Modification of dicyandiamide-cured epoxy resin with different molecular weights of polyethylene glycol and its effect on epoxy/glass prepreg characteristics

Epoxy resins are widely used in the manufacture of structural composites; however, the inherent brittleness of epoxy matrices has restricted their applications. In this work, a diglycidyl ether of bisphenol-A epoxy resin cured by dicyandiamide (DICY) was modified by adding polyethylene glycol (PEG) with molecular weights of 2000 and 4000g/mol in amounts of 10, 20, and 30phr. The effect of these PEGs on the mechanical properties and fracture toughness of epoxy resin was studied. Toughness (the area under the stress-strain curve) increased approximately four- and eightfold upon the addition of 20 and 30phr of the PEGs, respectively. Results of this study also showed a 73% increase in fracture toughness (K-IC) and increases in 300% and 425% in fracture energy (G(IC)) following the addition of 30phr of PEGs 2000 and 4000, respectively. Subsequently, prepregs having 50wt% resin content were prepared. Then relevant prepreg tests such as rheology, resin flow, and lap shear strength were performed. Increasing the PEGs continuously improved resin flow. Scanning electron micrographs (SEMs) of unmodified samples and some PEG-modified samples were examined. SEM showed homogeneous blends with no phase separation occurring.