Structure/transport property relationships within nanoclay-filled polyurethane materials using polycaprolactone-based masterbatches Samira Benali a,⇑ , Giuliana Gorrasi b , Leila Bonnaud a , Philippe Dubois a,⇑ a Centre d’Innovation et de Recherche en MAtériaux Polymères CIRMAP, Service des Matériaux Polymères et Composites, Université de Mons – UMONS and MATERIA NAOVA Research Center, Place du Parc 20, B-7000 Mons, Belgium b Department of Industrial Engineering, University of Salerno, Via Ponte don Melillo, 84084 Fisciano, Salerno, Italy article info Article history: Received 15 April 2013 Received in revised form 9 October 2013 Accepted 18 October 2013 Available online 7 November 2013 Keywords: A. Polymers A. Nanoclays A. Nanocomposites B. Thermomechanical properties B. Transport properties abstract The lamellar structure of montmorillonite (MMT) clays exhibits an interesting potential to improve the barrier properties of thermoplastic polyurethanes (TPU). However direct melt blending of an ester-based TPU and functional organoclays, despite showing good filler dispersion, did not allowed for improving neither barrier properties (i.e., sorption and diffusion to water vapor) not mechanical performances with respect to the unfilled TPU. Therefore, two alternative strategies involving poly(e-caprolactone) (PCL)/ organoclay masterbatches were explored to investigate the possibility to prepare materials with improved mechanical and barrier properties. In the first strategy, a PCL/organoclay masterbatch with high inorganic content was obtained by melt-blending (coined ‘‘free PCL’’ masterbatch), whereas in the second strategy PCL-grafted organoclay nanohybrids, also with high inorganic content were synthesized by in situ intercalative grafting/ring-opening polymerization of e-caprolactone (CL). Purposely, ROP of CL was initiated from hydroxyl groups available onto the MMT surface actually organo-modified by alkylammonium cations bearing hydroxyl functions (coined ‘‘nanohybrid PCL’’ masterbatch). These highly-filled PCL masterbatches (with ca. 25 wt% in inorganics) were then added into the ester-based TPU to prepare nanoclay/polyurethane nanocomposites by melt-blending. The morphology and disper- sion of the resulting materials were characterized by X-ray diffraction and transmission electron micros- copy. Improved sorption and diffusion properties towards water vapor as well as mechanical properties were measured. Herein, these results are discussed as a function of both clay dispersion and matrix/ organoclay interaction. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The research concerning polymer–clay nanocomposites [1–6] has highlighted the interest for organo-modified layered silicates such as montmorillonite (MMT) not only for increasing polymer stiffness [4] but also for enhancing other properties like thermal resistance [6], flame retardancy [6] and gas barrier properties [7,8]. The possibility of reaching large enhancement of polymer prop- erties lies upon reaching a high level of nanoplatelet dissociation and ultimate clay exfoliation throughout the polymer matrix [1,2,5]. Lightweight and economic competitiveness using a mini- mal amount of reinforcing materials, usually below 5 wt%, repre- sent other key-advantages of polymer–clay nanocomposites, which make them suitable for a broad variety of applications such as in automotive, electronic, food packaging, biotechnology, bio- medical field, and tissue engineering [9]. The wide applicability of polyurethane (PU) coatings is owing to versatility in selection of monomeric materials from a long list of macrodiols, diisocyanates and chain extenders [10]. With the development of low-cost polyols, PU coatings based on layered sil- icate-filled nanocomposites, for instance, are expected to display higher permeation-barrier properties towards water and oxygen molecules owing to the tortuous path created by the fine disper- sion of the impermeable clay nanoplatelets [11]. Many studies have been reported often employing traditional methods known for preparing nanocomposites such as (i) in situ polymerization of diisocyanates, macrodiols and chain extenders (CE), that are ini- tially intercalated between silicate layers [12–23] and (ii) melt intercalation and further dispersion/exfoliation of thermoplastic PU [9,24–28]. However, it is difficult to compare these different re- sults from literature because the monomers or polymers studied differ from one study to the other. Reported in situ polymerization methods lead to exfoliated structures, but no drastic changes of properties are observed. The preparation of PU nanocomposites based on an organosili- cate, e.g., a commercially available organo-modified MMT like Cloi- 0266-3538/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.compscitech.2013.10.015 ⇑ Corresponding authors. Tel.: +32 (0)65 373480; fax: +32 (0)65 373484. E-mail addresses: samira.benali@umons.ac.be (S. Benali), philippe.dubois@ umons.ac.be (P. Dubois). Composites Science and Technology 90 (2014) 74–81 Contents lists available at ScienceDirect Composites Science and Technology journal homepage: www.elsevier.com/locate/compscitech