Simultaneously Enhanced Cryogenic Tensile Strength, Ductility and Impact Resistance of Epoxy Resins by Polyethylene Glycol

Rubbers have been well accepted for modifying brittle epoxies but rubber modified epoxies usually posses lowered tensile strength though enhanced ductility and fracture resistance. In this work, a polyethylene glycol (PEG-4000) is used to modify diglycidyl ether of bisphenol A/methyltetrahydrophthalic anhydride system for enhancing cryogenic tensile strength, ductility and impact resistance. The results display that the cryogenic tensile strength, ductility (failure strain) and fracture resistance (impact strength) are all enhanced for the modified epoxy system at proper PEG contents. The maximum tensile strength (127.8 MPa) at the cryogenic temperature (77 K) with an improvement of 30.1% is observed for the modified system with the 15 wt% PEG content. The ductility and impact resistance at both room temperature and cryogenic temperature are all improved for the modified epoxy system with proper PEG-4000 contents. These observations are explained by the positron annihilation lifetime spectroscopy results and scanning electron microscopy results. Moreover, the glass transition temperature decreases slightly with increasing PEG content.