Introduction to Special Rubber Materials - Chlorosulfonated Polyethylene Rubber (CSM)

Chlorosulfonated polyethylene (also known as Hypalon) is a special type of rubber produced by chlorination and chlorosulfonation of polyethylene. After chlorination and sulfonation treatment of polyethylene, its structural regularity is disrupted, and it becomes a soft and elastic chlorosulfonated polyethylene rubber at room temperature.
Chlorosulfonated polyethylene is obtained by dissolving polyethylene in carbon tetrachloride, tetrachloroethylene or hexachloroacetylene, using Azobisisobutyronitrile as catalyst or under ultraviolet light irradiation, passing through the mixture of chlorine and sulfur dioxide, or treating with sulphonyl chloride SO2CI. The brief structure is as follows:
The performance of chlorosulfonated polyethylene rubber depends on the molecular weight of the raw polyethylene and the relative content of chlorine and sulfur. The molecular weight of polyethylene has a significant impact on the properties of chlorosulfonated polyethylene: low molecular weight leads to high viscosity and low tensile strength of the finished product; Its physical and mechanical properties increase with the increase of polyethylene molecular weight, but after reaching a certain limit, the impact on its performance is not significant. The molecular weight of polyethylene commonly used is between 2w and 10w. Chlorosulfonated polyethylene 20 and 30 use high-pressure polyethylene with low molecular weight of 2w~4w; Chlorosulfonated polyethylene 40 and 45 are commonly used low-pressure polyethylene with molecular weights ranging from 8w to 10w.
Introducing chlorine atoms into the polyethylene molecular chain can maintain the excellent performance of polyethylene while eliminating the crystallinity of molecules, resulting in a soft and easy to process elastomer. Polymers with chlorine content ranging from 25% to 38% have the lowest hardness and strength, and further increasing the chlorine content will increase the hardness and strength of the polymer. Experiments have shown that the optimal chlorine content is approximately 27%. When the chlorine content is high, the resulting polymer has good solvent and oil resistance, and its strength is also relatively high at higher temperatures. However, compression permanent deformation and brittleness increase at low temperatures. When the chlorine content is 27%~30%, the polymer has sufficient plasticity and good processing performance.
The function of sulfur dioxide is to bind it with chlorine, forming sulfinyl chloride groups in chlorosulfonated polyethylene, in order to form cross-linking bonds with this group. Therefore, its content has a significant impact on the vulcanization performance of the rubber compound. If the content is too high, it is easy to scorch. If the sulfur content in this group is calculated, it is generally recommended to use 1.5%.
Chlorosulfonated polyethylene is a white or milky white flake or granular solid with a relative density of 1.07-1.28. Its solubility parameter δ= 8.9, easily soluble in Aromatic hydrocarbon and chlorinated hydrocarbons; Low solubility in ketones, esters, and cyclic ethers; Insoluble in acids, aliphatic hydrocarbons, monohydric alcohols and Diol. When chlorosulfonated polyethylene rubber is continuously heated at a temperature of 121 ℃ or above for several hours, the sulfinyl chloride group will undergo cracking, resulting in an increase in the viscosity of the polymer and its solution. Early vulcanization is prone to occur during the processing.

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