The blends with added sulfur are heated to produce products with reduced plastic deformation and excellent properties such as elasticity and tensile strength. The operation is called vulcanization, and the substance used for vulcanization is called vulcanizing agent (cross-linking agent). Cross-linking agents generally form cross-linking bonds between elastomer molecules. In the cross-linking reaction, the cross-linking agent is partially or fully introduced into the molecule to form a cross-linked bond.

Most of the vulcanizing agent is based on the role of thermal energy agent, more stable in the process of matching, while in the vulcanization process and the rubber quickly react to form a three-dimensional network structure.
In addition, the vulcanizing (cross-linking) agent is sold in granular form or made of master refining rubber, seeking to prevent pollution of the environment, improve the operability and dispersibility, etc.
1.1 Sulfur yellow
Light yellow to yellow powder or lump. Tasteless and odorless. There are amorphous and crystalline form, the melting point of the two is slightly different. Sulfur yellow contains a small amount of water and acid as impurities, and some also contain other mixtures.
Sulfur yellow is the most common vulcanizing agent, for natural rubber soft rubber products with the addition of 0.3 to 4 parts. The use of more than one easy to produce the phenomenon of spray frost, and aging resistance to reduce the physical properties of poor performance.

1.2 Sulfur-containing compounds
1.2.1 Sulfur monochloride
Role Used as the so-called cold vulcanization vulcanizing agent, suitable for thin products and latex products. Now basically not used.

1.2.2 Morpholine disulfide
Function Used for vulcanizing NR, SBR, IR, BR, NBR, IIR, which can be vulcanized by releasing active sulfur (27%) under vulcanization temperature.

1.2.3 Polymeric polysulfide compounds
 Because of the affinity with rubber and low melting point (69～72℃), they are dissolved and easily dispersed at the mixing temperature, and are not allowed to be made into powder. Suitable for vulcanizing tires, tapes, industrial products, rubber shoes, as well as sulfur yellow dispersion difficulties of nitrile rubber and ethylene propylene rubber.

1.2.4 Sulfur-containing accelerator
Disulfide tetramethylthiuram (promoter TMTD), dimethyl selenium dithiocarbamate (promoter SEMD), 2-(4´-morpholine-based dithiocarbamate) benzothiazole (promoter MDB) and other promoters can be used as sulfur-free vulcanizing agent. Dosage 3 to 4 parts. Must be formulated with zinc oxide.

1.3 Inorganic sulfurizing agent other than sulfur yellow
1.3.1 Selenium
Function As a second vulcanizing agent of NR, SBR is added to sulfur-free to low sulfur compound using Thuleum accelerator to improve aging resistance.

1.3.2 Tellurium
Role Used as the second vulcanizing agent of NR, SBR, the role is the same as selenium, but slightly less active.

1.3.3 Magnesium oxide
Role Widely used as vulcanizing agent of chloroprene rubber. Although the process does not produce activity, but at the vulcanization temperature shows significant vulcanization effect.

1.3.4 Lead monoxide
The vulcanizing agent of chloroprene rubber, chlorosulfonated polyethylene, chlorinated polyethylene, polysulfide rubber. Compared with the case of magnesium oxide or zinc oxide, very good water resistance vulcanization is obtained, but there is a risk of scorching.

1.3.5 Zinc oxide
Vulcanizing agent for chloroprene rubber, chlorosulfonated polyethylene, chlorinated polyethylene, polysulfide rubber

1.4 Oximes and nitroso compounds
1.4.1 p-quinone dioxime
Action Effective sulfur-free vulcanizing agent for butyl rubber and polysulfide rubber. Especially suitable for butyl rubber. Lead tetraoxide or dibenzothiazole disulfide (promoter DM) oxidizer has an activating effect on it. In the carbon black with and the use of lead monoxide occasions have a tendency to scorch amount, but if the use of anti-coke agent, salicylic acid or tetramethylthiuram disulfide (promoter TMTD) can effectively improve operational safety.

1.4.2 p,p´-dicarbonylbenzoquinone dioxime
Action An effective sulfur-free vulcanizing agent. One of the most suitable vulcanizing agents for butyl rubber. The effect is the same as p-quinone dioxime, but the vulcanization speed is quite slow, not easy to scorch, even for carbon black with the operation safety is also very good.

1.4.3 Tetrachlorobenzoquinone
Role The main sulfur-free vulcanizing agent of butyl rubber. When used in butyl rubber, if used with p-quinone dioxime and dibenzothiazole disulfide (promoter DM), can accelerate the scorching time and vulcanization time, as well as improve the tensile strength and tensile stress.

1.4.4 Poly(p-nitroso)
Role Because of weak vulcanization, it is used as heat treatment auxiliary of butyl rubber or plasticity regulator of butyl rubber compound.
 
1.5 Polyamines
1.5.1 Hexamethylene diamine or 1,6-hexanediamine
Function Used for vulcanization of fluorine rubber, acrylate rubber, chlorinated polyethylene. For acrylate rubber, with a small amount of sulfur yellow can improve the heat resistance.

1.5.2 Triethylenetetramine
Action The same as hexamethylene diamine.

1.5.3 Tetraethylenepentamine
Actions Same as hexamethylenetetramine.

1.5.4 Hexamethylene-diamine carbamate
Role Sulfurizing agent for fluoroelastomer and acrylate rubber.

1.5.5 N,N´-bis-cinnamyl fork-1,6-hexanediamine
Action A vulcanizing agent for fluoroelastomers and acrylate rubbers. Excellent physical properties of vulcanization, and higher safety of processing operation than hexamethylene diamine carbamate.

1.5.6 4,4´-methylenebis(cyclohexylamine) carbamate
Function Safe and rapid vulcanization of fluoroelastomers with high process safety.

1.5.7 4,4´-methylene-bis-o-chloroaniline
Role Cross-linking agent for polyurethane elastomer. Used for cross-linking various rubber rollers, solid tires, sealing of floor plates and joints, etc. and foamed polyurethane products.