The polysulfide crosslink bond has the lowest bond energy and the carbon-carbon crosslink bond has the highest bond energy. he ordinary vulcanization system, that is, the multi-sulfur cross-linking bond has the strongest tensile strength, and the radiation vulcanization has the lowest tensile strength, that is, the strength of the tensile strength is opposite to the size of the bond energy. The phenomenon of high energy and low strength is related to the chemical characteristics and deformation characteristics of the cross-linking bonds themselves. When the rubber product is deformed by an external force, uneven stress distribution may cause stress concentration. For long and soft crosslink bonds (such as polysulfide crosslinks), it is easy to deform under the action of external force, so that the macromolecular chain of rubber can be oriented and crystallized, and the polysulfide crosslinks are easily exchanged and rearranged. The ability of the vulcanizate to resist stress concentration is enhanced. For the carbon-carbon cross-linking bond with higher bond energy, the cross-linking bond is too short (such as radiation cross-linking), or the cross-linking bond is too rigid, and the flexibility is poor (such as peroxide vulcanization), so that the cross-linking bond The elongation at break is low, the rubber segments may not be in contact with each other, the cross-linking bonds are broken, the stress is more concentrated, and these cross-linking bonds often do not have the characteristics of reconnection, so the overall strength is relatively low.
The effect of cross-link type on dynamic performance
Different cross-linking types not only have an effect on the strength of the vulcanizate, but also have an effect on the dynamic fatigue properties. The polysulfide crosslinks in the vulcanizate help to improve the fatigue properties of the vulcanizate. It may be that under certain temperature and repeated deformation stress, the fracture and rearrangement of the polysulfide crosslinks alleviate the stress.
The effect of cross-linking type on thermal performance
Different cross-linking types have different stability to thermal oxygen aging, which is mainly related to the level of bond energy. The bond energy of a one is high, and the bond energy of a key is low, so the heat-resistant oxygen aging property of the vulcanized rubber is good. The commonly used stress relaxation rate constant K represents the thermo-oxidative aging stability of the crosslinked bond.
In the sulfur-containing vulcanization system, the polysulfide cross-linking bond has the highest stress relaxation rate constant, that is, the stability to thermal oxygen aging is the worst, and the thermal oxygen aging of the sulfur-sulfurized monosulfide cross-linking is stable.