing timeframe, a casting of a standard epoxy was also tested under these same conditions which served as a reference. As can be seen in the graphs, the standard epoxy was markedly less resistant to DMSO than the other epoxies tested. It demonstrated a significantly greater change in weight over time, and the casting ultimately dissolved in DMSO after less than one year.

In general, a swelling of less than 4-5% 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 DMSO might not be as severe or direct as in the above test conditions.

Compared with other chemical resistance testing, the products in these tests gained a bit more weight. This suggests the somewhat more aggressive nature of DMSO. Therefore, those products tested that held up well offer superior chemical resistance properties.

Please note, when choosing an epoxy for an application where the resistance to DMSO is critical, many other factors must be considered in addition to the chemical resistance. Each of the epoxies in the charts above offers a distinct set of performance properties. For example, if thermal conductivity and high temperature resistance are needed, EP46HT-2AO Black may be a good option. If a fast cure is required and there is full access to a light source with no shadows, UV25 can be considered. For longer term exposure to DMSO over a year or longer, the likes of EP125 and EP62-1HT are excellent candidates. These products all need to be processed or cured differently and although some of them can be cured with UV light or at room temperature alone, for enhancing/optimizing chemical resistance especially to DMSO, it is critical to add heat.

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