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Water vapour permeable edible membranes
In this study, polysaccharide based edible films were prepared and characterized. Also water vapour sorption, diffusion and permeability characteristics of these films were studied. For these purposes cellulose ethers such as sodium salt of carboxymethyl cellulose (NaCMC) and hydroxypropylcellulose (HPC) were used as a film forming materials. Distilled water and glycerin were used as solvent and plasticizer respectively. To determine the effect of polymer concentration of the film forming solution on the film properties, NaCMC and HPC films were prepared from three different concentrations (3, 4, 5g polymer/100ml distilled water) of film forming solutions. During the characterization studies of the films, to determine the elements and structural composition of the films, energy dispersive X-Ray and scanning electron microscopy analyze were applied to NaCMC and HPC based edible films. Also, X-Ray diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry analysis were applied to determine the form of elements, functional groups and glass transition temperature.Water vapour sorption capacities of NaCMC and HPC based films were measured nearly 70%w and 25%w respectively. GAB and Halsey models were found to give the best fit for the water vapour sorption data of both NaCMC and HPC films. Diffusion coefficient of water vapour in vacuum microbalance test was higher than that determined using the humidity chamber, this case could be result of the structural changes of films such as formation of porous structure in microbalance tests due to the fast drying of films by high vacuum. NaCMC based edible films showed higher diffusion coefficient values than HPC based films, due to the heterogeneous structure and bigger pore dimensions of the NaCMC films that was observed in the scanning electron micrographs. Water vapour permeability (WVP) of both films increased with increasing thickness and increasing film forming solution concentration and WVP values of NaCMC based films were higher than the WVP values of HPC films. In mechanical properties, while NaCMC films have brittle, stronger and stiffer structure, HPC films show elastic and ductile property.