The natural rubber is reacted with a cyclizing agent (which may be any one of sulfuric acid, nitric acid, phosphoric acid, chlorosulfonic acid, and benzenesulfonic acid) under heating at 100 to 150 ° C for several hours to several tens of hours. After undergoing the isomerization process, the obtained cyclic molecular structure product is called a cyclized rubber. Depending on the degree of cyclization, its hardness is not equal, it can be inelastic or even thermoplastic. However, their chemical formula is C5H8, which is the same as natural rubber. The difference is that the double bonds in the long-chain structure are greatly reduced, and the degree of unsaturation is lowered.
(1) Basic performance
The cyclized rubber has a softening point of 90 to 120 ° C and a relative density of 0.992, and is soluble in aromatic hydrocarbons and aliphatic hydrocarbon solvents, and the solubility depends on the degree of cyclization.
(2) Manufacturing method
1 Cyclization with an acid usually uses sulfuric acid or a sulfonyl chloride as a cyclizing agent in an amount of about 10%. The cyclization is carried out by heating them with natural rubber at 125 to 145 ° C for about 1 to 4 hours.
2 Halogenated cyclization The dissolved natural rubber is reacted with a halogen-containing (chlorine) compound, and dried by heating to obtain an amorphous powder having a relative density of 0.98, which is soluble in a rubber solvent. It can also be obtained by reacting solid natural rubber with chlorostannic acid at 130 to 150 ° C for 5 to 6 hours.
3 Heating Cyclization The rubber solution is heated at a high temperature of 250 to 300 t for several hours to remove the decomposed volatiles to obtain a yellow powder (i.e., a cyclized rubber) having a molecular weight of 3,500.
4 Dehydrogenation reduction The natural rubber is heated and chlorinated and reduced with zinc powder to finally form a cyclized rubber having a molecular weight of 2500-15000.
Of course, cyclized rubber can also be prepared from natural latex. First, a non-ionic type is added to the concentrated sulfuric acid as a cyclizing agent. The reaction was carried out at 100 ° C for 2 h. Since the reaction is “exothermic”, attention should be paid to cooling. A cyclized rubber is obtained after drying.
(3) Application range
2 As a reinforcing agent for rubber (including dry glue and latex).
2 As an adhesive for footwear, printing coatings and bonding of metal to rubber.