Vulcanized rubber refers to the vulcanized rubber, which has the characteristics of constant viscosity and is not easy to break. Most rubber products are made of this kind of rubber.It is also called mature rubber, commonly known as rubber or rubber.Rubber compoundThe general term for vulcanized products.After vulcanization, the raw rubber has a three-dimensional structure with high elasticity, heat resistance, tensile strength and insolubility in organic solvents.Rubber productsMost of them are vulcanized rubber.
Chinese name
Vulcanized rubber
Foreign name
Vulcanized Rubber
Also called
Cooked rubber or rubber
Features
High elasticity and heat resistance
Compression set
One of the important performance indexes of rubber products
Rubber becomes soft when heated, hard and brittle when cooled, difficult to form, easy to wear, and soluble in organic solvents such as gasoline. It has double bonds in the molecule, easy to react with addition, and easy to age.In 1839,GoodyearVulcanized rubber was unintentionally made.
To improveRubber productsIn production, a series of processing processes should be carried out for raw rubber. Under certain conditions, the raw rubber in the rubber compound can react with the curing agent to make it cross-linked from linear macromolecules to three-dimensional network macromolecules, so that the rubber compound has high strength, high elasticity, high wear resistance, corrosion resistance and other excellent properties.This process is called rubber vulcanization.
Vulcanization is the basic process of preparing vulcanizate by crosslinking raw rubber molecules to form a three-dimensional network structure.Different curing systems are suitable for different raw rubbers.The synthetic body is made of rubber (raw rubber) as the main body and a variety of auxiliary materials (there are several systems of auxiliary materials, such as filling reinforcement, vulcanization, protection, plasticization, special material additives, etc.). Vulcanization is a treatment method after covering the insulation layer or sheath layer. Its purpose is to make the vulcanization system in the auxiliary system work, so that the rubber can be permanently cross-linked, and increase elasticityReduce plasticity.The term "vulcanization" is used today because it was first used to crosslink rubber with sulfur.
Generally, the vulcanization process is divided into four stages, namely induction pre sulfuration positive sulfuration over sulfuration.In order to achieve this reaction, it is necessary to apply energy to make it reach a certain curing temperature, and then let the rubber insulation complete all the curing reactions within the curing temperature range.
As raw rubber of vulcanized rubber, it can only be usedsulfurorperoxideCrosslinked rubber.
Vulcanized rubber system
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Unsaturated rubber
The following curing systems are commonly used.
(1) With sulfur, organicDisulfideandPolysulfideThiazole, diphenyl guanidine, zinc oxide and stearic acid based vulcanizing agents.This is the most common curing system.However, the heat and oxygen aging properties of the vulcanizate prepared are not high.
According to the curing conditions, it can be divided into cold curing, room temperature curing and hot curing.
Cold vulcanization
Cold vulcanization can be used for vulcanization of film products. When the products contain 2%~5% sulfur chloridecarbon disulfideImmerse in the solution, then wash and dry.
Room temperature vulcanization
During room temperature vulcanization, the vulcanization process is carried out at room temperature and normal pressure, such as using room temperature vulcanized rubber slurry (rubber mixture solution) for bicycle inner tube joints, repairs, etc.
Thermal vulcanization
Thermal vulcanization is the main method of vulcanization of rubber products.According to different vulcanizing media and methods, thermal vulcanization can be divided into direct vulcanization, indirect vulcanization and gas mixture vulcanization.
(1) Direct vulcanization: put the product directly into hot water or steam medium for vulcanization.
(2) Indirect vulcanization: products are vulcanized in hot air. This method is generally used for some products with strict appearance requirements, such as rubber shoes.
