Effects of the incorporation of modified kraft lignin on the mechanical properties of epoxy adhesive: experimental and theoretical approaches

Several lignin-based adhesives were developed during the last decades. More recently, lignin isolation methods were improved, leading to technical grade lignins with constant properties. This recent scenario created the required conditions for the industrial use of lignin in adhesive applications, at large scale, with reliable properties. In this work, technical grade kraft lignin was epoxidized and incorporated in industrial epoxy resin, resulting into a partly biobased epoxy resin. Notwithstanding, the mechanical properties of cured partly biobased epoxy were investigated using Arcan device, aiming to reproduce realistic load conditions for the adhesively bonded joints. At last, failure envelopes were obtained from Drucker–Prager and von Mises models, revealing the most reliable model to calculate the failure prediction. Results pointed out to the development of a partly biobased epoxy adhesive with slightly superior mechanical properties, in comparison with industrial epoxy adhesive. Indeed, an important contribution was provided for the lignin revalorization and the mechanical characterization and failure prediction of epoxy adhesive based on the modified lignin.