Cryogenic mechanical properties of epoxy resin toughened by hydroxyl-terminated polyurethane

In this work, we evaluated the room temperature (RT) and cryogenic temperature (77K) mechanical properties of diglycidyl ether of bisphenol A (DGEBA)/diethyl toluene diamine (DETDA) system modified by two kinds of hydroxyl-terminated polyurethanes (HTPU1 and HTPU2) with different molecular weights, in expectation of investigating the influence of phase structure on the overall resin performances. The morphological changes with different contents of HTPU were examined by scanning electron microscopy (SEM) and two phase structures of homogeneous phase and sea-island structure were proved to be successfully obtained by introducing of HTPU1 and HTPU2, respectively, which can be explained by the Flory-Huggins solution theory. The mechanical properties of the two kinds of modified resins were adequately compared at both RT and 77K. In general, the homogeneous phase resulted in higher enhancing effects on impact and tensile properties, while the sea-island structure showed better retention in the glass transition temperature (Tg) of the mixture. The mechanism of these property differences depended on the phase structure were discussed in detail and the conclusions achieved in this work could be reference valuable for the design and apply of modified resins with difference phase structures at cryogenic temperature.