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Classification and characteristics of rubber products

Edit: John 2020-02-11 Mobile

  

  1.Definition of rubber products

  Rubber products are a kind of high elastic polymer compound, which is an amorphous high polymer, also called elastomer. That is to say, under the action of a small external force, a large deformation can be generated, and the original state can be restored after removing the external force. The term rubber products comes from the Indian language cau-uchu, which means "tree of tears." In the 18th century, the French discovered that there was a wild rubber product tree in the Amazon River in South America. The rubber product bark was cut out and the emulsion flowed out. Then the product of this emulsion after coagulation was a natural rubber product. In the middle of the 19th century, the British took the seeds of rubber products trees and planted them successfully in Ceylon (Sri Lanka), and gradually expanded to places such as Malaysia and Indonesia. However, how to dissolve and process raw rubber in manufacturing natural rubber products is a big problem. Until the 1840s, Americans discovered that turpentine, sulfur, and lead carbonate were heated together to obtain non-sticky and elastic products, the so-called vulcanization technology. Therefore, around 1920, the export volume of natural rubber products in Asia reached more than 700,000 tons. , The same volume of wild rubber products exported to Brazil at that time.

  Let us briefly understand why raw rubber is used after curing. From the point of view of raw rubber, when heated, it will become soft, and when cold, it will become hard, brittle, difficult to form, and easy to wear; it will be easily dissolved in gasoline. This is mainly due to the fact that the molecules of the raw rubber products are linear polymers, which have a buckled shape. They change from buckling to extension under the action of external forces. After the external force disappears, they can restore their original buckling state. This is a necessary condition for elasticity. However, the chain is easy to slide between chains, and the strength and toughness are poor. It must be cross-linked to make a chemical bond between the molecular chain and the molecular chain. Through the cross-linking, the linear polymer is cross-linked into a network structure. It can't slide in between, it has reversible high elastic deformation, and its strength and toughness are greatly enhanced, so it becomes a practical rubber product. The method of crosslinking is usually vulcanization. Vulcanization is to mix a certain amount of sulfur in raw rubber products, then put it into a molding mold and heat it (about 140 ° C), and sulfur atoms will crosslink the polymer chains through chemical bonds to obtain vulcanized rubber products. The vulcanization process is very complicated. Disulfide bonds are often formed for cross-linking. The obtained vulcanized rubber products have high elasticity and important properties such as cold resistance, heat resistance, ozone resistance, oil resistance, solvent resistance, shock absorption, wear resistance, fatigue resistance, sealing and dielectric properties. The main characteristic of rubber products is that the molecular weight is particularly large, which is the largest of all polymer materials, generally in the hundreds of thousands, and some can even reach millions. Secondly, rubber products have polydispersity, that is, the molecules of rubber products They vary in size and have a distribution range. The operating temperature range of rubber products is between glass transition temperature and viscous flow temperature.

  2. Classification

  Rubber products are mainly divided into two categories: natural rubber products and synthetic rubber products. Natural rubber products are mainly derived from the three-leaf rubber product tree. When the skin of this rubber product tree is cut open, milky juice will flow out, called latex. The latex is agglomerated, washed, shaped, and dried to obtain a natural rubber product. . Synthetic rubber products are prepared by artificial synthesis methods. Different types of rubber products can be synthesized using different raw materials (monomers).

  (1) According to its performance and use: general rubber products and special rubber products

  General rubber products refer to rubber types that are used in place of part or all of natural rubber products, such as styrene-butadiene rubber products, butadiene rubber products, isoprene rubber products, etc., and are mainly used to manufacture tires and general industrial rubber products. General rubber products have a large demand and are the main varieties of synthetic rubber products. All rubber products with special properties such as weather resistance, heat resistance, oil resistance, ozone resistance, etc., used to make rubber products used under specific conditions are special rubber products. Such as nitrile rubber products, silicone rubber products, fluorine rubber products, polyurethane rubber products and so on.

  Below we briefly introduce several general rubber products:

  SBR products

  Styrene butadiene rubber products are made by copolymerizing butadiene and styrene. They are the most versatile rubber products. They include milky polystyrene butadiene rubber products, solvent polystyrene butadiene rubber products, and thermoplastic rubber products (SBS).

  Butadiene rubber products

  Manufactured from butadiene by solution polymerization, butadiene rubber products have particularly excellent cold resistance, abrasion resistance and elasticity, and also have good aging resistance. The majority of butadiene rubber products are used in the production of tires, and a small part is used in the manufacture of cold-resistant products, cushioning materials, tapes, and rubber shoes. The shortcomings of butadiene rubber products are poor tear resistance and poor wet skid resistance.

