Poly(ethylene-co-methacrylic acid) (EMAA) as an efficient healing agent for high performance epoxy networks using diglycidyl ether of bisphenol A (DGEBA)

The use of poly(ethylene-co-methacrylic acid) (EMAA) as an efficient and repeatable thermally activated healing agent in a high performance diglycidyl ether of bis phenol A (DGEBA)/diethyl toluene diamine (DETDA) mendable epoxy composite is presented. Despite curing above the melting point of EMAA (T-m = 85 degrees C), healing was facilitated by incorporating a preliminary low temperature curing step of 5 h at 80 degrees C, prior to epoxy cure at 150 degrees C. Healing was subsequently shown to occur at 130 degrees C, 150 degrees C and 200 degrees C via a pressure delivery mechanism derived from a condensation reaction between EMAA and the residual hydroxyl groups formed during epoxy cure. Healing was repeatable over 5 healing cycles despite a gradual reduction in efficiency, while efficiency increased with increasing healing temperature. Importantly, healing was evident at 130 degrees C, despite the epoxy network remaining in the glassy state at this temperature (T-g = 150-158 degrees C). As well as creating high performance mendable composites based upon DGEBA/DETDA, EMAA particles distributed evenly on the surface of the crack plane were found to enhance mode I interlaminar fracture toughness by up to 200% for both DETDA and 4,4 diamino diphenyl sulphone (44 DDS) systems. (C) 2016 Elsevier Ltd. All rights reserved.