All kinds of rubber products have their specific useful properties and process requirements. In order to meet its physical requirements, it is necessary to select the most suitable polymer and compounding agent for reasonable formulation design. The first step is to understand the relationship between formulation design and the physical properties of vulcanized rubber. The physical properties of vulcanized rubber are closely related to the design of the formula, and the different types and amounts of materials used in the formula will produce differences in performance.

1. tensile strength

Tensile strength is the root limiting ability of an article to resist tensile failure. It is one of the important indicators of rubber products. The life of many rubber products is directly related to tensile strength. For example, the durability of the cover rubber and rubber shock absorber of the conveyor belt is improved with the increase of tensile strength.

The tensile strength is related to the structure of the rubber, and the secondary valence of intermolecular interactions is smaller when the amount is smaller. Therefore, when the external force is greater than the intermolecular action, intermolecular sliding will occur and the material will be destroyed. On the contrary, the molecular weight is large, the intermolecular force increases, the cohesion of the rubber material increases, and the chain segment is not easy to slide during stretching, so the damage degree of the material is small. All other factors that affect the intermolecular force have an effect on the tensile strength. Such as NR/CR/CSM these rubber main chain has crystalline substituents, the valence between molecules is greatly improved, and the tensile strength is also increased. This is one of the main reasons for the good self-reinforcing performance of these rubbers. Generally, the tensile strength of rubber increases with the increase of crystallinity. The tensile strength is also related to the root temperature, and the tensile strength at high temperature is much lower than that at room temperature. The tensile strength is related to the cross-linking density. With the increase of cross-linking density, the tensile strength increases. After the maximum value, the cross-linking density continues to increase, and the tensile strength decreases significantly. The tensile strength of vulcanized rubber decreases with increasing crosslinking bond energy. Can produce tensile crystallization of natural rubber, weak bond early fracture, is conducive to the orientation of the main key crystallization, so there will be a higher tensile strength. Through the vulcanization system, the use of sulfur vulcanization, selection and use of accelerators, DM/M/D can also improve the tensile strength, (except for carbon black reinforcement, because of carbon black heat generation),

1. The relationship between tensile strength and filler

The reinforcing agent is one of the important factors affecting the tensile strength, the smaller the filler diameter, the larger the specific surface area, the greater the surface activity, the better the reinforcing performance. The vulcanized rubber of crystalline rubber has a monotonous decline because it is a self-reinforcing non-crystalline rubber such as styrene-butadiene. With the increase of dosage, the reinforcing performance increases and excessive use will decrease. The low and low rubber can remain unchanged as the amount increases to reach the maximum value.

2. Relationship between tensile strength and softener

The addition of softener will reduce the tensile strength, but a small amount is added, generally below 7 parts of the open training machine, and the dense training machine below 5 parts will improve the dispersion, which is beneficial to improve the tensile strength. The different softeners have different degrees of reduction in tensile strength. General natural rubber is suitable for vegetable oils. Non-polar rubber with aromatic oils such as SBR/IR/BR.. Such as IIR /EPDM with paraffin oil, naphthenic oil. DBP/DOP for NBR/CR. Something like that.

Other methods to improve tensile strength include blending rubber with resin, chemical modification of rubber, and surface modification of fillers (e. g., cassia, etc.)

2. tear strength

The tearing of rubber is caused by the rapid expansion of cracks or cracks in the material when the force is applied. Tear strength is not directly related to stretching. In many cases tear is not proportional to stretch. In general, crystalline rubber tearing stronger than non-crystalline rubber. Tear strength is temperature dependent. In addition to natural rubber, tear strength at high temperatures are significantly reduced. The tear strength of the rubber filled with carbon black and white carbon black is obviously improved. The tear strength is related to the vulcanization system. The polysulfide bond has higher tear strength. High sulfur dosage and high tear strength. But too much sulfur content will significantly reduce the tear strength. The use of a promoter having better flatness is advantageous for increasing the tear strength.

