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Nanoscale Self Assembly of Triblock Copolymers in Epoxy Polymer Composites: A Comparison to Traditional Rubber Toughening



This research investigated the ability of a traditional rubber toughening agent, namely carboxyl-terminated butadiene-acryltonitrile (CTBN) and the triblock copolymer (poly)-styene-block-(poly)-butadiene-block-(poly)-methylmethacrylate (SBM) (Arkema E21) to toughen a diglycidyl ether of bisphenol-A (DGEBA) epoxy resin cured with m-phenylenediamine (mPDA). It was found that both CTBN and SBM additives led to decreases in epoxy polymer composite (EPC) flexural properties and increases in fracture toughness (KQ). Fracture surface investigation by scanning electron microscopy showed that CTBN phase separated into particles with diameters on the order of microns, while SBM self assembled into 100 nm spherical micelles which, at larger concentrations in the epoxy, tended to aggregate to form an interpenetrated network. In both systems, cavitation of spherical rubbery domains and matrix shear yielding were identified as toughening mechanisms. Additionally, the SBM EPC fracture surfaces showed pullout of SBM particles. The finer particle size of the SBM terpolymer in DGEBA led to a 215% increase in KQ at 10 phr SBM, while 10 phr CTBNx13 led to a 90% increase in KQ. Also, it was found that KQ increased linearly with concentration for the SBM EPCs, while CTBN EPC KQ did not increase linearly with concentration. Further, dynamic mechanical analysis showed that CTBN plasticizes the epoxy matrix, leading to decreases in glass transition temperature (Tg). A decrease in cured epoxy Tg by the addition of SBM at 5, 10 and 15 phr was not observed. Finally, the influence of curative concentration on cured DGEBA mechanical, thermomechanical and KQ was explored. Maxima in flexural strength and modulus were observed for epoxide rich networks and maximum KQ was observed for amine rich networks. Therefore, SBM was used to modify amine rich networks, which showed more ‘toughenibility’ and a 300% increase in KQ at 10 phr SBM additive.

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