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Fabrication of layered thermoplastic polymer products involves applying heat and pressure to contacting thermoplastic surfaces and consolidating the interface. Polymer healing, referring to the intermolecular diffusion across the interfaces of thermoplastic tape layers in intimate contact, is one of the important steps responsible for the development of interlaminar bond strength and is strongly influenced by the temperature history. While the theory for healing under isothermal conditions is well established in the literature, the available descriptions of healing under nonisothermal processing conditions lack a sound fundamental basis. In this paper, a model for the healing process under nonisothermal conditions is developed starting from a fundamental formulation of the reptation of polymer chains. Considering the temperature dependence of the welding time, the bond strength is described as a function of temperature history. It is shown that, under certain nonisothermal conditions, considerable errors could be introduced in the prediction of the healing development using the models in the literature.

The electrical contact resistance between gas diffusion layers and bipolar flow channel plates is one of the important factors contributing to the operational voltage loss in polymer electrolyte membrane (PEM) fuel cells. Effective analysis and design of fuel cells therefore need to account for the contact resistance in deriving the polarization curve for the cell. Despite its significance, relatively scant work is reported in the open literature on the measurement and modeling of the contact resistance in fuel cell systems, and the present work aims to fill this void. Experimental data are reported for the first time to show the effects of different gas diffusion layer materials and contact pressure on the electrical contact resistance. A fractal asperity based model is adopted to predict the contact resistance as a function of pressure, material properties, and surface geometry. Good agreement is observed between the data and the model predictions for a wide range of contacting pressures and materials.

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