Rubber is characterized by both high elasticity and high viscosity. The elasticity of rubber is caused by the change in the confirmation of its coiled molecules. The intermolecular interactions between rubber molecules impede the movement of the molecular chains and show the characteristics of stickiness, resulting in stress. And the strain is often in an imbalanced state. The crimped long-chain molecular structure of rubber and the weak secondary forces existing between the molecules make the rubber material exhibit unique viscoelastic properties and therefore has good shock absorption, sound insulation, and cushioning properties. Rubber parts are widely used for vibration isolation and shock absorption because they have hysteresis, damping, and reversible large deformation.
The hysteresis and internal friction characteristics of rubber are usually expressed as loss factors. The greater the loss factor, the more significant the damping and heat generation of the rubber, and the more significant the damping effect. The size of the rubber material loss factor is not only related to the structure of the rubber itself but also related to temperature and frequency. At room temperature, natural rubber (NR) and butadiene rubber (BR) have small loss factors, styrene butadiene rubber (SBR), neoprene (CR), ethylene propylene rubber (EPR), urethane rubber (PU) and silicone rubber. The loss factor is centered, and butyl rubber (IIR) and nitrile rubber (NBR) have the largest loss factor.
Rubber materials used for shock absorption purposes are generally divided into 5 types, namely NR, SBR, BR for ordinary rubber materials; NBR for oil vulcanizates; CR for weather-resistant vulcanizates; IIR for high damping vulcanizates; EPR for Heat-resistant vulcanizates. Although NR has a small loss factor, it has the best comprehensive performance, excellent elasticity, good fatigue resistance, low heat generation, small creep, good adhesion to metal parts, and good cold resistance, electrical insulation, and processing properties. Therefore, NR is widely used as a shock-absorbing object, and when it is required to be resistant to low temperature or weather resistance, it can be used together or blended with BR or CR. Nishiue et al. used NR, BR, and a shock absorber made of a metal salt containing an —OH group organic acid having a carbon number of more than 4 to have better durability, and compression at 70° C.×22 h and 40° C.×148 h. The permanent deformations were 1710% and 1117%, respectively.
Due to its excellent weather resistance, ozone resistance, electrical insulation, heat resistance, and cold resistance, EPDM has received extensive attention in recent years. Recently, Japan has jointly developed a new type of heat-resistant shock-absorbing rubber material by adopting high-molecular-weight EPDM and low-molecular-weight EPDM in combination and obtained a Japanese patent. The tests of the shock-absorbing rubber show that its shock absorption performance is the same as that of NR, but its heat resistance and low-temperature flexibility are better than those of NR and other rubbers . Izumi uses EPDM to make rubber materials for shock absorbers on automotive parts. It has good heat resistance. After heat aging at 190°C for 5 hours, the material still has good interlayer adhesion properties. Silicon rubber is often used for shock-absorbing rubbers with stringent requirements for low-temperature dynamic performance; IIR or halogenated IIR can be used when high damping is required; PU has excellent resistance to abrasion, flexing, and to hydrocarbon fuels and most organic solvents. The resistance, while having high physical properties, good electrical insulation, adhesion and aging resistance. PU has also been widely used in shock absorption and sound insulation.