Unified model for low-Earth-orbital atomic-oxygen and atomic-oxygen/ultraviolet induced erosion of polymeric materials

An attempt is made by applying the chain reaction theory on the study of the interactions of atomic-oxygen and atomic-oxygen/ultraviolet radiation (referred to as atomic-oxygen and synergistic effects, respectively) with polymeric materials. A unified kinetic model describing the non-branching chain reacting processes induced by atomic-oxygen and synergistic effects on hydrogen-containing polymers is first constructed. A unified form of equations in terms of mass change of polymeric materials is then deduced by incorporating the kinetic model into the mass loss model due to Colin et al. The resulting equations can be simplified under certain conditions, and analytic solutions describing the nonlinear mass variation can be obtained via the bulk reactive rate in the fractal reaction dynamics. For demonstration, the mass change associated with four types of polyethylene and Kapton were simulated, and the results are in good agreement with the experimental data. The dependencies of the mass loss on crystallinity, the fractal dimensions of erosion surface, and environmental factors for all four types of polyethylene are explained briefly. The theoretical framework is generalized to yield a mass evolution prediction formula for heterogeneous media induced by the diffusion–reaction process of incoming particles impinging into the media. Hereby, mass losses of polymers such as Teflon FEP, etc., as well as polymer-layered silicate nanocomposites caused, respectively, by the vacuum ultraviolet irradiation and oxygen plasma are simulated. The fitted curves agree well with the experimental data. The validation through the chosen materials reveals that the present unified model is capable of providing a tool for evaluating the non-linear mass loss of both polymers and nanocomposites.