Acrylic copolymer/montmorillonite (MMT) nanocomposites for warp sizing were prepared in the presence of Na+-MMT by the in situ intercalative polymerization of acrylic acid, acrylamide, and methyl acrylate in water solution. The properties of the solution and cast film were tested according to an application in sizing process of the nanocomposite size with various MMT contents. The results indicate that, for an exfoliated structure corresponding to the MMT content increasing to 7 wt %, the performance parameters of solution viscosity, glass-transition temperature, and tensile strength of the film increased and the moisture sorption, abrasion loss, and elongation at break of the film decreased. When the intercalated structure of MMT was 9 wt %, the gathered MMT layers acted as a common inorganic filler in the copolymer matrix, with limited contribution to the properties of the composite. The adhesion work of the nanocomposite solution was calculated by use of the Young-Dupre relation, which showed maximum values at an MMT content of 3 wt % on the surfaces of both the polyester and cellulose films. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 2958-2964, 2010