Exploring resin viscosity effects in solventless processing of nano-SiO2/epoxy polymer hybrids

Abstract

Bisphenol A diglycidylether (DGEBA) based low viscosity, liquid epoxy resins are widely used as basis for advanced polymers and nanocomposites, adhesives, protective coatings and encapsulation. We present “green” synthesis of nano-SiO₂/epoxy polymer hybrids by a two-step chronological polymerization of inorganic and organic monomers without the use of diluents (solvents). Two types of liquid epoxy resins, D.E.R. 330 and D.E.R. 332, are used to demonstrate the influence of resin viscosity on microstructure, tensile strength and thermal stability of resulting hybrids. Obviously, differences in viscosity of two epoxy resins originate from variations in respective chain lengths, i.e. molar mass, which affect the overall crosslink density and properties of hybrids. In addition, grafting of nano-SiO₂ phases with organosilane is performed to achieve inorganic–organic (IO) phase interlinking and to investigate its consequences. Nano-SiO₂/epoxy hybrids are characterized by FTIR spectroscopy and XPS. AFM is used to study microstructure and surface properties of hybrids. AFM images show good distribution of nano-SiO₂ phases within epoxy polymer. It is observed that the size of nano-SiO₂ grows significantly, if resin viscosity is increased or if covalent IO phase interlinks are not present. Tensile measurements show considerable improvement in strength and modulus of nano-SiO₂/epoxy polymer hybrids as compared to neat epoxy polymers. DSC and TGA also demonstrate an increase in glass transition temperature (T_g) and thermal stability. We observe that viscosity effects are evenly pronounced in solventless processing of nano-SiO₂/epoxy polymer hybrids, and small changes in resin viscosity influence the miscibility of IO phases, the dispersion of SiO₂ and the performance of resulting hybrids.