(3) For gas mixture vulcanization, air vulcanization is used first, and then direct steam vulcanization is used.This method can not only overcome the disadvantages of steam vulcanization affecting the appearance of products, but also overcome the disadvantages of long vulcanization time and easy aging due to slow heat transfer of hot air.
influence factor
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Main factors affecting vulcanization process
(1) Sulfur consumption.The higher the dosage, the faster the vulcanization speed and the higher the degree of vulcanization can be achieved.The solubility of sulfur in rubber is limited, and excessive sulfur will be separated from the rubber surface, commonly known as "sulfur injection".In order to reduce sulfur injection, it is required to add sulfur at the lowest possible temperature or at least below the melting point of sulfur.According to the use requirements of rubber products, sulfurSoft rubberGenerally, the dosage in the semi hard glue is about 20%, and the dosage in the hard glue can be as high as 40%.
(2) Vulcanization temperature.If the temperature is 10 ℃ higher, the curing time will be shortened by half.As rubber is a poor heat conductor, the vulcanization process of products is different due to the temperature difference of each part.In order to ensure a more uniform degree of vulcanization, thick rubber products are generally vulcanized for a long time by gradually heating up and low temperature.
(3) Cure time.This isVulcanization processThe important link of.The time is too short, and the degree of vulcanization is insufficient (also called sulfur deficiency).The time is too long, and the degree of vulcanization is too high (commonly known as over sulfur).Only the appropriate degree of vulcanization (commonly known as positive vulcanization) can ensure the best comprehensive performance.
Deformation factor
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Compression setIt is one of the important performance indicators of rubber products.The compression set of vulcanized rubber is related to the elasticity and recovery of vulcanized rubber.The size of permanent deformation is mainly controlled by the change of rubber recovery ability.The factors affecting the resilience include the force between molecules (viscosity), the change or destruction of network structure, and the displacement between molecules.When the deformation of rubber is caused by the extension of the molecular chain, its recovery (or the size of permanent deformation) is mainly determined by the elasticity of rubber: if the deformation of rubber is accompanied by the destruction of the network and the relative flow of the molecular chain, this part can be said to be irrecoverable, and it is independent of elasticity.Therefore, all factors that affect the elasticity and recovery of rubber are factors that affect the compression set of vulcanized rubber.These factors include elasticity, impact elasticity (resilience), elasticity and modulus, compression permanent deformation, tensile permanent deformation, etc.
1. Elasticity - the elasticity of rubber should be a theoretical concept, which indicates the degree of difficulty in rotation of rubber molecular segments and side groups, or the flexibility of rubber molecular chains andIntermolecular forceSize of.For vulcanized rubber, its elasticity is also cross-linkedNetwork densityAnd regularity.
2. Elasticity and permanent deformation at breakNatural rubberIts elasticity is very good, but its permanent deformation at break is often very large, which is mainly due to the large elongation of natural rubber, the damage of the network and the displacement of the molecular chain caused by the elongation process are very large, and the recovery process after fracture is long and the unrecoverable part increases.If the permanent deformation of fixed intermediate length is compared, the permanent deformation of natural rubber is not necessarily great.
3. The impact elasticity or resilience is fixedloadThe elasticity and crosslinking degree of vulcanizate measured under (or constant energy) conditions[1]Or modulus has a direct relationship, which represents the integration of rubber elasticity and viscosity (or absorption).
4. The compression set is measured under the condition of constant deformation, and its value is related to the elasticity and resilience of rubber.
In the higher strain rate range, the dynamic stress-strain relationship of vulcanized rubber is related to the strain rate, and the elastic modulus, yield stress and flow stress all increase with the increase of the strain rate, so the material shows obvious strain rate effect in the dynamic experiment.Vulcanized rubber is insensitive to strain rate under low strain rate loading[2]。
Brittleness test
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The maximum temperature at which the specimen is damaged by impact under specified conditions isbrittleThe performance temperature can be used for comparative evaluation of the performance of non rigid plastics and other elastic materials under low temperature conditions.The brittleness temperature and low temperature properties of vulcanized rubber with different rubber materials or different formulations can be measured.Therefore, it is indispensable for scientific research on quality inspection of materials and their products and control of production process.
