NJPST Volume 12: 2017 ISSN: 1119 - 4111 Nnamdi Chibuike Iheaturu Mechanical and Cryo-Fracture Properties of Core-Shell Clay Filled Epoxy Composites §§ Nnamdi Chibuike Iheaturu Department of Polymer & Textile Engineering, Federal University of Technology, PMB 1526, Owerri, Imo, Nigeria Abstract The fracture characteristics and mechanical stability of thermoset composites are of utmost importance in some engineering applications. In this study, novel 3-aminopropyltriethoxysilane coupled nanoporous organically modified calcites, “core-shell”, clay “SOBM-Ormocal” was used to reinforce phenol-free epoxy matrix. Such particulate nanoporous core-shell fillers are meant to diffuse stress concentrations within their host matrices thereby enhancing shear yielding in composite structures. But, on the contrary, this phenomenon greatly limits yielding and post-yield behaviour in particulate filled thermosets giving interesting fracture characteristics which were clearly evident in electron microscopy images obtained after cryo-fracture of the phenol-free epoxy composite samples. A careful assessment of the matting cracked surfaces presented features of brittle fracture even at very low filler loading, with no discernible stretch fibrils or ribs. Instead, crack pinning, tongues, inclusions, river markings, valleys and plateaus and bifurcations, were evident. Keywords: 3-Aminopropyltriethoxysilane, Nanoporous, Core-Shell, Calcite, Organophilic, Ormocal Introduction The use of conventional fillers such as talc, calcium carbonate, mica, layered double hydroxides, sodium or calcium montmorillonite clays, often leads to a temptation of using large quantity of fillers in the polymer matrix, first to cheapen the material, and secondly to have significant improvements in the composite properties, especially mechanical and thermal properties (Dai et al., 2005; Azeez et al., 2012). However, size, shape and form of filler or reinforcement play very significant roles in performance property enhancement (Choudhury et al., 2010; Lee et al., 2003). Polymer composites filled with nano-sized fillers have received considerable attention leading to an upsurge in various engineering applications due to their unique multifunctional property enhancement. Furthermore, it has been widely reported that, the combination of filler nanoscale dimension §§ Department of Polymer & Textile Engineering, Federal University of Technology, Owerri, (N. C. Iheaturu, nnamdi.iheaturu@futo.edu.ng) and high aspect ratio accompanied by surface modification and a high level of nanoscale dispersion and distribution within the polymer matrix usually leads to the improvements in the polymer properties at thresholds of filler volume fractions not more than 5 percent (Azeez et al., 2012; Dai et al., 2005; Fertig & Garnich, 2004; Ha et al., 2007). Nanoporous fillers with high surface area may also produce good composites at very high filler loading up to 85 percent mass fraction (Carrado, 2000). However, this usually has consequences, and in some cases may be associated with some undesirable properties such as brittleness, unbearable stiffness or loss of opacity in the final nanocomposite material. In an extensive review, Pavlidou and Papaspyrides (2008) reported that the efficiency of properties improvement depends largely on the nature of Nigerian Journal of Polymer Science and Technology, 2017, Vol. 12, pp 75-84 Received: 01 March 2018 Accepted: 03 September 2018 75