Accelerators
Vulcanization of rubber by sulfur alone is an extremely slow process and can take several hours at elevated temperatures (140°C or more). This is problematic because long exposure to temperature and oxygen leads to oxidative degradation which, in turn, results in poor mechanical properties. It is also not very economical. Accelerators are usually employed to minimize rubber degradation and speed up the vulcanization process. An accelerator is defined as a compound that increases vulcanization speed and enables vulcanization to proceed at lower temperatures and with greater efficiency. The accelerator also decreases the amount of sulfur needed to cross-link the polydiene, improving the vulcanized rubber’s aging properties. Some of the accelerators also function as sulfur donors and thus, allow vulcanization to proceed at lower sulfur content.
Classification
- Primary accelerators are relatively slow and have a delayed onset of cure. These are used primarily to build physical properties.
- Secondary accelerators are fast and used to affect the cure rate and to activate primary accelerators. The dosage of secondary accelerators is typically only a fraction of that of the primary accelerator
Different types of accelerators
Based on the effect given to the vulcanization speed, the accelerators are subdivided into:
- "Slow" accelerators, for example, guanidines
- "Fast" accelerators, such as sulphenamides and thiazoles
- "Super-fast" or "ultra-accelerators", for example, thiourames and carbamates
Antioxidants, Antidegradents, and Antiozonants: Protect your rubber compounds
Vulcanized rubber goods have the need, more or less marked, to be protected from the effect of external factors that can accelerate aging. These factors are of various kinds: oxidative agents (e.g. oxygen), agents that speed up oxidative processes (such as heavy metals), ozone, UV rays, heat, mechanical stress, and aggressive chemicals. These factors can cause substantial changes in the physical properties of the rubber products and can shorten their expected service life
Depending on the application and the polymer (elastomer), the use of the right protective system is crucial to guarantee optimal performance throughout the life of the finished article and effectively increase the life of the rubber products.
Vulcanizing Agents
These products are used in the vulcanization process where rubber parts acquire the physical properties required for the intended application. They are critical and essential chemicals that define the type of curing network including crosslinking density, length of bonds, speed of reaction, or scorch safety. These agents accelerate the sulphur cross-linking reaction (vulcanization) and impart desired physical properties to rubber products whilst enabling large-scale, cost-effective production of rubber products. They are also used in other production processes such as vulcanization using peroxide or diamine.
Retarders
Retarders delay the beginning of the reaction avoiding any issues during the process.
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