Chloroprene rubber (CR, Chloroprene rubber), also known as chloroprene rubber, is an elastomer produced by α-polymerization of chloroprene (ie 2-chloro-1,3-butadiene) as the main raw material. It was first made by Wallace Hume Carothers of DuPont on April 17, 1930. DuPont publicly announced in November 1931 that it had invented neoprene, and in 1937 It was officially introduced to the market, making neoprene the first synthetic rubber variety to be industrially produced.
Neoprene Properties
Neoprene, also known as chloroprene (neoprene) rubber, English name: Chloroprene Rubber (CR). The appearance is milky white to beige or light brown flakes or lumps, free of mechanical sundries other than talcum powder, and free of scorched particles. Its physical and chemical properties are: a homopolymer made of 2-chloro-1,3-butadiene by emulsion polymerization. The relative density (d420) of chloroprene rubber is 0.958, the melting point is -130°C, the boiling point is 59.4°C, the refractive index (nD20) is 1.4583, and the vapor pressure (20.8°C) is 26.66kPa. Soluble in various organic solvents such as ethanol, acetic acid, acetone, slightly soluble in ethylene glycol and water. Easily polymerized in the presence of light, heat, ionizing radiation and catalysts. Its molecular weight is generally 100,000 to 200,000, its relative density is 1.15 to 1.25, and its glass transition temperature is -45°C. It is polar, has regular molecular arrangement and reversible crystallization properties.
Neoprene production process
Chloroprene rubber is produced by emulsion polymerization, and the production process is mostly single-pot batch polymerization. The polymerization temperature is mostly controlled at 40~60°C, and the conversion rate is about 90%. Polymerization temperature, high final conversion or the entry of air (oxygen) during polymerization can lead to a decrease in product quality. In production, the sulfur-thiuram (tetraalkylmethylaminothiocarbonyl disulfide) system is used to adjust the molecular weight. The main disadvantage of the sulfur-thiuram system is that the sulfur bond is not stable enough, which is one of the important reasons for affecting storage. This performance can be improved if the molecular weight is adjusted with mercaptans. Neoprene rubber is different from general synthetic rubber, it does not vulcanize with sulfur, but with zinc oxide, magnesium oxide, etc. vulcanization.
Variety classification of neoprene
The varieties and grades of neoprene can be divided according to the following situations.
①According to the molecular weight adjustment method, it can be divided into sulfur adjustment type, non-sulfur adjustment type and mixed adjustment type.
② According to the crystallization rate and degree, it can be divided into rapid crystallization type, medium crystallization type and slow crystallization type.
③ According to the Mooney viscosity, it can be divided into high Mooney type, medium Mooney type and low Mooney type.
④ According to the type of anti-aging agent used, it is divided into polluting type and non-polluting type.
Neoprene can be divided into general-purpose (sulfur-adjusted and mercaptan-adjusted, hybrid) and special-purpose (adhesive and other special-purpose) types according to their uses. The sulfur-adjusted type (G type) has a relatively regular structure and can be used for general rubber products, so it is a general-purpose type. This kind of rubber has good physical and mechanical properties, especially the resilience, tear strength and flex crack resistance are better than W type, the vulcanization rate is fast, and it can be vulcanized with metal oxides, and the elastic recovery is low during processing. Good adhesion, the main disadvantage is that the sulfur bond is not stable enough, the storage is not good, it is easy to burn, and there is sticking phenomenon. This performance can be improved if the molecular weight is adjusted with mercaptans. The molecular structure of the non-sulfur-regulated type (W type) is more regular than that of the G type, and the content of 1,2 structure is less.
The main chain of this type of molecule does not contain polysulfide bonds, so it has good storage stability. Compared with G type, the advantages of this type of rubber are that it is not easy to scorch and roll during processing, and the operating conditions are easy to master. The vulcanized rubber has good heat resistance and low compression denaturation. However, the crystallinity is large, the viscosity is poor during molding, and the vulcanization rate is slow. Adhesive neoprene is widely used as an adhesive.
Post time: Feb-02-2023