Development of hybrid materials consisting of SiO2 microparticles embedded in phenolic-formaldehydic resin polymer matrices

A phenolic-formaldehydic resin (PFR) of the Novolac-type and modified by the incorporation of carboxylic end groups (MPFR), is used to influence the morphological and optical properties of sol-gel synthesized SiO2 materials. Silica microparticles are formed from the hydrolysis of silicon alkoxide solutions in ethanol and in the presence of polymerizing PFR or MPFR resins, hence rendering a final product consisting of SiO2 globules entangled inside a resin network. Under appropriate experimental conditions, chemical unions are established between silanol groups anchored on the surface of the SiO2 particles and MPFR carboxylic chains, to provide SiO2/MPFR core-shell compounds. The presence of PFR or MPFR resins during the SiO2 sol-gel production influences: (i) the size of SiO2 particles; and (ii) the transparency, translucency or opacity properties of the final hybrid products. Either one of the latter optical conditions is established by the amounts of reactants used to prepare a given hybrid specimen. FTIR, TGA and SEM are employed to determine the chemical and textural properties of SiO2/PFR and SiO2/MPFR solids. Results confirmed the existence of chemical bonds at the interface between silica and MPFR resin, as well as superior properties of these hybrid materials with respect to pure PFR or MPFR polymerized materials.