Nanostructured adhesive layers were prepared by adsorbing and/or grafting polyvinylamine (PVAm) onto carboxylated poly(N-isopropylacrylamide) (PNIPAM) microgels that were then assembled between layers of wet oxidized cellulose. The wet delamination force was measured as functions of PVAm content, PVAm molecular weight, coverage (mass adhesive/joint area), and the distribution of carboxyl groups in the PNIPAM microgels. The use of microgels is attractive because simple physical adsorption onto the cellulose surfaces before lamination gives much higher adhesive content and strength compared to the corresponding adsorbed linear PVAm. Wet adhesion increased with PVAm content in the microgels and the quantity of microgels in the joint whereas adhesion was independent of PVAm molecular weight. Physical adsorption of the PVAm onto/into the microgels gave the same adhesion as covalently coupled PVAm. Finally, the roles of microgel diameter, elasticity, and coverage were simulated by a simple peel adhesion model in which the microgels were treated as ideal springs.

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The ability of carboxylated PNIPAM microgels bearing adsorbed PVAm to increase the strength of wet paper and wet cellulose film laminates was measured as a function of the microgel diameter, cross-linking degree, PVAm molecular weight, and roughness of the cellulose substrates. The experimental results and simulations from a model led to the following design rules: (1) For low microgel dosages, small microgels are better because they cover more surface; however, very small gels can get buried in pores. (2) For high microgel dosages, larger gels are better because a saturated monolayer of adsorbed large gels puts more adhesive in the joints. (3) Adhesion increases with decreasing microgel modulus (cross-linking). (4) Adhesion is not sensitive to the molecular weight of the reactive PVAm microgel coating polymer.

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