Fracture toughness of core-shell rubber modified epoxies at low and cryogenic temperatures: Evaluating the influence of the glass transition temperature of the rubber core

Epoxy matrices intended for use at low and cryogenic temperatures are susceptible to embrittlement and cracking. To assess whether core-shell rubber (CSR) modification remains effective under these conditions, this study determines the glass transition temperatures of three commercial CSR cores by dynamic mechanical thermal analysis (DMTA) and examines how fracture toughness evolves at temperatures positioned above, between, and below these transitions. CSR particles improve crack-propagation resistance at room temperature; however, their toughening efficiency declines with decreasing temperature, independent of core glass transition temperature. By −196 °C, fracture behaviour becomes largely determined by the epoxy matrix, with scanning electron microscopy (SEM) confirming suppression of cavitation and shear-driven toughening mechanisms. These results indicate that network constraints within the epoxy matrix, rather than rubber core mobility alone, control fracture performance at low and cryogenic-temperatures, and should be considered in the design of CSR-modified epoxies for extreme environments.