Vulcanization (British: vulcanisation) is a chemical process, invented by Charles Goodyear, used to harden rubber.[1] Vulcanization traditionally referred to the treatment of natural rubber with sulfur and this remains the most common example, however the term has also grown to include the hardening of other (synthetic) rubbers via various means. Examples include silicone rubber via room temperature vulcanizing and chloroprene rubber (neoprene) using metal oxides.
Vulcanization can therefore be defined as the curing of elastomers; with the terms 'vulcanization' and 'curing' sometimes used interchangeably in this context. It works by forming cross-links between sections of polymer chain which results in increased rigidity and durability, as well as other changes in the mechanical and electrical properties of the material.[2] Vulcanization, in common with the curing of other thermosetting polymers, is generally irreversible.
Main article: sulfur vulcanization rubber vulcanizing machine
By far the most common vulcanizing methods depend on sulfur. Sulfur, by itself, is a slow vulcanizing agent and does not vulcanize synthetic polyolefins. Accelerated vulcanization is carried out using various compounds that modify the kinetics of crosslinking,[3] this mixture is often referred to as a cure package. The main polymers subjected to sulfur vulcanization are polyisoprene (natural rubber) and styrene-butadiene rubber (SBR), which are used for most street-vehicle tires. The cure package is adjusted specifically for the substrate and the application. The reactive sites—cure sites—are allylic hydrogen atoms. These C-H bonds are adjacent to carbon-carbon double bonds. During vulcanization, some of these C-H bonds are replaced by chains of sulfur atoms that link with a cure site of another polymer chain. These bridges contain between one and several atoms. The number of sulfur atoms in the crosslink strongly influences the physical properties of the final rubber article. Short crosslinks give the rubber better heat resistance. Crosslinks with higher number of sulfur atoms give the rubber good dynamic properties but less heat resistance. Dynamic properties are important for flexing movements of the rubber article.
Rubber Curing Oven Can Be Used For Vulcanization Of Polychloroprene
Rubber Curing Oven Can Be Used For Curing Of Silicone Resin
Rubber Curing Oven Can Improve Rubber's Aging Resistance
Rubber Curing Oven Can Improve Rubber Elasticity
Rubber Curing Ovens Can Improve The Weatherability Of Rubber
Vulcanization of polychloroprene
The vulcanization of neoprene or polychloroprene rubber (CR rubber) is carried out using metal oxides (specifically MgO and ZnO, sometimes Pb3O4) rather than sulfur compounds which are presently used with many natural and synthetic rubbers. In addition, because of various processing factors (principally scorch, this being the premature cross-linking of rubbers due to the influence of heat), the choice of rubber curing oven is governed by different rules to other diene rubbers. Most conventionally used accelerators are problematic when CR rubbers are cured and the most important accelerant has been found to be ethylene thiourea (ETU), which, although being an excellent and proven accelerator for polychloroprene, has been classified as reprotoxic. The European rubber industry has started a research project SafeRubber[4] to develop a safer alternative to the use of ETU.
Vulcanization of silicones
Room-temperature vulcanizing (RTV) silicone is constructed of reactive oil-based polymers combined with strengthening mineral fillers. There are two types of room-temperature vulcanizing silicone: Hardens due to the action of atmospheric humidity, a catalyst, and acetoxysilane. Acetoxysilane, when exposed to humid conditions, will form acetic acid.[5] The curing process begins on the outer surface and progresses through to its core. The product is packed in airtight cartridges and is either in a fluid or paste form. RTV-1 silicone has good adhesion, elasticity, and durability characteristics. The Shore hardness can be varied between 18 and 60. Elongation at break can range from 150% up to 700%. They have excellent aging resistance due to superior resistance to UV radiation and weathering.
