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Sulfur vulcanization
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<p>Sulfur vulcanization is a <a href="/facts/Chemical_process/EBSGtK3y">chemical process</a> for converting <a href="/facts/Natural_rubber/CbsjJxhY">natural rubber</a> or related <a href="/facts/Polymer/eF32E50K">polymers</a> into materials of varying hardness, elasticity, and mechanical durability by heating them with <a href="/facts/Sulfur/IK0amTfM">sulfur</a> or sulfur-containing compounds. Sulfur forms <a href="/facts/Cross-link/zeQ9hEAA">cross-linking</a> bridges between sections of <a href="/facts/Polymer_chain/eF32E50K">polymer chains</a> which affects the mechanical properties. Many products are made with vulcanized rubber, including <a href="/facts/Tire/TUgHKMQb">tires</a>, shoe soles, hoses, and <a href="/facts/Conveyor_belt/SC1VXcm6">conveyor belts</a>. The term <a href="/facts/Vulcanization/jmBUqGaz">vulcanization</a> is derived from <a href="/facts/Vulcan_(mythology)/GsnuwMWr">Vulcan</a>, the <a href="/facts/Roman_god/sA0FnmbG">Roman god</a> of fire. </p><p>The main polymers subjected to sulfur vulcanization are <a href="/facts/Polyisoprene/XDNArVtr">polyisoprene</a> (natural rubber, NR), <a href="/facts/Polybutadiene/RxVmrf4B">polybutadiene</a> rubber (BR) and <a href="/facts/Styrene-butadiene/HgU5cek0">styrene-butadiene</a> rubber (SBR), and ethylene propylene diene monomer rubber (<a href="/facts/EPDM_rubber/U03Nlm0L">EPDM rubber</a>). All of these materials contain <a href="/facts/Allyl/CDxPwyvF">alkene groups adjacent to methylene groups</a>. Other specialty rubbers may also be vulcanized, such as <a href="/facts/Nitrile_rubber/teqn52n5">nitrile rubber</a> (NBR) and <a href="/facts/Butyl_rubber/4szk5Xn1">butyl rubber</a> (IIR). Vulcanization, in common with the curing of other <a href="/facts/Thermosetting_polymer/EagnsydT">thermosetting polymers</a>, is generally irreversible. Efforts have focussed on developing de-vulcanization (see <a href="/facts/Tire_recycling/hC3KpeWS">tire recycling</a>) processes for recycling of rubber waste but with little success. </p>