Raymond A. Pearson Research
Epoxy resins are used in many industrial applications and are often toughened to increase their flaw tolerance. Approaches used to toughen epoxies include the incorporation of soft, butadiene based copolymers such as carboxyl terminated butadiene-acrylonitrile copolymers (CTBN) or the addition of rigid inorganic fillers such as silica. Such approaches have been around for nearly 40 years and an extensive amount of papers has been published on both approaches - including papers from my group. Recently, several research groups have published work on the use of nanometer-size rubber particles or nanometer-size silica fillers to toughen epoxies with a modest amount of success. Interestingly, my group has been very successful in using nanometer-size toughening agents (based on commercial triblock terpolymers or commercially available nanosilica pre-dispersed in epoxy) to toughen a lightly crosslinked epoxy. The result is toughened epoxies that are as tough if not tougher than conventionally toughened epoxies. We have employed various microscopy studies in an effort to understand the toughening mechanisms. In the case of nanosize rubber particles, extensive matrix dilation is observed. In the case of nanosilica fillers, enhance matrix ligament bridging is observed. My group has also shown that the combination of soft rubber particles with rigid nanosilica particles can produce synergistic toughening.
40 nm rubber particles cavitate and induce intense plastic void growth in a crosslinked epoxy matrix.