Rubber toughening and damage competition theory. In material selection it is important to look at the interaction between the matrix and the secondary phase. For example, crosslinking within the rubber phase will promote high strength fibril formation that will toughen the rubber, preventing particle fracture. Carboxyl-terminated butadiene-acrylotnitrile (CTBN) is often used to toughen epoxies, but using CTBN alone increases the toughness at the cost of stiffness and heat resistance. Amine-terminated butadiene acrylonitrile (ATBN) is also used. Using ultra-fine full-vulcanized powdered rubber (UFPR) researchers have been able to improve all three, toughness, stiffness, and heat resistance simultaneously, resetting the stage for rubber toughening
Rubber toughening measure the separate contributions. Shear yielding is a constant volume process and cannot be measured with tensile dilatometry. Voiding can be seen with optical microscopy, however one of two methods, using polarized light or low angle light scattering are necessary to observe the connection between cavitation and shear bands. In order to gauge the toughening effects of a dispersed secondary phase, it is important to understand the relevant characteristics of the continuous polymer phase. The mechanical failure characteristics of the pure polymeric continuous phase will strongly influence how rubber toughened polymer failure occurs. When a polymer usually fails due to