Changes In Tensile Mechanical Properties Of Carbon Black Filled Rubbers By Thermal Aging

Rubber regarded as a visco-hyperelastic composite material has a wide range of applications in our daily life and industry. Though the strength of natural rubber can not fully satisfy the industrial requirements, rubber strength and crosslink density increase with the absorption of carbon black. In spite of the excellent mechanical performance of the carbon black-filled natural rubber, it has disadvantage of easily ageing in processes of using, transportation and storage by increasingly complex environment. After aging, the cross-linked structure comes to break and rearrange, which causes a great change of the mechanical properties. This paper mainly focuses on the analysis of thermal oxidative aging mechanism of carbon black-filled rubber under the condition of different temperatures and time scales. Meanwhile, the effect of thermal oxidative aging on the molecular-chain network crosslink density and the mechanical properties has been investigated by utilizing the means of crosslink density and mechanical property test. The main research work and conclusions are as follows:1. The crosslink density of carbon black-filled rubber subjected to different aging time has been determined with the equilibrium swelling method. The results show that the crosslink density increases with the increase of aging time and temperature. Besides, under the same ageing condition, the crosslink density increases with the increase of carbon black content.2. The tests of uniaxial tension and tearing were conducted by Instron 5943 mechanical testing machine. After analysis of the tensile stress-strain curve, the mechanical properties have been obtained such as initial elastic modulus, tensile strength and fracture stretch ratio. The results show that the tensile strength, the tear strength and fracture stretch ratio decrease gradually with the increase of aging time temperature. However, the initial elastic modulus tends to increase. Besides, the tearing test shows that the tearing strength decreases gradually with the prolonging of ageing time.3. The relationship between crosslink density and tensile mechanical properties has been established. The tests show that the tensile strength, the tear strength and fracture stretch ratio decrease gradually with the increase of crosslink density. Moreover, there is a direct relation between crosslink density and initial elastic modulus.4. This paper describes briefly the rubber hyperelastic constitutive theory and after the analysis of fitting curves it can be concluded that under moderate deformation the material mechanical properties can be described by the Neo- Hooke model rather than Mooney-Rivlin model.