Moisture absorption by various polyamides and their associated dimensional changes

Abstract The dimensional changes associated with moisture absorption were examined for various polyamides (PAs). Plaques of varying thickness were compression‐molded or injection‐molded and then immersed in water. Periodically, the plaques were removed from water and their mass and dimensions were measured. This was continued until they were completely saturated. The more polar PA46 absorbed more water than less polar PA6 and PA66 and therefore, was more susceptible to moisture‐induced dimensional growth. For a given polymer, it was found that the thicker samples took longer to reach saturation, but had the same diffusion coefficient as thinner ones. Changes in dimensions coincided with changes in mass. Sorption and swelling followed slightly different paths, but arrived at their respective equilibrium values at the same time. Within experimental error, dimensional expansion due to water absorption was the same in all directions. Injection‐molded samples absorbed slightly more water than compression‐molded ones, but their absorption rates were equal. Equilibrium water absorption data were used to approximate the dimensional changes associated with the swelling of the PAs. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008