Get to know the types of synthetic rubber
Get to know the types of synthetic rubber
Synthetic rubbers include a wide range of products in the rubber industry, and at the same time, they have wide applications in various industrial sectors. In this article, we will get to know the types of synthetic rubber that are currently produced and supplied in the rubber industry.
butadiene-styrene copolymers
Both styrene and butadiene resins are a type of synthetic rubber that has more than 50% butadiene, they are called SBR. The normal ratio of single resins is 70 to 75 parts of butadiene to 25 to 30 parts of styrene. Above 50%, the product becomes highly plastic and can be used in liquid colors. SBR synthetic rubber does not crystalize due to stretching like natural rubber and therefore is weak unless it is reinforced with carbon black or other materials. Even in this case, it is weaker than natural rubber. Its vulcanization properties are good and its aging characteristics are satisfactory. More than 70% of the produced SBR is used in tire tread, 15% in mechanical parts and about 10% in the form of leachate.
Nitrile Synthetic Rubber (NBR)
This type of synthetic rubber called butadiene and acrylonitrile, like many SBRs, is made through emulsion deposition.
However, depending on the required properties, the amount of acrylonitrile varies from 20 to 50%. As the amount of nitrile increases, resistance to hydrocarbons, solvents, wear and gas penetration increases. Reducing the amount of nitrile increases properties at low temperatures and elasticity. NBR synthetic rubbers are resistant to oils, solvents, water, salts, aliphatic compounds, soaps and most food. They work in air and at 150 degrees Celsius in oil environment.
Neoprene synthetic rubber
These synthetic rubbers are obtained from the emulsion deposition of pure chloroprene at a temperature of 38 degrees Celsius in the vicinity of sulfur. It is resistant to oxidation, oil, heat and fire and has special uses in car parts, adhesives, sealants and coatings. It is more expensive than natural rubber. For this reason, it is used when special properties are needed.
Thiokol synthetic rubber
It is a type of polysulfide rubber that was invented in the United States in the early 1920s. This rubber was the first synthetic rubber that was commercially produced in this country. Thiokol synthetic rubbers are prepared from the compaction of an alkaline polysulfide and an organic dihalide. The product of these reactions is especially suitable for lining oil tanks, construction mud and putty. , adhesives and sealants, and recently rocket fuel adhesives, abrasion coatings and other parts that require ease of use and good weathering resistance.
Silicone synthetic rubbers
Silicone rubbers are mixed mineral-organic resins that are obtained from the resinization of various silanes and siloxanes. Although they are expensive, their significant resistance to heat leads to the exclusive use of these rubbers in high temperature applications. The chain of these compounds is made of silicon. and oxygen is fixed and carbon free. Silicon compounds and their derivatives are notable for their unusual properties, such as solubility in organic solvents, insolubility in water and alcohols, thermal stability, chemical inertness, high dielectric properties, relatively low flammability, viscosity Low in high percentage of resin, little change in viscosity with temperature and non-toxicity. Due to these properties, silicone synthetic rubber compounds are used as hydraulic fluid and heat transfer, lubricant and grease, sealant for electrical applications, working layer resins and coating and glaze resistant in High temperature, silicone rubber, hydrophobic compounds, waxes, and polishing materials can be used. The most common use of silicone rubber is in the aerospace industry, where they are used in antifreeze devices, washers, wear shields, and similar uses where temperature is an issue.
Butyl synthetic rubber
Isobutylene copolymer with about 2% of isoprene is called butyl rubber. Isoprene creates enough unsaturation in the chain structure for curing or vulcanization to take place.
Butyl rubber has infinite general permeability against gases, and for this reason, its main use is in the manufacture of tubes and tubeless tires. Butyl rubber is also neutral against oxidation and is useful for anti-weathering purposes. Another type of synthetic butyl rubber is butyl rubber. It has halogen. It has better resistance to aging, is more compatible with other tires and is used in tubeless tires.
