1) What is natural rubber? Natural rubber (NR) is a natural polymer compound with cis-1,4-polyisoprene as the main component, and 91% to 94% of its components are rubber hydrocarbons (cis-1,4-polyisoprene). Diene), the rest are non-rubber substances such as protein, fatty acid, ash, sugar, etc. Natural rubber is the most widely used general purpose rubber.     Usually, what we call natural rubber refers to the elastic solid material made from natural latex collected from the Brassica napus through coagulation, drying and other processing procedures. Natural rubber is a natural polymer compound with cis-1,4-polyisoprene as the main component. Its rubber hydrocarbon (cis-1,4-polyisoprene) content is more than 90%, and it also contains A small amount of protein, fatty acids, sugar and ash, etc. 2) Structure of natural rubber The structure of natural rubber is mainly the chain structure of macromolecules, molecular weight and its distribution and aggregation structure. The macromolecular chain structural unit of natural rubber is isoprene, and the macromolecular chain is mainly composed of polyisoene. It accounts for more than 97%, and there are aldehyde groups on the molecular chain, and each macromolecular chain has an average of one. It is the aldehyde group that is condensed or reacted with protein decomposition products to form branching and cross-linking, which makes rubber. The viscosity increases during storage, and there are epoxy groups on the natural rubber macromolecular chain, which are more active.    The macromolecular end of natural rubber is generally inferred to be dimethylallyl, and the other end is pyrophosphate group. The end group, the aldehyde group of the molecular chain and the polymerized elements are very few. In terms of the molecular weight and distribution of natural rubber, Its molecular weight range is wide. According to foreign reports, most of the molecular weights are around 30,000. The strength of natural raw rubber, mixed rubber and vulcanized rubber is relatively high. Generally, the strength of natural rubber can reach three MPa.     The main reason for the high mechanical strength of natural rubber is that it is a self-reinforcing rubber series. When stretched, the macromolecular chain will be oriented along the stress direction to form crystallization. The reason for the equally high strength is the tight agglomeration of tiny particles in its internal structure. 3) Classification of natural rubber ①Natural rubber by form It can be divided into two categories: solid natural rubber (film and granular rubber) and concentrated latex. In daily use, solid natural rubber accounts for the vast majority of the proportion. ②The film is manufactured according to the manufacturing process and shape It can be divided into smoked film, air-dried film, white wrinkled film, brown wrinkled film, etc. Tobacco sheet glue is the most representative variety of natural rubber. It has always been a kind of rubber with large dosage and wide application. Tobacco sheet glue is generally graded according to its shape, and it is divided into special grade, first grade, second grade, third grade and fourth grade. , Grade 5, etc., there are six grades, and those that do not reach Grade Five are classified as equal outer rubber. ③ Granular rubber (ie standard rubber) is classified according to the internationally unified physical and chemical performance and indicators. These physical and chemical properties include impurity content, initial plastic value, plastic retention rate, nitrogen content, volatile matter content, ash content and color index, etc. Seven items, of which the impurity content is the dominant indicator, and it is divided into five levels, 5L, 5, 10, 20 and 50, according to the amount of impurities. 4) Characteristics of natural rubber 1. The chemical properties of natural rubber. It is easy to undergo sulfidation reaction (structural reaction) with vulcanization, oxidation and cracking reaction with oxygen and ozone, chlorination and chemical reaction with halogen, chemical reaction under the action of catalysis and acid, etc. 2. Natural rubber has excellent comprehensive physical and mechanical properties. 3. Natural rubber has good elasticity at room temperature 4. Heat aging natural rubber is a high elastic body at room temperature, softens slowly after being heated, begins to flow at 130-140 degrees, and begins to decompose at about 200'270 and decomposes violently. 5. Medium resistance. The medium refers to oil, liquid chemical substances, etc. Natural rubber is not resistant to cyclohexane, gasoline, benzene and other media, insoluble in polar acetone, ethanol, etc., insoluble in water 6. Good processing technology performance. Due to the high relative molecular weight of natural rubber, the molecular chain is easy to break, and there are a certain number of gel molecules in the raw rubber, so it is easy to plasticize, knead, calender, extrude, and shape. 5) Application of natural rubber ① Transportation ②Industrial mines There are more large and small rubber products needed by the industrial sector, with many varieties and wide uses, and some have special requirements. The main products are tapes, hoses, gaskets, rubber rollers, rubber sheets, rubber linings and labor protection products. In mining, coal, metallurgy and other industries, the application of tape to transport finished products is constantly appearing everywhere. In order to meet the needs of large-scale production, steel wire rope core conveyor belts and synthetic fiber conveyor belts are also produced. ③ Agriculture, forestry and water conservancy In the development of agriculture, forestry and water conservancy, there are also a variety of rubber products, in addition to various tires for tractors and agricultural machinery, rubber tracks used in combine harvesters, rubber anti-seepage layers used in irrigation pools and reservoirs and rubber dams , rubber boats, life-saving supplies and other supplies are growing, and there are rubber accessories in agricultural and sideline product processing equipment and forestry, animal husbandry, and fishery technical equipment. ④Military solid defense Rubber is an important strategic material, and there are many kinds of ships, tents, warehouses, protective equipment and bathing clothing made of rubber. ⑤ Civil construction Sealing rubber strips for glass windows in buildings, acoustic floors, sponges, rubber carpets, rainproofing materials and painting walls with milky paints. Machinery used in construction, transportation equipment, protective equipment, etc. have rubber accessories. ⑥Electrical communication Another characteristic of rubber is that it has good insulating properties and is not easy to conduct electricity. All kinds of wires and cables are mostly made of rubber. Hard rubber is also used to make rubber hoses, glue sticks, rubber sheets, partitions and battery shells. In addition, it is also widely used as protective equipment, insulating gloves, insulating rubber boots and shoes. ⑦Medical and health There are many rubber products in the medical and health sector, such as anesthesiology, urology, surgery, brain surgery, orthopaedics, pentasphy, radiology, etc. in hospitals. Gloves, ice bags, sponge seat cushions, etc. used in various plastic-colored operations for diagnosis, blood transfusion, catheterization, and gastrointestinal lavage are mostly rubber products. ⑧ commodity storage For storage of fruits and vegetables. Silicone rubber of various sizes is embedded on the plastic film, so that the appropriate amount of c02 can be maintained in the bag, forming a good gas storage environment, thereby inhibiting the respiration intensity of fruits and vegetables, delaying the metabolic rate, and delaying the post-ripening process of fruits and vegetables. Reduce moisture evaporation to prevent rot. ⑨Culture, education and sports Various ball bladders, table tennis racket sponge rubber surfaces, toy leather balls, gold pen bladders, erasers, rubber lines, rubber stamps, blankets, balloons and sponge rubber pads, etc., are widely used in cultural and educational institutions, offices, design drawing and sports Sports equipment, etc. ⑩Daily necessities There are many rubber products serving us in daily life, such as raincoats, elastic bands, children's toys, sponge seat cushions and latex impregnated products, etc., which are playing their role in people's lives.