Inorganic Particles and Preformed Modifiers

Some inorganic particulate fillers have also been considered as toughening agents for epoxy materials. Glass beads, fly ash, alumina trihydrate, and silica were used early on to improve the toughness of filled epoxy resins. Various studies, however, have demonstrated that the fracture energy of filled epoxies reaches a maximum at a specific filler concentration. 

Brittle, hollow glass beads have been found to be both an extender and an impact modifier for coatings and adhesives. The extender particles have to be designed in such a way that they actively dissipate deformation energy and hence reduce the likelihood of loss of adhesion between the epoxy and the substrate.25 

A surface activated rubber particle, Vistamer, was recently introduced as a low-cost toughener for epoxy and polyurethane adhesives. The source of the rubber is reprocessed 

FIG URE 8.7 Morphology of a core-shell toughened epoxy adhesive. 

Recently it has also been shown that modified spherical nanosilica particles can be used to toughen epoxy resins without the loss of other properties, such as glass transition temperature or modulus.28 When such surface modified nanoparticles are added to CTBN toughened epoxy resins, the performance of both one- and two-component epoxy adhesives was greatly improved. 

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