Lap shear strength and thermal stability of diglycidyl ether of bisphenol a/epoxy novolac adhesives with nanoreinforcing fillers

Nanoreinforcing fillers have shown outstanding mechanical properties and widely used as reinforcing materials associated to polymeric matrices for high performance applications. In this study, a series of multiwalled carbon nanotubes (MWCNTs)‐, nano‐Al₂O₃‐, nano‐SiO₂‐, and talc‐reinforced epoxy resin adhesives composites were developed. The influence of different types and contents of nanofillers on adhesion, elongation at break, and thermal stability (under air and nitrogen atmospheres) of diglycidyl ether of bisphenol A (DGEBA)/epoxy novolac adhesives was investigated. A simple and effective approach to prepare adhesives with uniform and suitable dispersion of nanofillers into epoxy matrix was found to be mechanical stirring combined with ultrasonication. Transmission electron microscopic and scanning electron microscopic investigations revealed that nanofillers were homogeneously dispersed in epoxy matrix at optimized nanofiller loadings. Adhesion strength was measured by lap shear strength test as a function of nano‐Al₂O₃ and MWCNTs loadings. The results indicated that the lap shear strength was significantly increased by about 50% and 70% with addition of MWCNTs and nano‐Al₂O₃ up to a certain level, respectively. The highest lap shear strength was reached at 1.5 wt % of nano‐Al₂O₃ loading. MWCNTs at all loadings (except 3 wt %) and nano‐Al₂O₃ have enhanced onset of degradation temperature and char yield of the adhesives. By combined incorporation of 0.75 wt % nano‐Al₂O₃ and 0.75 wt % MWCNTs into the epoxy novolac/DGEBA blend adhesives a synergistic effect was observed in the thermal stability of the adhesives at high temperatures (800°C). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40017.