Properties Of Vulcanized Rubber During Aging Studied By Means Of Fox-H Function

Polymers have been widely used in industry, agriculture, advanced science and technology and our daily life. The main reason is that it has a series of good mechanical properties. However, during the course of machining, storing, transport and using, mechanical properties of polymers usually result in aging owing to composite effect of inside and outside factors.Viscoelasticity is representative mechanical characteristics of polymer. Fractional calculus was imported into the constitutive equation in the field of viscoelasticity, that made a great development in the viscoelastic theory. These models possess a small number of single elements and parameters, but can describe complex viscoelastic behavior very well. By the method of mechanics of continuous media, we study properties of polymer during aging using a tool of fractional calculus. This study has the important theoretical value and practical significance for finding out the relation between property and structure of polymer.The stress relaxation characteristics of the generalized fractional Maxwell model are detailedly analyzed in this thesis. We briefly introduce the experimental description and measurement of properties of the stress relaxation and compression set of VR during aging.Based on experiment, starting with the fractional viscoelastic theory, through reasoning, hypothesis and analogy, a mathematical model is put forward to describe the degradation rule of properties of the stress relaxation and compression set of VR during the isothermal thermo-oxidative aging by means of Fox-H function. The model is respectively used to simulate data of stress relaxation coefficient and compression set ratio of NBR and CR during thermo-oxidative aging with the changing of the time. Macroscopical differences of the property of sample are mainly represented byτand E0 , whereasαandβreflect the degenerate characteristics of its property in the different stage. The model is used to simulate data of stress relaxation coefficient of EPDM in oven during accelerated aging with the changing of the time. Logarithm of relaxation time of sample decreases linearly with the increase of temperature.Based on experiment, starting with the fractional viscoelastic theory, through analogy, a mathematical model is put forward to describe the stress relaxation of polymer during the isothermal physical aging by means of Fox-H function. The model is respectively used to simulate data of stress relaxation modulus of PPS and PEEK during physical aging with the changing of the time. Under the same temperature, logarithm of relaxation time of sample increases linearly with the increase of logarithm of the aging time. Relaxation time and modulus strength of sample have crucial effect on the of structure relaxation during the physical aging.