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Abstract The aim of this study was to characterize the adhesive properties of epoxy resins toughened with pre-formed polyamide-12 particles in comparison to the conventional approach using core–shell rubber particles. Dicyandiamide-cured diglycidyl ether of bisphenol-A was used as the base epoxy resin. The T-peel adhesive strength of the toughened resin containing 20 phr polyamide-12 particles was about 3-times higher than that of the unmodified resin. In the case of rubber toughening, the improvement in adhesive strength tended to reach a plateau, even after improvement in the resin toughness itself. Besides, the polyamide particle toughening utilizes the bulk resin toughness for the peel adhesive strength, even in a thin adhesive layer between the substrates. The polyamide particles embedded in epoxy resin matrix were fractured after bridging cracks and stretching in the peel process. The crack-bridging mechanism by the pre-formed thermoplastic polymer particles was operative behind the crack-tip and would, therefore, experience a relatively small constraint by the presence of rigid metal substrates in comparison to conventional rubber toughening. The requirements for the polymer particles to work as a modifier using the bridging mechanism would be good adhesion to the epoxy matrix, high toughness and a relatively lower modulus of elasticity than that of matrix resin. Keywords: EPOXYPOLYAMIDETHERMOPLASTICPARTICLESTOUGHENINGPEELSHEARADHESIVE STRENGTH
Kishi et al. (Sat,) studied this question.