Reinforcement of Epoxy Resins with POSS for Enhancing Fracture Toughness at Cryogenic Temperature

Abstract

Although epoxy resins have been widely used for engineering applications, because of their good mechanical properties, they are usually brittle and vulnerable to cracking. This problem becomes more severe when thermosetting epoxy resins are employed in extremely low temperature environments. Hence improvement in fracture toughness is desired. Therefore, fillers such as clay, carbon nanotube, etc. have been used to enhance mechanical properties. Though these reinforcements showed promising results at room temperature, at cryogenic temperature they deteriorate the mechanical properties of epoxy resins. This is due to free space, free volume and thermal contraction effect. This study reports on the mechanical characterization of POSS–epoxy nanocomposites at cryogenic temperature (77 K). POSS (Polyhedral oligomeric silsesquioxne) is a hybrid organic–inorganic nanoadditive that directly interact with epoxy resin. These nanocomposites were prepared using DGEBF (diglycidyl ether of bisphenol F) based epoxy resin and three different functionalities of POSS, namely, glycidyl, trisilanol phenyl, and methacryl. POSS was added at various weight fractions of 0.5%, 1%, 3%, 5% and 8% and an amine-based hardener was used to cure epoxy resin. The test results show that the addition of POSS leads to significant improvement in fracture toughness at 77 K. There is no change in flexural modulus observed. Differential scanning calorimetry is used to measure the glass transition temperature.