The tear strength is related to the filling system, and various reinforcing fillers such as carbon black, white carbon black, white brilliant, zinc oxide, etc., can obtain higher tear strength. Some coupling agents such as laurane can improve tear strength. The tear strength is usually reduced by the addition of a softener. Such as paraffin oil will make the tear strength of styrene butadiene rubber extremely unfavorable. And aromatic oil is not much changed. Such as CM/NBR with ester plasticizers than other softeners on the impact is much smaller.

3. stress and hardness at constant elongation

The constant elongation stress and hardness are important indicators of the stiffness of rubber materials. They are the force required to produce a certain deformation of vulcanized rubber. They are related to the larger tensile deformation. The correlation between the two is good, and the change law is basically one. The greater the molecular weight of the rubber, the greater the effective crosslinking stress at constant elongation. In order to obtain a predetermined stress at constant elongation, the crosslink density may be appropriately increased for a rubber having a relatively small molecular weight. Any structural factor that increases intermolecular forces. Can improve the ability of the vulcanized rubber to resist deformation. Such as CR/NBR/PU/NR, etc. have a higher tensile stress. The constant elongation stress has a great influence on the crosslink density. Whether it is pure rubber or reinforced vulcanized rubber, with the increase of crosslinking density, the constant elongation stress and hardness also increase linearly. It is usually achieved by adjusting the variety of vulcanizing agent, accelerator, vulcanizing agent, active agent, etc. The promotion of sulfur has a more significant effect on improving the stress at constant elongation. Polysulfide is beneficial to improve the stress of fixed elongation. The filler can improve the constant elongation stress and hardness of the product. The higher the reinforcement performance and the higher the hardness, the higher the constant elongation stress. The constant elongation stress increases with the increase of hardness, the higher the increase of filling. On the contrary, with the increase of softener, the hardness decreases and the constant elongation stress decreases. In addition to increasing the reinforcing agent and the use of alkyl phenolic resin hardness of up to 95 degrees, high styrene resin. Using resin RS, accelerator H and the hardness of the system can reach 85 degrees, etc.

4. wear resistance

Abrasion resistance characterization is the ability of vulcanizates to resist material loss due to surface damage under the action of friction forces. It is a mechanical property closely related to the service life of rubber products. Its forms are:

1, wear and tear, in the friction on the surface of the uneven sharp rough objects continue to cut, rub. As a result, the contact points on the rubber surface are cut and torn into tiny particles, which fall off the rubber surface and form abrasion. Abrasion strength is proportional to pressure and inversely proportional to tensile strength. Decreased as resilience increased.

2. Fatigue wear, the vulcanized rubber surface in contact with the friction surface is subjected to periodic compression, shear, tensile and other deformation effects in the repeated process, causing fatigue on the rubber surface and gradually producing micro cracks in it. The development of these cracks causes microscopic spalling of the surface of the material. Fatigue wear increases with the increase of elastic modulus and pressure of rubber, and increases with the decrease of tensile strength and the deterioration of fatigue performance.

3. Curling and abrasion. When the smooth surface under the rubber is in contact, due to the effect of friction, the uneven surface of the vulcanized rubber is deformed, and is torn and destroyed, resulting in a rolled off surface.

The wear resistance is related to the main mechanical properties of vulcanizates. In the design of the formula to try to balance the relationship between the various properties. Generally speaking, NBR>BR>SSBR>SBR(EPDM)>NR>IR(IIR)>CR

The wear resistance is related to the curing system, and the appropriate amount of cross-linking can improve the wear resistance. The more single sulfur, the better the wear resistance, which is the best reason for the wear resistance of semi-effective vulcanization systems. The wear resistance of CZ as the first accelerator is better than other accelerators, and the best amount of reinforcing agent will improve the wear resistance. The proper use of softeners will minimize the wear resistance. Such as natural rubber, styrene butadiene rubber with aromatic oil.

Effective use of antioxidants can prevent fatigue aging. Improving the dispersion of carbon black can improve the wear resistance.

The wear resistance can be greatly improved by using the modification of the surface treatment agent.

The use of rubber and plastic blending to improve wear resistance, such as the use of tintin and polyvinyl chloride, the manufacture of textile skin.

