Effect of tethering on the structure-property relationship of TPU-dual modified Laponite clay nanocomposites prepared by ex-situ and in-situ techniques Ananta K. Mishra a , Santanu Chattopadhyay a, * , P.R. Rajamohanan b , Golok B. Nando a, ** a Rubber Technology Center, Indian Institute of Technology Kharagpur, Kharagpur 721302, India b Central NMR Facility, National Chemical Laboratory, Pune 411008, India article info Article history: Received 7 June 2010 Received in revised form 27 September 2010 Accepted 7 October 2010 Available online 15 October 2010 Keywords: Thermoplastic polyurethane Nanocomposites Dual modification abstract Novel Thermoplastic Polyurethane (TPU)-dual modified Laponite clay nanocomposites were prepared by ex-situ and in-situ techniques. Two types of modified clays used in this work differ from each other by the number of active functional groups (tethering). Modified nanoclays are characterized by FTIR, Solid State NMR, XRD and TGA. Structural differences in the modified clays lead to novel tubular, elliptical and spherically aggregated morphologies of clays together with the hard segments of TPU. Changes in such morphology result in the difference in segmental relaxation, mechanical and rheological properties of the nanocomposites. In-situ prepared nanocomposites register inferior properties as compared to their ex-situ counterparts. The percent improvement in tensile strength and elongation at break of the ex-situ prepared nanocomposites with the modified clay having lesser tethering are found to be 67% and 208%, respectively. Thermal stability is enhanced by 35  C as compared to that of the neat TPU. Ó 2010 Published by Elsevier Ltd. 1. Introduction Thermoplastic polyurethane (TPU) is a block copolymer of (AB) n type consisting of soft segments (B) and hard segments (A). The soft segment is prepared by the reaction of diisocyanate with the olig- omeric polyol and the hard segment is formed by the reaction between the diisocyanate with the short chain diol or diamine. Due to the difference in polarity between the two segments and pres- ence of higher degree of H-bonding in the hard segments, phase segregation occurs. This leads the hard domains to provide rein- forcing effect to the soft segments [1e6]. When nanoclays are added into the TPU matrix, the mechanical and dynamic mechan- ical properties, thermal stability and barrier properties are improved significantly. Three different techniques are normally adopted to prepare TPU-clay nanocomposite (TPUCN), e.g., melt blending, ex-situ (solution mixing) and in-situ synthesis techniques. Ex-situ and in-situ preparation techniques are more favorable in the laboratory for the preparation of the nanocomposites [7,8]. In general, in-situ synthesis technique has been found to provide better improvement in property of the resulting nanocomposites as compared to the ex-situ prepared nanocomposites. This is because of the improved state of dispersion of the nanoclay that can be achieved by the former technique. At present, researchers are more focused towards using tethered clay as a pseudo chain extender [9e14]. Tethering of the clay (clay with modifiers containing active functional groups) is found to provide improved property spectrum as compared to the nontethered clay in nanocomposites prepared by both ex-situ and in-situ techniques [15]. It is observed that among the available nanoclays, modified montmorillonite (popularly known as Cloisite Ò ) is most widely used and very well explored for the preparation of TPU-clay nanocomposite. However, literature is strikingly scanty [16e21] on TPU-Laponite clay nanocomposites, despite of several advantages associated with Laponite clay. Laponite (synthetic hectorite nanoclay) possess well controlled dimensions, chemical purity and smaller diskette size (25e30 nm). The size scale of the individual diskettes matches well with the size of the hard domains in TPU. Laponite RD in the unmodified state remains aggregated in organic solvents like tetrahydrofuran (THF). Hence, it is mandatory to modify the surface of the clay by using either ionic [19,20,22] or covalent [23e27] modification techniques to improve its state of dispersion in polymers. Literature on the dual modification of Laponite [28e30] (combined ionic and covalent modification) is strikingly small in number. In one of our recent communications, we have illustrated salient aspects of dual modified Laponite RD in commercial TPU matrix by solution mixing technique for the first time [31]. This manuscript deals with the preparation of TPU-dual modified Laponite nanocomposite by both ex-situ and in-situ techniques. Ionic * Corresponding author. Tel.: þ91 3222 281758 (mob); fax: þ91 3222 282292. ** Corresponding author. Tel.: þ91 3222 283194 (mob); fax: þ91 3222 282292. E-mail addresses: santanuchat71@yahoo.com (S. Chattopadhyay), golokb@rtc. iitkgp.ernet.in (G.B. Nando). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer 0032-3861/$ e see front matter Ó 2010 Published by Elsevier Ltd. doi:10.1016/j.polymer.2010.10.010 Polymer 52 (2011) 1071e1083