Elastic Modulus and Molecular Influence of Shock-Absorbing Rubber
The stiffness, or elastic modulus, of shock-absorbing rubber, is primarily influenced by the adjustment of fillers and plasticizers and is less dependent on the rubber type. The rubber’s damping performance hinges largely on its molecular structure. For instance, introducing side groups into the molecular chain or expanding the volume of these side groups can restrict the movement of the rubber’s macromolecules, leading to an increase in internal molecular friction. This enhances the damping coefficient, tanδ. The introduction of crystals can, however, reduce the damping qualities. For example, blending crystallized isoprene rubber with chlorobutyl rubber, which has a superior shock absorption effect, will decrease the system’s damping coefficient as the isoprene rubber content rises.
Elastic Modulus and Molecular Influence
Among the common rubbers, butyl rubber and nitrile rubber possess the highest damping coefficients. In contrast, styrene-butadiene rubber, chloroprene rubber, silicone rubber, polyurethane rubber, and ethylene-propylene rubber have medium damping coefficients. Natural rubber and butadiene rubber have the lowest damping coefficients. Even though natural rubber has a modest damping coefficient, it excels in overall performance — showcasing excellent fatigue resistance, minimal heat generation, reduced creep, and strong adhesion to metal components.
As a result, natural rubber is a popular choice for shock-absorbing applications. If there’s a need for resistance to cold temperatures, it can be combined with butadiene rubber. If resistance to weathering is necessary, chloroprene rubber is a good option. For oil resistance, low-acrylonitrile content nitrile butadiene rubber can be used. For shock-absorbing rubber with stringent low-temperature dynamic performance criteria, silicone rubber is frequently the go-to choice. Generally, natural rubber is used when low damping is desired, while butyl rubber is chosen for high-damping applications. Choosing a rubber blend with compatibility and co-vulcanization can effectively widen the damping peak, improving damping characteristics and other properties.
Influence of Vulcanization on Performance
The vulcanization process greatly impacts the stiffness, damping coefficient, heat resistance, and fatigue resistance of shock-absorbing rubber. In general, the fewer sulfur atoms and free sulfur present in the cross-linked bonds of vulcanized rubber, the stronger the cross-linking becomes. This results in a higher elastic modulus of the vulcanized rubber and a reduced damping coefficient. Utilizing the traditional vulcanization process and moderately increasing the cross-linking degree can enhance shock absorption and dynamic fatigue resistance. However, this may compromise heat resistance. For instance, when using an efficient vulcanization system or a semi-efficient one with natural rubber, although the heat resistance might improve, there’s a risk of reduced fatigue resistance and metal part adhesion. Thus, it’s crucial to strike a balance between these properties.
