Received: 30 December 2008, Revised: 4 February 2009, Accepted: 11 February 2009, Published online in Wiley InterScience: 24 March 2009 Effect of process variables on mechanical properties of polyurethane/clay nanocomposites Mehrnaz Joulazadeh a and Amir. H. Navarchian a * This paper addresses the effects of operating variables on mechanical properties of polyurethane/clay nanocompo- sites including tensile strength, abrasion resistance, and hardness. The variables were prepolymer type, clay cation, clay content, and prepolymer–clay mixing time. The experiments were carried out based on the design of experiments using Taguchi methods. The nanocomposites were synthesized via in situ polymerization starting from two different types of prepolymers (polyether- and polyester-types of polyol reacted with toluene diisocyanate), and methyle- ne-bis-ortho-chloroanilline (MOCA) as a chain extender/hardener. Montmorillonite with three types of cation (Na R , alkyl ammonium ion, and MOCA) were examined. Among the parameters studied, prepolymer type and clay cation have the most significant effects on mechanical properties. Polyester nanocomposites showed larger improvements in mechanical properties compared to polyether materials due to higher shear forces exerted by polymer matrix on clay aggregates during polymer–clay mixing. The original MMT with Na R cation results in weak improvements in mechanical properties compared to organoclays. It is observed that the stress and elongation at break, and abrasion resistance of the nanocomposite samples can be optimized with 1.5% of clay loading. The morphology and chemical structure of the optimum sample were examined by X-ray diffraction and FT-IR spectroscopy, respectively. Copyright ß 2009 John Wiley & Sons, Ltd. Keywords: polyurethane; nanocomposites; clay; mechanical properties INTRODUCTION In recent years polymer nanocomposites have attracted extensive interests around the world due to the many superior properties they offer compared to traditional micro-size composites. [1–4] One of the most promising polymer nanocom- posite systems is a hybrid based on organic polymers and inorganic clay minerals consisting of layered silicates. [5] Crystal lattice of montmorillonite (MMT), widely used in nanocompo- sites, consists of two-dimensional layers in which a central octahedral sheet of alumina or magnesia is fused to two external silica tetrahedrons. [6–8] Due to the presence of sodium cations in the interlayer spaces (galleries), the natural MMT is hydrophilic and is only miscible with hydrophilic polymers. Therefore, it is necessary to exchange the alkali counter-ions with hydrophobic organic cations to improve the compatibility of MMT with organic polymers. [7,8] Polyurethanes (PU) have widespread applications as coatings, adhesives, foams, rubbers, and thermoplastic elastomers. [9–11] These polymers possess good mechanical properties such as high abrasion resistance, tear strength, flexibility and elasticity and outstanding oil resistance [12,13] ; however, it is possible that these properties could even more be improved by using organophilie MMT nanofillers. The various processing methods used to prepare polyurethane nanocomposites cause different filler distribution and exfoliation of the clay layers. The structure of polyurethane matrix as well as the type of hydrophobic cation in the clay can alter the variety of properties in PU/clay systems. [5] Thus the clay dispersion in the PU matrix, and therefore the ultimate properties of nanocomposite could be influenced by the factors including the process variables such as the type or molecular weight of polyol in PU structure, the type of cation (modifier) and the content of clay, [3,9,10,14–18] and mixing parameters. [19–21] The experimental design including the Taguchi method is a statistical approach that reduces the number of experiments necessary for investigating the effects of various parameters on the product quality and/or quantity. The Taguchi method also screens the significant factors affecting the response from those with less significance, and gives the optimum condition to attain the most desirable performance. Although there are a lot of papers recently published on the PU/clay nanocomposite field, [1–21] there is no report available regarding the application of experimental design for comparative analysis of the effects of operating variables on the mechanical properties of PU/clay nanocomposites. In this study, the influences of prepolymer type (A), clay content (B), mixing time (C) and clay cation (D), on the stress and elongation at break, abrasion resistance, and hardness (www.interscience.wiley.com) DOI: 10.1002/pat.1424 Research Article * Correspondence to: A. H. Navarchian, Department of Chemical Engineering, Faculty of Engineering, University of Isfahan, P.O. Box 81746-73441, Isfahan, Iran. E-mail: Navarchian@eng.ui.ac.ir a M. Joulazadeh, A. H. Navarchian Department of Chemical Engineering, Faculty of Engineering, University of Isfahan, P.O. Box 81746-73441, Isfahan, Iran Contract/grant sponsor: The Iranian Nanotechnology Initiative. Polym. Adv. Technol. 2010, 21 263–271 Copyright ß 2009 John Wiley & Sons, Ltd. 263