971-15-3 Dipentamethylenethiuram Hexasulfide Rubber Accelerator DPTT (DPTH) C12H20N2S8

Promoting efficiency of rubber vulcanization is an important standard to measure the quality of accelerator. According to reports, the characterization of accelerators at home and abroad is mainly carried out from the two aspects of vulcanization promotion characteristics and physical and mechanical properties of vulcanized rubber. The main characteristics of vulcanization promotion are the vulcanization rate, Mooney coke time, positive vulcanization time, positive vulcanization temperature, vulcanization flatness and anti-vulcanization returnability in overvulcanization stage. The physical and mechanical properties of vulcanized rubber are mainly investigated in terms of hardness, elasticity, tensile properties, friction properties and thermal aging properties. However, in recent years, a lot of research has been done on the influence of accelerators on the dynamic viscoelastic properties of vulcanizates.

In fact, the effectiveness of the accelerator depends on the physical and mechanical properties of the vulcanizate it imparts, and the nature of the cross-linked bonds in the vulcanizate (type and density) plays a decisive role in its application and working characteristics. The strength and dynamic mechanical strength of vulcanized rubber not only depend on the properties of the polymer chain itself, but also directly related to the number of network support chains in the total interconnection network (referring to the connection chain between two connecting points). The crosslinking density determines the number of supporting chains in the network. It has been reported [14] that the hardness and constant elongation stress of vulcanized rubber increase with the increase of crosslinking density, and the tear strength, fatigue life, toughness and tensile strength begin to increase with the increase of crosslinking density, and then decrease with the increase of crosslinking density after reaching a certain maximum value. The hysteresis and permanent deformation characteristics decrease with the increase of crosslinking density.

An accelerator of vulcanization of rubber is a chemical substance that increases the rate of vulcanization, which is the chemical process that involves adding sulfur to rubber to create cross-links between the polymer chains. Accelerators speed up this cross-linking reaction without significantly raising the temperature required for vulcanization.

There are several classes of accelerators, including thioureas, sulfenamines, guanidines, and dithiocarbamates. Each class works through different mechanisms to promote the vulcanization process. For instance:

- Thioureas, such as N-cyclohexyl-2-benzothiazole sulfonamide (CBS) and N-tert-butyl-2-benzothiazole sulfonamide (MBTS), are some of the most commonly used accelerators. They react with sulfur to form radicals that can insert themselves into the rubber polymer chains, facilitating cross-linking.
- Sulfenamines, like diphenylguanidine (DPG), also react with sulfur to produce active species that can participate in the vulcanization process.

- Dithiocarbamates, exemplified by tetramethylthiuram disulfide (TMTD), decompose to yield sulfur and a radical that can participate in the vulcanization reaction.

The choice of accelerator depends on factors such as the type of rubber being processed, the desired rate and extent of vulcanization, and the end-use requirements of the rubber product. Accelerators are crucial in achieving optimal cure rates and final properties of vulcanized rubber.

Dynamic vulcanization, also known as in situ vulcanization or reactive processing, is a process used in the manufacturing of thermoplastic elastomers (TPEs). It involves the simultaneous vulcanization and melting of a thermoplastic and a rubber component. This process allows for the formation of a material with both thermoplastic and elastomeric properties.

During dynamic vulcanization, the rubber (often based on natural rubber or synthetic polymers like styrene-butadiene rubber, SBR) is combined with a thermoplastic (such as polypropylene, PP, or ethylene propylene diene monomer, EPDM) and vulcanizing agents (sulfur or equivalent chemicals). The mixture is then processed in an internal mixer or twin-screw extruder, where it is subjected to elevated temperatures and shear forces.
 

The high shear and temperature initiate a chemical reaction that cross-links the rubber component while simultaneously melting the thermoplastic. This dynamic equilibrium results in a material that exhibits elastic behavior similar to vulcanized rubber at room temperature but can be processed and recycled like a thermoplastic.

Dynamic vulcanization is facilitated by the addition of specific chemicals, such as peroxides or catalysts that promote the cross-linking reactions at the higher temperatures achieved during processing. The precise conditions-temperature, time, and shear-must be carefully controlled to optimize the material properties, ensuring the rubber becomes sufficiently cross-linked without degrading the thermoplastic matrix.

This technology offers several advantages over traditional vulcanization processes, including easier machining, faster cycle times in manufacturing, and the ability to recycle the material more readily. Dynamic vulcanization enables the creation of materials with a broad range of applications, from automotive seals and hoses to medical devices and consumer products.

The most significant change is that non-vulcanized rubber is thermoplastic, meaning it softens when heated and hardens when cooled. Vulcanization transforms rubber into a thermoset material, which means it retains its shape even when the original molding temperature is reached.

Vulcanized rubber is stronger and more elastic than its non-vulcanized counterpart. The cross-linking between the polymer chains enhances the material's resistance to tensile forces and elongation.

Cross-linking improves the resistance of vulcanized rubber to oils, fats, acids, and alkalis, making it suitable for applications requiring protection against these substances.

The cross-links reduce the diffusion of gases through the rubber, which is beneficial for sealing applications where gas or airtight integrity is necessary.

Vulcanized rubber can withstand higher temperatures without deforming or losing its mechanical properties compared to non-vulcanized rubber.

The cross-linking network increases the durability of rubber, making it less prone to wear from friction.

Vulcanized rubber has enhanced resistance to weathering and UV radiation, which slows down degradation and extends the service life of the material.

Vulcanization allows for better control over the hardness of the rubber through the adjustment of the vulcanizing system (sulfur content, accelerator type and amount, curing time, and temperature).

Depending on the degree of cross-linking and the formulation, vulcanized rubber can exhibit either insulating or conductive properties, making it suitable for a range of electrical applications.