When looking for low-outgassing products, keep in mind that not all adhesives start on a level playing field when it comes to passing ASTM E595. Some adhesives, such as two-part epoxies, can be specially formulated to achieve outgassing levels well below what ASTM E595 requires.
Other types of adhesive chemistries have traditionally not been able to pass ASTM 3595. UV-curable adhesives once fell into this category, which kept these fast-curing adhesives out of some otherwise suitable applications. Only recently have Master Bond’s chemists been able to “crack the code” of UV-curables that do pass the test.
The adhesives that outgas most severely are those that cure through the action of solvents or moisture. These would include a variety of pressure-sensitive and contact adhesives as well as cyanoacrylates. These types of adhesives are not the best choice in applications that have a known sensitivity to outgassing.
It’s worth noting that even within a given family of adhesives, the outgassing potential of the individual adhesive grades can vary substantially. This variance results from the optimization of each grade’s physical and mechanical properties through modifications to the underlying adhesive chemistry. To take one common example, the more flexible grades within the epoxy family tend to be more prone to outgassing—possibly because they have a lower crosslink density than their more rigid counterparts.
At the end of the day, adhesives are best looked at as individuals rather than families when evaluating outgassing performance. And the only way to know for certain whether a specific adhesive meets the low outgassing criteria spelled out in ASTM E595 is to test it.