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Physical Aging of Polymers Studied by the Fractional Model

Author: HouZuoZuo
Tutor: ChenHongShan
School: Northwest Normal University
Course: Atomic and Molecular Physics
Keywords: Polymer Glassy Physical aging Fraction model Superposition principle
CLC: O631.3
Type: Master's thesis
Year: 2011
Downloads: 63
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Abstract


Polymer and polymer materials in the work civil defense and other fields with wide applications. The basic characteristics of this kind of material will occur in the course of aging. With increasing aging time, the mechanical properties of the material, the thermal properties and dielectric properties are changed, such as creep compliance, tensile strength, thermal conductivity, specific heat capacity and dielectric constant. Under actual conditions of use, physical aging is generally associated with chemical or biological aging (main bond breaking or reorganization). In terms of physical aging, gradually to the equilibrium state of the material from the glassy evolution. Glassy statistics and dissipative dynamics has been an important research topic in physics. The physical aging caused structure (aggregation structure) change is bound to affect the mechanical properties of the material. The viscoelastic Is the typical characteristics of the mechanical properties of the polymer. The introduction of fractional calculus viscoelastic theory, a breakthrough development. Fractional derivatives and integrals provide a powerful tool to describe different things memory and hereditary. This is one of the most obvious feature of the fractional-order model. Also Fractional viscoelastic model in practice, one of the reasons for such a successful practice. This article is based on experimental data, viscoelastic fractional calculus model for the study of the tools of the polymer physical aging properties. The study has important theoretical and practical significance for the understanding of the relationship between the performance and structure of the polymer, Generalized fractional Maxwell model based on polyether ether ketone (PEEK) and polyphenylene sulfide (PPS), stress relaxation curves and creep curves under different aging temperature and aging time were fitted. The use of genetic algorithm combined with the conjugate gradient method to optimize the model parameters. The fitting results show that the fractional Maxwell model to describe the process of stress relaxation and creep, the fractional (relaxation index) decided by the material structure, aging temperature and time only affect the relaxation time. Relaxation time scale transformed in the number of coordinates, the stress relaxation curves and creep curves under different aging temperature and aging time each almost perfectly superimposed, that time - aging time superposition principle and time - temperature The principle of superposition is naturally present. This also gives reliable predictions of polymer mechanical properties under different conditions of long-time behavior.

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CLC: > Mathematical sciences and chemical > Chemistry > Polymer chemistry ( polymer ) > Polymer physics and physical chemistry of polymers > The chemical nature of polymers
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