Toughening of aromatic epoxy via aliphatic epoxy copolymers

- Aromatic epoxy was toughened by adding di- and tri-functional aliphatic epoxies.
- Low aliphatic concentrations showed significant increases in impact strength.
- No reduction in mechanical properties seen at low aliphatic concentrations.

While aromatic diglycidyl ether of bisphenol A (DGEBA) based epoxy polymer matrix systems are important for high-performance applications, their brittle nature is an issue that needs to be addressed. In this paper the authors show that small additions of a more flexible aliphatic epoxy copolymers, both di- and tri-functional, can significantly increase the notched Izod impact strength (56-77%) over the neat DGEBA, while not detrimentally affecting other mechanical properties such as glass transition temperature and flexural properties. In fact, at 1 wt% concentrations, the tri-functional epoxy shows a slight increase (∼2%) in the glass transition temperature compared to neat DGEBA. The improvement in impact toughness is attributed to the more flexible backbone of the aliphatic epoxy molecules. The total miscibility of the aromatic and aliphatic epoxies within the investigated concentration range (up to 20 wt%) allows for this toughening approach to be directly applied to current composite production methods, such as resin transfer molding (RTM).

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