Rubber is different from the elastic energy represented 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 deformation on the basis of the entropy elasticity generated by the contraction and spring off of the molecular lock.
02Reflect the viscoelasticity of rubber
According to Hooke's Law, the so-called viscoelastic body has the property between elastic body and complete fluid.That is to say, the deformation and other behaviors caused by external forces are dominated by time and temperature conditions, and show the phenomenon of creep and stress relaxation.During vibration, the phase difference of stress and deformation also shows the hysteresis loss, and the energy loss is shown in the form of heating according to its size.Moreover, in the dynamic phenomenon, the cycle dependence can be seen, which is applicable to the time temperature conversion rule.
zerothreeWith anti vibration and buffer function
The interaction of the softness, elasticity and viscoelasticity of rubber shows that it can ease the transmission of sound and vibration.Therefore, it is used in the countermeasures to reduce the noise and vibration pollution.
zerofourThere is a great dependence on temperature
In general, many physical properties of polymer materials, not only rubber, are affected by temperature. Rubber has a strong tendency of viscoelasticity and is also greatly affected by temperature.Generally speaking, rubber is easy to embrittle at low temperature;At high temperatures, a series of processes such as softening, dissolution, thermal oxidation, thermal decomposition and combustion will occur.Moreover, because rubber is organic, it does not have flame resistance.
zerofiveFeatures of electrical insulation
Like plastic, rubber was originally an insulator.It is used in insulation skin and other aspects. Due to different formulations, the electrical insulation characteristics are also affected. In addition, there are "conductive rubber" that actively reduces the insulation resistance to prevent electrification.
zerosixAging phenomenon
Compared with the corrosion of metal, wood, stone and the deterioration of plastic, the material change caused by environmental conditions is called aging phenomenon in the rubber field. In general, it is difficult to say that rubber is a material with excellent durability.UV, heat, oxygen, ozone, oil, solvent, medicine, stress and vibration are the main reasons for aging.
zerosevenSulfur addition required
The process of connecting rubber chain macromolecules with sulfur is called sulfur addition. Due to the reduction of plastic flow, the formability, strength and other physical properties have been improved, the range of application temperature has been expanded, and the practicability has also been improved.In addition to sulfur addition for elastomers with double bonds, there are also peroxide sulfur addition and ammonium sulfur addition using peroxides.There are also thermoplastic rubbers, also known as rubbery plastics, that do not need to be sulfurized.
zeroeightRecipe required
Among synthetic rubbers, such as polyurethane, there are exceptions that do not need formulation (except crosslinking agent). Generally, rubber needs various formulations.It is very important in rubber processing technology to call the selection of the type and addition amount of this formula agent "establishment formula".The fine parts of the practical formula corresponding to the use and required performance can be said to be the technology of each processing factory.
zeronine
Other characteristics
proportion
For raw rubber, natural rubber is 0.91~0.93, EPM 0.86~0.87 is the smallest, and fluororubber is the largest in 1.8~2.0.The practical rubber varies according to the formula. The specific gravity of carbon black and sulfur is about 2. The heavy metal compounds such as zinc oxide are 5.6. The organic formula is about 1. In most cases, the specific gravity is in the range of 1 to 2.Moreover, in exceptional cases, there are also products of heavy quality, such as noise masks filled with lead powder.Generally speaking, it is a lighter material than metal.
Hardness
Generally speaking, it is soft.Although the surface hardness is relatively small, hard rubber like polyurethane rubber can also be obtained, which can be changed according to different formulations.
Ventilatory
Generally speaking, it is difficult to penetrate air and other gases to be used as sealing equipment.Butyl rubber has excellent air impermeability, while silicone rubber is relatively easier to breathe.
Waterproofness
In general, it is waterproof, and its water absorption rate is larger than that of plastic. It can also reach dozens of percent in boiling water.On the one hand, in terms of water resistance, due to temperature, immersion time, acid and alkali intervention and other factors, polyurethane rubber is likely to decompose by adding water.
Drug resistance
In general, it has strong resistance to inorganic drugs, and almost all rubbers can withstand low concentration of alkali.Many rubbers become brittle in contact with strong oxidizing acids.Although relatively resistant to organic drugs such as alcohol, ether aliphatic.However, in hydrogen carbide, acetone, carbon tetrachloride, carbon disulfide, phenolic, etc., it is easy to be invaded and become weak due to swelling.In addition, in terms of oil resistance, many animals and vegetable oils are resistant, but they will deform after contacting with petroleum, and it is also easy to swell.Moreover, it is also affected by the type of rubber, the type and amount of formulation, temperature, etc.
Wear resistance
It refers to the characteristics specially required in the field of tires, ribbons, shoes, etc. Compared with the wear caused by sliding, rough wear is more of a problem.Carbamate rubber, natural rubber, butadiene rubber, etc. have good wear resistance.
Fatigue resistance
It refers to the durability during repeated deformation and vibration.Although the pursuit is that heating is difficult to produce cracks and progress, it is also related to the change of materials caused by mechanical action.SBR is superior to natural rubber in terms of crack generation, but its growth rate is very fast and quite poor.It is affected by the type of rubber, force amplitude, deformation speed, and reinforcing agent.
strength
The rubber strength has tensile properties (breaking strength, elongation,% modulus), compression strength, shear strength, tear strength, etc.Like polyurethane rubber, there are pure rubber with quite good strength, and there are also many rubber improved by compounding agent and reinforcing agent.
Flame resistance
It refers to the comparison of the ignitability, burning speed, etc. of materials when they come into contact with fire.However, dropping property, toxicity of the produced gas and amount of the smoke are also problems.Because rubber is an organic substance, it cannot be non combustible, but it is also developing in the direction of flame-retardant. There are also rubbers with flame-retardant properties like fluororubber and neoprene.
Adhesion
Generally speaking, the adhesion is good.It can be dissolved in solvent to carry out gluing processing. By this method, it can have the adhesion of rubber system.The tires are joined according to the sulfur addition.Natural rubber and SBR are actually used in the combination of rubber and rubber, rubber and fiber, rubber and plastic, rubber and metal, etc.
toxicity
In the formulation of rubber, there are some harmful substances in some stabilizers and plasticizers, and attention should also be paid to cadmium pigments.
