Four series of waterborne polyurethane (WBPU)/clay nanocomposite adhesives were prepared using three different countercations, namely triethylamine (TEA), lithium hydroxide (LiOH) and copper hydroxide (Cu(OH)(2)) as well as one mixed countercation of TEA and Cu(OH)(2) (1:0.5). The interaction of carboxyl acid salt group using different countercations with clay platelet was characterized by SEM and TEM, and the interaction effects on properties such as water swelling (%), thermal stability, tensile strength, glass transition temperature (T(g)), and adhesive strength were investigated. The tensile strength, water resistance and adhesive strength increased with increasing clay content up to an optimal value at which point the maximum tensile strength, water resistance and adhesive strength were recorded for each series. However, the optimal clay contents were 1.00 and 0.50 wt% for TEA/LiOH mixed countercation series and (Cu(OH)(2)) series, respectively. Among all of the samples the maximum tensile strength, water resistance and adhesive strength were found using mixed countercation (TEA and Cu(OH)(2) = 1:0.5) with 1 wt% clay content. (C) Koninklijke Brill NV, Leiden, 2011