778 Research Article Received: 11 July 2009 Revised: 14 September 2009 Accepted: 25 September 2009 Published online in Wiley Interscience: 2 February 2010 (www.interscience.wiley.com) DOI 10.1002/pi.2788 The effect of organo-modifier on the structure and properties of poly[ethylene – (vinyl alcohol)]/organo-modified montmorillonite composites Edgar Franco-Urquiza, * Jos ´ e Gamez Perez, Miguel S ´ anchez-Soto, Orlando O Santana and Maria L Maspoch Abstract Ethylene – (vinyl alcohol) (EVOH)/organo-modified montmorillonite clay (OMMT) composites were prepared using commercial OMMTs with two different organo-modifiers. The first one has polar groups, which interact with EVOH chains, whereas the second one is non-polar. Composites with a high weight percentage of OMMT were prepared by melt-extrusion in a twin-screw extruder. Films were prepared in a cast-film line in order to evaluate the tensile and fracture parameters. The morphology of the EVOH/OMMT composites was characterized using wide-angle X-ray scattering and transmission electron microscopy, complemented by image analysis. The mechanical properties were evaluated using uniaxial tensile tests; the fracture behaviour was analysed using the essential work of fracture (EWF) method. Results show differences in composite morphologies and crystalline fraction, depending on the content and the nature of the organo-modifier. The mechanical and fracture behaviours are strongly influenced by those parameters, which act in opposite senses. The EWF method is shown to be a useful tool for the analysis of the structure – properties relationships of these composites. c  2010 Society of Chemical Industry Keywords: ethylene-(vinyl alcohol)/montmorillonite composites; essential work of fracture (EWF); morphology; structure–property relationship INTRODUCTION Ethylene–(vinyl alcohol) (EVOH) copolymer is a semi-crystalline polymer material with excellent gas-barrier properties and resistance to oil and organic solvents. 1,2 For such reasons, EVOH is widely used in many industrial applications such as food packaging, biomedical science and aerospace technology. 3–5 However, for high relative humidity conditions, EVOH loses some of its properties, which is the main reason why EVOH is commonly co-extruded in the middle of multilayer films. 6 Polymer–layered silicate (PLS) nanocomposites can have improved thermal, mechanical and barrier properties compared to pure polymers or conventional composites (microscale particle reinforcement). 7 The main properties of PLS nanocomposites have been widely studied over the past decade, it being found that very high performances can be reached through good dispersion of clay platelets inside the polymer matrix. 8 PLS nanocomposites are commonly based on montmorillonite (MMT), which is a type of smectite clay, a so-called 2 : 1 layered silicate. 9 This clay tends to form lamellar structures consisting of repeating sheets of two silica tetrahedral layers fused to an edge-shared octahedral layer of either alumina or magnesia. Stacking of the layers leads to regular van der Waals gaps between the layers, called interlayer distances or galleries. The galleries are occupied by cations, which balance the charges generated by isomorphic substitutions (Al for Si or Mg for Al) within the layers. 10 Ion-exchange reactions with cationic surfactants (alkylammo- nium cations) can be used to render organophilic the hydrophilic silicate surface and to increase the gallery distance. These organo- modified montmorillonites (OMMTs) make intercalation of many engineering polymers possible. Indeed, the organic cations can provide functional groups to interact with specific polymers, in- creasing their chemical compatibility, improving the strength of the interface between the inorganic phase and the polymer chains. The optimum compatibility depends on the functionality of poly- mer and modifier, packing density between layers and length of the organic modifiers. 11,12 Much work has been carried out in order to study the effect of organo-modifiers on several properties of PLS nanocomposites. However, most of this work has been focused on the enhancement of thermal and barrier properties 13–15 or mechanical properties, 16 only a few works being focused on fracture behaviour. 17,18 Melt intercalation might be the most convenient method for the synthesis of OMMT nanocomposites because it is broadly applicable to a wide range of polymer matrices, is more economic ∗ Correspondence to: Edgar Franco-Urquiza, Centre Catal` adelPl` astic, Universitat Polit` ecnica de Catalunya (UPC), Colom 114, 08222 Terrassa, Spain. E-mail: edgar.adrian.franco@upc.edu Centre Catal` a del Pl` astic, Universitat Polit` ecnica de Catalunya (UPC), Colom 114, 08222 Terrassa, Spain Polym Int 2010; 59: 778–786 www.soci.org c  2010 Society of Chemical Industry