Engineers often use room temperature curable epoxies in applications and do not apply any heat either for curing or post curing. However, by omitting a heat cure or post cure, performance properties will not be optimized, especially in regards to chemical resistance. Master Bond offers a wide variety of two part systems that cure at room temperature when you mix part A and part B together. Although these systems are capable of curing at room temperature, adding heat helps the resulting product in numerous ways.
Not only does adding heat accelerate the cure and decrease the cure time, it also increases the cross linking and the polymerization. This helps improve the cured properties like physical strength, electrical insulation, and chemical resistance. In an application context, epoxies that are cured/post cured with heat typically outperform the systems that only cure at room temperature.
This was recently shown by a comparative study performed by Master Bond involving EP41S. EP41S is a two component room temperature curing epoxy system, which offers a relatively rapid cure at room temperature, convenient handling, and superior chemical/solvent resistance properties. A few thin castings, roughly 2 inches in diameter, and around 0.125 inches thick, were prepared using two different cure schedules, wherein half of these samples were cured at room temperature for 5 days with no addition of heat whatsoever; while the other half were cured at 80°C for more than 4 hours.
All of the castings of EP41S were then soaked in acetone, which is considered to be one of the more challenging chemicals for epoxies to resist. They were soaked for a period of one month, in order to measure the weight change before and after. After 30 days, the samples that were cured at room temperature had an average weight change of 5.80%. On the other hand, the samples that were heat cured only had an average weight change of 1.84%, not exhibiting as much absorption.
The samples that were heat cured ultimately resisted the acetone much better than those only cured at room temperature with no addition of heat. In conclusion, the importance of adding heat for curing cannot be overemphasized for applications involving long term chemical exposure.