Role of blend morphology in rubber-toughened polymers

The influence of blend morphology on mechanical behaviour of rubber-toughened polymers was investigated. Diglycidyl ether of bisphenol A epoxies toughnened by core-shell rubber particles were employed as the model systems. The blend morphology was varied by changing the composition of the shell of particles, the curing agent, and the extent of agitation prior to casting. It is shown that the most uniform dispersion of particles is obtained when the shell of the modifiers contains reactive groups. In the absence of the reactive groups and when a slow curing agent is employed, however, a highly connected microstructure is obtained. It was found that a blend with a connected microstructure provides significantly higher fracture toughness compared to a similar blend containing uniformly dispersed particles. The reason for this observation is that the connected morphology enables the shear bands to grow further from the crack tip and thus consume more energy before fracture occurs. Also, the yield strength in uniaxial tensile testing is significantly lower in the blend with the connected morphology. Therefore, it should contribute to a larger plastic zone size.