Natural rubber (NR) is a natural polymer compound mainly composed of cis-1,4-polyisoprene. In the composition of natural rubber, rubber hydrocarbons account for approximately 91% to 94%, while the rest are non rubber substances such as proteins, fatty acids, ash, and sugars. Due to its widespread application, natural rubber is considered a common universal rubber. The natural rubber commonly referred to is an elastic solid material made from natural rubber latex collected from Brazilian rubber trees, processed through processes such as solidification and drying.

Structural characteristics

Natural rubber has the main macromolecular chain structure, with the unit of the macromolecular chain being isoprene. More than 97% of rubber is composed of polyisoprene. On macromolecular chains, there is an aldehyde group, with an average of one aldehyde group per macromolecular chain. These aldehyde groups can undergo condensation reactions or reactions with protein decomposition products to form branching and cross-linking, leading to an increase in viscosity of rubber during storage. In addition, natural rubber also has epoxy groups on its macromolecular chains, which have high reactivity. The macromolecular end of natural rubber is usually speculated to be a dimethylallyl group, while the other end is a pyrophosphate ester group, which is the end group. The number of aldehyde groups and polymerization elements in the macromolecular chain is relatively small.

Main categories

Natural rubber can be divided into two categories based on its morphology: solid natural rubber (including film and particle rubber) and concentrated latex. In daily use, solid natural rubber accounts for the vast majority. Film is a form of solid natural rubber, which can be divided into cigarette adhesive, air dried film, white wrinkled film, brown wrinkled film, etc. according to different manufacturing processes and shapes. Among them, tobacco adhesive is a representative variety, with a large dosage and wide application. Cigarette adhesive is usually classified according to its appearance, into six levels: special grade, first grade, second grade, third grade, fourth grade, fifth grade, etc. Those that do not meet the fifth grade standard are classified as equivalent adhesive. Granular adhesive (also known as standard adhesive) is classified according to internationally unified physical and chemical performance indicators. These physical and chemical performance indicators include seven aspects: impurity content, initial plasticity value, plasticity retention rate, nitrogen content, volatile matter content, ash content, and color index.

Main features

▲ Chemical reactivity: Natural rubber is prone to oxidation and cracking reactions with oxygen and ozone, chlorination and conversion reactions with halogens, and chemical reactions under catalysis and acid action.

▲ Elastic performance: Natural rubber has good elasticity at room temperature. Thermal aging characteristics: Natural rubber will slowly soften after being heated, starting to flow at around 130-140 degrees, decomposing at around 200 degrees, and experiencing severe decomposition at around 270 degrees.

▲ Medium resistance: Natural rubber has a certain degree of medium resistance. It is not resistant to media such as cyclohexane, gasoline, benzene, and is insoluble in polar acetone, ethanol, and water.

▲ Processing performance: natural rubber is easy to be plasticized, mixed, calendered, extruded and molded due to its high molecular weight, easy to break molecular chains, and a certain amount of gel molecules.

▲ Sulfurization characteristics: Generally, natural rubber is vulcanized with sulfur. Selenium and tellurium also have sulfidation effects, but their effectiveness is not as good as sulfur, and they are only used in special occasions. However, when used in combination with sulfur