Polymer International Polym Int 57:292–296 (2008) Polyamide – silica nanocomposites: mechanical, morphological and thermomechanical investigations Muhammad Ilyas Sarwar, 1∗ Sonia Zulfiqar 1 and Zahoor Ahmad 2 1 Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan 2 Department of Chemistry, Faculty of Science, Kuwait University, PO Box 5969, Safat 13060, Kuwait Abstract BACKGROUND: The physical properties of polyamides can be enhanced through incorporation of inorganic micro- and nanofillers such as silica nanoparticles. Transparent sol-gel-derived organic-inorganic nanocomposites were successfully prepared by in situ incorporation of a silica network into poly(trimethylhexamethylene terephthalamide) using diethylamine as catalyst. Thin films containing various proportions of inorganic network obtained by evaporating the solvent were characterized using mechanical, dynamic mechanical thermal and morphological analyses. RESULTS: Tensile measurements indicate that modulus as well as stress at yield and at break point improved while elongation at break and toughness decreased for the hybrid materials. The maximum value of stress at yield point (72 MPa) was observed with 10 wt% silica while the maximum stress at break point increased up to 66 MPa with 20 wt% silica relative to that of pure polyamide (44 MPa). Tensile modulus was found to increase up to 2.59 GPa with 10 wt% silica in the matrix. The glass transition temperature and the storage moduli increased with increasing silica content. The maximum increase in the T g value (144 ◦ C) was observed with 20 wt% silica. Scanning electron microscopy investigation gave the distribution of silica, with an average particle size ranging from 3 to 24 nm. CONCLUSION: These results demonstrate that nanocomposites with high mechanical strength can be prepared through a sol-gel process. The increase in the T g values suggests better cohesion between the two phases, and the morphological results describe a uniform dispersion of silica particles in the polymer matrix at the nanoscale.  2007 Society of Chemical Industry Keywords: polyamide; composites; sol-gel process; stress-strain curves; glass transition temperature; morphology INTRODUCTION Polyamides are recognized for their outstanding prop- erties in terms of thermal stability, mechanical proper- ties, high glass transition temperature and good resis- tance to solvents. Aromatic polyamides, due to their high performance and superb properties, are widely utilized for aerospace applications. The aliphatic ana- logues of these polymers are generally referred to as nylons and are used in many everyday appli- cations. There is another class of glassy copolymer obtained from condensation of aromatic diacids and aliphatic diamines. 1,2 These are often known as glass- clear nylons with exceptional properties such as good transparency, rigidity, thermal resistance and hard- ness, and have many industrial applications. Some of their applications, however, require further prop- erty enhancements; the desired improvements can be obtained through incorporation of inorganic micro- and nanofillers such as silica nanoparticles. Recently, various polyamides have been used as polymeric matri- ces for hybrid organic–inorganic systems prepared through a sol – gel process. 3–6 Organic – inorganic com- posites are an important class of new-generation materials which combine the desirable properties of a ceramic phase (heat resistance, retention of mechan- ical properties at elevated temperatures and low thermal expansion) with those of organic polymers (toughness, ductility and processability). The properties of a composite material depend not only on the properties of each component, but also on the composite’s phase morphology and interfacial interactions. On the basis of interfacial interactions between the two phases, hybrid composites are of two types. The first type involves the formation of extensive hydrogen bonding between the composite materials, and the second type involves the connection of the two phases by covalent bonds. These composite materials are generally strong, stiff and tough materials capable of withstanding a wide ∗ Correspondence to: Muhammad Ilyas Sarwar, Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan E-mail: ilyassarwar@hotmail.com (Received 13 March 2007; revised version received 10 April 2007; accepted 17 May 2007) Published online 3 August 2007; DOI: 10.1002/pi.2343  2007 Society of Chemical Industry. Polym Int 0959–8103/2007/$30.00