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An overview of the molding and use properties of rubber
Author：admin Time：2017-07-22 15:09:58
The molding and use properties of rubber depend mainly on the internal structure of rubber.
(1) the rubber molecular structure rubber also belongs to the polymer compound, and the relative molecular weight can reach hundreds of thousands. The molecular size of a polymer is not fixed, and the average relative molecular mass refers to its average relative molecular mass. The relative molecular mass has great influence on the strength of rubber. Generally, only a large number of molecules show a certain degree of strength. The aging resistance of polymer decreases with the increase of polymer concentration (the index of polymer molecular size). But rubber in the process of molding will break the rubber molecules, the relative molecular weight becomes smaller, so that the plasticity can be increased and the processing conditions are improved.
From the geometric shape of the rubber chain, it can be divided into three types: line type, branched chain type and crosslinked type (also known as body type). Different geometries, with completely different physical properties. Rubber has a strong flexibility, because the carbon atoms in the C-C chain of the rubber molecules can revolve around the chemical bonds.
(2) the aggregation properties of rubber are called aggregation states. The aggregation state can be divided into three states, solid, liquid and gas. Rubber has a liquid nature, because the molecular chain of rubber can move more freely like a low molecular liquid. Rubber also has the properties of solid, because from the whole large molecular chain, its molecular chain can not be relative displacement, and can maintain a certain shape and greater strength. Rubber also has the property of gas, for example, the elastic modulus increases with the increase of temperature, and when it is compressed, the heat generation is just like when the gas is compressed.
(3) the viscoelastic rubber of rubber has good elasticity. Besides, it has obvious characteristics of viscous liquids. It mainly shows that the deformation of rubber is linear with time after viscous force. Therefore, rubber is considered to be a kind of viscoelastic material, resulting in a series of viscoelastic phenomena, such as creep, stress relaxation, internal friction and so on.
(4) although rheologic rubber of rubber has high elasticity, its molding process, such as plastication, mixing, extrusion or calendering, needs to be deformed in the flow state, so the molding process will inevitably involve the mobility of rubber. Viscosity is an important parameter for characterizing liquid fluidity. The viscosity of rubber is different from that of plastic. Plastics can greatly reduce the viscosity of the melt by raising temperature, while the viscosity of rubber is affected by temperature very little, mainly depending on the relative molecular mass. Reducing the relative molecular weight can reduce the viscosity and elasticity, and will be beneficial to the molding of rubber.
(5) the vulcanization of rubber under the condition of heating, raw rubber and vulcanized rubber. In chemical reaction, high molecular rubber by linear structure into the crosslinking process of three-dimensional mesh structure is called vulcanization, vulcanized rubber called glue. The physical, mechanical and other properties of the rubber have been greatly improved by vulcanization.
The change of rubber properties during vulcanization is due to the change in molecular structure. Unvulcanized rubber is linear structure of large molecules, the molecular chain has the independence movement, and showed plasticity and high elongation, and soluble. The rubber molecules after vulcanization, cross chain generation between molecular chains become a spatial network structure, thus in the intermolecular bond except in molecular force, combined with each other and the main bonding force, so the rubber glue than high tensile strength, low elongation and elasticity. In the production of rubber products, vulcanization is the last processing procedure.
With the development of the cow, curing concept also has new progress, curing agent and high temperature vulcanization is no longer necessary, some special sizing material at low temperature, even at room temperature curing, can also be in the rubber and vulcanizing agent, and the use of physical methods (such as the gamma ray crosslinking).
