Hydrolytic degradation at elevated temperatures is a key reason for failure in offshore flexible risers. In this article, the aging of polyamide 11 in deoxygenated water at 90 C and 120 C was studied. Tensile and dynamic mechanical thermal analysis tests were performed to measure changes in mechanical properties. Viscometry, gravimetric measurements, differential scanning calorimetry, and thermogravimetric analysis were used to link these properties with morphological changes. General trends are increased stiffness, tensile strength, and glass transition temperature as well as decreased glassy state damping efficiency with increased aging times. Changes can be initially ascribed to plasticizer depletion and then to interplay between molecular weight decrease and crystallinity increase. Viscosity at hydrolysis equilibrium indicates that brittle failure typically involves oxidation or UV exposure. V C 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41971.

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Accelerated aging tests are the conventional way to evaluate long-term degradation of polymers, in particular for offshore flexible risers. In this article, a multiscale model has been developed combining diffusion, chemical kinetic reactions, structure-property relationships, and composite models to provide faster and less labor extensive property predictions. A general methodology is presented and applied to predict the density and crystallinity evolution. Results are compared with experimental ageing of polyamide 11 in deoxygenated water at 120 8C. For both density and degree of crystallinity the modeled trend is close to the experimental test results. Accurate prediction of the morphological parameters during degradation allows extension of the multiscale model for the prediction of mechanical properties.

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A holistic general multiscale model of polymer degradation has been applied to predict the mechanical properties of polyamide 11 after the hydrolytic ageing. Results for elastic modulus, tensile strength, and embrittlement threshold have been compared with experimental aging in deoxygenated water at 1208C. For all studied properties the modeled trend is close to the experimental test results confirming hydrolysis induced chain scission and chemicrystalization as the two main mechanisms of property change. This suggests that the multiscale modeling methodology can provide a valuable alternative to accelerated aging tests. The model also indicated that the crystalline phase does play a role in the plastic deformation. Moreover, the mechanical equilibrium between effects of macromolecule degradation and an increased degree of crystallinity has been described.