Bio-based poly(hydroxyurethane) glues for metal substrates

Bio- and CO2-based high performance thermoset poly(hydroxyurethane) (PHU) glues were designed from solvent- and isocyanate-free formulations based on cyclocarbonated soybean oil, diamines (aliphatic, cycloaliphatic or aromatic) and functional silica or ZnO fillers. Shear strength values and cohesive or adhesive failure of glues were correlated with the crosslinking, mechanical and thermal properties of the nanocomposite PHU thermosets. The addition of SiO2 or ZnO fillers bearing cyclic carbonate groups at their surface enabled strong improvement in the adhesion performances of the glues up to 173% compared to the unfilled PHUs. The most performing reinforced PHU adhesives showed a shear strength up to 11.3 MPa for an aluminum substrate, and 10.1 MPa for stainless steel with cohesive failure. This study highlights that bio-based nanocomposite PHU thermosets are promising sustainable alternatives to conventional glues made of toxic formulations containing isocyanates.