In the process of changing mechanical properties, the physical mechanization of rubber is significant. Therefore, in the production process, the degree of vulcanization is often measured by the change of physical properties. The physical properties of rubber generally refer to strength (tensile strength, tensile strength, tear strength, etc.), elongation at break, hardness, elasticity, permanent deformation, degree of swelling, and the like. Although the changes of physical and mechanical properties of rubbers with different structures during vulcanization have different trends, most of the changes in properties are basically the same. During the vulcanization of natural rubber, the plasticity is significantly reduced, the strength and hardness are significantly increased, and the elongation and swelling degree are reduced accordingly. These phenomena are characteristic of the transformation of linear macromolecules into a network structure. For rubbers with side vinyl structure, such as styrene-butadiene rubber, nitrile rubber, etc., there are similar changes in the vulcanization process, but in a long time, the changes in various properties are relatively flat, and the curve appears The maximum or minimum values are not obvious.
1. The soluble vulcanization process will gradually reduce the rubber's ability to dissolve in the solvent, and can only swell; after vulcanization reaches a certain time, the swelling value will reach a minimum value, and the vulcanization will gradually increase when the vulcanization continues.
2. Thermal stability vulcanization improves the thermal stability of rubber, that is, the degree of change in the physical and mechanical properties of rubber with temperature decreases. For example, when the unvulcanized natural rubber is below 10 ° C, crystallization hardens during long-term storage; the temperature exceeds 70 ° C. , Plasticity increased significantly; above 100 ℃, it is in a viscous state; 200 ℃ began to decompose. However, after vulcanization, the temperature range of high elasticity is expanded, and the brittleness temperature can be lowered below -20 ~ -40 ° C, and the plastic flow state of the raw rubber does not appear. Therefore, vulcanization greatly increases the temperature range of use of natural rubber.
3. Density and air permeability In a certain range of vulcanization time, as the crosslinking density increases, the rubber density increases, while the air permeability decreases as the crosslinking density increases. This is due to the limited thermal movement of the macromolecular segments.