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
Toughening several mechanisms that can be employed to toughen a given material such as limiting the initial amount of inclusions, dispersing small particles that will not initiate fracture, or the addition of plasticizers in the case of polymers. Toughening Toughening refers to improving the fracture resistance of a given material. Crack propagation has an associated irreversible work, which is related to a material's toughness. Designing against this crack propagation leads to toughening the material. For the case of a ductile material such as a metal, this toughness is typically proportional to the fracture stress and strain as well as the gauge