Mass transfer of water vapor, carbon dioxide and oxygen on modified cellulose fiber-based materials

Mass transfer properties of fibre network and coated paper are essential for understanding the barrier properties of the products and further advance in their application. In this study, different unmodified and coated papers, e.g., (Poly lactic acid (PLA), zein grafted paper) were prepared and characterized with regard to mass transfer properties. Water vapor, carbon dioxide (CO2) and oxygen (O-2) transmission rates through the cellulose paper films were measured and the results discussed. The effects of sample film thickness and temperature on water vapor transmission rates (WVTR's) were also examined. The WVTR's of the investigated samples were found to be strongly dependent on the temperature and the relative humidity difference (mass transfer driving force). On the other hand water vapor permeabilities (WVP's) were found independent of relative humidity. Water vapor diffusivities of the samples were also measured from the uptake rate measurements using Fickian diffusion slab model for a wide range of relative humidities. WVTR's and vapor diffusivity of the modified samples were found to be generally low compared to unmodified (reference) paper sample. Among the investigated samples, PLA/polyhedral oligomeric silsesquioxane POSS-bentonite modified paper sample showed higher mass transfer resistance to water vapour and the gases investigated in this study (CO2 and O-2). It showed lower water transmission rate (104 g/m(2).day) compared to PLA-coated paper (130 g/m(2).day), zein coated paper (179 g/m(2).day) and control sample (359 g/m(2).day) at the relative humidity gradient Delta RH=74% and temperature of 25 degrees C. The oxygen transmission rate for PLA/(POSS-Bentonite) coated paper was found to be lower than for the other modified papers. Zein grafted paper showed better barrier property for water vapor than oxygen. Water vapor permeation through paper films shows an Arrhenius type of dependency with temperature, indicating activated process. The activation energies reveal diffusion dominated process for all paper samples investigated in this study, according to the solution-diffusion mechanism used to describe the permeation processes.