What are the commonly used rubber accelerators?

　Rubber accelerator TETD: Zinc dimethyldithiocarbamate (accelerator PZ). Chemical name: Tetraethylthiuram disulfide. Molecular formula: C10H20N2S4. Structural formula: … 1. Technical specifications: Q/ZYCH·13-1999. Grade: First-class; Qualified. Appearance (visual inspection): White powder. Initial melting point: ℃ ≥ 67.0; 66.0. Loss on heating: % ≤ 0.30; 0.40. Ash content: % ≤ 0.30; 0.50. Residue on sieve (250μm): % ≤ none; none. 2. Properties: White powder, odorless. Its density is 1.17–1.30 g/cm3; it is insoluble in water, dilute acids, and dilute bases, slightly soluble in gasoline, and soluble in propane, benzene, toluene, carbon disulfide, and chloroform. It is irritating to the skin and mucous membranes. Stable during storage. 　　3. Applications: Superaccelerators and vulcanizing agents for natural rubber, styrene-butadiene rubber, nitrile rubber, butyl rubber, cis-butadiene rubber, and latex. It is commonly used in the manufacture of cables, adhesive tape, rubber shoes, inner tubes, and brightly colored products.

Based on their chemical structures, accelerators can be divided into eight categories: thiazole types, thiuram types, sulfenamide types, guanidine types, dithiocarbamate types, aldoamine types, xanthate types, and thiourea types. I. Thiazoles: These are among the earlier types of organic accelerants. It belongs to acidic accelerators. It is characterized by high vulcanization activity, which enables the vulcanized rubber to possess excellent aging resistance and fatigue resistance. Therefore, it is widely used in the rubber industry, with a high consumption volume. The main varieties are the following two. (1) 2-Thiolbenzothiazole, commercially known as accelerator M. This product is a pale yellow powder with an extremely bitter taste; it is non-toxic and stable when stored. It is a general-purpose accelerator that provides rapid acceleration for natural rubber as well as various synthetic rubbers based on dienes; it offers good vulcanization consistency, with a vulcanization critical temperature of 125°C. There is a risk of encephalitis-like symptoms during mixing. It disperses easily in rubber, does not cause contamination, but is not suitable for rubber products used in food. The amount used as the first accelerator is 1–2 parts, while the amount used as the second accelerator is 0.2–0.5 parts. It can also be used as a plasticizer for natural rubber. (2) Dibenzothiophene disulfide is commercially known as accelerator DM. This product is a light yellow powder with a bitter taste; it is non-toxic and remains stable during storage. Its properties and uses are similar to those of M, but its vulcanization critical temperature is 130°C. Activity increases above 140°C, it exhibits good aftereffect, and the vulcanization process is safe. It is often used in combination with other accelerators to enhance their activity. II. Thiurams: This type of accelerator is acidic in nature. It belongs to the category of superaccelerants. Including thiuram monosulfide, thiuram disulfide, and polythiuram. Thiuram disulfide can be used for sulfur-free vulcanization as well as with vulcanizing agents. As a accelerator, it is generally used as a secondary accelerator, together with thiazole and sulfenamide accelerators, to increase the vulcanization speed. When used in combination with thiosulfamide accelerators, it can delay the time at which the rubber compound begins to react; once vulcanization starts, the reaction proceeds very rapidly, and the degree of vulcanization of the resulting rubber is also high. This production and utilization system is particularly important in low-sulfur vulcanization. The physical and mechanical properties as well as the aging resistance of vulcanized rubber using thiuram accelerators are affected by the ratio of the amount of accelerator to the amount of sulfur. Generally speaking, when the amount of sulfur used is appropriate, the elongation set strength of the vulcanized rubber is high, and its other physical and mechanical properties are also good ； When the amount of sulfur used is low and the amount of accelerator used is high, the heat aging resistance of the vulcanized rubber can be improved. The most commonly used type of thiazole accelerator is tetramethylthiuram disulfide, which is commercially known as accelerator TMTD, or simply accelerator TT. It can be used as both a accelerator and a vulcanizing agent. When used as a catalyst, the amount is generally 0.2 to 0.3 parts. III. Thiosulfamates: These are a type of slow-acting accelerator that are acidic in nature. It features a long scorching time and high vulcanization activity. The vulcanized rubber has a high degree of vulcanization, excellent physical and mechanical properties, and good aging resistance. The rubber compound exhibits a wide range of vulcanization flatness. Due to the development and widespread use of synthetic rubber, as well as the adoption of highly dispersed furnace-black, there is a particular need for accelerators with good retardation properties. Therefore, this type of accelerator holds a quite important position, becoming the fastest-growing and most promising category of accelerators in recent years. Among the various accelerants used in the world today, thiazamide derivatives are by far the most common; those that are widely used include CZ, NOBS, NS, DZ, and OTOS, all of which are