Natural rubber is the most traditional rubber variety in the production of rubber products. It has high mechanical strength, good elasticity, small hysteresis loss, and low heat generation. It is widely used in automobile tires, industrial conveyor belts, agricultural irrigation hoses, and life and medical treatment. Carbon black is second only to rubber in the rubber product industry, and its reinforcing effect is remarkable in rubber products. In the production formula of natural rubber products, we often see the figure of carbon black; but the natural rubber itself has high mechanical strength, must it be reinforced with carbon black?
1. Natural rubber can be reinforced without carbon black
Natural rubber has cis-1,4-polyisoprene as the main component, and the macromolecular chain is mainly composed of polyisoene. When natural rubber is stretched, the rubber macromolecular chain will be oriented in the stress direction to form crystals. These crystals Granules can play a reinforcing role in amorphous macromolecules. After the crystallinity of natural rubber is increased, the corresponding molecular chains are closely arranged, the pores are low, the intermolecular force is increased, the intermolecular macromolecular chain segments are difficult to move, and the tensile strength of natural rubber is improved.
The test shows that the tensile strength of the natural rubber vulcanizate not reinforced with carbon black is between 20-30MPa, and the tensile strength of the vulcanizate after carbon black filling is between 15-35MPa. Natural rubber, as a typical crystalline rubber, is self-reinforcing when stretched and has high tensile strength. The reinforcement effect after filling with carbon black is not very obvious. Therefore, in actual production, some natural rubber products are not reinforced with carbon black.
2. Pure natural rubber basic formula design
When natural rubber products are not reinforced with carbon black, rubber product manufacturers generally choose sulfur vulcanization, combined with zinc oxide, stearic acid, accelerators, and appropriate amount of anti-aging agent 2LLYY58 to further improve the anti-aging properties of natural rubber products. You can refer to the following pure natural Basic rubber formula: 100 parts of natural rubber, 5 parts of zinc oxide, 2 parts of stearic acid, 1 part of anti-aging agent, 1 part of accelerator, 2.5 parts of sulfur, a total of 111.5 parts.
Natural rubber can produce tensile crystallization, and early weak bond breaking is beneficial to the orientation crystallization of the main chain, so vulcanizates with a large number of weak bonds have greater tensile strength. In general, the tensile strength of natural rubber vulcanizates decreases in the order of the following cross-link bonds: ionic bond> polysulfide bond> disulfide bond> single sulfur bond> carbon-carbon cross-link bond.
Natural rubber has high mechanical strength and can be reinforced without carbon black in some occasions. In the actual application process, natural rubber is easy to age in the air, and swells and degrades in oil media. In addition, natural rubber itself has high product prices and large price fluctuations. Therefore, it is often used in conjunction with synthetic rubber or recycled rubber to further improve natural rubber. Comprehensive index of rubber products to reduce costs. Because synthetic rubber (except for isoprene rubber and neoprene rubber) without vulcanizate reinforced with carbon black has poor mechanical properties, natural rubber and other types of rubber are often reinforced with carbon black.