The effect of SiO 2 filler content and its organic compatibility on thermal stability of epoxy resin Adeel Afzal • Humaira M. Siddiqi • Naseer Iqbal • Zahoor Ahmad Received: 21 August 2011 / Accepted: 20 January 2012 / Published online: 14 February 2012 Ó Akade ´miai Kiado ´, Budapest, Hungary 2012 Abstract Thermal properties of the organic–inorganic bicontinuous nanocomposites prepared via in situ two- stage polymerization of various silanes, epoxy, and amine monomers are investigated, and the impact of filler content and its organic compatibility on thermal stability of these nanocomposites is studied. Two series of epoxy–silica nanocomposites, namely, EpSi-A and EpSi-B containing 0–20 wt% silica, are synthesized. An epoxy–silane cou- pling agent is employed to improve the organic compati- bility of silica in EpSi–B nanocomposites. The composites synthesized via two-stage polymerization are characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric (TG) analysis. DSC and TG/differential thermogravimetric results reveal substantially high glass transition (T g ) and excellent thermal stability of the bicontinuous nanocom- posites as compared with pristine epoxy polymer. Both T g and thermal properties, however, considerably vary depending on the organic compatibility of the nanocom- posites. Significantly higher decomposition temperatures are recorded in case of EpSi-B nanocomposites owing to the chemical links between the epoxy and silica phases. Kinetic studies also show relatively higher activation energies of pyrolysis for EpSi-B nanocomposites. Keywords Epoxy networks Á Sol–gel Á Bicontinuous nanocomposite Á Thermal stability Á Thermogravimetry Á Glass transition Introduction The organic–inorganic hybrid materials are commonly constructed from nanostructured domains of the inorganic filler homogeneously dispersed in the organic macromo- lecular matrix. The nano-sized inorganic filler such as sil- ica can be produced in situ via the sol–gel process that is by polymerizing the mixture of an alkoxysilane and either a polymer, polymerizable monomers, or network-forming oligomers [1, 2]. Such organic–inorganic hybrids are often referred to as bicontinuous nanocomposites owing to the interconnectivity of constituent phases [2, 3]. It is well known that physical properties of these nanocomposites largely depend on the properties of silica and polymeric matrix, their respective concentrations, and their interactions [1–3]. The excellence in thermal prop- erties of epoxy–silica nanocomposites, for instance, can be achieved through smaller size, efficient dispersion, and better interfacial cross-linking of silica with the matrix, i.e., epoxy networks in this case [4]. In effect, the inclusion of silica into epoxy networks augments char formation and its yield, consequently improving their thermal stability, because the char layer acts as a thermal insulator and a barrier to oxygen diffusion [5]. In the past, thermal degradation of epoxy–silica nano- composites has been extensively investigated owing to their widespread use as high-performance materials [5–7]. A. Afzal Á H. M. Siddiqi (&) Á N. Iqbal Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan e-mail: humairas@qau.edu.pk Present Address: A. Afzal Dipartimento di Chimica, Universita ` degli Studi di Bari—‘‘Aldo Moro’’, 4, via Orabona, 70126 Bari, Italy Z. Ahmad Department of Chemistry, Kuwait University, 13060 Safat, Kuwait 123 J Therm Anal Calorim (2013) 111:247–252 DOI 10.1007/s10973-012-2267-9