Rubber is divided into two main categories, natural rubber and synthetic rubber. Among them, synthetic rubber is divided into general-purpose synthetic rubber and special synthetic rubber according to the characteristics of its application requirements.
1. Natural rubber
The main component is cis-polyisoprene (molecular formula C5H8) n (cis-1,4-polyisoprene) content of more than 90%, has a large elasticity, high tensile strength, good tear resistance and wear resistance, easy to bond with other materials and other characteristics, widely used in the production of tyres, tapes and other rubber products. It is generally a flaky solid, with a relative density of 0.94, a refractive index of 1.522, a modulus of elasticity of 2 to 4 MPa, softening at 130 to 140°C, viscous and soft at 150 to 160°C, and starting to degrade at 200°C. Highly elastic at room temperature, slightly plastic, crystalline hardening at low temperature. Has good resistance to alkali, but not to strong acids. Insoluble in water, low grade ketones and alcohols, swellable in non-polar solvents such as trichloromethane and carbon tetrachloride.
Natural rubber, as we usually refer to it, is an elastic solid made from the natural latex collected from the rubber trees in Brazil, after coagulation, drying and other processing processes. Natural rubber has a wide range of uses due to its physical and chemical properties, especially its excellent resilience, insulation, water barrier and plasticity, as well as its valuable properties such as oil, acid, alkali, heat, cold, pressure and abrasion resistance after appropriate treatment. Of the various chemical reactions in natural rubber, the most important are oxidative cracking and structuring reactions. The former is the theoretical basis for the plasticizing process of raw rubber and the reason for the ageing of leaf acid rubber; the latter is the theoretical basis for the vulcanization process of raw rubber to produce vulcanization. The chlorination, cyclisation and hydrogenation of natural rubber can be applied to the modification of natural rubber. With the development of industrial market demand, the demand for rubber is so great that relying on rubber trees alone is simply not enough to meet actual production needs (the large increase in the number of cars used to make tyres also becomes a large demand for rubber). Faced with such a serious situation, countries are competing to develop synthetic rubber.
2、Synthetic rubber
Broadly speaking, it refers to the rubber made by chemical synthesis, to distinguish the natural rubber produced from the rubber tree, is a highly elastic polymer synthesized by artificial, is one of the three synthetic materials. Its production is only lower than that of synthetic resins and synthetic fibres. Synthetic rubber has a long history of development and holds great promise for research. Production began in the early 20th century and has developed rapidly since the 1940s. Synthetic rubber is generally less comprehensive in performance than natural rubber, but it has high elasticity, insulation, airtightness, oil resistance, high or low temperature resistance and other properties, and is therefore widely used in industry and agriculture, national defence, transportation and daily life. In recent years, China’s synthetic rubber production capacity has increased rapidly, but it has not been able to fundamentally meet the huge domestic demand, and the annual import volume is still very large. In terms of market segmentation, butadiene rubber and styrene-butadiene rubber are the most widely used and most in demand.
The main purpose of industrial synthetic rubber materials is to save costs and improve the characteristics of natural rubber products. It is the first choice for many companies producing low- and mid-range types of products. Synthetic rubber materials have excellent heat resistance, cold resistance, corrosion resistance and are affected by environmental factors, synthetic rubber materials can be used normally in extreme environments (-60°C-250°C). However, the main drawback lies in its poor tensile effect, tear strength and poor mechanical properties. Its performance varies depending on the monomer, with a few varieties having similar properties to natural rubber. Some synthetic rubbers have better resistance to temperature, wear, ageing, corrosion or oil than natural rubber. Synthetic rubber is made of different monomers in the role of initiator, polymerisation of a variety of polymer compounds, monomers have butadiene, styrene, acrylonitrile, isobutylene, chloroprene and many others. Polymerisation processes include emulsion polymerisation, solution polymerisation, suspension polymerisation and ontogenetic polymerisation.
There are many ways to classify synthetic rubber. According to the use of characteristics into general-purpose rubber and special rubber two categories. General-purpose rubber refers to rubber that can be used partially or completely instead of natural rubber, such as styrene butadiene rubber, isoprene rubber, cis-butyl rubber, etc., mainly used in the manufacture of various tyres and general industrial rubber products. General-purpose rubber is in high demand and is the main variety of synthetic rubber. And special rubber refers to synthetic rubber with high temperature resistance, oil resistance, ozone resistance, ageing resistance and high air tightness, etc., commonly used in silicone rubber, various fluorine rubber, polysulfide rubber, chlorohydrin rubber, nitrile rubber, polyacrylate rubber, polyurethane rubber and butyl rubber, etc., mainly used for special occasions requiring certain characteristics
The production process of synthetic rubber can be roughly divided into three parts
Production processes
(1) Monomer production
The basic raw material of synthetic rubber is monomer, and the common methods of refining are distillation, washing, drying, etc.
(2) Polymerisation process
The polymerisation process is the process of polymerisation of monomers under the action of initiators and catalysts to produce polymers. Sometimes a polymerisation plant is used, sometimes several are used in tandem. Synthetic rubber polymerisation process is mainly applied to emulsion polymerisation and solution polymerisation method two. Nowadays, the use of emulsion polymerization of butadiene rubber, isoprene rubber, butyl rubber, butyl rubber, etc.
