Dynamic mechanical properties of aged filled rubbers

摘要

It is well known that the macromolecular structure and the microstructure of the fillers play an important role in the mechanical properties of filled rubbers. This paper focuses on the dependence of the complex modulus of aged natural rubber vulcanizates on the filler network and polymer structure. Dynamic mechanical analysis (DMA) at 30degreesC, 50degreesC, and 70degreesC on the aged rubbers with/without prestrain showed the Payne effect, i.e., a storage modulus drop with increasing amplitude, and the appearance of a loss tangent maximum at strain of about a few percent. The storage modulus increased with the aging time at 70degreesC, 24 < 72 < 240 hr, in the case of nonprestrain. When the prestrain was applied, strain-induced crystallization was generated that enhanced the storage modulus. As time passed, the prestrain relaxed and the crystalline structures began to disappear. After 72 hr, the crystalline structures had almost disappeared, and they had only a weak effect. Consequently, there existed a higher modulus for an aging time of 24 hr than 72 hr at testing temperatures of 30degreesC and 50degreesC. It was concluded that the storage modulus was determined by the postvulcanization, strain-induced crystallization, aging, and relaxing time.