The forming characteristics and service performance of rubber mainly depend on the internal structure of rubber.
(1) the molecular structure of rubber is also a kind of macromolecular compound, and the relative molecular weight of rubber can reach several hundred thousand.The molecular size of macromolecular compound is not fixed, and the relative molecular mass usually refers to its average relative molecular mass.The relative molecular weight has a great influence on the rubber strength. Generally, only when the molecular weight reaches a certain level does it show a certain strength. The aging resistance of the polymer decreases with the increase of the degree of polymerization (an index to measure the molecular size of the polymer).But rubber in the plastication process will make rubber molecules fracture, relative molecular mass smaller, so as to increase the degree of plasticity, improve the processing conditions.
From the geometric red shape of rubber molecular chain, it can be divided into three types: linear type, branched chain type and crosslinked type (also known as body type).Different geometry, with completely different physical properties.Rubber is very flexible because the carbon atoms in the c-c chain of rubber molecules can rotate around chemical bonds.
(2)The aggregation state of rubber molecules is called the aggregation state.The aggregation state can be divided into three states: solid, liquid and gas.Rubber has the properties of a liquid because its molecular segments can move as freely as a low molecular liquid.Rubber also has the properties of a solid, because the whole macromolecular chain, the molecular chain can not relative displacement, can maintain a certain shape and greater strength.Rubber also has the properties of a gas, such as the elastic modulus increases with temperature and generates heat when stretched, just as heat is generated by energy conversion during gas compression.
(3)the viscoelastic rubber of rubber has good elasticity, in addition, it also has some characteristics of obvious viscous liquid, which is mainly manifested in the linear development of its deformation with time after the rubber is subjected to force, just like the viscous liquid.Therefore, rubber is considered as a viscoelastic material, which produces a series of viscoelastic phenomena such as creep, stress relaxation and internal friction.
(4)although the rheological rubber of rubber has high elasticity, its molding processing, such as plastication, mixing, pressing or rolling, all need to be in the flow state of deformation, so the molding process is bound to involve the fluidity of rubber.Viscosity is an important parameter to characterize liquid fluidity. The viscosity of rubber is different from that of plastics, which can greatly reduce the viscosity of melt by increasing the temperature. However, the viscosity of rubber is little affected by temperature, mainly depending on the relative molecular weight.Reducing the relative molecular weight can reduce the viscosity and elasticity, which will be beneficial to the molding of rubber.
(5)under the heating condition of vulcanization of rubber, the raw rubber in the rubber and vulcanized vitreous have a chemical reaction. The crosslinking process of rubber from linear structure to three-dimensional network structure is called vulcanization, and the vulcanized rubber is called cooked rubber.The physical, mechanical and other properties of the compound are obviously improved by vulcanization.
The change of rubber properties during vulcanization is the result of the change of molecular structure.The unvulcanized gels are linear structure macromolecules, whose molecular chains have the independence of movement, and show great plasticity, high elongation and solubility.After vulcanization of rubber macromolecules, in the molecular chain between the formation of transverse chain into a space network structure, so in addition to the secondary bond force between molecules, in the binding of molecules and the main valence bond force, so cooked rubber than raw rubber tensile strength is high, elongation is small and elastic.Vulcanization is the last working procedure in the production of rubber products.
With the development of bovine production, the concept of vulcanization also has a new progress, vulcanizing agent and high temperature is no longer necessary conditions for vulcanization, some special rubber materials can be vulcanized at a lower temperature, even at room temperature, also can be in the rubber material without vulcanizing agent, and physical methods (such as gamma rays) for crosslinking.