(3) Post-processing
Post-processing is to make the polymerization reaction after the material (latex or rubber liquid), by removing unreacted monomer, coalescence, dehydration, drying and packaging and other steps, and finally the finished rubber process. The coalescence process of emulsion polymerisation mainly uses the addition of electrolytes or polymer coagulants to destroy the emulsion so that the rubber particles precipitate out. The coalescence process of solution polymerisation is based on hot water coagulation. After the coalescence of the precipitated rubber particles, containing a large amount of water, need to be dehydrated, dry.
Industry prospects
At present, Asia has accounted for half of the global production of synthetic rubber, the major synthetic rubber enterprises scrambling to invest in Asian countries, and the scale of the device is getting bigger and bigger, coupled with the obvious transfer of synthetic rubber production capacity in Europe and the United States to Asia, the future of Asian butyl rubber, ethylene propylene rubber, nitrile rubber, butadiene rubber and other synthetic rubber production will gradually occupy a dominant position in the world. China’s synthetic rubber production capacity and output has ranked first in the world. With the increase of uncertainties in the global economy, China’s tyre export trade friction intensified, domestic overcapacity and other issues are particularly worrying in the future, China’s synthetic rubber industry will face greater challenges.
Speciality rubbers
Synthetic rubbers with special properties and special applications that can be adapted to use under harsh conditions. Such as 300 ℃ high temperature resistance, strong erosion resistance, resistance to ozone, light, weathering, radiation and oil resistant fluorine rubber; -100 ℃ low temperature and 260 ℃ high temperature, low temperature dependence, low viscous flow activation energy and physiological inertia of silicone rubber; heat, solvent and oil resistance, good electrical insulation of acrylate rubber. Other polyurethane rubber, polyether rubber, chlorinated polyethylene, chlorosulphonated polyethylene, propylene oxide rubber, polysulphide rubber, etc., they also have excellent unique properties, can meet the general general rubber can not meet the specific requirements, in national defence, industry, cutting-edge science and technology, medical and health fields have an important role.
Special rubber classification
1、Nitrile rubber
NBR is made from butadiene and acrylonitrile by emulsion polymerization. NBR is mainly produced by low-temperature emulsion polymerization, with excellent oil resistance, high abrasion resistance, good heat resistance and strong adhesion. The disadvantages are poor low temperature resistance, poor ozone resistance, poor electrical properties and slightly lower elasticity. NBR is mainly used in the manufacture of oil-resistant rubber products.
2、Butyl rubber
Butyl rubber is made of isobutylene and a small amount of isoprene copolymerization, mainly using the slurry method of production. Low permeability, excellent airtightness, heat resistance, ozone resistance, good ageing resistance, its chemical stability, electrical insulation is also very good. The disadvantage of butyl rubber is that it is slow to vulcanise and has poor elasticity, strength and adhesion. The main use of butyl rubber is the manufacture of a variety of vehicle inner tube, for the manufacture of wire and cable covering, heat-resistant conveyor belt, steam hose, etc.
3、Fluorine rubber
Fluorine rubber is a synthetic rubber containing fluorine atoms, with excellent heat resistance, oxidation resistance, oil resistance and chemical resistance, it is mainly used in aviation, chemical, petroleum, automotive and other industrial sectors, as sealing materials, media materials and insulation materials.
4、Silicone rubber
Silicone rubber by silicon, oxygen atoms to form the main chain, side chain for the carbon group, the largest amount is the side chain of vinyl silicone rubber. Both heat and cold resistance, the use of temperature between -100 ~ 300 ℃, it has excellent weather resistance and ozone resistance and good insulation. The disadvantages are low strength, poor tear resistance and poor wear resistance. Silicone rubber is mainly used in the aviation industry, electrical industry, food industry and medical industry.
5、Polyurethane rubber
Polyurethane rubber is made of polyester (or polyether) and diisocyanate compounds polymerised. Good abrasion resistance, followed by good elasticity, high hardness, oil resistance, solvent resistance. The disadvantage is that it is poorly resistant to heat ageing. Polyurethane rubber in the automotive, shoe, machinery industry in the most applications.
6、Chlorosulfonated polyethylene rubber
Chlorosulphonated polyethylene rubber (CSM) is a special rubber made of polyethylene after chlorination and chlorosulphonation treatment CSM is known for its superior ozone resistance and good colour stability under sunlight, its oxidation, weathering, corrosion, oil and heat also has good resistance, so it is widely used in coatings, wire and cable sheathing, various rubber products and roofing waterproofing membrane and other fields.
7, chlorhydrin (CHC)
Chloroform rubber (CHC), also known as chlorine ether rubber, table chloroform rubber, is an epoxy compound as a monomer, in the role of the catalyst to open the ring polymerization and made of highly saturated polymer elastomer. The main bond of CHC contains an ether bond. A, side chain contains polar chloromethyl a CH, Cl, so has excellent oil resistance, high and low temperature resistance and excellent chemical stability, and small gas permeability.
8、Acrylate rubber (ACM)
ACM is an acrylic ester (such as ethyl acrylate, butyl acrylate) as the main component, and a small number of monomers with active groups copolymerization of functional polymer materials, its molecular structure of the main chain for the saturated structure, while the side chain with a number of polar ester groups, so it has excellent resistance to high temperatures, oil, weathering performance, the production of high-temperature conditions used in oil-resistant rubber products have special advantages, has become “ACM’s production methods are mainly suspension polymerisation and emulsion polymerisation.