derivatives of thiol-based benzothiazoles. (1) N-cyclohexyl-2-benzothiazolesulfenamide, commercially known as accelerator CZ. This product is a pale yellow powder with a slight odor; it is non-toxic, has a specific gravity of 1.31–1.34, a melting point of not less than 94°C, and remains stable when stored. Its vulcanization critical temperature is 138°C, and it boasts excellent resistance to scorching as well as a fast vulcanization speed. This product shows slight discoloration, is in the form of a spray foam, and possesses excellent aging resistance for vulcanized rubber. The typical amount used is 0.5 to 2 parts. (2) N-oxydiethylen-2-benzothiazolysulfonamide or 2-(4-**ylthio)benzothiazole, commercially known as accelerator NOBS. This product is a light yellow powder and is non-toxic. The specific gravity is 1.34~1.40. The melting point is 80°C to 86°C. It gradually decomposes when exposed to heat, so it should be stored at low temperatures. When the storage time exceeds 6 months, the tendency of the rubber compound to scorch increases; the vulcanization critical temperature is above 138°C, the scorching time is longer than that with accelerator CZ, making it safer to handle. This product disperses easily in rubber compounds, does not cause frosting, and shows minimal discoloration. The typical dosage range is 0.5 to 2.5 parts, along with 2 to 0.5 parts of sulfur. (3) N-tert-butylbenzothiazolysulfenamide, commercially known as accelerator NS. This product is a light yellow powder with a distinctive odor. The specific gravity is 1.29, and the melting point is not lower than 105°C. Its performance and usage are roughly similar to those of accelerator CZ, but it exhibits greater delayed action in natural rubber. This product shows slight discoloration and contamination. (4) N,N-Dicyclohexyl-2-2-benzothiazolesulfenamide, commercially known as accelerator DZ. This product is a brownish-yellow powder that is odorless. The specific gravity is 1.2. The melting point is not lower than 90°C. Stable for storage. This product has good dispersibility in rubber. The vulcanization leveling performance is similar to that of accelerator CZ. The vulcanized rubber exhibits good dynamic physical and mechanical properties, with high elasticity and modulus at fixed strain. However, due to the bitter taste of vulcanized rubber, it cannot be used in the manufacture of products that come into contact with food. Its dosage range is generally 0.5 to 1 part, while sulfur amounts to 2.5 parts. IV. Guanides: These accelerators are alkaline in nature and were used as medium-speed accelerators quite early on. It has poor vulcanization flatness, a slow start to vulcanization, a short scorching time, low safety during vulcanization, and is polluting. It is rarely used alone or as the primary accelerator. It is generally used as a second accelerator. Its vulcanized rubber has high tensile strength and rebound rate, as well as low heat generation. The main commonly used variety is diphenylguanidine, commercially known as Accelerator D or Accelerator DCP. This product is a white powder that is non-toxic, but it is irritating when in contact with the skin. Its specific gravity ranges from 0.13 to 1.19. The melting point is not less than 144°C. The vulcanization critical temperature of this product is 141°C, and its vulcanization flatness is poor. It is polluting and not suitable for white or light-colored products, as well as rubber products that come into contact with food. When used as the primary accelerator, the amount is 1–2 parts; when used together with thiazole accelerators as a secondary accelerator, the amount is 0.1–0.5 parts. V. Dithiocarbamates: These are a type of ultra-fast accelerator that is acidic in nature. The vulcanization rate is particularly fast, the flat portion of the vulcanization curve is narrow, and the scorching time is short; as a result, premature vulcanization can occur easily during the processing process, making the vulcanization operation unsafe. If the vulcanization conditions are not properly controlled, under-vulcanization or over-vulcanization can easily occur. When used properly, the vulcanized rubber exhibits excellent physical and mechanical properties as well as aging resistance, and it does not cause contamination. It is suitable for the vulcanization of thin products that require high-temperature vulcanization over a short period of time, as well as products that undergo vulcanization at room temperature and latex products. The most commonly used zinc salts are dimethyldithiocarbamic zinc, which is commercially known as accelerator PZ. Also known as accelerator ZDMC. This product is a white powder, tasteless, and non-toxic. But contact with skin can cause inflammation. The specific gravity is 1.65~1.74. The melting point is 240~255°C. The vulcanization critical temperature is around 100°C. Its vulcanization activity is similar to that of the accelerator TT, but it exhibits higher activity at low temperatures and a greater tendency to scorch. This product disperses easily in rubber, and the resulting products are odorless, non-toxic, and do not cause contamination. It is mainly used in latex products, naturally vulcanized pastes, adhesive tape products and cold-vulcanized products, light-colored and colored products, as well as food-grade rubber products. The typical amount used in latex compounds is 0.3 to 1.5 parts. VI. Aldehyde amine