High-strength, degradable polymer composites based on fully bio-based lignin reinforcement: Strong interfacial adhesion properties and adhesive applications

Traditional adhesives are facing severe challenges, mainly reflected in their poor degradation performance and the raw materials are mostly derived from petroleum-based resources. A self-curable benzoxazine epoxy curing agent was synthesized in this work. Lignin-based polybenzoxazine modified epoxy resin (PL-PBz-AE) was obtained by curing acrylpimaric acid diglycidyl ester (AE) with phenolic lignin-ethanolamine benzoxazine (PL-BOZ). The anchoring effect can be accelerated by the use of ether bonds, the formation of a specific molecular structure after ring opening of the oxazine ring, and multiple hydrogen bonds, which form localised hydrophobic zones. PL-PBz-AE exhibits excellent and stable adhesion properties in underwater environments on a variety of substrates, including stainless steel, aluminum, and ceramics. The incorporation of lignin-derived polyphenolic architecture endows PL-PBz-AE with remarkable interfacial adhesion capabilities, demonstrating superior shear strength values of 3.96 MPa for stainless steel substrates, along with 2.15 MPa and 0.73 MPa for aluminum and ceramic interfaces respectively. This binder system hydrolyzes its carboxyl group in an alkaline solution, and we have a strategy for the specific design of a 1 N NaOH solution, which exhibits a unique alkali-responsive degradation, in which case the resulting oligomer intermediate can rapidly decompose the material through a solution-mediated chain cleavage mechanism. In addition, PL-PBz-AE can also be applied to underwater bonding and underwater pipeline leakage. These multifunctional attributes-combining robust adhesion, controlled degradability, environmental stability, and thermal stability establish PL-PBz-AE as a next-generation adhesive platform that successfully reconciles industrial performance requirements with sustainable material design principles.