Design and Formulation of a Completely Biobased Epoxy Structural Adhesive

We have successfully engineered a fast-curing, completely biobased epoxy adhesive that can exhibit lap shear strengths of above 20 MPa. The rigid, fast-curing, biobased epoxy monomer was co-polymerized with a flexible long-chain biobased monomer to increase toughness. The 60:40 weight ratio blend was identified for a nanoscale mixed morphology and an anomalous increase in mechanical properties and adhesive strength. The rheological behavior of the adhesive was further tuned by dispersing a biobased filler, cellulose nanocrystals (CNCs), into the optimized blend. The addition of CNC increased the curing rate, induced shear-thinning behavior, as well as further increased the adhesive strength. For 1 wt % and higher CNC fractions, filler network prevented the adhesive flow after application resulting in stable joints. Finally, the petroleum-derived curing agent was replaced with a biobased one (bis-(furfurylamine)) to cure the optimized resin formulation, resulting in stable crack growth and, thus, a dramatic change in fracture behavior. This brittle to ductile transition in fracture behavior corresponded to a significant increase in adhesive strength.