The role of additives in the rubber vulcanization process

Each year the rubber industry in the world consumes about 2 to 2.5 million tons of fillers functions, of which about 600 to 700 thousand tons of industrial minerals (predominantly black soot).

They mix rubber materials (elastomers - elastomer, amorphous polymers) with other components to form a complex (compound), then take to make vulcanized rubber. Since there are so elastic rubber products can stretch to several times the original length and can return to the original form without distortion. Also, rubber also eliminated due to viscous energy elastic and durable under the influence of static or dynamic force. Rubber has high abrasion resistant than steel, waterproof and air, no swelling in the solvent and chemical corrosion.
Commercial elastomers include polyisopren (or natural rubber - NR), a synthetic rubber (such as synthetic isoprene rubber, polybutadien rubber, styrene-propylene rubber, rubber etylenpropylendien, rubber butyl rubber and thermoplastic rubber nitryl).
NR latex rubber is processed. Therefore, pure raw rubber physical properties change with temperature and easily oxidized by the oxidizing agents, even with air.
Synthetic rubber is produced by condensation or polymerization (polymerization) some unsaturated hydrocarbons. Commercial synthetic rubber mainly composed of rubber, neoprene, buna, butyl rubber and other special types.
Most of the rubber must undergo curing process to change the structure and thermal stability.
To facilitate the process of curing, chemical curing with liquid, catalysts and accelerators were added in processing, along with other additives such as plasticizers, antioxidants, substances anti-ozonation, the coloring and fillers function.
Catalysts and active metabolite
Sulfur (S) is a vulcanized (cross-linking) is slow. When increasing the amount of S as required prolonged heating time and reduces the bonding strength. However, some organic matter such thiocarbanilit alinin and reduce curing time and reduce oxidative degradation of the rubber vulcanization process, thus improving the properties of rubber products.
Initially, the curing catalyst is the metal oxide (such as "white lead powder" and "lime"), then we use five kinds of organic compounds mainly guanidin, thiazol, dithiocarbamat, xantat and thiuram . In this type, catalyst type curing speed guanidin slowest, while beginning the process of "scorched" is also slow.
In general, when using organic catalysts require the use of the active metabolite (promotion) to increase their effectiveness on the basis of increased curing speed, curing temperature reduction and improved mechanical properties of vulcanized rubber. Zinc oxide (zinc white) is very popular and active metabolite is effective because it reduces the cross-linking of S, while stimulating the formation of CC link increases thermal stability of vulcanized rubber. The ultra-fine zinc oxide is used to have a minimum content of 99.5% ZnO and be treated to a large specific surface area. In addition to activation of the vulcanization process S and zinc oxide as an active cross-linking of polymers containing carboxyl groups or halogen (such as rubber clopren, rubber brombutyl, clobutyl rubber, or nitrile rubber chemical and rubber carboxyl styrene - butadiene carboxyl chemical).
Several other compounds are used as the active metabolite of vulcanized rubber are:
- Magnesium oxide (MgO) is used primarily with the type of neoprene elastomer.
- Lead oxide (PbO) is less common but still used along with thiazol, dithiocarbamat, or other types of thiuram sulfide catalysts.
- The fatty acids, for example, stearic acid, oleic acid and dibutyl ammonium oliat be used (in the form of zinc salts) to improve the dispersion of zinc oxide.
Vulcanization retarders / retardant scorched process
The vulcanization retarders or retardant scorched process is used to prevent this process in rubber processing. Additional anti-sem (as magnesium oxide, salicylic acid, benzoic acid, acetylsalicylic acid, phthalic anhydride, N-nitroso-diphenylamin or stearic acid) at concentrations of 0.2 to 1% will stretch the time that started to burn rubber not reduce the speed of vulcanization process. These compounds are particularly indicated when the catalyst efficiency caused vulcanization process early in the process of mixing and staff training.
Chemically, alkaline calcined magnesium oxide and reactive functions as an acid acceptor, fluid chemical, stabilizer, and quality for all kinds of vulcanized rubber and elastomer.
Fillers, and coloring brake fire
Filler reinforcement increases the stiffness of the component is not curing and improving the properties of vulcanized rubber, which increases the tensile strength, abrasion resistance, anti-tear, and increases the hardness of rubber. Reinforcing fillers can dramatically change the viscosity and the properties of vulcanized rubber with increasing filler content, while the inactive fillers such as ground calcium carbonate (GCC) and kaolanh not have these properties, even reduce the mechanical properties of vulcanized rubber.
Currently, there are two types of reinforcing fillers are mostly commercial carbon black and silica. Material is carbon black can create interactive surface chemical characteristics of organic films with elastomer. In contrast, silicon oxide is a chemical substance interaction surface characteristics of inorganic membranes with elastomer, so chemically, silica fillers
can be treated with Silane compound to the rubber. The fillers are available with particle size 100 anstrom.
The main inert mineral fillers used in rubber industry is stone powder, light powder, kaolanh, clay, talc, mica, and minerals such as diatomite, feldspar, nephelin syenite, gypsum, pyrophylit, zeolites, etc. ..
People still use a filler in rubber processing for the effect of fire retarders, anti-smoking and some other functions (eg, aluminum trihydrate (ATH), zinc borate, antimoni oxide, etc. ..) .
Some minerals and chemicals are added to the distribution of rubber (not containing carbon black) to color rubber as titanium dioxide, iron oxide, zinc oxide, litopon and some organic dyes. Titanium dioxide is considered the top white coloring, very stable chemical and rubber to help against UV degradation of the high, making rubber products fastness.

Source: vinachem.com.vn

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