Epoxy toughening with nano-sized amphiphilic block copolymer micelles
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abstract
An amphiphilic poly(ethylene-alt-propylene)-b-poly(ethylene oxide) (PEP-PEO) block copolymer (BCP) was blended with a bisphenol A-based epoxy resin formulation and self-assembled into a worm-like micelle structure. With an incorporation of 5 wt% of the BCP material, the fracture toughness was improved by more than 100% over the neat epoxy. The morphology and mechanical properties of this BCP-modified epoxy were investigated using transmission electron microscopy (TEM) and fracture toughness measurements. Toughening mechanisms from the worm-like micelle modified material were investigated using the double-notch four-point-bending (DN-4PB) technique, and the results are compared to data obtained from the same epoxy thermoset formulation containing a BCP that self-assembled into spherical micelles. Elongated cylindrical micelles produce improved toughness, which is interpreted based on a combination of mechanisms including crack tip blunting, cavitation, particle debonding, limited shear yielding, and crack bridging. The implications of the present study for polymer toughening in general are also discussed.
