Fabrication and evaluation of structural film adhesive using oxazolidinone modified novolac epoxy resin

摘要

Epoxy film adhesives are of prime importance for the fabrication of lightweight honeycomb structures for aerospace industries. This work involves the synthesis of oxazolidinone modified epoxy novolac resin (EPN-OXA) via the reaction of EPN and toluene diisocyanate. EPN-OXA was characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, gel permeation chromatography, and epoxy equivalent weight. EPN-OXA was blended with solid epoxy resin, polyethersulfone (PES) toughened liquid epoxy resin, dicyandiamide, and aluminum powder to fabricate a film adhesive curing at 170-180 degrees C. Effect of additives and curative on the adhesive property was studied to optimize the composition. Effect of PES on the optimized composition was studied in detail. The best composition exhibited lap shear strength of 370 +/- 10 kgf cm(-2) at 25 degrees C and the strength was retained to 75% at -196 degrees C and 52% at 120 degrees C. PES significantly enhanced the interfacial strength at different temperatures (similar to 1.6-fold at -196 and 25 degrees C and similar to 1.8-fold at 120 degrees C). It also improved tensile strength and fracture toughness by 1.4- and 2-fold, respectively. The toughening effect of PES was further confirmed by scanning electron microscopy images. PES marginally reduced the glass-transition temperature and it exhibited no effect on thermal stability. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47520.