This a two-stage technique for producing composites. In the first stage, a glass or carbon fiber fabric is impregnated with resin and partially cured (advanced) to a minimally tacky state. This prepreg (pre-impregnated fabric) is sold in rolls to fabricators. Prepregs generally require refrigeration to prevent further cure from occurring. In the second stage, the fabricator lays up prepreg sheets in molds to build appropriate part thickness and then applies heat to induce the final cure. Some pressure is usually employed. This technique allows for minimal material handling and the avoidance of formulation errors.
BTDA-based epoxy prepregs resist high temperatures and chemicals during final service, as well as enhanced stability of the prepreg, often without refrigeration. Combining BTDA with liquid anhydrides such as MTHPA and NMA further allows optimization of the processing properties for the prepregger. Catalyst selection enables a range of cure profiles in the fabrication stage.
Dianhydrides such as BTDA and 6-FDA are also used to produce polyimide prepregs for aerospace composite applications.