A bisphenol A-based epoxy was modified with an amphiphilic poly(ethylene-alt-propylene)-b-poly(ethylene oxide) (PEP-PEO) block copolymer as a toughening agent. PEP-PEO molecules self-assemble into spherical micelles in epoxy with an average diameter of 15 nm and give rise to 180% improvement in fracture resistance. The fracture and tensile behaviors of the PEP-PEO-modified epoxy were investigated at loading rates ranging from 0.51 to 508 mm min-1. The toughened epoxy exhibits mechanical properties that are significantly more rate dependent than the neat epoxy material. As expected, a higher test rate leads to a more brittle behavior of the material and a lower fracture toughness value. With careful systematic study of their micromechanical deformation processes, the observed strain rate dependence is explained. The implications of the current findings on nano-sized rubber toughening of epoxy are also discussed in detail.
Bibliographical noteFunding Information:
The authors from Texas A&M University thank the Microscopy and Imaging Center for TEM technical assistance. Financial support from the U.S. Department of Energy through subcontract to UT-Battelle No. 4000041622 is gratefully acknowledged by the authors from the University of Minnesota. This research is also funded by The Dow Chemical Company.
- Block copolymer
- Rubber toughening
- Strain rate dependence