Custom-shaped malleable, recyclable and reversible structural adhesives based on vanillin polyimine vitrimers

A series of polyimine vitrimers were prepared from a synthesized dialdehyde derivative of vanillin. This derivative was then crosslinked with two different ratios of amines (Jeffamine T403 and m-xylylenediamine), forming imine bonds responsible for the exchange reactions. This process resulted in three distinct materials which exhibited glass transition temperatures (Tgs) ranging from 20 to 60 degrees C, along with good thermal stability, and strong mechanical and thermomechanical properties. Their dynamicity resulted in a fast relaxation rate achieving a complete relaxation in less than 15 min at 140 degrees C. Additionally, the polyimines could be mechanically recycled up to three times without significant loss in their final properties, demonstrating the possible enhancement of their lifespan. Moreover, they could be chemically recycled under mild conditions through acid hydrolysis or transamination, which significantly contributes towards a better circular economy. Furthermore, these vitrimers were tested as reversible structural adhesives, achieving initial lap-shear strength values of 12.4 MPa and up to 97% of efficiency after re-bonding, highlighting their huge potential for industrial applications. Due to their pre-cured state, these adhesives were malleable, which allow them to be custom-shaped into different complex shapes. Finally, these imine materials showed outstanding self-welding capabilities with the repaired versions showing comparable performance to the original.