Formulation of Epoxy Prepregs, Synthesization Parameters, and Resin Impregnation Approaches—A Comprehensive Review

Prepregs are resin-impregnated, expensive composites mainly limited to high-end applications within the aeronautical, defense, automotive, and energy sectors. Prepreg technology is mainly protected by trade secrets, resulting in limited studies on prepreg resin matrix development and recent advancements. Three key parameters for epoxy resin matrix development including B-staging, viscosity, and tackiness, and their control strategies are discussed in detail. The B-stage is defined as the partially cured stage of epoxy prepregs and is extremely important for prepreg layup, pot life, and final performances. The three key parameters are interrelated and accurately controlled, and, hence, resin development plays a huge role in the prepreg development process. This review also discusses the measuring techniques of the parameters in detail. Based on the resin impregnation techniques and B-stage control, two approaches are proposed to develop the prepreg resin formulations: conventional resin impregnation and viscosity-controlled resin impregnation. The approaches would be extremely useful, especially for advancing beyond the existing prepreg applications and developing smart materials and functional composites through advanced resin modification strategies.