Novel thermally regenerated flexible cellulose-based films

In this work, cellulose powder obtained by acid hydrolysis of industrial Eucalyptus kraft pulp was dissolved in NaOH/Urea/H₂O system (7/12/81 wt%) in a concentration of 6% (w/v). Cellulose films were prepared by spreading the dissolved cellulose over glass plates, followed by thermal regeneration – a novel approach reported here for the first time. To obtain final flexible films, plasticization was carried out by immersion in aqueous glycerol solutions of various concentrations (10 to 70 wt%) and hot-pressing (at 0.1 MPa and 105 ºC) was used to dry and compress the cellulose films. The resulting films were characterized by Attenuated Total Reflectance Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, X-ray diffraction, contact angle measurements, transparency analysis, and gas permeabilities (oxygen and water vapor). Highly flexible films containing up to 50 wt% of glycerol were successfully obtained, exhibiting no glycerol release upon manual handling. Overall, the produced films demonstrated dense and compact structure, good transparency, flexibility and malleability, and very low oxygen permeability.