The influence of elastomer concentration on toughness in dispersions containing preformed acrylic elastomeric particles in an epoxy matrix

The influence of toughener concentration on the fracture behavior of two-ph ase, rubber-toughened epoxy is studied. To vary the concentration without a ltering other morphological features, samples generated from dispersions of preformed rubber (acrylic) particles in liquid epoxy monomer are used. By diluting with different amounts of epoxy prior to cure, the toughener conce ntration can be varied over a wide range. Thermal and microscope studies su pport the assertion of a constant morphology. The fracture results show tha t the toughness increases to a maximum and then decreases as the concentrat ion is increased. This suggests an optimum concentration of toughening. Mic rographs of the initiation zone on the fracture surface at high concentrati ons of rubber show less deformation than the equivalent surfaces at lower c oncentrations. This is consistent with a toughening mechanism based on part icles initiating yielding and plastic flow in the matrix. (C) 1999 Elsevier Science Ltd. All rights reserved.