What is the rubber

Rubber refers to a highly elastic polymer material with reversible deformation. It is elastic at room temperature and can be deformed under a small external force. It can be restored to its original state after removing external force. Rubber is a completely amorphous polymer with a low glass transition temperature (T g) and a large molecular weight of more than several hundred thousand.

The early rubber was obtained from rubber plants such as rubber trees and rubber grasses and was processed to produce materials that were elastic, insulating, impervious to water and air. It is a highly elastic polymer compound. Rubber is divided into natural rubber and synthetic rubber. Natural rubber is processed by extracting gum from plants such as rubber trees and rubber grasses; synthetic rubber is obtained by polymerization of various monomers. Rubber products are widely used in various aspects of industry or life.

 

Rubber composition

Natural rubber is made of latex, and a part of the non-rubber component contained in the latex remains in the solid natural rubber. Generally, natural rubber contains 92%-95% of rubber hydrocarbons, while non-rubber hydrocarbons account for 5%-8%. Due to different manufacturing methods, different production areas and even different rubber seasons, the proportion of these ingredients may vary, but they are basically within the range.

Protein can promote the vulcanization of rubber and delay aging. On the other hand, the protein has strong water absorption, which can cause the rubber to absorb moisture and mold, and the insulation is degraded, and the protein has the disadvantage of increasing heat build-up.

Acetone extracts are high-grade fatty acids and sterols, some of which act as natural antioxidants and accelerators, and others which help the powdered compounding agent disperse during the mixing process and soften the raw rubber.

The ash mainly contains salts such as magnesium phosphate and calcium phosphate, and has a small number of metal compounds such as copper, manganese, iron, etc., because these variable metal ions can promote rubber aging, so their content should be controlled.

The moisture in the dry glue does not exceed 1%, and it can be volatilized during processing. However, when the moisture content is too much, it will not only cause mildew during the storage of the raw rubber but also affect the processing of the rubber, such as the compounding agent during mixing. Group; bubbles are easily generated during calendering and extrusion, and bubbles or sponges are formed during the vulcanization process.

 

Rubber classification

According to the form, it is divided into block rubber, latex, liquid rubber, and powder rubber. Latex is a colloidal aqueous dispersion of rubber; liquid rubber is a rubber oligomer, which is generally a viscous liquid before being vulcanized; powdered rubber is processed into a powder to facilitate the formulation and processing. The thermoplastic rubber developed in the 1960s was formed by a thermoplastic processing method without chemical vulcanization. Rubber is divided into general and special types according to its use. It is an insulator and is not easy to conduct electricity, but it may become a conductor if it is wet or at a different temperature. Conductivity is an easy condition for the conduction of electrons with molecules or ions inside a substance. According to the source and method of raw materials: rubber can be divided into two categories: natural rubber and synthetic rubber. Natural rubber consumption accounts for 1/3, and synthetic rubber consumption accounts for 2/3.

According to the appearance of rubber: rubber can be divided into four categories: solid rubber (also known as dry rubber), milk rubber (referred to as latex), liquid rubber and powder rubber.

According to the properties and uses of rubber: in addition to natural rubber, synthetic rubber can be divided into general synthetic rubber, semi-generic synthetic rubber, special synthetic rubber, and special synthetic rubber.

According to the physical form of rubber: rubber can be divided into hard rubber and soft rubber, raw rubber, and rubber compound.

According to performance and use: general rubber and special rubber.

Advantages and disadvantages of various types of rubber

Natural rubber NR
(Natural Rubber) Made of rubber tree-collecting latex, a polymer of isoprene. Has good wear resistance, high elasticity, tear strength and elongation. It is easy to age in the air, becomes sticky when exposed to heat, easily swells and dissolves in mineral oil or gasoline, and is resistant to alkali but not strong acid.

Advantages: good elasticity, acid, and alkali resistance.

Disadvantages: not heat-resistant, oil-resistant (resistant to vegetable oil), is the raw material for making tapes, hoses, and rubber shoes, and is suitable for the production of shock-absorbing parts, products used in automotive brake oil, ethanol and other liquids with hydroxide.

SBR styrene SBR
(Styrene Butadiene Copolymer) The copolymer of butadiene and styrene, compared with natural rubber, uniform quality, less foreign matter, better wear resistance, and aging resistance, but weak mechanical strength, can be mixed with natural rubber Used together.

Advantages: low-cost non-oil resistant material, good water resistance, good elasticity below 70, and poor compression at high hardness.

Disadvantages: It is not recommended to use strong acids, ozone, oils, oil esters and fats and most of the hydrocarbons. Widely used in the tire industry, footwear, cloth industry, and conveyor belt industry.

Butyl rubber IIR
(Butyl Rubber) is a mixture of isobutylene and a small amount of isoprene. Since the steric obstacle of methyl group has less movement than other polymers, it has less gas permeability and is more resistant to heat, sunlight, and ozone. The electrical insulation is good; the resistance to the polar agent is large, and the general temperature range is minus 54-110 °C.
Advantages: It is impervious to most general gases, has good resistance to sunlight and odor, and can be exposed to animal or vegetable oils or gasification chemicals.

Disadvantages: Not recommended for use with petroleum solvents, rubber kerosene, and aromatic hydrogen. The inner tube, leather bag, rubber paste paper, window frame rubber, steam hose, heat-resistant conveyor belt, etc. for automobile tires.

Nitrile rubber NBR
(Nitrile Rubber) is a copolymer of acrylonitrile and butadiene with an acrylonitrile content of 18%-50%. The higher the acrylonitrile content, the better the resistance to fossil fuel hydrocarbon fuel oil, but the low-temperature performance changes. Poor, the general operating temperature range is minus 25-100 °C. Nitrile rubber is one of the most commonly used rubbers for oil seals and O-rings.

Advantages: Good resistance to oil, water, solvent, and high-pressure oil. Good compressibility, abrasion resistance, and elongation.

Disadvantages: Not suitable for use in polar solvents such as ketones, ozone, nitrohydrocarbons, MEK and chloroform. Used in fuel tanks, oil tanks, and petroleum-based hydraulic oils, gasoline, water, silicone oils, diesters. It is a rubber part used in a fluid medium such as lubricating oil, especially a sealing part. It can be said that it is the most widely used and lowest cost rubber seal.

Neoprene CR
(Neoprene, Polychloroprene) is a polymer of chlorobutene monomers. The rubber after vulcanization has good elastic wear resistance, is not afraid of direct sunlight, has good weather resistance, is not afraid of intense distortion, is not afraid of refrigerant, is resistant to dilute acid and silicon ester-based lubricating oil, but is not resistant to the phosphate ester hydraulic system. oil. It is easy to crystallize and harden at low temperature and has poor storage stability. It has a large expansion amount in mineral oil with low aniline point, and the general temperature range is -50~150 °C.

Advantages: good elasticity and good compression deformation, the formula does not contain sulfur, so it is very easy to make, with anti-animal and vegetable oil properties, not due to neutral chemicals, fat, grease, various oils, solvents Affects physical properties and has anti-combustion properties.

Disadvantages: It is not recommended to use R12 refrigerant seals, rubber parts or seals on household appliances, among the chemicals of strong acids, nitrohydrocarbons, esters, chloroforms and ketones. Suitable for making all kinds of parts that are in direct contact with the atmosphere, sunlight, and ozone. Suitable for all kinds of rubber and chemical resistant rubber products.