Chemical effects of organo-silanized SiO₂ nanofillers on epoxy adhesives

Although thermal and mechanical effects of organo-silanized SiO₂ nanofillers (NFs) incorporated into epoxy resins have been actively studied by many researchers, their chemical properties have rarely been reported. In this work, we investigated the chemical effects of organo-silanized SiO₂ NFs on epoxy adhesives with (3-glycidoxypropyl) methyldiethoxysilane (GPTMS) and (3-aminopropyl) trimethoxysilane (APTMS)-functionalized SiO₂ NFs. After curing epoxy-functionalized NF (EPOXY-NF) with triethylenetetramine (TETA) hardener, we were able to verify chemical crosslinking of the TETA hardener on EPOXY-NF with X-ray photoelectron spectroscopy, vacuum Fourier-transform infrared spectroscopy, and zeta potential analysis. Similarly, we found that after curing amine-functionalized NF (NH₂-NF) with bisphenol A diglycidyl ether (DGEBA) epoxy resin, the resin was chemically crosslinked on NH₂-NF as well. Finally, when we evaluated adhesion properties of adhesives composed of DGEBA resin/NH₂-NF and TETA hardener/EPOXY-NF on the basis of ASTM D3163, we observed improvements in the shear strength of 79 and 49%, respectively, in comparison with bare SiO₂ NF. This suggests that the chemical effects of organo-silanized SiO₂ NFs indeed contribute to the adhesion properties of adhesives.