Natural rubber (NR) is a kind of natural macromolecular compound with cis-1,4-polyisoprene as the main component. Among its components, 91%~94% are rubber hydrocarbons (cis-1,4-polyisoprene), and the rest are non rubber substances such as protein, fatty acid, ash, sugar, etc. Natural rubber is the most widely used general rubber.
Generally speaking, the natural rubber refers to the elastic solid made from the natural latex collected from the Brazilian rubber tree through solidification, drying and other processing procedures. Natural rubber is a kind of natural macromolecular 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 acid, sugar and ash.
Microstructure of natural rubber:
The structure of natural rubber mainly refers to the chain structure, molecular weight, distribution and aggregation structure of macromolecules. The macromolecular chain structure unit of natural rubber is isoprene, and the macromolecular chain is mainly composed of polyisopenes. The content of rubber accounts for more than 97%. There are aldehyde groups on the molecular chain, and there is an average of one on each macromolecular chain, It is the aldehyde group that condenses or reacts with protein decomposition products to form branching and cross-linking, which increases the viscosity of rubber during storage. The epoxy group is also active on the macromolecular chain of natural rubber.
The macromolecular end of natural rubber is generally inferred to be dimethyl allyl group, and the other end is pyrophosphate group, end group, aldehyde group of molecular chain and polymerized elements are few. In terms of molecular weight and distribution of natural rubber, its molecular weight range is relatively wide. According to foreign reports, most of the molecular weight is about 30000, The strength of vulcanizate is relatively high, and the strength of natural rubber can reach 3 MPa in general.
The high mechanical strength of natural rubber is mainly due to its self reinforcing rubber series. When stretched, macromolecular chains will be oriented along the stress direction to form crystals. The crystals play a reinforcing role in amorphous macromolecules. The strength of non expanded natural rubber is also high because of the close aggregation of small particles in its internal structure
Category:
Natural rubber can be divided into two categories according to its morphology: solid natural rubber (film and particle rubber) and concentrated latex. In daily use, solid natural rubber accounts for most of the proportion.
According to different manufacturing processes and shapes, films can be divided into cigarette adhesive, air dried film, white wrinkled film, brown wrinkled film, etc. Cigarette adhesive is the most representative variety of natural rubber, and has always been a kind of adhesive with large amount and wide application. Cigarette adhesive is generally classified according to its shape, which is divided into six grades, namely, super grade, first grade, second grade, third grade, fourth grade and fifth grade. Those less than five grades are classified as substandard adhesive.
Granular adhesive (i.e. standard adhesive) is classified according to the internationally unified physical and chemical efficiency and indicators. These physical and chemical properties include seven items, including impurity content, initial plastic value, plastic retention rate, nitrogen content, volatile matter content, ash content and color index. Among them, impurity content is the main conductivity indicator, which can be divided into five levels according to the amount of impurities, namely 5L, 5, 10, 20 and 50.
The delivery grades of natural rubber contracts in Shanghai Futures Exchange, China's futures trading market, are domestic Grade I standard rubber SCR5 and imported cigarette rubber RSS3, of which the domestic Grade I standard rubber SCR5 is usually also known as No. 5 standard rubber, which implements various quality indicators of natural rubber GB/T8081~1999 issued and implemented by the State Bureau of Technical Supervision. The imported cigarette rubber RSS3 implements the "International Standard for the Quality and Packaging of Natural Rubber Grades" (Green Book) (1979 version) determined by the International Rubber Quality and Packaging Conference.
Main purpose:
Because natural rubber has the above series of physical and chemical properties, especially its excellent resilience, insulation, water resistance and plasticity, and also has valuable properties such as oil resistance, acid resistance, alkali resistance, heat resistance, cold resistance, pressure resistance and wear resistance after proper treatment, it has a wide range of applications. For example, rain shoes, warm water bags and elastic belts used in daily life; Surgical gloves, blood transfusion tubes and condoms used in the medical and health industry; Various tires used in transportation; Conveyor belts, transport belts, acid and alkali resistant gloves used in industry; Drainage and irrigation hoses and ammonia bags used in agriculture; Sounding balloon for meteorological survey; Sealing and shockproof equipment for scientific test; Aircraft, tanks, artillery and gas masks used in national defense; Even sophisticated scientific and technological products, such as rockets, artificial earth satellites and spaceships, are inseparable from natural rubber.
