Epoxy adhesives are commonly toughened by carboxylic terminated butadiene nitrile (CTBN) rubber to improve the T-peel and Lap-shear strength of adhesives. Unfortunately, many key material properties, such as glass-transition temperature (Tg), Young’s modulus, thermal expansion coefficient, and processability, will be compromised if CTBN rubber is utilized for toughening. Furthermore, CTBN rubber has been shown to be ineffective in toughening high performance, highly crosslinked thermosets. Novel rubber toughening approaches have to be sought to overcome the above-mentioned problems.
The present work focuses on the use of a core-shell particle (CSP) technology, which is comprised of either a rubber core or a rigid plastic core and a shell that stabilizes the dispersion of particles in thermosets. The results indicate that the toughness can be greatly improved by introducing the CSP for toughening. No reduction in Tg is observed. The modulus of elasticity of the CSP-toughened epoxy systems can be maintained if the core of CSP being utilized is rigid. Furthermore, since the viscosity of the toughened epoxy only increases slightly, no compromise in processability is made. These CSP may be suitable for toughening highly filled thermosets for electronic applications.