accelerators: These accelerators are condensates of aliphatic aldehydes or amines (aliphatic or aromatic amines). It is acidic. When the varieties differ, there are significant differences in their vulcanization activity as well as the resulting vulcanization properties. Its activity range generally ranges from quasi-super to slow speeds. It has good flatness, and the scorching time is short. The most notable feature is the excellent aging resistance of the resulting vulcanized rubber. Among them, less active accelerators (such as hexamethylenetetramine) are often used as secondary accelerators for thiazole or sulfenamide-type accelerators. Only butyralaniline condensate is a strong accelerator, used as the primary accelerator when combined with thiazole-type accelerators. (1) Hexamethylenetetramine is commercially known as accelerator H. This product is a white to pale yellow crystalline powder, almost odorless, with a bitter taste. It is irritating to the skin. The specific gravity is 1.3. It sublimes and partially decomposes when heated to 263°C. Slightly deliquescent. The critical temperature is 140°C; it is less reactive at low sulfiding temperatures, resulting in a lower risk of charring. It is often used as a secondary accelerator. It does not change color, does not cause pollution, and is not easily decomposed. It is mainly used for transparent and thick-walled products. (2) The condensation product of n-butylaldehyde and aniline is commercially known as Accelerator 808. This product is a brownish-red or amber-colored, viscous oily liquid with a distinctive odor. Specific gravity 0.94~0.98. When exposed to air for a long time, its color deepens and its specific gravity increases. But the efficiency remains unchanged. Stable when stored in an airtight environment. It has high vulcanization flatness, with a critical temperature of 120°C; the most suitable vulcanization temperature is between 120°C and 160°C. It has good dispersibility in dry glue. Suitable for compounds containing recycled rubber and rigid rubbers. VII. Xanthates: These are also a type of super-accelerant with extremely high activity, and their accelerating effect is even faster than that of ammonium dithiocarbamate. The flattening range of vulcanization is very small. It is generally used in latex and low-temperature vulcanized pastes, and only in special cases is it used in dry glue. The commonly used variety is zinc n-butyryl xanthate, commercially known as accelerator ZBX. This product is a white powder with a distinctive odor and is non-toxic. The specific gravity is 1.40. It decomposes upon heating. It tends to decompose slowly during storage, therefore it needs to be stored at low temperatures (below 10°C). It is a super accelerator that does not cause pollution. VIII. Thioureas and other new types of accelerants: Research is currently being carried out on new types of accelerants in order to develop ones that offer high efficiency in accelerating vulcanization, good processing safety, excellent resistance to reversion, and high aging resistance. Furthermore, the variety of sulfur donors is increasing, and sulfur-free crosslinking systems are continuously emerging. Moreover, recognized toxic accelerants such as ethylenethiourea are being phased out. (1) Triazine accelerators: The most important among them is bis(2-ethylamino-4-diethylaminotriazin-6)-disulfide. This product offers a higher acceleration effect than conventional accelerators, enables faster vulcanization, and is safe to use during processing. The vulcanization rate in natural rubber is similar to that of the accelerator NOBS, while its processing safety lies between NOBS and CZ. A small amount is required when used in combination; in natural rubber containing 1.5–2.35 parts of carded yellow rubber, only 0.3 parts are needed to replace 0.5 parts of sulfenamide. This accelerator can improve the resistance to reversion of sulfur-crosslinked rubbers at low sulfur levels, and can be used in styrene-butadiene rubber, isoprene rubber, and nitrile rubber. (2) Thiocarbamoyl sulfenamide: These accelerators mainly include N-oxydiethylenethiocarbamoyl-N-oxydiethylenesulfenamide. They offer high operational safety, rapid vulcanization speeds, and strong accelerating effects. Suitable for styrene-butadiene rubber, nitrile rubber, ethylene-propylene-diene monomer rubber, and other general-purpose synthetic rubbers. The vulcanization speed of the rubber compound using 0.67 parts is faster than that using 1 part of thiosulfurate accelerator. And satisfactory operational safety performance can be achieved. The activity is very high above 149°C, while below 149°C, a small amount of accelerators such as NOBS, M, or DM can be added. (3) Thiophosphoryl accelerator: Bis(diethylthiophosphoryl)trisulfide. This accelerator can be used as a sulfur donor in natural rubber. Replacing part or all of the sulfur can improve the heat resistance of the vulcanized rubber, and enhance its resistance to vulcanization reversal and compression set during high-temperature vulcanization. It is an excellent accelerator for EPDM; it is safe to use, enables fast vulcanization, possesses excellent heat resistance without frosting, and also has good resistance to compression deformation. Unlike many other accelerators as well as sulfur and sulfur donors, it does not cause degradation when polyester fibers come into contact with rubber during vulcanization.

