Evolution of transient states and properties of an epoxy-silica hybrid cured at ambient temperature

An epoxy-silica hybrid was produced from a mixture of an amine-silane functionalized bisphenol-A resin and a siloxane precursor derived from tetraethoxysilane with small amounts of glycidoxypropyltrimethoxysilane coupling agent. The low temperature curing characteristics and final properties of the hybrid system were compared to those of two epoxy controls. Examinations were carried out by differential scanning calorimetry, dynamic mechanical analysis, electron microscopy, thermogravimetric analysis, UV-Vis spectroscopy, SAXS and densitometry. The modulus, strength and ductility were measured in 3-point bending mode at 23 and 50 degrees C. The siloxane hybridization of the original epoxy resin was found to increase the glass transition temperature (Tg) of cold cured systems by more than 10 degrees C and to produce large improvements in mechanical properties. The study has also provided new insights for the events taking place during gelation, vitrification and curing to the equilibrium state. (C) 2013 Elsevier Ltd. All rights reserved.