Adhesive strength and mechanisms of epoxy resins toughened with pre-formed thermoplastic polymer particles

摘要

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.