Thermal properties of ethylene octene copolymer (Engage)/ dimethyldioctadecyl quaternary ammonium chloride-modified montmorillonite clay nanocomposites

The nanocomposites of ethylene octene copolymer (Engage ) with an organically modified (dimethyldioctadecyl quaternary ammonium chloride) montmorillonite (M-MMT) clay were synthesized by using a solution intercalation technique. The intercalation of M-MMT layers for M-MMT loading of 2.5–7.5% was verified by the shift of X-ray diffraction peak to a lower angle, showing change in basal d-spacing from 1.26 for M-MMT to 1.35 nm. Internal structure and the dispersion state of M-MMT in the nanocomposites were observed by transmission electron microscope, which confirmed the clay in the intercalated state. Thermomechanical analysis results showed improved dimensional stability under compression at 30 C for nanocomposites with increasing M-MMT. By DMA, the storage moduli of nanocomposites below glass transition temperature were higher than the neat Engage and increased with increasing M-MMT content. The glass transition temperature was lowest for the nanocomposite containing 2.5% M-MMT (E-2.5M-MMT), suggesting the optimal concentration of M-MMT in nanocomposite being 2.5% or higher from the viewpoint of thermal properties. The oxidation induction time (OIT) of the nanocomposites was obtained by using pressure-differential scanning calorimeter. The Engage/M-MMT nanocomposites were superior in thermal oxidation resistance as compared to the neat Engage, with E-5.0M-MMT yielding highest OITtime value. Introduction In the past two decades, the research in polymer/layered silicate nanocomposite has attracted the interests of academics and industries due to their improved mechanical, thermal, flame retardation, ablation resistance, and enhanced barrier properties [1–6]. Montmorillonite, more specifically a 2:1 phyllosilicate consisting of layers built by two silica tetrahedral sheets and one octahedral sheet of aluminum or magnesium hydroxide, has been well recognized to improve the mechanical strength and thermal properties of the polymer to which it is added [7–9]. By isomorphic substitution of Al by divalent (Fe or Mg) cations, negative charge is generated, which is counterbalanced with cations such as Li, Na, Ca. Such layers organize themselves as parallel layers with a regular van der Waals gap (called interlayer or gallery). It is also common to render the originally hydrophilic surface organophilic by exchanging the alkali counterions with cationic organic surfactants such as alkylammoniums [10]. The addition of organically modified montmorillonites (M-MMTs) to polymers further imparts flame retardancy, barrier properties, and ablation resistance to the resulting composite due to nanoscopic distribution and to a synergetic effect of the nano-sized crystals with the polymer chains [11]. Polymer/layered silicate nanocomposites are synthesized by four techniques: in situ polymerization, intercalation from polymer solution, intercalation by polymer melt or melt intercalation, and sol–gel technique [12]. The melt intercalation technique is a low-cost method by which the polymer chain can be intercalated into the galleries of clay by heating the polymer and organo–clay mixture to the glass transition temperature or the melting temperature of polymer. The mobile polymer chain can diffuse into the clay galleries and expand the silicate layer G. Latta Q. Lineberry R. Ozao H.-Y. Zhao W.-P. Pan Thermal Analysis Laboratory, Institute for Combustion Science and Environmental Technology, Western Kentucky University, Bowling Green, KY 42101, USA R. Ozao (&) SONY Institute of Higher Education, Atsugi, Kanagawa, Japan e-mail: [email protected] 123 J Mater Sci (2008) 43:2555–2561 DOI 10.1007/s10853-008-2468-6