General properties of rubbers
General properties of rubber
Rubbers are high molecular weight materials whose average molecular weight is not constant and varies depending on the operations they perform before and during processing. For example, the molecular weight of hydrocarbon rubber in natural freshly collected latex is higher. Of 1,000,000 However, when exposed to air, its molecular weight decreases rapidly.
Thus, for example, butyl and natural non-polar rubbers are dissolved in non-polar liquids, including oil. Polar rubbers such as chloroprene and acrylonitrile butane DNA are soluble in polar liquids such as methyl ethyl ketone. Most rubbers are soluble in aromatic solvents and chlorinated hydrocarbons. The viscosity of the resulting product is soluble in concentration, as well as in operation, which is reduced by the molecular weight of the rubber. Some of the properties of rubber change dramatically with temperature. As a result, the rubber hardens in the cold. This phenomenon may be observed during prolonged storage of natural rubber in cold places or when transported in winter.
Resistance of rubber
For example, rubber becomes brittle when it is too cold with liquid air However, no irreversible change occurs during cooling, and if the rubber is not mechanically damaged in the frozen state, it returns to its original state after heating. Thus, the changes that occur in the rubber only cause it to mass. These changes can be observed, for example, based on the dependence of volume on temperature. As the temperature decreases, the volume also decreases linearly until it breaks in a certain range of temperature. It has, but it has a lower slope. This fracture is called the glass transition temperature Tg and is of practical importance in assessing the resistance of rubber at low temperatures. The amount of Tg depends on the nature of the monomers and their arrangement.
Molecular weight in natural rubber
The molecular weight of all types of commercial natural rubbers is about 350,000. This is still a very high molecular weight for direct rubber processing operations. It is reduced to 100,000 to 150,000. The molecular weight of rubber is not insignificant in the mechanical properties of rubber and it is recommended that it should not be reduced too much to achieve the desired process ability. In contrast can also be mixed with a large amount of oil before processing, either during the production of rubber or in subsequent processing units, which is called oil dispersion. They matter. Depending on the monomers used, the rubbers are soluble in some solvents and this solubility depends on the polarity of the solvent and the solute. The strength of the rubbers increases in the following order: butyl rubber, natural rubber, chloroprene, and acrylonitrile rubber. The polarity of the consumable liquid hydrocarbons is thus increased