| Abstract: | It has been determined that when a polyacrylic acid p(AA)] macromolecule primer is used in polyurethane (PU)/p(AA)/FPL-etched aluminum joint systems, it interacts preferentially both with the hydrated Al2O3 or aluminum hydroxide adherend surface through the formation of hydrogen bonds and with the isocyanate groups in the PU adhesive to yield polymer-to-polymer chemical bonding. This chemical crosslinking between the hydrated adherend and the polymeric adhesive acts significantly to promote interfacial adhesive bonds. It appears that a near monolayer of p(AA) is enough to occupy all the available functional groups at the PU and aluminum surface sites. This arrangement plays a key role in improving the adhesion durability of the joint system upon exposure to a hot NaOH solution. It was also determined that the presence of excessive carboxylic acid groups resulting from the use of a thick p(AA) layer caused gel-formation-induced adhesion failures; namely, the locus of failure of the joint after exposure was clearly identified to be cohesive failure in the primer. |
