Wood polyphenolic extracts, commonly called tannins,
are excellent
candidates for the production of bioplastics due to their abundance
in nature, their commercial availability, and their reactivity. In
particular, they were tested as wood adhesives with several hardeners,
but their low moisture resistance and their rigidity reduced their
technological interest. In the present study, we combined regenerated
silk (RS) with tannin-furanic formulations to improve their properties.
Three-layer plywood glued with these several fully renewable tannin-silk-furanic
adhesives were tested for their mechanical properties: the modulus
of elasticity, the modulus of rupture, and both dry and wet shear
strength were enhanced when 20 wt % of RS was added. Initially, the
cross section of the prepared samples was investigated by scanning
electron microscopy, indicating a good dispersion of RS within the
tannin-furanic matrix. Afterward, thermomechanical analysis of the
adhesive highlighted that RS slows down the polymerization rate, decreasing
the cross-linking kinetics of polyfurfuryl alcohol. Chemical investigations
through ATR-FTIR and 13C-NMR show the formation of covalent
bonds between RS and the furanic matrix. In summary, the combination
of bioresources from the vegetal and animal kingdom allows the manufacturing
of fully bio-based adhesives with enhanced mechanical properties and
water resistance. This represents an important breakthrough in the
exploitation of polyphenols, opening perspectives for their application
in material science.