Urethane synthetic rubber
The reaction product of some polyglycols and organic diisocyanates are rubber products known as polyurethane. These compounds are special synthetic rubbers with special properties. In this way, they have high abrasion resistance, and while they can be used at high temperatures, they are also resistant to high concentrations of solvents, oxygen and ozone. The main use of this type of rubber is the production of flexible sponges and The use of these materials in the manufacture of furniture, mattresses, insulating materials, oscillators and other fields related to rubber sponges is expanding.
Hypalon synthetic rubber
Hypalon rubber is obtained from the radical catalyzed reaction of chlorine and sulfur dioxide with polyethylene. The result of this reaction is the transformation of soft heat polyethylene into a vulcanizable resin. Hypalon is extremely resistant to ozone, weathering, and heat, and its chemical resistance is also excellent.
Special space synthetic rubbers – polyisoprene and polybutadiene
The discovery that Ziegler-Natta catalyst (alkyllithium) catalyzes the polymerization of isoprene or butadiene in such a way that the cis structure is mainly obtained. This process made it possible to simulate natural rubber through synthesis. Polyisoprene rubber (IR), which is completely similar to natural rubber, is even superior in some respects, such as better color, more uniform quality, less odor, faster processability and mixing, more favorable lamination and perforation, excellent mold flow, and controlled molecular weight. In contrast, the tear strength, adhesiveness and tensile strength of natural rubber are higher.
Polyisoprene is produced commercially and is consumed alone or together with natural rubber. 1 and 4- Polybutadiene with a high percentage of cis is soft and dissolves easily. It has little residue and good abrasion resistance. On the other hand, 1 and 4-polybutadiene with a high percentage of trans is hard, crystalline and has poor solubility. This resin can be used to cover golf balls.
Ethylene-Propylene resins and resins
Ethylene and propylene copolymers (EPM) which are made by solution polymerization method and using a Ziegler catalyst. The copolymers do not have double bond and for this reason, they do not have vulcanization power and at the same time they are resistant to oxygen and ozone. The reactivity of ethylene and propylene is very different. EPR synthetic rubbers can be vulcanized by heating in the presence of peroxide. In this method, chains are connected by direct connection of carbon atoms. This is contrary to connecting chains through sulfur connections in usual processes. These rubbers can be used for many applications without being vulcanized. For easier vulcanization, ethylene-propylene resins are made with a DN (EPDM). EPDM resins have a unique resistance to heat, oxygen and ozone and are used as a replacement roof covering for asphalt. Other uses include wire and cable insulation, which compete with neoprene.
Different methods of producing synthetic rubber
Cold emulsion method
It is placed in an emulsion at a temperature of 5 degrees Celsius for 8 to 12 hours. This operation is often performed in a reaction complex. The reaction is terminated at 60 to 75% conversion. The emulsion is mixed in the form of leachate in storage tanks and to achieve the desired type of rubber. The mixture is first coagulated, then completely washed and drained before drying. Most SBR tires are pre-lubricated.
Solution method
In this type of resin, there is more control over the spatial structure of the resulting resin and, naturally, its physical properties. The distribution of styrene units at the top of the chain is random. Compared to emulsion coating, this coating has better wear and fatigue resistance, higher springiness and less heat generation. Under special coating conditions, batch copolymers of styrene and butadiene can be produced. These resins are thermo-soft and do not require vulcanization to be useful.
Important points in the production of synthetic rubber
Takpar recovery
The quality of the rubber and the speed of the reaction both decrease as the curing progresses, so it is customary to stop the reaction before complete conversion. Recovery of unreacted monolayer and purification is a necessary step in the industrial unit of synthetic rubber production. Recovery methods are used through steam stripping of leachates or distillation from the solvent system.
Coagulation and drying
The finishing process is usually the deposition of rubber from leachate emulsion or from a solvent solution in lump form, after which the rubber is dried and compacted into bales.
Tire packaging
The packaging of synthetic or synthetic rubber is important because it is sometimes possible to overcome problems such as sticking to the packaging bag and contamination due to insufficient protection, and some rubbers lose their shape due to flow.