Chemical Resistance

Master Bond’s paper offers a guide to evaluating and selecting adhesive products exposed to harsh chemical environments. This article examines the importance of exposure variables, chemical interactions, testing and includes practical suggestions of procedures on how to avoid generalities in the selection process. Additionally, Master Bond supplies data results from its own unique ten year database of chemical immersion. The information contained in this white paper will give you a head start in choosing the right adhesive for these most critical applications.

Chemical resistant, two part epoxy, EP41S-5 has exemplary resistance to a wide array of chemicals, such as acids, bases, alcohols, fuels, including gasohol, and many solvents, such as methylene chloride. It is widely used for bonding, sealing and coating, as well as encapsulating, which can be seen in this video demonstration. This epoxy combines formidable physical strength properties and electrical insulation values.

Many Master Bond epoxy systems are formulated with superior acid resistance. 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 hydrochloric acid. The compounds Master Bond used for testing are a variety of two component and one component epoxies, and one component UV curing systems with good overall chemical resistance. For the first round of testing, which involved exposure to 15% hydrochloric acid, the products tested were UV25, EP41S-5, EP62-1HT, EP21ARHT, EP17HT, EP125, and EP62-1BF. For the second round of testing, which involved exposure to 25% hydrochloric acid, the same products were tested. For both tests, these products were compared against the resistance of a generic or standard non-chemically resistant epoxy. A few thin castings were made for each product and cured in accordance to their specifications. Once the cured samples were created and initial weight was recorded, the castings were immersed in either 15% or 25% hydrochloric acid. Then, we continued recording frequent weight measurements. Below you will see the results of soaking for more than one year in each concentration. The castings were weighed periodically and the graphs shown below demonstrate the percentage of weight change over time.Analyzing ResultsFor the purpose of comparison, please notice that for each concentration, 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 hydrochloric acid than the other epoxies tested. It demonstrated a significantly greater change in weight over time, and at both 15% and 25% concentration levels, the casting ultimately dissolved in hydrochloric acid after approximately seven months.Acids can etch the surface of an epoxy (resulting in loss of weight) or they can cause swelling of the sample (resulting in weight gain). In general, a weight change of less than 4-5% (gain or loss) can be considered excellent, especially since these tests 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 hydrochloric acid 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 hydrochloric acid is critical, many other factors must be considered in addition to the chemical resistance. Depending on the concentration level of hydrochloric acid, each of the epoxies in the charts above offers a distinct set of performance properties. For example, at both 15% and 25% concentrations, if electrical insulation and low outgassing are needed, EP41S-5 may be a good option. If a moderate viscosity and long working life are needed, EP62-1HT can be considered. If a one part system is needed at either concentration, EP17HT is an excellent candidate. These products all need to be processed or cured differently but the key in all cases is the addition of heat for enhancing/optimizing chemical resistance especially to hydrochloric acid.Disclaimer: The findings in this article are not meant to be used for specification purposes.

EP62-1HT is a two-component moderate heat curing epoxy system with a long working life of 12–24 hours at room temperature. It is suitable for many highly demanding aerospace, electronic, and specialty OEM applications, especially where resistance to aggressive chemicals is necessary, even at higher temperatures. It has versatile cure schedules that can be adapted to meet the needs of specific bonding applications, such as adhering an optical pinhole to borosilicate glass, as discussed in this case study.

One of the most effective approaches to prevent and inhibit corrosion of metals is to create a protective barrier over the component. This is most easily achieved with the use of a coating compound. Coatings protect against corrosion, moisture and other chemicals from attacking metal parts. Learn more about different types of corrosion and the ideal coating compounds that help prevent against damaging environments.

Many Master Bond epoxy systems are formulated with superior acid resistance. 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 by 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.IIn this experiment, we focused on testing our epoxies for their resistance to nitric acid. The compounds Master Bond used for testing are a variety of two-component and one-component epoxies with good overall chemical resistance. For the first round of testing, which involved exposure to 10% nitric acid, the products tested were EP125, EP62-1HT, EP21ARHT, EP62-1BF, EP17HT, and EP41S-5. For the second round of testing, which involved exposure to 20% nitric acid, the same products were tested. For both tests, these products were compared against the resistance of a generic or standard non-chemically resistant epoxy. A few thin castings were made for each product and cured in accordance with their specifications. Once the cured samples were created and initial weight was recorded, the castings were immersed in either 10% or 20% nitric acid. Then, we continued recording frequent weight measurements. Below you will see the results of soaking for more than one year in each concentration at room temperature ~ 75°F. The castings were weighed periodically, and the graphs shown below demonstrate the percentage of weight change over time.For comparison, note that for each concentration, 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 nitric acid than the other epoxies tested. It demonstrated a significantly greater change in weight over time, and at both 10% and 20% concentration levels, the casting ultimately dissolved in nitric acid after approximately seven months.Acids can etch the surface of an epoxy (resulting in loss of weight), or they can cause swelling of the sample (resulting in weight gain). In general, a weight change of less than 4-5% (gain or loss) can be considered excellent, especially since these tests 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 nitric acid 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 nitric acid is critical, many other factors must be considered in addition to the chemical resistance. Depending on the concentration level of nitric acid, each of the epoxies in the charts above offers a distinct set of performance properties. For example, at both 10% and 20% concentrations, if electrical insulation and high temperature resistance are needed, EP125 may be a good option. If moderate viscosity and a moderate heat cure is needed EP62-1HT can be considered. If a one-part system is needed at either concentration, EP17HT is an excellent candidate. These products all need to be processed or cured differently but the key in all cases is the addition of heat for enhancing/optimizing chemical resistance especially to nitric acid.Disclaimer: The findings in this article are not meant to be used for specification purposes.