Effect of post-cure on the glass transition temperature and mechanical properties of epoxy adhesives

The effects of post-curing and cure temperature on the glass transition temperature, T-g, and the mechanical properties of epoxy adhesives were studied. T-g was measured by a dynamic mechanical analysis apparatus developed in-house and the mechanical properties of the adhesives (yield strength, Young's modulus and failure strain) were measured by a tensile machine. The relationships between T-g and mechanical performance under various post-cure conditions were investigated. The curing process was the same for all tests, consisting of an initial stage performed at different temperatures followed by cooling at room temperature. Three sets of specimens were considered, sharing the same initial cure process, but with a different post-curing procedure. In the first set, the specimens were only subjected to a curing process; in the second set, the specimens were subjected to a curing process followed by a post-cure performed at a temperature below the T-g of the fully cured network, T-g; and in the third set, the specimens were subjected to a curing process followed by a post-cure performed at a temperature above the T-g. When post-cured at a temperature above T-g, the mechanical and physical properties tend to have a constant value for any cure temperature.