Thermoplasticity
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brief introduction
heatplasticityVulcanized rubber[3](Thermoplastic Vulcanize in English), referred to as TPV for short. Thermoplastic Rubber in Chinese is referred to as TPR for short, but this name is easy to compare with other types ofThermoplastic elastomerThermoplastic ElastomerThermoplastic rubberEspecially for styrene elastomers, it seems that "TPR" has become its proprietary name at least in China. When TPR is mentioned, it means SBS, SEBS and other benzeneethyleneThermoplastic elastomer with elastomeric like base material, which is inseparable from the large consumption of styrene elastomers in the field of civil and terminal consumer goods.
Thermoplastic vulcanized rubberIf the name of "dynamic" is more detailed, it should be thermoplastic dynamic vulcanizate. The addition of the word "dynamic" more specifically describes the process of producing this thermoplastic vulcanizate - dynamic vulcanization, which refers to the process of rubber andThermoplasticThe rubber is vulcanized in the process of melt blending. Of course, when the rubber is vulcanized, it is also constantly mixed with the thermoplastic. Therefore, the vulcanized rubber is distributed as a dispersed phase in the continuous phase of the thermoplastic.The corresponding thermoplastic static vulcanized rubber means that the rubber is first vulcanized according to the traditional method, then the vulcanized rubber is ground into powder by grinding equipment, and finally blended with the molten thermoplastic. Theoretically, this method can also produce TPV with excellent performance, but until now, it is only in the laboratory stage.
Composition of thermoplastic vulcanized rubber
TPV is mainly composed of two parts, one is plastic as continuous phase, and the other is rubber as dispersed phase.Usually rubber needs to be matched with softening oil or plasticizer.Vulcanizing agentAnd some auxiliary additives are also essential.In addition, some inorganic fillers will be added to reduce costs or improve some performance.
TPV can be formed between many plastics and rubber, but only a few blends have practical value after dynamic vulcanization. At present, PP/PE/EPDM is commercially available,PP/NBR，PP/ACM，PS/SEBS。In the book Thermoplastic Elastomer published by the Chemical Industry Press, 99 kinds of rubber/plastic blends prepared from 11 kinds of rubber and 9 kinds of plastics were reviewed. The research found that the following conditions must be met to obtain the rubber/thermoplastic dynamic vulcanization blend with the best performance:
(1) The surface of plastic and rubber polymers can match;
(2) The length of rubber entangled molecular chain is low;
(3) The crystallinity of plastics is greater than 15%.When the polarity or surface energy between plastic and rubber is quite different, adding appropriate compatibilizer and dynamic vulcanization can also obtain a blend with excellent performance.
Regeneration research
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A large amount of waste vulcanized rubber produced in the production and use of rubber products has become a major challenge in the development of rubber industry[4]。Waste rubber belongs toThermosetting polymerMaterials are insoluble and insoluble under normal conditions and difficult to degrade under natural conditions. Their recovery and regeneration technology has always been a worldwide problem, which is related to global environmental protection and sustainable utilization of resources. Therefore, they have received more and more attention in the industry.Recycled rubber is the reclaimed rubber from waste rubber. As a filler, it plays an important role in raw rubber formulation.Although the addition of reclaimed rubber will reduce the physical and mechanical properties of raw rubber, such as tensile strength, modulus, tear strength, etc., it can provide features that raw rubber does not have.On the one hand, it can shorten the mixing time and reduce the energy consumption of rubber compound in the mixing process;Secondly, the feeding speed is faster in the process of extrusion or calendering. When the compound contains recycled rubber, extrusion expansion and calendering shrinkage problems can be avoided;Third, during vulcanization, reclaimed rubber can play an anti-aging role, and its effect is better than adding other anti-aging agents.Understanding the reaction mechanism and preparation process of reclaimed rubber is of great significance to better study the reclaimed rubber.