  Isoprene rubber products

  Isoprene rubber products are short for polyisoprene rubber products and are produced by solution polymerization. Isoprene rubber products, like natural rubber products, have good elasticity and abrasion resistance, excellent heat resistance and good chemical stability. The strength of the raw rubber of isoprene rubber (before processing) is significantly lower than that of natural rubber products, but the quality uniformity and processing performance are better than those of natural rubber products. Isoprene rubber products can replace natural rubber products to make truck tires and off-road tires, and can also be used to produce various rubber products.

  Ethylene-propylene rubber products

  Ethylene-propylene rubber products are synthesized with ethylene and propylene as the main raw materials, and have outstanding aging resistance, electrical insulation properties and ozone resistance. Ethylene-propylene rubber products can be filled with a large amount of oil and carbon black. The price of the products is relatively low. The ethylene-propylene rubber products have good chemical stability. Ethylene-propylene rubber products have a wide range of uses. They can be used as tire sidewalls, rubber strips and inner tubes, as well as automotive parts. Can also make rubber shoes, sanitary products and other light-colored products.

  Neoprene products

  It uses chloroprene as the main raw material and is made by homopolymerization or copolymerization of a small amount of other monomers. It has high chemical stability, high tensile strength, good water resistance, excellent heat resistance, light resistance and aging resistance, and oil resistance is better than natural rubber products, styrene butadiene rubber products, butadiene rubber products, and has strong flame resistance. And excellent flame retardancy. Its disadvantages are its electrical insulation properties, its poor cold resistance, and its instability during storage. Neoprene products are widely used, such as used to make transportation belts and transmission belts, covering materials for wires and cables, manufacturing oil-resistant hoses, gaskets, and chemical-resistant equipment linings.

  (2) According to structural characteristics: saturated and unsaturated rubber, polar rubber and non-polar rubber

  For example, ethylene-propylene rubber is a saturated non-polar rubber, nitrile rubber is an unsaturated polar rubber, and butyl rubber is an unsaturated non-polar rubber.

  (3) By application: tires, tapes, hoses, rubber shoes and industrial rubber products

  Industrial rubber products commonly known as rubber products miscellaneous goods, in addition to tires, tapes, refers to machinery, equipment, instruments, vehicles, ships and aircraft, spacecraft tools, etc. used in industry, national defense, transportation, medical and health services, etc. The types of rubber products or accessories are extremely diverse and can be roughly divided into two categories: model products and non-model products.

  Model products are compression-vulcanized products using metal molds, including sealed shock-absorbing products, such as various oil-resistant and water-resistant seals, gaskets, oil storage diaphragms, waterproof protective covers, bridge and railway sleeper pads, sound-proof rubber product accessories, insulation insulation Thermal products, machinery and equipment cushion cushions, medical and health products, rubber rollers, rubber sheets, etc.

  Non-model products are mainly adhesive tapes and adhesive tape products, which are divided into protective adhesive tapes and their products and industrial adhesive tapes and their products. Protective tapes and products such as daily-use tapes, tarpaulins, pads, diving suits, production suits, water jackets and raincoats, as well as oil-resistant, chemical-resistant, heat-resistant, insulating, gas-proof, and radiation-proof tapes Industrial tape products include rubber boats, life rafts, airships, water bladder, etc.

  3. Features

  (1) High flexibility

  The elastic modulus of rubber products is small, generally 1 to 9.8 MPa. Large elongation deformation, elongation can be as high as 1000%, still exhibits recoverable characteristics, and can maintain elasticity in a wide range of temperature (-50 ~ 150 ℃).

  (2) Viscoelasticity

  Rubber products are viscoelastic. Due to the existence of large intermolecular forces, rubber products are subject to external forces. When deformation occurs, it is affected by conditions such as time and temperature, and it has obvious stress relaxation and creep phenomena.

  (3) Shock absorption

  Rubber products have a mitigating effect on sound and vibration and transmission. This feature can be used to prevent noise and vibration.

  (4) Electrical insulation

  Rubber products are electrical insulation materials like plastics. The volume resistivity of natural rubber products and butyl rubber products can reach more than 1015Ω? Cm.

  (5) Temperature dependence

  Polymer materials are generally affected by temperature. Rubber products are hardened and brittle in a glass state at low temperatures, and soften, melt, thermally oxidize, thermally decompose, and even burn at high temperatures.

  (6) With aging phenomenon

  Just like metal corrosion, wood decay, and rock weathering, rubber products also age due to changes in environmental conditions, which deteriorates performance and shortens life.

  (7) Must be vulcanized

  Rubber products must be added with sulfur or other substances that can vulcanize (or cross-link) the rubber products, so that the macromolecules of the rubber products are cross-linked into a spatial network structure in order to obtain rubber product products with useful values. In addition, it should be noted that thermoplastic rubber products need not be vulcanized.

  In addition, rubber products have low density, are lightweight materials, have low hardness, and good flexibility; they have poor air permeability and can be used as air-tight materials; they are also better waterproof materials. The application range of rubber products and rubber products is particularly wide, and there are tens of thousands of products.

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