Sulfur vulcanization sulfur is not miscible in the polymer prior to vulcanization and attention is paid to prevent sulfur bloom, where it migrates to the surface of the article. Accelerators act much like catalysts allowing vulcanisation to be performed cooler yet faster and with a more efficient use of sulfur. They achieve this by reacting with and breaking the sulfur ring to form a reactive intermediate, referred to as a sulfurating agent. This in turn reacts with cure sites in the rubber to bring about vulcanization. There are two major classes of vulcanization accelerators: primary accelerators and secondary accelerators (also known as
Rubber toughening The action of a given mechanism in a toughened polymer can be studied with microscopy. The addition of rubbery domains occurs via processes such as melt blending in a Rheomix mixer and atom-transfer radical-polymerization. Current research focuses on how optimizing the secondary phase composition and dispersion affects mechanical properties of the blend. Questions of interest include those to do with fracture toughness, tensile strength, and glass transition temperature. Different theories describe how a dispersed rubber phase toughens a polymeric substance; most employ methods of dissipating energy throughout the matrix. These theories include: microcrack theory, shear-yielding theory, multiple-crazing theory, shear band