1. Reflecting rubber like elasticity
Rubber is different from the elastic energy reflected by the longitudinal elastic coefficient (Young’s modulus). It refers to the so-called “rubber elasticity” that can be restored even for hundreds of percent of deformation based on the entropy elasticity generated by the contraction and rebound of molecular locks.
2. Reflecting the viscoelasticity of rubber
According to Hooke’s law, a so-called viscoelastic body with properties intermediate between an elastic body and a complete fluid. That is to say, for actions such as deformation caused by external forces, they are dominated by time and temperature conditions, and exhibit phenomena of creep and stress relaxation. During vibration, there is a phase difference in stress and deformation, which also shows hysteresis loss. The energy loss is manifested in the form of heat generation based on its magnitude. Moreover, in dynamic phenomena, periodic dependence can be observed, which is applicable to the time temperature conversion rule.
3. It has the function of anti vibration and buffering
The interaction between the softness, elasticity, and viscoelasticity of rubber demonstrates its ability to mitigate sound and vibration transmission. So it is used in measures to reduce noise and vibration pollution.
4. There is a significant dependence on temperature
Not only rubber, but many physical properties of polymer materials are generally affected by temperature, and rubber has a strong tendency towards viscoelasticity, which is also greatly affected by temperature. Overall, rubber is prone to embrittlement at low temperatures; At high temperatures, a series of processes such as softening, dissolution, thermal oxidation, thermal decomposition, and combustion may occur. Furthermore, because rubber is organic, it does not have flame retardancy.
5. Characteristics of electrical insulation
Like plastic, rubber was originally an insulator. Applied in insulation skin and other aspects, the electrical insulation characteristics are also affected due to different formulations. In addition, there are conductive rubbers that actively reduce insulation resistance to prevent electrification.
6. Aging phenomenon
Compared to the corrosion of metals, wood, stone, and the deterioration of plastics, material changes caused by environmental conditions are known as aging phenomena in the rubber industry. Overall, it is difficult to say that rubber is a material with excellent durability. UV rays, heat, oxygen, ozone, oil, solvents, drugs, stress, vibration, etc. are the main causes of aging.
7. Need to add sulfur
The process of connecting the chain like polymers of rubber with sulfur or other substances is called sulfur addition. Due to the reduction of plastic flow, the formability, strength, and other physical properties are improved, and the temperature range of use is expanded, resulting in improved practicality. In addition to sulfur sulfidation suitable for elastomers with double bonds, there are also peroxide sulfidation and ammonium sulfidation using peroxides. In thermoplastic rubber, also known as rubber like plastics, there are also those that do not require sulfur addition.
8. Formula required
In synthetic rubber, exceptions are made where formulations such as polyurethane are not required (except for crosslinking agents). Generally, rubber requires various formulations. It is important to refer to the type and amount of formulation chosen as “establishing a formula” in rubber processing technology. The subtle parts of the practical formula corresponding to the purpose and required performance can be said to be the technology of various processing manufacturers.
9. Other features
(a) Specific gravity
Regarding raw rubber, natural rubber ranges from 0.91 to 0.93, EPM ranges from 0.86 to 0.87 being the smallest, and fluororubber ranges from 1.8 to 2.0 being the largest. Practical rubber varies according to the formula, with a specific gravity of about 2 for carbon black and sulfur, 5.6 for metal compounds such as zinc oxide, and approximately 1 for organic formulations. In many cases, the specific gravity ranges from 1 to 2. Furthermore, in exceptional cases, there are also products with heavy quality such as soundproof films filled with lead powder. Overall, compared to metals and other materials, it can be said to be lighter.
(b) Hardness
Overall, it tends to be soft. Although there are many with lower surface hardness, it is also possible to obtain a hard adhesive similar to polyurethane rubber, which can be changed according to different formulations.
(c) Ventilatory
Overall, it is difficult to use air and other gases as sealing equipment. Butyl rubber has excellent non breathability, while silicone rubber is relatively more easily breathable.
(d) Waterproofness
Overall, it has waterproof properties, a higher water absorption rate than plastic, and can reach several tens of percent in boiling water. On the one hand, in terms of water resistance, due to factors such as temperature, immersion time, and the intervention of acid and alkali, polyurethane rubber is likely to undergo water splitting.
(e) Drug resistance
Overall, it has strong resistance to inorganic drugs, and almost all rubber can withstand low concentrations of alkali. Many rubbers become brittle when in contact with strong oxidizing acids. Although it is more resistant to fatty acids such as organic drugs such as alcohol and ether. But in hydrogen carbide, acetone, carbon tetrachloride, carbon disulfide, phenolic compounds, etc., they are easily invaded and cause swelling and weakening. In addition, in terms of oil resistance, many can withstand animal and vegetable oils, but they will deform and are prone to swelling when in contact with petroleum. Furthermore, it is also influenced by factors such as the type of rubber, the type and amount of formulation, and temperature.
(f) Wear resistance
It is a characteristic that is particularly required in the fields of tires, thin belts, shoes, etc. Compared to wear caused by slipping, rough wear is more of a problem. Polyurethane rubber, natural rubber, butadiene rubber, etc. have excellent wear resistance.
(g) Fatigue resistance
It refers to the durability during repeated deformation and vibration. Although the pursuit is difficult to generate cracks and progress due to heating, it is also related to the material changes caused by mechanical effects. SBR is superior to natural rubber in terms of crack generation, but its growth rate is fast and quite poor. Affected by the type of rubber, amplitude of force, deformation speed, and reinforcing agent.
(h) Strength
Rubber has tensile properties (fracture strength, elongation,% modulus), compressive strength, shear strength, tear strength, etc. There are adhesives like polyurethane rubber that are pure rubber with considerable strength, as well as many rubbers that have been improved through compounding agents and reinforcing agents.
(i) Flame resistance
It refers to the comparison of the ignitability and combustion rate of materials when they come into contact with fire. However, dripping, toxicity of gas production, and amount of smoke are also issues. Because rubber is organic, it cannot be non flammable, but it is also developing towards flame retardant properties, and there are also rubbers with flame retardant properties like fluororubber and chloroprene rubber.
(j) Adhesiveness
Overall, it has good adhesion. Dissolved in a solvent and subjected to adhesive processing, this method can achieve the adhesive properties of the rubber system. Tires and other components are joined based on sulfur addition. Natural rubber and SBR are actually used in the bonding of rubber to rubber, rubber to fiber, rubber to plastic, rubber to metal, etc.
(k) Toxicity
In the formulation of rubber, some stabilizers and plasticizers contain harmful substances, and cadmium based pigments should also be noted.
Post time: Mar-08-2024
