Epoxy networks toughened by core-shell particles: Influence of the particle structure and size on the rheological and mechanical properties

The core-shell particles considered were poly(butyl acrylate) core/epoxy gr oups functionalizing the poly(methyl methacrylate) shell. Physical and ther momechanical properties of benzyl dimethylamine (BDMA)-catalyzed diglycidyl ether of bisphenol A (DGEBA)/dicyandiamine epoxy networks toughened with c ore-shell particles were studied. The blends were prepared under well-defin ed processing conditions. The resulting properties were found to depend on the state of the dispersion of the particles in the prepolymer matrix befor e crosslinking. These particles were dispersed at different volume fraction s in order to vary the interparticle distance. The relationships between th e size of the core-shell particles and the level of toughening are reported . Static mechanical tests were performed in tension and compression modes o n these core-shell polyepoxy blends. A slight decrease in the Young's modul us and an increase in the ability to plastic deformation were observed. Usi ng linear fracture mechanics (LEFM), an improvement of the fracture propert ies (K-IC) was measured. By varying the volume fraction of core-shell parti cles, an optimum toughness improvement was found for an interparticle dista nce equal to 400 nm (with an average particle size of 600 nm). (C) 1999 Joh n Wiley & Sons, Inc.