Water vapor transport properties of regenerated cellulose and nanofibrillated cellulose films

Water vapor diffusivities were also measured from the uptake rate measurements for a wide range of relative humidities. The diffusivities generally showed dependency on the moisture content of the sample. The effective diffusion coefficients (Deff) of NFC and regenerated cellulose films are 1-2 orders of magnitude lower in comparison with the unmodified paper, depending on the moisture content. The mechanisms of water vapor transport through the cellulose films were also evaluated from the uptake rate experiments. The results showed that the external surface resistance was a more dominant mechanism to mass transfer in the NFC and regenerated cellulose films. On the other hand, water vapor uptakes on unmodified paper seem to be consistent with internal diffusion control mechanism, except at the high moisture contents. At the high relative humidity or moisture contents of the films, both the external surface resistance and diffusion control the transport in transparent cellulose films and paper samples.