Aqueous dispersion of novel silylated (polyurethane-acrylic hybrid/clay) nanocomposite Sankaraiah Subramani, Sung-Wook Choi, Jun-Young Lee, Jung Hyun Kim * Nanosphere Process and Technology Laboratory, Department of Chemical Engineering and Biotechnology, Yonsei University, 134 Shinchon-Dong, Sudaemoon-Ku, Seoul-120-749, Republic of Korea Received 27 March 2007; received in revised form 12 June 2007; accepted 13 June 2007 Available online 16 June 2007 Abstract Organofunctional silane-modified clay was synthesized using an ion exchange technique. The evolution of the ion exchanged or grafted amount and of the yield were monitored as a function of the initial silane concentration by thermogravimetric analysis. Qualitative evidence of the presence of chemically attached silane molecules on clay was proved by Fourier transform infrared spectroscopy. The grafted amount determined by thermogravimetric analysis was in good agreement with the cation exchange capacity of pristine clay, as determined by confirm- ing that the silanes, which replaced the sodium ions, are grafted onto the clay edges. Using the silane-modified clay, novel aqueous silylated (polyurethane-acrylic/clay) nanocomposite dispersions (SPUA e silylated polyurethane-acrylic) were prepared and studied. X-ray diffraction and transmission electron microscopy examinations indicate that the clay platelets are mostly intercalated or partially exfoliated in the SPUA matrix with a d-spacing of w2e2.50 nm. SPUA/clay dispersion with higher clay content exhibits a marginal increase in the average par- ticle size, however, silane-modified clay has a pronounced effect. In addition, the incorporation of clay can also enhance the thermal resistance and mechanical properties of SPUAs dramatically through the reinforcing effect of organophilic clay. Clay does not influence the location and peak broadness of the glass transition temperature (T g ) of the soft segment as well as hard segment domains in the SPUA/clay films. However, the T g of hard segment domains of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AEAPTMS)-clay nanocomposites were higher than those of commercial clay-based nanocomposites. Better water and xylene resistance of the silane-modified clay nanocomposites proved that trifunc- tional organosilane can be used as effective modifiers for clays. This method provides an efficient way to incorporate silane-modified clay in the SPUA matrix. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Aqueous; Silylated polyurethane; Modification 1. Introduction During the past several years, nanocomposite materials have attracted significant attention because the intimate com- bination of organic and inorganic components at the nanoscale offers prospects of new and synergistic properties. Nanopar- ticles often strongly influence the properties of composites at very low-volume fractions. This is mainly due to the small dis- tance between particles and the conversion of large fractions of the polymer matrix near their surfaces into an interphase with different properties, as well as the consequent change in morphology. The geometrical shape of the particles plays an important role in determining the properties of the compos- ites [1]. In general, the key step in the synthesis of these materials is the establishment of a chemical link between orig- inally non-mixing phases. Although the interaction between the organic polymers and the inorganic surfaces has long been a common operation, a major need for new bonding tech- niques arose when glass fibers were first used as reinforcing agents in organic resins. Organosilanes are known as the best surface treating agents for hydrophilic silicas and many other types of substrates. Organically modified alkoxysilanes * Corresponding author. Tel.: þ82 2 2123 7633; fax: þ82 2 312 0305. E-mail address: jayhkim@yonsei.ac.kr (J.H. Kim). 0032-3861/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2007.06.023 Polymer 48 (2007) 4691e4703 www.elsevier.com/locate/polymer