Bisphenol E cyanate ester as a novel resin for repairing BMI/carbon fiber composites: Influence of cure temperature on adhesive bond strength
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The increasing use of polymer matrix composites (PMCs) in structural applications created demand for advanced repair techniques to fix internal delaminations in PMCs. One of a variety of repair techniques is injection repair, which involves injecting a low viscosity resin directly into the damaged area and subsequently curing the resin to heal the damage. In this study, bisphenol E cyanate ester (BECy) was investigated as a potential resin for injection repair of bismaleimide-carbon fiber based composite panels for aircraft. Temperature sensitive repair applications required a technique that avoided the high temperature post-cure of the injection repair resin. Modulated differential scanning calorimetry (MDSC) experiments were used to examine the degree of cross-linking and the glass transition temperature (Tg) of under-cured injection repair resin. The chemistry of cross-linking in under-cured BECy was studied by Fourier transform infrared spectroscopy (FTIR). Lap shear tests of the under-cured injection repair resin on composite substrates revealed the influence of change in isothermal under-cure temperature on the bond strength. Temperature dependent dynamic mechanical analysis disclosed the significance of sub-Tg relaxations on the adhesive properties of the under-cured resin. Post-fracture surface analysis of the lap shear specimens, performed using Scanning Electron Microscope (SEM) micrographs, indicated a mixed mode of fracture in the form of a combination of resin and resin–composite interface failure.