Simultaneous improvements in the cryogenic tensile strength, ductility and impact strength of epoxy resins by a hyperbranched polymer

Abstract

Improvements in mechanical properties at low temperatures are desirable for epoxy resins such as diglycidyl ether of bisphenol A (DGEBA) that are often used in cryogenic engineering applications. In this study, a hydroxyl functionalized hyperbranched polymer (H30) is employed to improve the mechanical properties of a DGEBA epoxy resin at liquid nitrogen temperature (77K). The results show that the tensile strength, failure strain (ductility) and impact strength at 77K are simultaneously improved by adding a proper content of H30. The maximum tensile strength at 77K is increased by 17.7% from 98.2MPa of pure epoxy resin to 115.6MPa of modified epoxy system for the 10wt% H30 content. The failure strain at 77K increases consistently with the increase of H30 content. The maximum impact strength at 77K is attained by introduction of 10wt% H30 with an improvement of 26.3% over that of pure epoxy resin. For the purpose of comparison, the mechanical properties of modified epoxy resins at room temperature (RT) are also investigated. It is interesting to note that the impact strength is not lower at 77K than that at RT for the modified systems. Moreover, the glass transition temperature (Tg) is not reduced by the addition of H30 in appropriate amounts.