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The aim of this study is to investigate the dimensional variation of polypropylene composites reinforced with UD flax fibers, and the modification of its dynamical mechanical properties after moisture absorption. The effects of fiber content, coupling agent and moisture content were also examined. Results have shown that the swelling increases significantly when increasing the fiber content and the moisture content. It was also concluded that the addition of a coupling agent reduces the swelling of the composite, by improving the adhesion at the fiber/matrix interface. It is interesting to note that the coefficient of hygroscopic swelling of the composites presents a non-linear evolution, with respect to moisture content. Moreover, it was proved that the addition of fiber and the presence of a coupling agent improve the dynamical mechanical properties of the material. However, following moisture absorption, the storage modulus seems to be decreasing, which might be due to the micro-cracks created as a result of the internal swelling of fibers. Additionally, the coupling agent was found to increase the storage modulus of the composite at dry state, whereas following moisture absorption, it was found that the coupling agent does not modify the storage modulus of the material. Moreover, the results reveal that the dynamic mechanical properties of the composites are hardly dependent on the quality of the material, such as the state of the adhesion at the fiber/matrix interface, a possible misalignment of the fibers within the material and the moisture content within the material at the testing time. [ABSTRACT FROM AUTHOR]

The aim of this work is to study the relevance of the diffusion parameters identified on kinetics whose saturation levels are unknown. Two types of diffusion kinetics have been considered: a Fickian and a non-Fickian kinetics. Numerical experiments, based on the generation of noisy data corresponding to reference values of diffusion parameters, have been carried out. The two models used in this study are Fick's model and the «Dual-Fick» model. Identification procedures were then applied on these data sets, truncated at different critical times. In the specific case of Dual Fick kinetics, the classical least square method was compared to an alternative approach based on the piecewise analysis of the shape of the diffusion curves. The identified parameters may deviate significantly from the expected reference values when the truncation threshold of the data set precedes the steady state. Also, these inaccurate parameters impact the predictions of global water uptake, water concentration profiles and stresses gradients through the thickness of the sample. [ABSTRACT FROM AUTHOR]