Salicylhydroxamic acid containing structural adhesive†

The feasibility of utilizing salicylhydroxamic acid (SHAM) as a new adhesive molecule for designing structural adhesives is investigated in this study. SHAM-containing polymers were prepared with a hydroxyethyl methacrylate (HEMA) or methoxyethyl acrylate (MEA) backbone and mixed with polyvinylidene fluoride (PVDF). PVDF was included to increase the cohesive property of the adhesive through hydrogen bond (H-bond) formation with the adhesive polymers. SHAM-containing adhesive demonstrated lap shear adhesion strength (S_adh) greater than 0.9 MPa to glass, metal, and polymeric surfaces. Adhesive formulations with elevated SHAM-content also demonstrated increased adhesive properties with S_adh values reaching as high as 4.8 MPa. Due to the physically crosslinked nature of these adhesives, formulations with extensive H-bonding resulted in strong adhesion and stability. HEMA consists of a terminal hydroxyl group with both H-bond donor and acceptor, which enabled HEMA-containing adhesives to demonstrate strong adhesion even without PVDF. On the other hand, MEA contains a methoxy group that lacks H-bond donors for forming H-bonding and MEA-containing adhesives required PVDF to provide H-bond acceptors to increase its cohesive property. An aging study was performed on the bonded joints. While the adhesive joints did not demonstrate any reduction in S_adh values over 25 days when incubated in a dry condition, S_adh values decreased by 80% over 48 h when incubated in water. This is potentially due to the hydrophilic and physically crosslinked nature of the adhesive. Nevertheless, the SHAM-containing adhesive outperformed a catechol-containing adhesive and epoxy glue and is a promising new adhesive molecule for designing structural adhesives.