Georgia Tech researchers have developed a new approach to enable pressure-free repair, surface welding, and recycling of covalent adaptable network (CAN) polymers by using a small-molecule solvent (e.g., ethylene glycol), in a closed-loop, near-100-percent recycling paradigm. The technique was applied to engineering thermosetting polymers and their carbon fiber reinforced polymer (CFRP) composites – expensive, but commonly used materials for aerospace, automotive, and other industries requiring high strength-to-weight ratio materials. 

Immersing epoxy-based CFRPs in ethylene glycol and increasing the temperature resulted in the epoxy matrix being depolymerized as the ethylene glycol molecules participate in bond exchange reactions (BERs) within the CAN. This effectively breaks the long polymer chains into small segments, allowing for the clean carbon fibers to be reclaimed with the same dimensions and mechanical properties (e.g., strength, elasticity, etc.) as freshly created fibers. Heating the depolymerized solution further leads to repolymerization of the epoxy matrix, so a new generation of composites can be fabricated by using recycled fiber and epoxy. 

In addition, epoxy composites with surface damage can be fully repaired. Both the recycled and the repaired composites exhibit the same level of mechanical properties as virgin composites.