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
Union Sulphur Company original patents thus expired in 1908. Competitors such as the Freeport Sulphur Company quickly emerged and began to use the Frasch Process to extract sulfur from other nearby salt dome sites. The Union Sulphur Company tried to stop the Freeport Sulphur Company by suing on the basis of later patents that improved upon the original patents. The Delaware District Court largely sided with the Union Sulphur Co. The Third Circuit Court of Appeals, however, reversed the district court, concluding that the new patents were not really new inventions, but merely extensions of the original expired patents. Union Sulphur appealed to