NOBS, NS, M, DM, DPG, TMTD,

Vulcanizing agents: S-80, IS-60, T(VC)D-40P (odorless DCP), No. 1 Vulcanizing Agent-70, TCY-70, KE8675 (butyl rubber vulcanization resin)
Accelerators: MBT-80 (accelerator for M), MBTS-75 (accelerator for DM), TMTD-80, TMTM-80, ZDBC-80, ZDEC-80, DPTT-70, TDEC-70, DTDM-80, CBS-80 (accelerator for CZ), ETU-80, DPG-80, HEXA-80, DOTG 9
Activators: ZnO-80, Schordguard O (pasty magnesium oxide), PbO-80, TRIM/S (co-crosslinking agent)
Antioxidants: DDA-70, OCD-80, P-50 (hydrolysis inhibitor, polycarbodiimide)
Foaming agents: OB-75, AC-75

Type, Product Name, English Abbreviation, Chemical Name:
Thiazoles: Accelerator D, DPG; Diphenylguanidine; Accelerator DT, DOTG; Di-o-tolylguanidine; Accelerator BG, OTBG; o-Tolylbiguanide.

Thiazoles: Accelerator M, MBT; 2-Thiophenylbenzothiazole; Accelerator DM, MBTS; Dibenzothiazole disulfide.

Thioureas: Accelerator CZ, CBS; N-Cyclohexyl-2-benzothiazylthiourea; Accelerator NS, TBBS; N-tert-Butyl-2-benzothiazylthiourea; Accelerator NOBS (MSA), OBS; N-Oxydithioethylene-2-benzothiazylthiourea; Accelerator DZ, DZ; N,N-Dicyclohexyl-2-benzothiazylthiourea; Accelerator OTOS, OTOS; N-Oxydithioethylenethiocarbamoyl-N’-oxydithioethanethiourea.

Thurams: Accelerator TS, TMTM; Tetramethylthuram monosulfide; Accelerator TT, TMTD; Tetramethylthuram disulfide; Accelerator TET, TETD; Diethylthuram disulfide; Accelerator TBT, TBTD; Tetrabutylthuram disulfide; Accelerator TRA, DPTT; Pentamethylenetetramine disulfide; Accelerator TE, Diethyldiphenylthuram disulfide; Accelerator TBzTD, TBzTD; Tetrabenzylthuram disulfide.

Dithiocarbamates: Accelerator PZ (ZDMCZ), ZnMDC; Zinc dimethyldithiocarbamate; Accelerator EZ (ZDC), ZnEDC; Zinc diethyl dithiocarbamate; Accelerator BZ (ZDBC), ZnBDC; Zinc dibutyl dithiocarbamate; Accelerator PX, ZnBzDC; Zinc ethylphenyl dithiocarbamate; Accelerator ZnBzDC, ZnBzDC; Zinc dibenzyl dithiocarbamate; Accelerator TeEDC, TeEDC; Ethyldithiocarbamate of tellurium; Accelerator TTEE, FeMDC; Iron dimethyldithiocarbamate; Accelerator TTUC, CuMDC; Copper dimethyldithiocarbamate.

Thiophosphates: Accelerator ZDEP, ZDEP; Zinc diethyl thiophosphate; Accelerator ZDBP, ZDEP; Zinc dibutyl thiophosphate; Accelerator ZADP, Zinc aminothiophosphate.

Thioureas: Accelerator Na-22, ETU; 1,2-Ethylenethiourea; Accelerator DETU, DEU; N,N-Diethylthiourea.

Amines: Accelerator H, H; Hexamethylenetetramine.

Xanthates: Accelerator ZBX, ZnBX; Zinc n-butyl xanthate; Accelerator ZIX (ZIP), ZnPX; Zinc isopropyl xanthate