Preparation and characterization of poly(vinylalcohol)/modified bentonite nanocomposites Yasemin Turhan, Zeliha Gamze Alp, Mahir Alkan, Mehmet Dog ˘an ⇑ Balikesir University Faculty of Science and Literature, Department of Chemistry, 10145 Balikesir, Turkey article info Article history: Received 3 January 2013 Received in revised form 4 February 2013 Accepted 5 March 2013 Available online 13 March 2013 Keywords: Poly(vinylalcohol) Bentonite Nanocomposite Thermal stability Solution intercalation method abstract This study describes an effective way for the preparation of well-dispersed poly(vinylalcohol) (PVA)/ben- tonite and poly(vinylalcohol)/modified bentonite nanocomposites with improved thermal properties. Nanocomposites were synthesized by effectively dispersing the inorganic nanolayers of bentonite in PVA matrix via the solution intercalation method. Bentonite was calcinated at 150 and 650 °C and mod- ified with 3-aminopropyltrimethoxysilane (3-APT), dimethylsulfoxide (DMSO) and methanol (MeOH). The surface areas of bentonite and modified bentonite samples were measured by BET surface analyzer. In order to determine thermal stabilities of PVA and its nanocomposites, it was used thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The interactions between polymer, PVA, and filling material, bentonite were determined using Fourier transform infrared spectroscopy attenuated total reflectance (FTIR-ATR). The dispersion and exfoliation of the clay layers in PVA matrix were exam- ined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The contact angles of PVA and its nanocomposites were determined for nanocomposites by sessile drop method. The activation energies were calculated using the Kissinger method. XRD and TEM results showed that bentonite layers were dispersed in nanoscale and homogenously in PVA matrix. Microscopic and XRD techniques revealed highly organized regions. Clay content up to 5 wt.% led to nanocomposites with high degree of exfolia- tion. Thermogravimetric analysis indicated that introduction of clay to the polymer network resulted in an increase in thermal stability. Activation energy values at both stages for PVA/bentonite nanocom- posite were higher than those of pure PVA, indicating that addition of bentonite particles improves ther- mal stability of PVA. Ó 2013 Elsevier Inc. All rights reserved. 1. Introduction Filled polymer systems are very popular in the composite industry, because of their low cost and story performance. In re- cent years, a number of studies have been devoted to obtain nanomaterials with better chemical–physical properties than the pure polymer [1]. Nanocomposites are a relatively new family of composite materials in which, at least one of the dimensions of the filler, is in the nanometer range [2,3]. In general, polymer nano- composites are made by dispersing inorganic or organic nanoparti- cles into either a thermoplastic or thermoset polymer offering remarkable improvement in performance properties of the poly- mer. Nanoparticles can be three-dimensional spherical and polyhe- dral nanoparticles (e.g., colloidal silica), two-dimensional nanofibers (e.g., nanotube, whisker) or one-dimensional disc-like nanoparticles (e.g., clay platelet). Such nanoparticles offer enor- mous advantages over traditional macro- or micro-particles (e.g., talc, glass, carbon fibers) due to their higher surface area and as- pect ratio, improved adhesion between nanoparticle and polymer, and lower amount of loading to achieve equivalent properties. One general approach to prepare polymer nanocomposites is to employ intercalation chemistry of layered inorganic solids in which poly- mer is inserted into the interlayer space. Such layered solids in- clude graphite, clay minerals, transition metal dichalcogenides, metal phosphates, phosphonates and layered double hydroxides, etc. Among them, clay minerals have been widely used and proved to be very effective due to their unique structure and properties. Such minerals include both natural clays (e.g., montmorillonite, hectorite and saponite) and synthesized clays (e.g., fluorohectorite, laponite and magadiite) [4]. Polymer/clay nanocomposites, in which nanosized silicate plates of clay are uniformly dispersed in the polymer matrix, pro- vide enhanced mechanical and thermal properties compared to conventional composites [5]. However, aggregation of nanolayers, to various degrees, is unavoidable. Hence, much work has been de- voted to achieve maximum dispersion of nanolayers into polymer matrices. Generally, the clays have poor compatibility with the polymer matrix. Therefore, the clay must be organically modified using organic modifiers to improve compatibility. Intercalation 1387-1811/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.micromeso.2013.03.002 ⇑ Corresponding author. Tel.: +90 266 612 10 00; fax: +90 266 612 12 15. E-mail address: mdogan@balikesir.edu.tr (M. Dog ˘an). Microporous and Mesoporous Materials 174 (2013) 144–153 Contents lists available at SciVerse ScienceDirect Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso