Preparation, characterization, and properties of Novolac type phenolic/SiO2 hybrid organic-inorganic nanocomposite materials by sol-gel method

This article describes the preparation of novolac-type phenolic resin/silica hybrid organic-inorganic nanocomposite, with a sol-gel process. The coupling agent was used to improve the interface between the organic and inorganic phases. The effect of the structure of the nanocomposite on its physical and chemical properties is discussed. The coupling agent reacts with the resin to form covalent bonds. The structure of the modified hybrid nanocomposites was identified with a Fourier transform infrared spectroscope. The silica network was characterized by nuclear magnetic resonance imaging (Si-29 NMR). Results revealed that Q(4) (tetrasubstituted) and T-3 (trisubstituted) are the dominant microstructures. The size of the silica in the phenolic resin was characterized with a scanning electron microscope. The size of the particles of inorganic silica in the modified system was less than 100 nm. The nanocomposite exhibited good transparency. Moreover, the thermal and mechanical properties exhibited significant improvement. The modified hybrid composite exhibited favorable thermal properties. The temperature at which a weight loss of 5% occurred increased from 281 to 350 degreesC. The flexural strength increased by 6-30%. The limiting oxygen index of the nanocomposite reached 37, and the Underwriters Laboratory test was 94V-0. Consequently, these materials possess excellent flame-retardant properties. (C) 2003 Wiley Periodicals, Inc.