Ding Jing and ternary nylon are used together, Ding Qing and phenolic resin are used together.

Add solid lubricants and anti-friction materials. For example, adding graphite, molybdenum disulfide, silicon nitride and carbon fiber to the butyl rubber compound can reduce the friction coefficient of the vulcanized rubber and improve its wear resistance.

5. Fatigue and Fatigue Failure

The phenomenon that the structure and properties of the material change when the vulcanizate is subjected to alternating stress is called fatigue. As fatigue passes, the phenomenon leading to material failure is called fatigue failure.

1, the influence of rubber structure, low glass transition temperature of rubber fatigue resistance is good. Rubber with polar groups has poor fatigue resistance. Rubber with large groups or side groups in the molecule, rubber with poor fatigue resistance and regular structural sequence, easy to polymerize to crystallization, and poor fatigue resistance.

2. The influence of rubber vulcanization system, the vulcanization system of single sulfur health, the minimum fatigue performance, good fatigue resistance, increasing the amount of crosslinking agent will reduce the fatigue performance of vulcanized rubber. Therefore, the amount of crosslinking agent should be minimized.

3, the influence of filler, the smaller the reinforcing performance of the filler, the smaller the influence, the greater the amount of filler, the greater the influence, the filler should be used as little as possible.

4, the impact of the softening system, as far as possible to choose a low softening point of non-viscous softener; softener as much as possible, on the contrary, high viscosity softener should not be used, such as pine tar fatigue resistance is poor, lipid plasticizer fatigue resistance is good.

6. elasticity

The most valuable property of rubber is its elasticity. High elasticity comes from the movement of rubber molecules, which is completely caused by the conformation change of coiled molecules. It can be restored immediately after the external force is removed, which is called ideal elastomer. The interaction between rubber molecules will hinder the movement of molecular segments, showing stickiness or viscosity. Therefore, the characteristics of rubber are both elastic and viscous. The factors affecting elasticity are deformation size, action time, temperature and so on. When the interaction between the rubber molecules is increased and the regularity of the molecular chain is high, tensile crystallization is likely to occur, which contributes to the improvement of strength and shows high elasticity. In the general rubber of natural, butyl rubber elasticity is best, followed by butyl, neoprene. Butadiene benzene and butyl are poor.

The elasticity is related to the cross-linking density, with the increase of the cross-linking density, the elasticity of the vulcanized rubber increases, and the maximum value appears, and the cross-linking density continues to increase. An appropriate increase in the degree of fluidization is advantageous for elasticity. The use of sulfur and CZ in high elastic combination and the use of vulcanized rubber with promoting D have higher resilience and small hysteresis loss.

The elasticity is related to the filling system, and increasing the gum content is the most direct and effective way to improve the elasticity, and the better the reinforcement is, the more unfavorable the filling is to the elasticity.

Relation between elasticity and softener. The softener is related to the compatibility of rubber, and the smaller the compatibility, the worse the elasticity. Such as natural, cis-butyl, butyl plus paraffin oil, better than adding naphthenic oil. Butyl eye plus DOP is better than the use of naphthenic oil, aromatic oil. Generally speaking, plasticizers will reduce the elasticity of rubber, and plasticizers should be used as little as possible.

7. elongation at break (elongation)

Elongation at break is related to tensile strength. Only with high tensile strength and ensuring that it is not damaged during deformation, will there be a higher elongation. Generally, with the increase of the stress and hardness of the fixed elongation, the elongation at break decreases, the resilience is large, the permanent deformation is small, the elongation at break is large. Different rubber has different elongation at break. When the rubber content of natural rubber is above 80%, its elongation at break can reach 1000. Rubber that is prone to plastic flow during deformation will also have higher elongation. Such as butyl rubber.

The elongation at break decreases with the increase of crosslinking density. Manufacture of high tensile products, the degree of vulcanization should not be too high, can be slightly less sulfur or reduce the amount of vulcanizing agent. Increasing the amount of filler will reduce the elongation at break, and the higher the structure of the reinforcing agent, the lower the elongation at break.

Increasing the amount of softener can obtain a larger tear elongation.