Absorption and diffusion of humidity in fiberglass-reinforced polyamide

A statistical study of railway fastening insulating plates from various points of the Spanish territory reveals that high responsibility structural components injected with a hygroscopic material such as polyamide (PA) rein-forced with short fiberglass can absorb varying amounts of water, depending on the working environment. This hygroscopic nature of PA6 means that the mechanical behavior of the matrix, and thus of the component as a whole, is heavily dependent on the content of water retained. This article studies the absorption and diffusion of water in the core of PA6. To verify the effects of humidity on the mechanical properties of reinforced PA6, the material was conditioned, that is, it was assigned a precise humidity content. The results obtained show that the interphase between the fiber and the matrix is a preferential way for the water advance in the composite. The diffusion of water in the PA core was carried out according to Fick’s Second Law and the diffusion coefficient responds to an Arrhenius exponential law. The material behavior was experimentally validated and so it can be applied to quantify the humidity content of a component in a specific environment of temperature and exposure